Students in Grade 6 start recognizing the need for accuracy in observation and measurement; and apply suitable methods to record, compile, interpret and evaluate observations and measurements. Students should be able to design and carry out an investigation in which variables are identified and controlled, and can test the scientific question being investigated.
We have learnt in previous grades that there are living and non-living things. Living things can also be called organisms. There are some obvious signs we can use to determine if something is living or non-living. For example, living things grow and can move from place to place. But its not easy to observe an organism grow. At the same time, there are some non-living things (such as clouds) that can also grow and move. So there is need to define more characteristics that define living things.
There are 5 basic functions that can be used to define living things:
Carolus Linnaeus developed the first system to classify living things. This system is still used today with some modifications.
Organisms that have the most characteristics in common are classified into the smallest unit of classification called Species. It is actually difficult to define species in a way that will apply to all scientific situations, but we can vaguely tell when organisms are of the same species. Species is a group of similar organisms that can reproduce more of their own kind and the offspring can also reproduce more of their own kind.
Similar species can be grouped together into Genuses and similar genuses can be grouped into families. Families that share characteristics are grouped into Orders. Similar orders form classes and several similar classes form a phylum. Several similar phyla combine to form a kingdom. The kingdom is the largest grouping of living things.
Organisms have different names in different communities and different languages, so to make it easier for scientists, there is need to develop a naming system that will be universal. Linnaeus developed a naming system that combines the genus and species name to form what is now referred to as an organism's scientific name. Most genus and species names are derived from Latin. For example, the name Canis familiaris desribes all domestic dogs. Canis is the genus name, familiaris is the species name.
The process of classifying organisms continues to change as more discoveries are made and especially as scientists incorporate genetic information. Organisms that were previously thought of as similar may now be classified into separate groups based on their genetic information and other new discoveries. Firstly, various scientists have proposed the introduction of anew taxonomic rank called the Domain. This is even higher than the Kingdom. But even at this point, there are two different ways of lcaasifying kingdoms into domains inclduing the 2 domain and the 3 domain systems. In the 2 domain system, the Archaea are classified into the Eukarya domain as shown below.
As already indicated, there are several ways to classify organisms into groups. The most recent classification splits organisms into 7 kingdoms. Old classification systems had 6 kingdoms and some scientists have classified organisms into 8 kingdoms. In this coourse, we will focus on the 7 kingdoms that have received more widespread acceptability in the scientific community.
The 7 kingdoms include:
But first, let's get 'viruses' out of the way. Scientific opinions differ on whether viruses are a form of life or organic structures that interact with living organisms. They have been described as "organisms at the edge of life", since they resemble organisms in that they possess genes, evolve by natural selection, and reproduce by creating multiple copies of themselves through self-assembly. Although they have genes, they do not have a cellular structure, which is often seen as the basic unit of life. Viruses do not have their own metabolism and require a host cell to make new products. They therefore cannot naturally reproduce outside a host cell.
Bacteria are mostly free-living organisms often consisting of one biological cell. Bacteria are present in soil, water, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Humans and other animals have large numbers of bacteria. Most are in the digestive system especially in the mouth and gut, and there are many on the skin. Most of the bacteria in and on the body are harmless or rendered so by the protective effects of the immune system, and many are beneficial for metabolism. Several species of bacteria are pathogenic (i.e. can cause infectious diseases) including cholera, syphilis, anthrax, leprosy, tuberculosis, tetanus, bubonic plague and many others.
Archaea: These are single-celled organisms that lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria, but this classification was revised. Archaea have genes and several metabolic pathways that are more closely related to those of eukaryotes. The first observed archaea were extremophiles, which means living in extreme environments such as hot springs and salt lakes with no other organisms. New technologies involving molecular characterization led to the discovery of archaea in almost every habitat, including soil, oceans, and wetlands. There is no known pathogenic archaea, instead they are mostly mutualists. They inhabit the gastrointestinal tract in humans and ruminants, where they facilitate digestion. Methanogens are also used in biogas production and sewage treatment
Historically, protozoans were regarded as "one-celled animals", because they often possess animal-like behaviours, such as motility and predation. Even the word 'protozoa' means 'first animal'. They are single-celled but large sized microorganisms. Some are parasitic while others are harmless. Traditional textbook examples of protozoa are Amoeba, Paramecium, Euglena and Trypanosoma.
This kingdom consists of single-celled and multicellular eukaryotic species that share similar features in their ability for photosynthesis. Members of this kingdom include some 'algae', diatoms, oomycetes, and certain 'protozoans'. Notice the overlap here with the 'Protozoa' kingdom.
Fungi (singular, fungus) include organisms such as yeast, mushrooms, and molds. Some members of the fungi kingdom cause diseases, but others play a vital role in the environment by breaking down dead organisms.
Historically, the plant kingdom included all living things that were not animals, and included algae and fungi. All current definitions exclude the fungi and some of the algae. Most plants are photosynthetic eukaryotes, forming the kingdom Plantae. Many are multicellular. Green plants obtain most of their energy from sunlight, using chloroplasts. Chloroplasts perform photosynthesis using chlorophyll, a pigment which gives plants their green color and is necessary to capture the energy from the sun.
Animals are multicellular, eukaryotic organisms. With only few exceptions, animals consume organic material, breathe oxygen, are able to move, can reproduce sexually. All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. They produce haploid gametes through a process called meiosis; the smaller gamete, motile gametes are spermatozoa and the larger, non-motile gametes are ova.
Most plants are multicellular, the cells differentiate and develop into multiple cell types that together form tissues and organs performing diverse functions such as vascular tissue with specialized xylem and phloem and roots (organs) to absorb water and minerals, leaves for photosynthesis, and flowers for reproduction.
Stems are structures that hold a plant up and support its leaves and branches. Some stems, such as those of many flowers, are soft stems. Woody stems are tough and strong, with protective bark. Some plants store food in their stems such as sugarcane. Other plants use their stems to store water such as cactuses.
Roots anchor the plant to the ground. They also sore food and absorb water and nutrients from the soil. Roots have root hairs which are well adapted to absorb water and dissolved minerals.
Leaves come in many shapes and sizes ranging from broad to narrow elongated leaves, and others are shaped like needles. Leaves may also be simple or compound leaves. The outermost layer of a leaf is the epidermis. It is covered by a waxy coating called the cuticle. On plants that stay green year-round, such as pine trees, the cuticle prevents the leaves or needles from losing too much water, especially during cold or dry weather.
Photosynthesis is the process where plants convert light energy into chemical energy that is used to conduct various functions such as growth. Some of the chemical energy is stored as sugar or starch. Photosynthesis occurs in structures called chloroplasts, which are found mainly in plant cells. Chloroplasts use carbon dioxide and water as the raw materials to produce food in form of glucose. Oxygen is also produced as a waste product of photosynthesis, and it is released into the atmosphere by the plant. Animals that eat plants obtain this chemical energy from the plants.
Plant reproduction is the process by which plants produce new plants, allowing plant species to grow, spread, and continue from one generation to the next. There are two main types of plant reproduction: sexual reproduction and asexual reproduction. Sexual reproduction usually involves flowers or cones, where pollen from one plant combines with an ovule to form seeds that can grow into new plants. Asexual reproduction does not require seeds or pollen and occurs when new plants grow from parts of the parent plant, such as stems, roots, or leaves. Both types of reproduction help plants survive, adapt to their environment, and maintain healthy populations.
Pollination is an important step in plant reproduction that allows plants to make seeds. It occurs when pollen is transferred from the male part of a plant (the anther) to the female part (the stigma) of the same plant or another plant of the same species. There are different types of pollination. Self-pollination happens when pollen is transferred within the same flower or between flowers on the same plant. Cross-pollination occurs when pollen is carried from one plant to another, often by wind, water, insects, birds, or other animals. Pollination helps increase plant diversity and leads to the production of fruits and seeds.
A seed is a structure that contains a young developing plantand stored food. Under suitable environmental conditions, the seed will grow into a new plant. Seed plants reproduce by sexual reproduction. The male sex cell is called a sperm, and it must unite with the femaile sex cell called the egg. Sperm cells are located within pollen grains, which are produced in the anther of the flower. Eggs are located in the flower's ovary. The ovary is located at the bottom of the stigma. The transfer of pollen from the anther to the stigma is called pollination. The transfer results in the union of male and female sex cells. This union is called fertilization and results in the formation of a viable seed.
Seeds need to be transferred from the parent plant/tree so that they can grow in a different area not too close from the parent. This process is called Seed dispersal. Some seeds are light and can be blown away by wind. Other seeds stick on animal fur and are carried by the animals to distant locations. Some other seeds are eaten by animals but not digested so the animal poops the undigested seed at a different location.
A plant's life cycle refers to the series of stages that a plant goes through as it grows and develops and eventually returns to the starting point. In seeded plants, the life cycle begins with a seed that germinates and grows into a mature plant that also produces seeds.
In seedless plants such as mosses, their life cycle has two separate stages, one is asexual where the plant producers spores. The other stage is sexual reproduction during which the plant needs both male and female cells so as to reproduce. The process of going from sexual to asexual reproduction is called alternation of generations (also known as metagenesis or heterogenesis.
Seeded plants can be classified into angiosperms (reproduce using flowers) and gymnosperms (do not use flowers). In gymnosperms, the seeds are produced in cones such as those in pine trees. Gymnosperms range in size but most of them are large trees and they make up the majority of forests in the nothern latitudes in North America and Europe. Most of the fruits and nuts we eat are produced by angiosperms.
There are many ways in which plants use to store food. Sweet potatoes, beets, carrots, parsnips all store food in their roots. Potatoes, sugarcane and ginger store their food in their stems. Some leaves such as lettuce, cabbage, spinach etc also have some energy stored in them though they dont primarily function as food storage organs. Cauliflower and broccoli are in fact flowers. As mentioned previously, seeds have a storage of food meant to be used during germination. People eat various kinds of seeds including beans, rice, corn, wheat, peanuts etc.
Vertebrates
Vertebrates includes all animals with a segmented backbone and have a nerve cord running down their backs thus are called chordates. Vertebrates also have an endoskeleton, i.e. an inner skeleton that gives them structure and helps them to move. The endoskeleton is made of bone and cartilage. Cartilage is a soft bone-like material found on the ends of bones or on in some structures on its own. Some vertebrates are tetrapods, i.e. thya have 4 feet, and others are Bipeds, i.e. have two feet. Vertebrates can be further subdivided into seven classes:
Invertebrates
More than 95% of all animals are invertebrates, i.e. they do not have a backbone.
Arthropods are the largest group of invertebrates with over 1 million species such as insects, spiders, crabs, shrimp and lobsters. Flat worms can live in water, in damp places or inside humans/animals. Unlike flatworms, segmented worms have bodies divided into compartments. They include earthworms. Cnidarians include jellyfish and corals. They have stining cells that they use to capture fish and other organisms. Sponges come in many colors and they attach themselves to the ocean fllor and filter small food particles from the water. Echinoderms include sea stars and sea urchins. They have spiny skin and move slowly. Mollusks include snails, squids, clam, oysters etc. Most of them live in water but some, such as snails, live on land.
Arthropods
They possess an exoskeleton with a cuticle made of chitin, often mineralised with calcium carbonate, a segmented body, and paired jointed appendages. In order to keep growing, they must go through stages of moulting, a process by which they shed their exoskeleton to reveal a new one. They are an extremely diverse group, with up to 10 million species.
The three largest groups of arthropods are crustaceans, insects and arachnids.
You have learnt previously that living things are made of cells and that many cells of the same type make up tissues. Tissues that perform the same function are organized into organs. and multiple organs that perform one function are organized into organ systems.
The human body has ten major systems which include the skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, urinary, and the reproductive system. These systems will be discussed in more detial in subsequent years.
In this section, you will learn the basics of some of the animal systems.
Living things obtain energy from food. Photosynthetic organisms can make their own food using the energy from the sun. Most other organisms obtain their food by consuming it in a process called ingestion. After the organism obtains (ingests) food, the food goes through a process where it is gradually broken down into smaller and simpler structures that the body can utilize for energy. Digestion is the process where ingested food is broken down into molecules that are usable by the body. Excretion is the removal ot waste material from the body. This waste material usually has little value to the body and in some cases, it can be toxic.
Invertebrates have several ways to digest food and release wastes. Sponges are filter feeders, the pores filter food from the water. In other invertebrates such as cnidarians and flatworms, food enters the body and leaves from the same opening. Invertebrates with more advanced digestive systems such as earthworms use a tube-within-a-tube system. These have separate openings for ingested food and for excreted wastes.
Vertebrates are more complex and so is their digestive system. They have many structures in order to handle different diets from teeth specialised to chew the type of food/feed, to digestive systems that have bacteria to help digest plant material.
Human digestion starts in the mouth. Nutrients are absorbed in the small intestines and then move into the blood. Solid wastes are processed and eliminated from the body. The kidneys, liver, lungs and skin also help eliminate other types of waste material.
The product of digestion of carbohydrates is glucose, which is a simple sugar. Glucose is used by most of the body cells to make energy through a process called cellular respiration.
Although there is a connection between cellular respiration and the respiratory system, students should not be confused. The respiratory system relates to how to body obtains oxygen from the environment and releases carbon dioxide and moisture, which are waste products. The oxygen is needed for cellular respiration, and the carbon dioxide and moisture are the waste products from cellular respiration.
Some soft bodied invertebrates such as flatworms rely on simple diffusion for their exchange of gases. Diffusion is the movement of molecules from an area of higher concentration to areas of lower concentration. For oxygen to diffuse effectively, the surface must be moist, which is why most worms and snails stay in moist places.
Other invertebrates such as crustaceans have gills specialised for the gas exchange. Gills are feathery structures with a rich supply of blood vessels and the gas exchange occurs in these blood vessels.
As indicated previously, vertebrates are more complex in structure, which also means they have more complex systems. Amphibians live in water when they are young and on land when they are adults. Young amphibians have gills where gas exchange occurs. Adults have lungs for gas excahnge. Gas exchange can also occur through their skin in both young and adults.
Birds, mammals and reptiles use lungs exclusively for respiration.
In humans, air enters through the nose and mouth and passes through the pharynx then into the larynx and then trachea. The trachea divides into bronchi, then bronchioles and finally ends with sac-like structures called alveoli. Alveoli are very thin-walled and have high blood supply to allow gas exchange.
The circulatory system is the body's transport system, it moves important materials such as oxygen, glucose and waste materials throughout the body to areas where the materials can be utilized, or eliminated.
Circulatory sytem can either be open or closed. In open circulatory system, the blood is not fully enclosed within blood vessels. Instead of moving into smaller blood vessels, the blood is released directly into the tissues. A closed circulatory system is where the blood is contained inside blood vessels. Materials diffuse in and out of the blood through the walls of the vessels.
Many processes in the body occur at a certain temperature. Therefore there is need for animals to maintain an internal temperature that will allow them to function properly. Some animals do not have to ability to regulate their body temperature and they rely on the environmental conditions. For example, when its hot, reptiles will burrow under rocks to stay cool, when its cold, they will bask in sunlight to stay warm. These animals that cannot regulate their internal tempeature and rely on the environment are named cold-blooded animals. Amphibians, reptiles and most fish are cold-blooded.
Mammals and birds are warm-blooded. Their body temperature remains the same even when the environmental temperature changes. These animals have several adaptations that allow them to give off heat when its hot (such as through perspiring) or some have a very thick coat of hair and fat that act as insulation to prevent heat from leaving their body when its cold outside.
An adaptation helps an organism to survive and reproduce in a specified environment. Organisms respond to a stimulus in their environment. A stimulus is something in the environment that can be detected/sensed by living organisms and can cause the living organismm to respond. This response, toward ot away from a stimulus is called tropism. The growth of a plant toward a stimulus is called positive tropism, while the growth of a plant away from a stimulus is called negative tropism.
Plants can respond to light, water and gravity. They respond to light by growing towards the source of light. Plants roots can also grow toward a water source. Plants roots also grow in the same direction as the pull of gravity.
The response of a plant to something in the environment is called Tropism.
The prefix 'hydro' means 'water'. When a plant’s roots grow toward water, they are demonstrating a positive called hydrotropism. Gravitropism is a plant’s response to gravity. The roots of a plant show positive gravitropism, and its stems show negative gravitropism.
Tropisms are caused by chemicals called auxins. Auxins can stimulate parts of a plant to grow quickly or slowly.
Many plants have adaptations that allow them to grow in harsh conditions. Desert plants are masters of survival. The stem of a cactus can store enough water from one rainfall to survive years of drought. Plants have other adaptations as well. For example, it is a bad idea to grab a poison-ivy plant if you want to pull it out of the ground. The plant produces oils that may cause a severe rash. Thorns are another adaptation that some plants have for protection.
Plants also have many adaptations to survive in their environments. Some have scented flowers to attract pollinators. Some aquatic plants, such as water lilies, have stomata on the top surface of the leaf instead of the bottom. This enables the stomata to take in and release carbon dioxide and oxygen.
Phototropism
Structural adaptations are adjustments to physcial structures on the organism. For example, it could be fur color, strong jaws, the ability to run very fast, having a long neck etc. Cactuses have a thick waxy cuticle that prevents water loss in their dry environment.
Desert animals are often nocturnal, which means they are active at night when the temperature is cooler. During the day, these animals stay in underground burrows to avoid the heat.
Camouflage
Camouflage is any coloring, shape, or pattern that allows an organism to blend in with its environment. Predators with camouflage can sneak up on prey. Camouflage also helps prey animals hide from predators.
Protective coloration is a type of camouflage where the color of an animal helps it blend in with its background. In winter, the arctic fox has a white coat that blends in with the snow. In summer, the foz's coat changes color to blend in with plants that grow in the warm weather.
Protective resemblance is when the organism combines multiple mechanisms such as protective coloration, shape, texture etc to resemble the environment.
Some animals have adapted to their environment by copying other well-adapted organisms. An adaptation in which an animal is protected against predators by its resemblance to an unpleasant animal is called mimicry.
Mimicry: The example here shows a coral snake that is poisonous and a milk snake that is harmless. The milk snake mimics the coloration of the coral snake so it will also appear to be poisonous.
Some individuals change their behavior to be able to survive in the ecosystem. For example, wolves travel in packs, this way they can hunt more successfully. Some fish swim in groups (called schools), which protects them from predators. Some behaviors help animals survive different climatic conditions in their ecosystem. Some animals move (migrate) to find food, water and a less severe climate. Other animals such as snakes, turtles, frogs etc hibernate to escape the cold. Hibernation is when an animal drastically reduces its activity and as a result, its metabolism, as a way to conserve energy during cold winters, and resumes normal activity when temperatures improve in Spring.
Some behavioral adaptations occur naturally and are therefore called Instincts. An instinct is an inherited behavior, one that is not learned. A newborn puppy can find its way to its mother’s milk. A spider can weave webs as soon as it hatches. Birds know how to build safe, strong nests. These animals are not taught how to do these things. The skill or knowledge is an instinct.
Birds know how to build safe, strong nests. This skill is an instinct.
All living things are made up of one or more cells. A cell is the basic unit of life and the smallest part of a living thing that is capable of life. Most cells are too small to be seen with the unaided eye. We need to use an instrument called a microscope to be able to visualize cells.
The term 'cell' was coined by a scientist called Robert Hooke, who was the first to develop a microscope and used it to study thin slices of cork.
Anton van Leeuwenhoek was a Dutch scientist who developed an improved version of the microscope that was almost ten times more powerful than the one developed by Hooke.
In 1831, another scientist named Robert Brown discovered the nucleus of a plant cell. After several sudies observing multiple tissues from plants, the German scientist Matthias Schleiden concluded that plants were made up of cells. Theodor Schwann conducted similar studies in animals and concluded that animal were also made up of cells. It was the work of these many scientists that resulted in the cell theory.
The cell theory is a scientific theory first formulated in the mid-nineteenth century, that organisms are made up of cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre-existing cells. Cells are the basic unit of structure in all organisms and also the basic unit of reproduction. The three tenets of the cell theory are:
All organisms are composed of one or more cells.
The cell is the basic unit of structure and organization in organisms.
Cells arise from pre-existing cells.
Organisms can either be unicellular (made up of only one cell) or Multicellular (made up of more than one cell, and may be made up of trillions of cells.) Cells can specialize to perform specific functions. For example, blood cells, muscles, nerves are all specialized to perform their function.
The first microscope as developed by Robert Hooke.
All matter is made up of tiny particles called atoms. There are over 100 kinds of atoms each with different properties.
An element is a pure substance that cannot be broken further into simpler substances. Atoms of the same element have the same structure, i.e. elements have only kind of atom.
Atoms can combine through chemical reactions to form a compound. A compound is a new substance formed by the chemical combination of two or more elements.
Cells have several compounds required to fultil the several biological processes occuring in the cell. Carbohydrates are compounds or carbon, hydrogen and oxygen. (you have heard people refer to some food as Carbs. This usually means the food is predominantly carbohydrates). Carbohydrates in the cell are a source of energy. Lipids (fats and oils) are made up of Carbon, hydrogen and oxygen. They store and release energy as needed. Proteins are made up of carbon, hydrogen, oxygen and nitrogen. Proteins are needed for cell growth, repair and maintaining cell structure. Nucleic acids are made up of carbon, hydrogen, oxygen, nitrogen and phosphorus. Nucleic acids are mainly DNA and RNA. They enable the cells to make proteins and are also important in genetics and inheritance.
The single cell of a unicellular organism carries out all the functions necessary to keep the organism alive. A group of similar cells that perform the same function make up a Tissue. Animals are mostly composed of 4 types of tissue:
An Organ is a group of two or more types of tissue that work together to carry out a specific function. The skin is the largest organ with several layers made up of different tissues. The heart is also an organ that is made up of muscle tissue, connective tissue and nerve tissue. The brain, lungs and eyes are more examples of organs.
Plants also have organs namely the roots, stem and leaves. These support photosynthesis, absorption of water absorption and transport.
A group of organs working together is called an organ system. The circulatory system in humans combines the heart, blood vessels and blood to deliver oxygen and nutrients to various parts of the body and eliminate waste material. The repiratory system obtains oxygen from the environment and carries it to the blood where it enters the circultory system. Carbon dioxide from the blood enters the respiratory system and is released as a waste product.
Plant and animal cells differ in:
The Nucleus
The nucleus is the brain of the cell. It is a large dark round spot inside Plant & Animal cells. It houses the nuclear DNA and controls the daily activities of the cell. Because it holds the genetic material in the DNA, it can be termed as the library of the cell. Inside the nucleus is a jelly-like fluid medium called the nucleoplasm, that provides support to the contents in the nucleus.
Cytoplasm
Inside the cell, but outside the nucleus is the cytoplasm, which is a gel-like substance that dissolves nutrients to be used for various physiological functions. The cytoplasm also suspends the organelles preventing them from crushing into each other.
Mitochondria
The mitochondria is the powerhouse of the cell. It produces ATP (Adenosine Triphosphate); which is the most common form of energy in the cell. The process involved in energy metabolism is referred to as Cellular Respiration. It is shaped like a sausage on the outside, but contains a double membrane on the inside (outer and inner membrane).
Vacuole
The vacuole appears hollow when viewed under a microscope. The organelle is more prominent in plant cells and is located somewhat at the center of the cell. Vacuoles function as storage organelles storing water, nutrients and waste.
Chloroplasts
Chloroplasts are only found in plant cells. They contain chlorophyll which s responsible for capturing light energy for photosynthesis.
Cell Wall
A cell wall is found in plant cells only. It is the rigid thick outer wall surrounding the cell. It gives the cell its regular shape and provides support to the plant. It's made up of cellulose which is also a structural molecule.
Cell Membrane
Also called Plasa membrane. It's present in both plants and animal cells. In plants, the cell wall is located on the inside surface of the cell wall. The cell membrane is made up of a phospholipid bilayer with other large molecules scattered. It retains cell contents inside the cell and allows movement of substances inside and outside the cell.
The anatomy of a plant cell
The anatomy of an animal cell
The plasma membrane is composed of phospholipids and proteins. The phospholipids are organized in two layers thus referred to as a phospholipid bilayer. As the name suggests, a phospholipid has a phosphate head that is hydrophilic (water loving - can interact with water) and a lipid tail that is hydrophobic (water hating - does not interact with water). Due to this property, the phosphate heads are oriented towards the side of the plasma membrane where water molecules are located.
Retains cell contents
Acts as a barrier, selectively allowing (and blocking) movement of certain material into and out of the cell.
Various proteins are embedded within the two layers of the phospholipids. These are known as membrane proteins. Proteins serve various functions including channels, carriers, signaling, receptor, or enzymes.
The structure of the plasma (cell) membrane
Transport across the cell membrane is either Active (requires energy) or Passive (does not require energy to occur).
Passive transport include Diffusion and Osmosis.
Simple Diffusion
The random movement of molecules from an area of higher concentration to an area of lower concentration until the concentration is uniform throughout the space, that's why when you add a drop of red dye into a clear glass of water it will spread throughout the water until it establishes an equilibrium.
Dynamic Equilibrium
Dynamic Equilibrium describes a scenario where the diffusing particles are still moving, (diffusing) but the movement no longer results in a net change in concentration at one location, more than another location. When there is a membrane, dynamic equilibrium is a state where the diffusing molecules move across the membrane at almost the same rate in either direction.
Diffusion across a membrane
Diffusion can occur across a semi-permeable membrane, from the side with higher solute concentration (lower water concentration) to the side with lower solute concentration (higher water concentration), until the concentration is equal.
Membranes can be classified as:
An illustration of simple diffusion
Facilitated diffusion uses transport proteins to facilitate the diffusion of particles across the plasma membrane. There are 2 types of transport proteins and they are recognized based on their shape, size, and electrical charge: Carrier Proteins are those protein that change shape to allow certain molecules to cross the membrane. Channel Proteins are proteins that form tunnel-like pores in the cell membrane, allowing electrically charged ions in and out of the cell.
An illustration of Facilitated diffusion
Osmosis is the movement of water through a selectively permeable (semi-permeable) membrane from an area of higher water concentration to an area of lesser water concentration.
A solute are molecules that are dissolved in a solvent to form a solution. A solvent is substance that dissolves the solute. In most biological reactions, the solvent will be predominantly water. A solution is the result of dissolving a solute in a solvent.
The environment inside a cell can be described as Intracellular while the environment outside the cell is termed as Extracellular. Usually these two environments differ in their chemical composition.
In plant cells, when cells lose water, they shrink and the plant appears wilted. However, in cases where water is entering the cells, the cell walls in plant cells allow them to resist the pressure so they do not burst. This pressure created by water moving into the cells is called Turgor pressure.
Osmosis
Cells grow for a certain length of time then they stop growing. After growth, some cells die while other divide to produce new cells. The process of cell division, growth death/further cell division to replace dead cells is called the cell cycle. Depending on the type of organism or the the part of the body, A bacterial cell can divide to produce two new cells every 20 minutes. The two new cells divide to produce 4 and those 4 divide to produce 8. In a matter of hours, a bacterial cell can produce millions of cells.
Cells can grow to different sizes but most cells are too small to be seen with the naked eye. The most important factor that regulates cell size is the ability to transport materials in and out of the cell. Materials needed for various cellular functions and those produced by the cellular processes as waste. The process of cell division and growth is controlled by intricate processes to ensure the cells do not divide too fast (or too slow), and they also do not grow too fast. Cancer is a condition characterised by failure of the control processes regulating cell division and growth. Vancer cells divide too fast and do not get sufficien ttime to grow before dividing again so they accummulate even more genetic defects. The increased cell division results in the formation of tumors, which are clusters of cancer cells. Some tumors can be life threatening when they affect important biological processes.
Cell division can occur through Mitosis or Meiosis. In mitosis, the cell divides into two cells that are more or less identical to the parent cell. Meiosis is cell division that results in formation of gametes which are involved in fertilization to form a zygote, which develops into a new organism.
Mitosis is a type of cell division which results in 2 identical 'daughter' cells being produced from a 'parent' cell. An average human being has about 60 trillion cells and millions of cells are constantly dividing to maintain this number. Some cell types divide faster (such as hair cells), relatively slowly (such as stomach epithelium) and others do not divide at all (nerve cells). Mitosis is necessary for growth, tissue/cell replacement and for tissue repair (after injury).
Mitosis is a continual process, but can be divided into 5 phases.
Mitosis - Animals versus Plants
There are 2 main differences between animal and plant cell division:
Meiosis is a type of cell division that results in the formation of gametes (sex cells). Gametes may be either sperms or ova (eggs). Gametes contain half the genetic information of other body cells, and are thus described as Haploid. Each sperm or egg produced carries 1 of over 8 million possible combinations of parental chromosomes. A human germ cell with 46 chromosomes will undergo meiosis and produce gametes that have 23 chromosomes. The 46 chromosomes number is referred to as diploid and is written as 2n. The 23 chromosomes number is referred to as haploid and is written as n. Fertilization occurs when 2 gametes (sperm & egg) fuse, forming a diploid zygote (46 chromosomes).
Meiosis occurs in two main phases namely Meiosis 1 and Meiosis 2. Meiosis 1 comprises of Interphase, Prophase I, Metaphase I, Anaphase I and Telophase I. These are followed by Meiosis 2, which comprises of Prophase II, Metaphase II, Anaphase II and Telophase II.
Interphase
As in mitosis, interphase (cell growth and DNA replication), must occur before cell can replicate. Interphase occurs before prophase I but not before prophase II.
Prophase I
Metaphase I
Anaphase I
Telophase I
An overview of Meiosis I. (Source: Wikipedia-CC BY-SA 3.0 )
The short phase between Meiosis I and II is referred to as interkinesis. There may or may not be an interphase II depending on species. The next set of cell divisions will separate the chromatids.
Prophase II
Metaphase II
Anaphase II
Telophase II
An overview of Meiosis II. (Source: Wikipedia-CC BY-SA 3.0)
It is important to remember that Meiosis I is referred to as reduction division because the chromosome number is reduced by half. Meiosis II is called equational division and is similar to mitosis as centromeres on sister chromatids separate and chromosome number remains unchanged.
Reproduction
The simplest means of reproduction is Asexual reproduction. This is the production of new organisms from one parent. The offspring is identical to the parent. Asexual reproduction can be an advantage because it enables organisms to increase in numbers quickly.
There are several types of asexual reproduction. In some cases, it is a simple mitosis such as binary fission in bacteria. In other cases, it involves a process called budding. Budding occurs when an outgrowth (a bud) develops as a product of increased cell division. Eventually the bud can break off and develop into a new organism. In some cases (such as se stars), a piece that breaks off can grow into a new organism in a process called regeneration. Some plants especially the grass family can grow new stems from underground roots. These stems can grow into complete plants.
Sexual reproduction occurs in the more complex animals and usually involves the fusion of two cells (gametes) in a process called fertilization. Fertilization can either occur inside the female body (internal fertilization) or outside the female body (external fertilization). Most fish and amphibians utilize external fertilization. Reptiles, bords and mammals utilize internal fertilization. The fusion of the gametes results in the formation of a zygote, which divides through mitosis eventually forming a new organism.
Life Cycle
Life cycle describes the stages that an organisms goes through from birth, youth, reproductive age, old age and death. The longest period an organism can live under the environmental conditions is called Life span. An organism's life span is usually influenced by its species, some species can live longer while others do not. For example, annual plants only have a life span of 1 year, while perennial plants can live longer. Bristlecone pines can live more than 7000 years. Life expectancy refers to the average amount of time that an individual of a species is likely to live. it considers many factors such as the environment, availability of food, healthcare and other factors that could affect an organism's livability. As an example, the lifespan of humans is more than 100 years, but the life expectancy of humans in the USA is 77 years. Life expectancy in developing countries is even lower (65 years in Ghana) and is even lower in countries with unstable political environments (55 years in Sudan).
A microorganism is an organism that is microscopic, it cannot be visible to the unaided eye. Microorganisms are also called microbes. They can be unicellular (made up of one cell) or multicellular (made up of more than one cell). Depending on the size of the cell, some unicellular microorganisms are easier to see while some multicellular organisms arent.
Microscopic Fungi
Microscopic fungi include mold and yeast. They obtain nutrients by absorbing from the environment. Mold and yeast are used to make foods such as cheese and bread. Louis Pastuer was one of the early scientists to study microorganisms. He described how yeast causes bread to expand. The yeast cells feed on starch through anaerobic respiration (fermentation) releasing carbon dioxide. It is the carbon dioxide that forms bubbles in the bread dough and swells/expands when heated.
Some fungi produce products that have antibacterial properties. Some species of the genus Penicillium produce Penicillin, which is one of the most popular antibiotics. Many fungal and yeast species cause disease such as Athlete's foot. Diseases caused by fungi range in severity from life threatening infections to low priority infections.
Bacteria
Bacteria are unicellular organisms. Most are harmful but a few are pathogenic and can cause severe infections.Streptococcus bacteria cause Strep infection (throat infection). Many Lactobacillus bacteria species are used in making yogurt and are not harmful to human health, they are in fact beneficial.
Microbiome
Most animals including humans have bacteria that reside on the skin and inside the gestrointestinal tract. These animals maintian a healthy balance of several bacterial species on the skin and gut. Most of these species are beneficial to the animal's metabolism. The combination of bacterial species resident on and in the animal are described as the animals microbiome.
Imbalances in the species of the microbiome can result in diseases. For example, people who consume antibiotics for an extended period of time will end up killing most of the bacterial species and this imbalance cause an increase in fungal species resulting in fungal infections. The continued use of antibacterial soaps when washing hands or showering can also cause imbalances in the microbiome of the skin and might result in infections.
Reproduction
Most protists reproduce by binary fission. Binary fission is a type of asexual reproduction in which the organism's cell divides into two.
Protists can also reproduce by conjugation. Conjugation is a form of sexual reproduction where organisms fuse, exchange genetic material then they break apart and divide by fission.
Some other protists reproduce using spores. Spores carry the genetic information within a protective membrane and can survive very harsh conditions. Under the right environmental conditions they grow and begin to multiply.
Some fungi such as yeast reproduce by budding. Budding is an asexual reproduction where a small growth appears on the parent cell called a bud. The nucleus in the parent cell divides into two so that the bud now has genetic material identical to the parent genetic information. Eventually the bud breaks off and lives as a new organism.
Some fungi also reproduce by spores. The spores are protected by a coating. If the spread to a suitbale place, they can develop into adult fungi.
Many bacteria reproduce by binary fission. Some bacteria can also reproduce by conjugation as described previously.
Bread Mold
Bread mold appears like adark gray or black fuzz growth on bread. It starts localised in circles but with time spreads throughout the bread. It occurs most commonly when the bread is stored in a warm moist environment. Bread mold is made up of tiny filaments called hyphae. Hyphae spread out in tangled mass that cover a large surface area. They secrete special chemicals that enable them to digest and absorb nutrients from the bread. These chemicals are called enzymes. Enzymes are chemicals/substances that cause certain chemcal reactions to occur, or make chemical reactions occur faster. Some hypahe grow upward. These are the hypahe that produce spores. The spores are the sexual part of the mold's life cycle. Sexual reproduction occurs when two hyphae fuse and form a new spore producing structure.
Genetics is the study of genes, variation and heredity, of how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence.
Lesson 1: Control of Traits Lesson 2: Human Genetics Lesson 3: Modern Genetics Lesson 4: Genetic ChangeLiving things usually tend to look like their parents. Parents pass some features (inherited traits) to their offspring. Inherited traits are characteristics that are passed from parent to offspirng. For example, eye color in humans is inherited from the parents. The passing of inherited traits from parents to offspring is called heredity. Inherited traits should be differentiated from acquired traits. Acquired traits are characteristics that are developed by an individual as they live and are influenced by the environment. For example, the ability to sign a complex song may be an acquired trait. Acquired traits are not passed on to offspring. For example, a heavy built weight-lifter does not produce heavily built children.
A lot of the basic genetic knowledge present today resulted from several experiments conducted by an Austrian monk named Gregor Mendel. Mendel is considered the founder of genetics.
In 1856, Greogor Mendel begun hsi experiments using pea plants to study how traits were passed from parents to their offspring. Mendel studied the inheritance of 7 mani traits. Organisms that always express a trait are called purebred. For example, a purebred tall plant will always produce tall offpsring. Mended crossed tall pea plants with short pea plants to produce hybrids. A hybrid is an organism that inherited two different forms of the same trait. Surprisingly, all the hybrid offspring were all tall. Mendel explained this by saying that the trait resulting in tall pea plants masked the trait for short pea plants.
Dominant and recessive traits
Mendel hypothesized that the presence of tall trait prevented the short form from being observed. He called the tall form dominant, which means that it masked the other form of the trait for height. Inheriting one dominant form caused the dominant trait to appear. Mendel called the short form of the trait the recessive trait, or the hidden form of the trait. He called the different forms of the traits factors.
Let's express the height trait using the letter T. Every individual plant receives one form of the trait from the two parent plants. So the height trait is represented by two letters. Depending on the form of trait received from the parents, an individual can either be TT, Tt or tt. If the tall trait is dominant, then individuals with TT and Tt will be tall, and only the tt individual plants will be short.
Genes
After several years of genetics research, today we call Mendel's factors Genes. A gene is a part of a chromosome that controls a particular inherited trait. Additional research has shown that there are traits that do not follow the pattern described above and its not always easy to predict how a trait will appear in the offspring.
Mendel used mathematical probability to predict the traits observed in offpspring if we know the traits in the parents. The image here shows 4 scenarios we can use to predict the traits of the offspring using the parents genes. Punnett squares are used to predic tthe possible outcomes of genetic crosses. Letters are used to represent different genes. Uppercase letters mostly represent the dominant gene, lowercase p represents the recessive form.
Punnett Square
To make a punnett square, create a table with 2 columns and 2 rows. On the left side, indicate the genes that came from the female. At the top, represent the genes that came from the male. Each parent's gene will combine to make pairs of genes in the offspring. These are represented inside the cells of the table as shown in the image alongside.
The probability is the likelihood of an event. However, it is not the actual distribution that will be observed, the actual observed distribution is usually close enough to the propability if you have large enough number of offspring. For example, when the two parents have the Tt genes, the punnett square shows that 25% of offspring will be TT, 50% will be Tt and 25% will be tt. If T is a dominant trait, then 75% of the offspring (TT and Tt) will look the same/will express the same trait. You could predict that there is a 25% chance that the offspring will be tt.
Selective Breeding
Genetics also controls traits that are desirable for different purposes. For example, genetics can influece whether a plant will be able to survive and produce better in a desert environment. Organisms that show desirable traits can be selected and used to produce offspring. The process of selecting and mating organisms that have desirable traits so as to influence the characteristics in the offspring is called selective breeding.
Genes are the basic units ot heredity. They are arranged along the length of the chromosome in the cell's nucleus. A chromosome is a threadlike structure made by the complex folding of DNA strand. When a cell divides, chromosomes transfer the genes to new cells.
Human cells contain 23 pairs of chromosomes for a total of 46 chromosomes. Most chromosome pairs have two copies of the same gene because each organism produced by sexual reproduction receives one copy of the same gene from each parent. Remember how we expressed the Punnett square in the previous section, we indicated that one copy was from the male and the other copy was from the female, and that resulted in the offspring having two copies of the same gene.
The reason why each parent contributes only one copy goes back to the topic on Mieosis. Meiosis is the process that results in the formation of gametes. Gametes are the cells that are involved in sexual reproduction. Meiosis results in gamates that only have 23 chromosomes (note, not pairs). So gametes only have half the number of chromosomes of other body (somatic) cells. When the female and the male gamete join during fertilization, they form a zygote, which will then have 23 'pairs' of chromosomes.
An individual genotype refers to all the genes that are inherited by an organism. This differs from the organism's phenotype, which is how the organisms traits are expressed. We observe the phenotype and through it, we can infer the genotype.
Sex Chromosomes
Sex chromosomes determine the gender of an individual. In humans the x and Y chromosomes are the sex chromosomes. Offspring that receive 2 X chromosomes, one from each parent, are female. Offspring that receive 1 X chromosome from the mother and a Y chromosome end up with an XY pair and they are males. Since females are all XX, they can only contribute an X chromosome to the offspring. Since fathers are always XY, they have the ability to contribute either an X or a Y chromosome to the offspring. This means only fathers are capable of contributing the chromosome that can result in baby boys.
The X chromosome is larger than the Y chromosome, and carries more genes, not only those that influence gender. Genes located in the sex chromosomes result in traits that can be called sex-linked traits. For example, color blindness is a sex linked trait. Men are 7 times more likely to develop color blindness than women.
Pedigree
There are three genes that affect eye color. Two are on chromosome 15 and one is on chromosome 19. All three genes influence eye color.
Many traits are either dominant or recessive. Familites often show patterns in the way they inherit traits. A pedigree is a chart that traces the history of a trait within a particular family. It shows whichfamily members expressed the dominant trait in their phenotypes and which individuals expressed the recessive trait. A pedigree can also be used to trace the origin of genetic disorders in families.
Below are some rules for drawing pedigree charts
Inheritance
A carrier is an individual who has inherited the gene for a particular trait but does not express it. So the trait is in the individuals genotype but not in the phenotype.
Genetic Disorders are conditions caused by genetic mutations or changes in a gene or set of genes. An example of a genetic disorder is Hemophilia. Hemophilia patients have a disorder in the blood clotting mechanisms which results in slow clotting. When they are injured, they tend to bleed excessively. Another genetic condition is sickle cell anemia. Normal red blood cells tend to be circular disk shaped. Patients suffering from sickle cell anemia have red blood cells shaped like sickles, (hald moon shape). These cells cannot move easily in the blood vessels and they have cannot carry sufficient oxygen. Sickle shaped cells are usually destroyed by the body. These result in several signs associated with the condition including general weakness, jaundice etc.
Down syndrome is a condition that occurs when an individual receives an extra copy of Chromosome 21, so individuals have 3 chromosome 21, instead of 2, therefore down syndrome can also be called trisomy 21. People with this condition might express varying levels of mental disabilities but most of them live productive lives.
Compared to many scientific fields, which were studied way back in the 1700 and many discoveries were already made, the field of genetics is still new. Most discoveries were made after 1950 and because there were no technologies to allow more research, knowledge in the area did not expand significantly until the later 20th century and into the 21 century. This means there are new discoveries being published and the content of this website will be revised and updated as necessary.
DNA is short for Deoxyribonucleic acid. It was discovered in 1953 by James Watson and Francis Crick. The DNA molecule itself looks like a long spiral made up of two strands twisted together. This structure is called a double helix. Watson and Crick showed that each rung of the double helix was made up of a pair of chemicals called bases, and that there are 4 different bases present in DNA: Cytosine (C), Guanine (G), Thymine (T) and Adenine (A). The bases from the two strands interact with each other using weak bonds such that A bonds with T and G bonds with C. The sides of the double helix are made of sugars (deoxyribose) and phosphates.
The order of the basepairs in each strand is what determines genetic characteristics and that order is only spcific for that individual organism, no two organisms share the same order. There are many controls to ensure each gene is expressed correctly. For example, this ensures that corneal tissue develops only in of the cornea of the eye and nail tissue only grows at the tip of fingers and toes.
DNA also differs between species. The DNA of a particular species is specific to that species. All the DNA that makes up an individual is called the individual's genome. The human genome is made up of about 3 billion bases (base pairs). The variation in the number and order of these base pairs is responsible for all the variation we onserve in living organisms.
Genetic Engineering
Genetic engineering is the process of altering/changing the genetic sequence of the DNA of an individual so as to alter the characteristic/trait expressed. Genetic engineering is a controversial topic though there has been many benefits achieved in the medical and agricultural sciences. For example, genetic engineering can be used to develop plants that can grow well in dry areas, or under certain disease pressure. Probably the most significant example of genetic engineering is in the production of insulin. The gene that produces insulin in humans is removed and placed in the genome of a bacteria. Then the bacteria will divide and all the offspring will have the insulin producing gene. This way, large amounts of insulin are produced by many genetically engineered E. coli bacteria.
Cloning
A clone is an individual that receives all of its DNA from one parent and is genetically identical to the parent. One of the most popular example of cloning is Dolly. In 1996, Ian Wilmut took a body cell from an adult female sheep and transferred the cell into an egg whose nuclues. The egg begun to divide behaving as if it had been fertilized. The dividing egg was then placed into a sheep (implanted) where it developed into a lamb. The DNA of the lamb that was born was identical to the DNA of the adult sheep from which the body cell was obtained.
When we observe and compare the individuals of the same variety or sub-variety such as genus or species, of plants and animals, we notice that they generally differ more between varieties that they do with individuals of the same variety. These differences seem to develop and increase over time. Parents will show more resemblane with their children than with their grandchildren. These differences we observe in a population are called variations.
The concept of variation was introduced by Charles Darwin in 1859 in his popular (and controversial) book titled 'On The Origin Of Species. In 1831, Charles Darwin boarded the H.M.S Beagle for a journey around the world and in 1835 th ship reached the Galapagos Island in South America. It was at this island that Charles made his important observations of different species of Finches. He observed that while the 13 species of finches were the same in size and shape, their beaks looked different in size and shape. But even with these differences in sizes of their beaks, Charles Darwin thought the finches had come from a common ancestor. It seemed as if each species of finch was well suited to its specific environment. The different shapes and sizes of their beaks enabled them to feed on different seeds and insects. Each beak type was a variation among members of the same species that enabled that species to survive better and reproduce in their specific environment.
The small changes observed are caused by small changes in the DNA called mutations. Such changes can occur dur to erros during mitosis or meiosis.
Variations result in adaptations, and therefore to survival. If birds are living in an environment where seeds are the main source of food, virds that have beaks that can crush seeds will be better adapted to that environment and will survive better than birds that cannot crush seeds. This concept translates across all other species including plants. Plants that have the ability to store water, such as cactuses, will sirvive in dry conditions while plants that cannot store sufficient amounts of water will wilt and die. And vice versa, only specific plants are adapted to live in marshy waterlogged environments. The same can be said for animals, only some animals can live in water, whether it is because they have gills, or they have to rise up to the water surface every so often to take large breaths of air into their lungs and then sink back into the water. Animals in the savanna survive better if they are able to catch prey, or if they are able to avoid being caught by predators.
Animals that survive better are able to reproduce more than those that do not survive better. So the better adapted animals produce more offspring than the less adapted animals. Over time, the population will have more individuals that are adapted than those that arent. And in some extreme cases, the less adapted individuals will be completely replaced by the adapted individuals. Charles Darwin described and named this concept Natural Selection. Natural Selection occurs when organisms that are best suited to their environments survive and reproduce successfully. This concept can also be called Survival for the fittest.
Because only the fittest individuals survive, organisms have to produce more offspring or reproductive cells (gametes) than those that are necessary to grow and to also reproduce. Plants produce a lot more pollen and only a few of them will be involved in the formation of seeds. But even then, plants produce a lot more seeds than those that will grow into new plants.
Bacteria and other micro-organisms are also affected by the same pressures. Bacteria multiply very fast increasing their population exponentially withinin very short periods of time. However, environmental conditions, such as heat and lack of moisture results in the death of several microorganisms. In the human body, when the levels of pathogenic bacteria increase and cause disease, humans take antibiotics that kill the pathgenic microorganisms. Guess what happens if bacteria are exposed to antibiotics..... They develop resistance to the antibiotic. The bacteria develop a mutation that enables them to survive in the presence of the antibiotic, and as a result only the bacteria that are resistant multiply and within a shor ttime there are large numbers of resistant bacteria. The antibiotic is no longer effective in killing the 'resistant' bacteria. This is the process that results in the development of 'superbugs'.
Parts of an Ecosystem
In Grade 3, we defined an ecosystem to be made up of all the living and non-living things that function together in one place. The living things are called Biotics factors and the non-living things are called Abiotic factors. Biotic factors include all the plants and animals living in the ecosystem. Abiotic factors include all the elements that affect the plants and animals, such as the temperature, type of soil, water, rocks, etc.
Each organism in an ecosystem has its own place where it lives. This is called a habitat.
Living things in an ecosystem depend on each other to survive. This relationship maybe beneficial, like when a bees obtains nectar but also results in pollination, but in other cases, this relationship may be negative, like when a bear feeds on salmon.
In Grade 3, we also defined the word population, we indicated that a population consists of all the members of a species that live a specified geographical area. For example the number of giraffes in a specified national park. When many populations (i.e., many different species) are considered together, it is called a community. So a community will include the number of giraffes, lions, cheetahs and all other species in a defined area, such as a national park.
Cycles in Ecosystems
The water cycle is made up of three manin processes.
Evaporation
When water heats up, some of it changes into a gas called water vapor. This process is called evaporation. Water evaporates from lakes, oceans, rivers, ponds and other water bodies. Water can also evaporate from the surface of leaves in a process called transpiration.
Condensation
The water vapor travels in the air. As it rises into the air, it cools down and turns back into a liquid. The change from gas to liquid is called Condensation.. If many water droplets in the sky come together they form clouds. A cloud is a group of water droplets in the atmosphere.
Precipitation
The water in the clouds and the water vapor in the air will then fall down to the ground as rain or other kids of precipitation. Precipitation refers to any liquid or frozen water that forms in the atmosphere and falls back to the earth. It comes in many forms, like rain, sleet, and snow. If its too cold, the water droplets in clouds will freeze into ice. Freezing refers to the change from liquid to solid. Some of the water that falls as precipitation collects on land and flows downhill. A watershed is an area from which water is drained. Precipitation that flows across the land’s surface and is not absorbed will flow into rivers, lakes, and streams as runoff. Most of the water will flow from rivers to the ocean. Some of the water will settle underground and become groundwater.
Plants and animals also play a role in the water cycle. Plants absorb water from the ground through their roots. Excess water in the plant is lost through transpiration. Animals drink water and then release the excess as waste and sweat.
Carbon is one of the most important elements in every living thing. About 18% of the body is Carbon. Carbon is also plentiful in the atmosphere in form or carbon dioxide CO2 gas. Carbon is also present in rocks (as limestone).
Carbon is exchaned continously between the different sites and chemical forms. Plants take up carbon dioxide from the air to fulfill their photosynthetic needs and produce sugars (remember sugars are made of C H and O). These carbon rich compounds are then eaten by herbivores (like cattle, sheep, deer, rabbits) and omnivores (such as humans). The herbivores and omnivores use the carbon rich compounds from plants to make their own carbon rich compounds such as proteins, sugars and fats. Herbivores and omnivores are then consumed by carnivores enabling the transfer of these carbon rich compounds to all different levels of the food chain. Living organisms can also transfer their carbon when they die and decompose. In such cases, the carbon may be transferred to the soil, or maybe used by decomposers such as bacteria and fungi. The breakdown of carbon compounds by decomposers releases carbon to the environment as methane, carbon dioxide, or other carbon compounds. After millions of years, the carbon that remained in the ground will turn into fossil fuels such as coal, oil and natural gas. These will be harvested/mined by humans and brought back into the atmosphere through their use in cars, heating homes or cooking. All these processes result in the formation of carbon dioxide which goes back into the atmosphere. Plants remain the most significant users of atmospheric carbon dioxide so it is important to ensure there are many trees to avoid too much increase in the levels of atmospheric carbon dioxide. Ofcourse, it is also important to reduce the release of carbon dioxide into the atmosphere.
The air is 78% nitrogen gas. Nitrogen cycles through both the abiotic and biotic parts of the Earth system. The largest reservoir of nitrogen is found in the atmosphere, mostly as nitrogen gas (N2). Nitrogen gas makes up 78% of the air we breathe. Most nitrogen enters ecosystems via certain kinds of bacteria in soil and plant roots that convert nitrogen gas into ammonia (NH3). This process is called nitrogen fixation. A very small amount of nitrogen is fixed via lightning interacting with the air. Once nitrogen is fixed, other types of bacteria convert ammonia to nitrate and nitrite, which can then be used by other bacteria and plants. Consumers (herbivores and predators) get nitrogen compounds from the plants and animals they eat. Nitrogen returns to the soil when organisms release waste or die and are decomposed by bacteria and fungi. Nitrogen is released back to the atmosphere by bacteria get their energy by breaking down nitrate and nitrite into nitrogen gas (also called denitrification).
Interactions in Ecosystems
Living things depend on each other for survival. They establish interlocking relationships. This relationship is called Interdependence. Symbiosis is the terminology used to define a relationship between two or more kinds of organisms that lasts over a period of time.
Mutualism is a symbiotic relationship where both organisms benefit and neither is harmed. The relationship between pollinators and flowers is a good example. Pollinators such as bees obtain food (nectar) from the flowers while the flowers obtain pollination.
Commensalism is an interelationship between two organisms where one organism benefits from the other, but it does not cause harm to the other.
Remora are fish that attach themselves to the bodies of rays and sharks. The remora gets food scraps, transportation, and protection from the ray. What does the ray get from the remora? While the remora does not hurt the ray in any way, it does not help the ray either.
Sometimes its difficult to be sure whether an organisms is benefiting from a relationship or getting harmed by the relationship.
Parasitism is a symbiotic relationship where one organism benefits and the other is harmed. The individual that benefits is called a parasite. The organism that gets harmed is called the host. A parasite may live ON or IN the host. For example, ticks are parasites to dogs, cattle, goats and many other animals. A tick attaches on the host, feeds on on the host's blood and may sometimes transmit diseases to the host. Tapeworms are parasites in the digestive system of humans and some other individuals.
Ecosystems can support only so many living things. There are limited amounts of food, water, sunlight, shelter and other resources. As a result, organisms struggle against one another to obtain what they need to survive. The struggle for these resources is called competition. For example, a fox will compete with other foxes to catch rabbits. Competition can also occur across different kinds of animals. For example, foxes also compete with hawks for rabbits. The rabbits compete with other herbivores for the food.
A limiting factor is any resource that restricts the growth of populations. A forest gets more rainfall and much warmer in summer than in winter. In summer, the forest can support many more organisms than in winter. Limiting factors may also include abiotic factors. Abiotic factors are non-living factors, such as water, temperature, soil type, shelter, sunlight and others.
Carrying capacity is the largest number of individuals within a population that an ecosystem can support. As the population increases, the food becomes harder to find and some of the individuals die to the level where there is an equilibrium where there is just enough individuals to survive successfully in the ecosystem.
Overcrowding (limited space) can also limit growth. A population of algae in a pond or bacteria in a petri dish will eventually become too thick that they exhaust the resources in the space such as oxygen. Without sufficient resources, the algae begin to die off.
We can define a habitat as the physical place where an organism lives and finds its food. Some individuals have small habitats like some bugs may spend almost their entire life under a rock. In some cases, an individual's habitat can be large. For example, a bee may occupy a large habitat where it goes around obtaining nectar.
A niche is the special role that an organism plays in a community. Two birds might live in the same location and eat the same food, but one bird is active at night, the other is active during the day. Or two birds might be in the same habitat but eating different food. Multiple animals can live in the same tree but some may be at the tallest tip of the tree and others may live closer to the ground.
Living things depend on each other. They also depend on nonliving things like sunlight. Living and nonliving things that interact in an environment make up an ecosystem. An ecosystem may be a pond, a swamp, or a field, maybe large or small.
Different organisms live in different parts of an ecosystem. Fish live in the water, so the water is the fish's habitat.
A food chain shows how energy passes from one organism to another in an ecosystem. When a buffalo feeds on grass, they obtain energy from the grass, and when a lion feed on the buffalo, they obtain energy from the buffalo. energy flows from grass to buffalo to lion.
The first organism in a food chain is called a producer, these are organisms that make their own food. Green plants are examples of producers. Most producers use energy from the Sun to make their own food. This means that the energy in most food chains starts with the Sun.
A consumer is the organism that eats other organisms. All animals are consumers. A food chain may have many consumers.
Consumers are classified by the levels they occupy in the food chain. Primary consumers are organisms that eat producers. Primary consumers are the second link in a food chain, after producers. On land, primary consumers include insects, mice, and elephants. The next link in the food chain consists of secondary consumers, which obtain energy by eating primary consumers. Some birds are secondary consumers because they eat insects that eat plants. A snake that eats such a bird is a tertiary consumer. Tertiary consumers are at the top of most of the food chains. There will almost always be many more producers than consumers in an ecosystem.
Organisms that eat mostly plants are herbivores. Some animals, such as herons, eat mostly other animals. These organisms are carnivores. Animals that eat both plants and animals are omnivores.
Predators hunt other organisms for food. The organisms they hunt are prey.
A decomposer is an organism that breaks down dead plant and animal material. Decomposers put nutrients back into the soil. Some worms and bacteria are decomposers.
Since consumers can eat many types of organisms, many food chains can join to form a food web.
Plants produce their own food.
Herbivores are primary consumers that eat only producers.
Carnivores are secondary and tertiary consumers. They eat other animals including herbivores.
Omnivores are consumers that can eat both plants and animals.
Decomposers utilize dead and decaying matter into waste and simpler substances.
Living things that hunt and kill other living things for food are predators. The organisms that they hunt are called prey.
A scavenger is an animal that feeds on the remains of dead animals that it did not hunt or kill. Jackals, vultures, worms, and crows are all scavengers.
Plants are called producers because they produce their own food. Animals are called consumers because they eat, or consume, other living things. Plants are essential to ecosystems because they produce the food which all other living things need. To represent how living things feed off other living things in an ecosystem, we can use a food chain.
Competition: Sometimes living things have to compete to get what they need. This is called competition. Predators compete with each other. For example, lions and cheetahs hunt the same herbivores. Plants in a forest compete for sunlight.
Cooperation: When living things help each other to survive in an ecosystem, this relationship is called cooperation. For example, a tree may provide a home for a bird's nest. Bees can pollinate flowers.
Energy Pyramid: Whenever we consume food, we do not use up all the energy available in that food. Some of it is wasted. For example, plants use the energy from the sun to produce their food. However, when herbivores and omnivores eat the plants, they cannot be able to extract all the energy. In fact, only about 10% of energy is transferred from one level of the food chain/web to the next. An energy pyramid is a representation of the energy transferred from one level of the food chain to the next, with producers at the base of the pyramid.
What are Biomes
A biome is one of Earth’s major land ecosystems with its own characteristic animals, plants, soil, and climate. Climate is the average weather pattern of a region over time. It is determined mainly by temperature and precipitation. Differences in climate from place to place produce different conditions for living things. How is a biome different from other habitats? You can think of a biome as a set of habitats or ecosystems all grouped together into a kind of 'super-ecosystem.'
There are 5 major land biomes:
Aquatic biomes include both freshwater and marine biomes. Freshwater biomes are bodies of water surrounded by land—such as ponds, rivers, and lakes - that have a salt content of less than one percent. Marine biomes cover close to three-quarters of Earth’s surface. Marine biomes include the ocean, coral reefs, and estuaries.
Grasslands are open regions that are dominated by grass and have a warm, dry climate. There are two types of grasslands: tropical grasslands (sometimes called savannas) and temperate grasslands. Savannas are found closer to the equator and can have a few scattered trees. They cover almost half of the continent of Africa, as well as areas of Australia, India, and South America. Temperate grasslands are found further away from the equator, in South Africa, Hungary, Argentina, Uruguay, North America, and Russia. Prairies are types of temperate grasslands; prairies are characterized as having taller grasses.
Forests are dominated by trees, and cover about one-third of the Earth. The three major forest biomes are temperate forests, tropical forests, and boreal forests (also known as the taiga). Tropical forests are warm, humid, and found close to the equator. Temperate forests are found at higher latitudes and experience all four seasons. Boreal forests are found at even higher latitudes, and have the coldest and driest climate, where precipitation occurs primarily in the form of snow.
Deserts are dry areas where rainfall is less than 50 centimeters (20 inches) per year. They cover around 20 percent of Earth’s surface. Deserts can be either cold or hot, although most of them are found in subtropical areas. Because of their extreme conditions, there is not as much biodiversity found in deserts as in other biomes.
A tundra has extremely inhospitable conditions, with the lowest measured temperatures of any of the five major biomes with average yearly temperatures ranging from -34 to 12 degrees Celsius. They also have a low amount of precipitation, just 15–25 centimeters per year, as well as poor quality soil nutrients and short summers. There are two types of tundra: arctic and alpine. The tundra does not have much biodiversity and vegetation is simple, including shrubs, grasses, mosses, and lichens. This is partly due to a frozen layer under the soil surface, called permafrost.
Aquatic Ecosystem
An aquatic ecosystem is an ecosystem formed by surrounding a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms-aquatic life-that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems
The organisms in water ecosystems are divided into three main categories. Plankton are creatures that drift freely in the water. They are not able to swim. Some plankton, such as diatoms, are producers, and others are consumers, such as some animal larvae.
The second group includes the larger, active swimmers in a body of water called nekton. Fish, turtles, and whales are all nekton. The third group, organisms that live on the bottom of a body of water, are called benthos. Many benthos are scavengers or decomposers because they feed on material that floats down from shallower water.
Unlike land ecosystems, water is never a limiting factor. However, the amount of light, dissolved salt, and dissolved oxygen are important. They can all affect the types of organisms that can live in bodies of water.
Running-Water Ecosystems: Faster-moving bodies of water tend to have more oxygen, because air mixes in as the water flows. Other nutrients are washed into the water from the land. Organisms that live in fast-moving streams or rivers have adaptations to prevent them from being swept away. Slower-moving waters have less oxygen and are less dependent on the land for nutrients. More producers, such as algae, are able to survive in slow-moving water.
Standing-Water Ecosystems: The typical freshwater lake or pond is divided into three zones. The shallow-water zone along the shore is where most of the organisms live. Cattails, sedges, arrowgrass, and other rooted plants grow here. The open-water zone includes the water away from the shore. This zone may be too deep for rooted plants to survive. Algae and plankton float near the surface. Nekton, such as trout, whitefish, and pike are found here. The third zone is below the openwater zone and includes the bottom. Very little light reaches the bottom, so producers cannot grow here. Benthos, including worms and mollusks, are found in this zone.
Freshwater Wetlands: Wetlands, such as marshes, swamps, and bogs, are regions that are wet for most of the year. Grasslike plants, moss, and some shrubs are found in wetlands. Beavers, muskrats, otters, birds, and fish live in wetlands.
Marine Ecosystems: The shallow part of the ocean ecosystem is called the intertidal zone. Every day, the pull of the Moon’s gravity causes ocean tides to rise and fall over the intertidal zone. Beyond the intertidal zone is the neritic zone. The key resource in this zone is sunlight. Algae, kelp, and other producers grow in huge numbers near the surface water where sunlight can penetrate. The third zone of the ocean is the oceanic zone. It is divided into the bathyal zone and the abyssal zone. The bathyal zone is home to many large consumers, such as sharks, but few producers. Further down is the abyssal zone, where it gets darker and colder because the sunlight is completely blocked. Organisms in this zone tend to be scavengers or decomposers. They live on nutrients that float down from other zones.
Estuary
The boundary where fresh water feeds into salt water is called an estuary. Estuaries are unique ecosystems that are part salt water and part fresh water. Like intertidal zones, estuaries change with the tides. When the tide comes in, estuary water becomes more salty. The tide also brings in nutrients from the land. Many ocean fish return to estuaries to lay their eggs. Countless insect larvae, young fish, and tiny crustaceans begin their lives in the calm, protected waters within an estuary. Larger organisms, including egrets, herons, frogs, turtles, muskrats, raccoons, otters, and bobcats feed on these smaller consumers.
Ecosystems can support only so many living things. There are limited amounts of food, water, sunlight, shelter and other resources. As a result, organisms struggle against one another to obtain what they need to survive. The struggle for these resources is called competition. For example, a fox will compete with other foxes to catch rabbits. Competition can also occur across different kinds of animals. For example, foxes also compete with hawks for rabbits. The rabbits compete with other herbivores for the food.
A limiting factor is any resource that restricts the growth of populations. A forest gets more rainfall and much warmer in summer than in winter. In summer, the forest can support many more organisms than in winter. Limiting factors can be biotic or abiotic factors. Abiotic factors are non-living factors, such as water, temperature, soil type, shelter, sunlight and others. Other limiting factors are biotic, or living. For example, the arrival of a nonnative, or invasive, species in an ecosystem can affect other organisms that live there. Humans can also cause significant impact on ecosystems. For example, people cut trees for lumber or firewood. They clear land for agriculture or to build homes, roads and malls. They can also cause pollution by burning fossil fuels at home for heating, or on their cars and other vehicles, or by applying chemical fertilizers and pesticides. These practices can upset the balance between predators and prey, causing changes in population levels. Trees and other green vegetations are important because during photosynthesis, they absorb carbon dioxide and produce oxygen. High levels of carbon dioxide in the air have negative effects on the environment so plants play an important role in cleaning the air.
Some ecosystem changes are permanent. Organisms must respond to changes in order to survive. Organisms that cannot respond to ecosystem changes begin to die. When the last member of a species dies, the species becomes an extinct species. Some extinct organisms include all species of dinosaurs, mammoths, the saber-toothed cat, and many others.
The Tasmanian wolf, for example, became extinct about 65 years ago as a result of human actions. These wolves once lived in Australia. Farmers saw the Tasmanian wolf as a threat to their livestock and hunted the animal to extinction.
Pollution, global warming, habitat destruction, and hunting can also threaten the survival of organisms.
Below are examples of extinct animals, the first is the Tasmanian wolf and the second is the Saber toothed cat.
When a species is in danger of becoming extinct, it is called an endangered species. The flying squirrel is an example of an endangered species. Usually, only a few hundred individuals of the species exist.
Species with low numbers that could become endangered are called threatened species. The gray wolf, the manatee, and many others are threatened species.
The Tasmanian wolf
The Saber Toothed Cat
Over time, an ecosystem can change to a new type of ecosystem, this change is called Succession. There are two kinds of succession:
Primary succession occurs where there are few living things that exist, or where the earlier community was wiped out. Primary succession occurs in barren, lifeless areas that have little or no soil. Particles of soil and seed blow from neighboring environments and lichens and mosses start to grow. In this case, the first organisms that begin to grow in the area are called Pioneer species. If there are multiple species that grow first in an area, this can be described as a pioneer community. As more plants grow, the soil quality and nutrients improve, the soil becomes more suited for even more plants and some animals. grasses, ferns, shrubs begin to sprout. Flowering plants attract pollinators to the area, such as insects, birds, and small mammals. These animals attract larger predators to the community. After many years, this community may become a grassland or prairie. A climax community is the final stage of succession. Unless the community is disturbed by some natural disaster or human activity, the climax community will remain.
Secondary succession is where a new community develops in a place where another community already exists. Secondary succession can occur in a forest after a fire has occured. Secondary succession utilizes soil that already has the nutrients and factors needed for good plant growth. For example, when a farm is abandoned, weeds begin to grow and after a couple of seasons, shrubs also begin to grow.
Organisms change over time. If you observe resemblance within families, you will notice that people resemble their children more than they resemble their grandchildren, and so forth. There is increased combinations of genetic material as you increase the number of parents involved in reproduction.
Scientists can compare features of modern organisms to look for similarities that may suggest that the organisms had a common ancestor. Similar features in different organisms are known as comparative structures. When body parts are similar but meet different needs, they are called homologous structures. An example of a homologous structure is the human hand, the bird wing and a dolphin or whale flipper.
Water covers about 75% of the Earth's surface. This part of the Earth that contains water is called the Hydrospehre. Water can be solid (ice or snow), liquid (in oceans, lakes and other water bodies) and as water vapor in the atmosphere.
The Earth's water can either be fresh or salty. More than 95% of the water on the Earth is salty. Ocean water has salts such as sodium chloride amd magnesium chloride dissolved in it. You can use the word salinity to describe how much salt is dissolved in the water.
Earth's Landforms
A landform is a physical feature on Earth's surface. Each landform has specific characteristics and each landform forms in a different way.
Land Features
Water Features
How to Map the Earth
Latitudes and Longitudes are necessary to precisely locate any place on the planet. Latitudes are a measure of how far a place is from the equator. The equator's latitude is 0 degrees (0°). The highest latitudes are at the North and South poles. Both are 90°. Longitudes show the location east or west of the prime meridian, the vertical line that passes through Greenwich, England. This line is also called the Greenwich Meridian.
To locate a place on the planet, find the latitude line nearest the city's lititude. If th city is between two latitude lines, estimate the distance between them. Latitude above the equator is north (N). Latitude below the equator is south (S).
Then find the longitude line that is closest to the longitude of the city. Longitude to the right of the prime meridian is east(E). Longitude to the left of the prime merdian is west (W). The point where the city's latitude and longitude lines cross is it's location. For example, the location of New York City is 41oN, 74oW.
Elevation
Elevation defines the height above or below sea level. On a map, elevation is shown by using contour lines. One contour line connects places a map that are of the same elevation. Elevation is used when describing alocation on the Earth. When the location of interest is in the air, the term altitude is used.
The Earth's Layers
The air around you is the Earth's atmosphere. The atmosphere includes all of the gases around Earth. All of Earth's liquid and solid water, including oceans, lakes, rivers, glaciers, and ice caps, makes up its hydrosphere. The hydrosphere covers approximately 70% of the Earth's surface.
Like an egg, Earth has several layers. The continents and ocean floor make up Earth’s outermost layer, called the crust. The crust is Earth’s thinnest and coolest layer. The layer below the crust is the mantle. Part of the mantle is solid rock. Part is nearly melted rock that is soft and flows. It is a lot like putty. At the center of Earth is the core. The core is the deepest and hottest layer of Earth. The outer core is melted rock. The inner core is solid rock. The biosphere means the parts of Earth where living things are found. Organisms have been found from the atmosphere to the ocean floor.
Continental Drift
In 1915 Alfred Wegener, a German scientist, published his book after noticing that the different large landmasses of the Earth almost fit together like a jigsaw puzzle. The continental shelf of the Americas fits closely to Africa and Europe. Antarctica, Australia, India and Madagascar fit next to the tip of Southern Africa. He presented his Continental Drift hypothesis on 6 January 1912. He analysed both sides of the Atlantic Ocean for rock type, geological structures and fossils. He noticed that there was a significant similarity between matching sides of the continents, especially in fossil plants.
Wegener concluded that all the continents had once been part of a single 'supercontinent.' He called this landmass a Primal continent or Pangaea (a greek term meaning All-Lands or All-Earth. He proposed that the mechanisms causing the drift might be the centrifugal force of the Earth's rotation. This concept became known as Continental drift.
Plate Tectonics
During Wegener's time, there was widespread rejection of the continental drift theory among geologists until the 1950s when additional evidence was discovered to prove his theory. Scientists developed a model called plate tectonics to explain how the continents and the ocean floor could move. According to this model, the Earth’s surface is broken into pieces, or plates. The plates move over the hot, fluid rock, or magma, in the mantle. The slow movements in the fluid part of the mantle drag the lithosphere and its plates sideways. As the lithosphere moves, so do the ocean floor and continental plates.
As some crustal plates move apart, magma enters the cracks and flows outward. The magma cools, hardens, and builds up into parallel ridges, or raised structures, on the ocean floor. The new rock exerts a sideways force called compression. Magma continues to flow between the plates, forcing them farther apart. This process is called seafloor spreading.
Plates can move in three ways, they can move apart from each other, they can collide or the can slide past each other.
Divergent boundaries (also called constructive boundaries or extensional boundaries) are where two plates slide apart from each other. As the ocean plate splits, the ridge forms at the spreading center, the ocean basin expands, and finally, the plate area increases causing many small volcanoes and/or shallow earthquakes. At zones of continent-to-continent rifting, divergent boundaries may cause new ocean basin to form as the continent splits, spreads, the central rift collapses, and ocean fills the basin. For example the East African Rift.
Convergent boundaries ( also known as destructive boundaries or active margins) occur where two plates slide toward each other to form either a subduction zone (one plate moving underneath the other) or a continental collision. Subduction zones are of two types: ocean-to-continent subduction, where the dense oceanic lithosphere plunges beneath the less dense continent, or ocean-to-ocean subduction where older, cooler, denser oceanic crust slips beneath less dense oceanic crust. At zones of ocean-to-ocean subduction a deep trench to forms in an arc shape. The upper mantle of the subducted plate then heats and magma rises to form curving chains of volcanic islands e.g. the Aleutian Islands, the Mariana Islands, the Japanese island arc. At zones of ocean-to-continent subduction mountain ranges form, e.g. the Andes, the Cascade Range. At continental collision zones there are two masses of continental lithosphere converging. Since they are of equal density, neither is subducted. The plate edges are compressed, folded, and uplifted forming mountain ranges, e.g. Himalayas and Alps.
Transform boundaries (also called conservative boundaries or strike-slip boundaries) occur where plates are neither created nor destroyed. Instead two plates slide, or perhaps more accurately grind past each other, along transform faults. The San Andreas Fault in California is an example of a transform boundary exhibiting dextral motion.
In the previous chapter, we described three types of tectonic plate movements and how they can influence the geography of the continents. When two plates slide past each other, they can result in shearing forces that work like the blades of a pair of scissors and can cause rocks to break. At divergent boundaires, plates separate from one another and result in tension forces on the rocks. When tension forces exceed the rock's strength, the rock breaks and forms a fault. A Fault is a break or a crack in the rock of te lithosphere along which movements take place. Faults are frequently located along the boundaries of tectonic plates.
There are three kinds of faults:
Mountains form when plates push against each other. Mountains made up mostly of rock layers folded by being squeezed together are called folded mountains. Mountains mad by huge tilted blocks of rock separated from the surrounding rock by faults are called fault-block mountains. A plateau occurs when a large area of the Earth's crust is pushed upwards forming a flat raised area on the land.
Earthquakes
The forces at plate boundaries cause stretching, pushing and bending responses on large sections of rocks. This can build up energy and when the rock breaks, energy is released (the same way an elastic band releases energy when it snaps after being stretched to its limit). When this energy is released, it causes the earth curst to move resulting in earthquakes.
The point below the earth where an earthquake begins is called the focus. The location on the earth directly above the focus is called the epicenter. People living near the epicenter will feel the earthquake first and most intensely. Earthquakes may include many smaller movements called aftershocks, that can last for days or even weeks.
Earthquakes (and volcanic eruptions) create vibrations that travel through the earth resulting in earthquake waves calles seismic waves.
Understanding Seismic Waves
There are two main types of seismic waves; surface waves and body waves. surface waves occur near the surface of the earth. Tehy travel on the surface of the earth slowly like ripples and are the most destructive waves. Body waves travel deep in the interior of the Earth. There are two types of body waves, primary waves (p waves) and secondary waves (s waves). P waves are the fastest seismic waves. They travel through gases, liquids and solids by pushing and pulling against the material they pass through. During movement, they cause the material to compress and stretch through their pushing and pulling forces. P waves move in the same direction as the shaking rock. S waves are slower than P waves and travel only through solids. They cause the marial to move eithe rup and down, or side to side. Therefore S waves vibrate at right angle to the direction of their movement.
Seismic waves can be detected, measured and recorded using a Seismograph.
The measurements of the seismograph can be used to locate the earthquake's epicenter by measuring how much time it takes for the waves to be detected by various earthquake monitoring stations close to the affected area. To find the location, three stations are needed. The distance is charted around each station in a circle. The point where the three circles intersect is the epicenter.
Earthquake Magnitude
The height of the wave on a seismogram indicates the magnitude of the earthquake and is a measure of the energy released during the earthquake.
There are two measures of earthquakes; The Richter scale and The Mercalli scale. The Richter scale measures earthquakes on a scale of 1-10. An increase of 1 on the scale means a tenfold increase in magnitude. The Mercalli scale rates what people feel and observe so it subjective and not reliable.
Tsunamis
A tsunami (Japanese for harbor wave) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions. In the open ocean, tsunamis move at speeds of 500 to 1,000 kilometers per hour. However, a tsunami slows down as it approaches a shore. The length of each wave decreases, but the height increases. The water piles up, and it is often pulled away from the coastline as the tsunami approaches land. Finally, the tsunami crashes onto the shore as a giant wall of water.
Volcanoes
Volcanoes are formed by powerful forces within Earth. As one crustal plate moves under another, the rock in the mantle and lower crust melts and becomes magma. Melting rock produces gases that mix with magma. Over time, the gas-filled magma rises, because it is less dense than the solid rock around it. Rising magma can build up in a weak part of overlying rock, forming a magma chamber. Magma chambers are the reservoirs from which volcanic materials erupt. When magma reaches the surface, it erupts through a central opening called a vent. Once magma reaches the surface, it is called lava.
There are three main kinds of landforms produced by volcanic eruptions.
1. Cinder cone volcano is a landform mainly made up of small rock particles, or cinders. As erupting lava shoots into the air, it breaks into small pieces. These fragments cool and harden as they fall back to the ground. The fragments pile around the vent, forming a cone with steep sides.
2. Shield volcano is a landform made up of many layers of rock. As fluid lava flows out to the surface from a vent, it spreads out in all directions, cools, and hardens into rock. Multiple layers of lava rock build up to form a volcano with broad, gently sloping sides.
3. Composite volcano is a landform made up of layers of thick lava flows alternating with layers of ash, cinders, and rocks. These layers form a symmetrical cone with steep sides that are concave, or curving inward.
Other Volcanic Landforms
An island arc is a string of island volcanoes which occurs when one oceanic plate is driven under another. Part of the sinking plate melts, and magma moves up through the crust along a line parallel to where the plates meet.
Rift volcanoes form where plates move apart and volcanoes form at gaps along the plates’ edges.
Dome mountains form when magma rises and pushes against rock layers above it forming large dome shaped mountains. The black hills of South Dakota are good examples.
If magma hardens in vertical cracks across horizontal layers, a dike forms. When magma hardens between horizontal layers of rock, a flat sill is formed.
Weathering
Weathering is the process where rocks break down into smaller pieces through natural processes. Weathering may either be Physical, chemical or biological.
Physical Weathering is also called mechanical weathering. Physical changes such as freezing water, moving water etc cause rocks to break down. When water sips into a crack in a rock and then freezes causing the rock to break apart it is called frost wedging. When the ice melts, the water sips even deeper into the crack and causes the rock to break down even further.
Moving water carries with it pieces of rocks and they collide against each other as they move. These collisions and the force of the water itself makes the rocks break apart causing weathering.
Biological weathering: This occurs when weathering is as a result of the direct involvement of a biological material. Animal hooves break down rocks into small particles. Plant roots also penetrate between tight rock spaces causing the rocks to crack as the plant root grows. burrowing animals such as ants and worms result in conditions that make weathering easier to occur. For example they might bring rock pieces to the surface. Or they create burrows whare ice can accumulate and cause further cracks.
Chemical Weathering: Some of the forces that cause weathering are chemical in nature. For example oxygen and acids are effective at causing chemical weathering. Rocks contain iron which reacts with the oxygen in the air resulting in rust which is easier to break down. When carbon dioxide in the air dissolves in water, it forms weak carbonic acid which results in acid rain. Acid rains can react with limestone and dissolves it and transports it as it flows.
Some other forces shape the Earth's surface by moving materials from one place to another. Erosion is the process where rock pieces and other particles are moved from one place to another either by wind or water. Deposition is the dropping off of particles in another location. Wind can cause erosion and deposition and these processes can result in other landforms such as sand dunes.
Flowing water is a major cause of eriosion. It carries particles as it flows downhill. The faster a river flows the larger the particles it can carry. When the river flows slowly, some of the particles are deposited as sediments. Deposition can cause a river to change course or to meander. Rivers with steep slopes that move faster are always straighter.
Two other causes of erosion are gravity and glaciers. Gravity can pull large masses of soil downhill in a process called mass wasting. Glaciers, on the other hand, move over the land like huge bulldozers and they scrape the surface of the soil and carry rocks in front of them and to their sides.
As a river travels, it carves the land surface and forms a channel. The river erodes the surface slowly and over time can result in deep canyons and valleys. Eventually the sediments reaches the sea and is deposited offshore.
Glaciers form when ice builds up over several years and when it reaches about 100m deep it becomes too heavy and begins to flow downhill. It scrapes the surface of land as it moves. Once it reaches the edge of the continent it breaks off and forms icebergs.
When glaciers move, rocks and other substances carried by the glacier are deposited as a mixture called till. As a glacier melts, till is deposited in front of or along the sides of the glacier. These deposits often take the form of a ridge or mound, called a moraine
Soil
Soil is a mixture of minerals, weathered rocks, and other things. It has bits of decayed plants and animals called humus. So we can define soil as consisting of organic and inorganic material. Organic material are those coming from or having to do with living things, such as decaying plant and animal material. Inorganic materials do not come from living things, such as minerals and weathered rocks.
The making of soil starts with weathering. Weathering causes rocks to break down into smaller and smaller pieces. The tiny bits of weathered rock build up into layers.
Soil Layers / Horizons
Generally, soil can be divided into three horizons; A, B and C.
The A horizon contains most of the nutrients and humus. The nutrients in the humus are used by plants to grow. In addition, the humus absorbs water and keeps it for a longer period of time and releases it to plants. The soil in this layer is called topsoil.
The horizon B is called subsoil. This layer contians less humus and more particles of rocks.
The C layer is mostly made of larger pieces of rocks. This layer sits on solid unweathered rock called bedrock.
Different places have different depths of each soil layer, and some areas may even lack one of the layers totally.
Soil in different places has different properties and each type of soil has different amount of nutrients and can support different plant and animal life. The soil in a forest has a thin layer of humus and topsoil. Frequent rains carries minerals deep into the ground. Crops with shallow roots do not grow well in such environments because their roots cannot reach the minerals. Desert soil is sandy and does not contain much humus. Because of the sarce rains in the desert, plants here have special adaptations to survive. Desert soil, however, is rich in minerals because they are not washed away by rain water. Plants may grow in deserts if they are supplied with water artificially (irrigation). The grasslands are good for crops such as wheat, rye and corn. The soil is rich in humus, which provides nutrients for the plants. Animals feed on the grasses and also drop their waste on the ground, which adds to the organic matter.
Soil is a resource that can be wasted through processes like erosion. Plants roots help to keep the soil aggregated and prevents erosion. Plants obtain nutrients from the soil as they grow, and they replace them when they die. If farmers remove all crops from the land, they are removing the nutrients from the land and over time the land becomes less able to support new crops.
Fossils and Rocks
Fossils are the remains of ancient organisms preserved in soil or rocks. When an organism dies and are covered in soil, sand or other sediments, the sediments harden over and around the organism's remains. Almost all fossils are found in sedimentary rocks. Scientists can study fossils to understand the characteristics of organisms that lived many years ago. These characteristics may also be used to determine the environmental conditions that were present many years ago.
Fossil fuel is a material that formed from the decay of ancient organisms and is used as a source of energy. For example, decayed parts of ocean organisms were buried deep under the ocean. There, a combination of the weight of rock, heat, and the action of bacteria turned the decayed materials into oil and natural gas. Oil and natural gas also are fossil fuels.
Scientists can estimate the age of fossils by observing the layers of the sediments. Fossils found on the top layers are more recent, were deposited more recently, than fossils found deeper in the sediments. This is called relative age. The word relative, means it has been estimated in comparison to something else. The Absolute age of a fossil is the actual age in years. It can be estimated by estimating the age of the rock layer where the fossil was found. The age of the rocks is estimated by the amounts of various elements. The concentration/amount of certain elements reduces at a contant way. For example, lets say it takes 1 million years for half of element A to change into Element B. After 1 million years, the rock contains equal amounts of element A and B. This time point is called an element's half-life. As mentioned, during the first half life, you will observe equal amounts of Element A and B. During the second half-life, more Elemebt A will be converted to Element B, so by the 2 million year mark, there will be 75% of element B and 25% of element A. at the 3 million year mark, there will be 87.5% of element B and 12.5% of element A. Notice that at every subsequent half-life, the concentration of element A is halfed. Different elements different half-lives.
Using the relative age of fossils and rocks, scientists estimated that the age of the earth is around 4.6 billion years. during those 4.6 billion years, there has been several eras. An era is a unit of time measured in millions of years. Geological periods divide eras into shorter periods of time where specific major geological events occured.
The geologic time scale is a system of chronological dating based on the rock record. It classifies geological layers to describe the timing and relationships of events in geologic history. Over hundreds to thousands of millions of years, continents, oceans and mountain ranges have moved both vertically and horizontally. Areas that were once deep oceans hundreds of millions of years ago are now mountainous or desert regions.
Introduction
A mineral is a solid, nonliving substance found in nature. Minerals are the building blocks of rocks.
There are more than 3000 kinds of minerals. Each mineral has its own properties.
Properties of Minerals
Kinds of Rocks
A rock is a non-living material made of one or more minerals. There are several types of rocks. SOme rocks are made of many minerals while others are made predomrinantly by one mineral.
Rocks are made of grains that give the rock its texture. Some rocks have large grains that can be seen easily with just the eyes. Such rocks end up having a rough/coarse texture. Other rocks have fine grains and as a result have a fine/smooth texture.
There are three main kinds of rocks.
Rocks and minerals have multiple uses from building houses, making jewelry and other even more common uses. The mineral graphite is used to make pencil points. Aluminum is used in cooking pans, and electric wires. copper is used in making coins, electric wires and water pipes. Calcium, a mineral which is found in milk, is essential for bone development. It is also predorminant in limestone and may be used to make chalk.
Minerals are usually made of crystals. A crystal is a solid that has a structure arranged in orderly, fixed patterns. A crystal’s shape depends on the way its structure is arranged.
Scientists generally begin identifying a sample by examining the shape of the mineral’s crystal structure. The way a mineral breaks is another important property. Some minerals tend to break along flat surfaces. This property is called cleavage. Cleavage is described by the number of planes, or directions, along which the mineral breaks. The cleavage of a mineral depends partly on its structure.
The Rock Cycle
The rock cycle is the process that describes the gradual transformation between the three main types of rocks: sedimentary, metamorphic, and igneous. It is occurring continuously in nature through geologic time.
Steps in the Rock Cycle:
Approximately 70% of the Earth's surface is covered with water. However, because most of this water is in oceans, it is salty. In fact, 90% of the earth's water is salty. About 2.5% of the Earth's water is frozen at the North and South poles. About 0.1% of the water is in the air as water vapor. Only 0.6% of the Earth's water is fresh liquid water. Many living things utilize the fresh water to survive. Most of the fresh water is obtained from running water, standing water and groundwater.
Running Water
Many cities are built close to sources of running water such as rivers or streams. running water is a source of fresh water for homes, businesses and farms.
Standing Water
Standing water includes bodies of water such as lakes and reservoirs. A reservoir is an artificial lake built to store water. Reservoirs are usually made by building a dam across a river. The water is stored behind the dam and is released when needed.
Groundwater
Water seeps into the ground through aquifers. An Aquifer is an underground layer of rock or soil that has pores and is capable of absorbing water. When the seeping water reaches a layer of rock that does not have pores, it settles there builds up and can be used by humans by drilling or digging into the ground. Once ground water has been harvested, more water must seep from the surface so as to replace the ground water again.
Some countries/regions use water for irrigation. Irrigation is supplying water to agricultural farms by artificial means.
The water used in most homes is supplied by a water company. The water usually undergoes some treatment processes then pumped through pipes into homes and businesses. Some homes may use well water. A well is used to obtain groundwater by drilling and installing a pipe deep into the ground and pumping water to the surface. This water may undergo treatment and then used for human consumption. Otherwise, well water may also be provided to farm animals.
Drinking water should be free from contamination. You should be on the look out for possible contamination in water, such as a change in color (fresh water should be clear), visible dirt in the water, any smell in the water (fresh water should not have any smell - odorless).
The water that runs in most homes is usually treated in a water treatment plant to remove contaminants. Water is first obtained from a fresh water source such as a reservoir or a lake and then it is run through several tanks, with each tank having a different function. The steps may vary with there the water was obtained from.
The first step is to remove dirt through a process called coagulation. This involves the use of sticky particles to attract the dirt.
The next step involves sedimentationwhere clumps of dirt and the sticky particles sink to the bottom of the tank.
The water then is passed through a series of filters made with layers of sand, gravel, and charcoal. These remove more particles from the water. Afte this tank, chlorine is added to the water to kill harmful bacteria. This step is called disinfection. The clean water is stored in tanks until it is pumped to homes and businesses.
Water conservation refers to all efforts made to reduce the waste of water. This may be targeting a small scale level at the individual level, like showering for a shorter time. Conservation can also be aimed at a larger scale, like a lake or a watershed.
Water protection involves the use of government regulations to limit the uses of water. For example, a government may restrict the use of water to domestic uses only and regulate the use of water for irrigation such as watering the lawn.
The Earth's atmosphere holds the gases that living things need to stay alive. You cannot see air (its invisible), you cannot smell air (its odorless) and if air is not moving, you cannot feel it. Air is made up of Oxygen, carbon dioxide and nitrogen. Plants take in carbon dioxide and with the help of sunlight, they are able to make the food they need to survive. Some bacteria in the soil can convert nitrogen into forms that plants can absorb and use to grow.
Air pollution occurs when toxic gases, dust or chemicals are released into the atmosphere from vehicles, factories, mines and other sources. Smog is a type of air pollution caused by oarticles and gases from burning fossil fuels in factories/industries.
Some gases and chemicals have been shown to affect the ozone layer. The ozone layer is a layer of ozone gas (similar to oxygen) found about 30 kilometers above the earth's surface. It protects the earth from dangerous energy from the sun. Some pollutants from air conditioners, aerosol cans have been shown to destroy the ozone layer. The destruction of the ozone layer results in dangerous radiations from the sun reaching the earth's surface and these may be associated with the occurrence of skin cancer.
Earth's natural resources can be classifed as either renewable or nonrenewable depending on much time it takes to replace them. Renewable resources include water (which can be replenished fast) or solar energy (which is continuously supplied by the sun). Nonrenewable resources include minerals, petroleum, coal etc, which either cannot be replenished, or it would take a very long time to replace them. Nonrenewable resources also tend to be available in limited quantities, or are used up faster than they can be replaced. Trees grow relatively fast and can be grouped as renewable resources. However, if the population cuts down trees faster than the amount of time it takes for them to grow, then the trees can be regarded as nonrenewable. This explanation also applies for wildlife and fish if they are harvested faster than the time it takes to replenish them.
Rocks, Minerals and Soil
A rock is a non-living material made of one or more minerals. There are several types of rocks. Some rocks are made of many minerals while others are made predominantly by one mineral. Rocks are made of grains that give the rock its texture. Some rocks have large grains that can be seen easily with just the eyes. Such rocks end up having a rough/coarse texture. Other rocks have fine grains and as a result have a fine/smooth texture.
Rocks that contain useful substances, such as minerals, are known as ores. People mine for ores so as to obtain the valuable minerals from them. Some minerals are used as gems. Gems are minerals that are rare and beautiful such as diamonds, emeralds, sapphires, and rubies etc. Quartz, which is usually found as sand, is used to make concrete and glass. Quartz contains silicon, the element used in the production of computer chips. Pieces of quartz are used in watches and clocks. Energy from a battery keeps the quartz vibrating steadily, and this makes the watch or clock keep very accurate time. Crystals of quartz, mica, and other minerals can be found in granite, a hard rock used in buildings. Minerals also make up marble, a rock that artists use frequently to make statues and monuments.
Fossil fuel is a material that formed from the decay of ancient organisms and is used as a source of energy. For example, decayed parts of ocean organisms were buried deep under the ocean. There, a combination of the weight of rock, heat, and the action of bacteria turned the decayed materials into oil and natural gas. Oil and natural gas also are fossil fuels. Limited deposits of oil and natural gas exist in North America, the Middle East, Indonesia, and Venezuela. Once these deposits are used up, they will be gone.
Soil is a mixture of minerals, weathered rocks, and other things. It has bits of decayed plants and animals called humus Humus is dark in color. It adds nutrients to soil. Plants use these nutrients for their growth. Humus works like a sponge to soak up rainwater and keep the soil moist. Water, air, and living things are also found in soil. The making of soil starts with weathering. Weathering causes rocks to break down into smaller and smaller pieces. The tiny bits of weathered rock build up into layers. The top layer is called topsoil. Topsoil is dark and has the most humus and minerals. Below the topsoil is subsoil. This layer is lighter in color and has less humus. Below the subsoil is bedrock, or solid rock.
Pollution
Pollution is a harmful change to the natural environment. Pollution occurs because Earth’s land, water, and air have a limited capacity to absorb wastes and to recycle them naturally. People may hamr the soil through activities such as mining for minerals, oil spills and other contaminants. Leaving the soil bare results in soil erosion either by wind or by moving water. When soil is left bare, it also becomes degraded faster due to lack of organic matter. Planting the same crop on the same land in successive years means the same nutrients are taken up by the crop every year, leaving the land infertile. This has forced many farmers to utilize large amounts of fertilizers, which, although they increase the nutrients, they do so only for specific elements, Usually Nitrogen, phosphorus and sulfur. This helps plants grow but does not necessarily increase organic matter in the soil. Cutting down trees results in the loss of roots that would have held the soil together and therefore results in erosion. Land use changes resulting from urbanization, changing agricultural land into homes for expanding urban populations can harm ecosystems and means that land is no longer available for food production.
Human activities such as bathing, washing clothes, flushing toilets or sending harmful residues into water can harm water resources. Some factories may dump watses and chemicals into lakes and rivers. Agriculture producers usually use fertilizer and pesticides on their farms and some of these chemicals can dissolve in rain water and get washed away into rivers, lakes or ponds. These residues may be conusmed by fish or birds. Fertilizer deposited in water bodies can affect ecosystems leading to increased growth of algae which is usually observed as green coloration in water. When the algae die they use up oxygen from the water as they decompose, resulting in reduced oxygen levels available to fish.
Cars and factories release smoke into the atmosphere, which sometimes combines with fog to form smog. Smog irritates the eyes and throat and could affect people with pre-existing respiratory problems.
Acid rain forms when nitrogen, sulfur and carbon gases produced by burning fossil fuels combine with water vapor in the air forming acids. The acids fall to earth as acid rain or snow. Acid rain can pollute water and soil, kill plants and fish and damage the stone and metal used to build houses or statues.
Proper disposal of garbage and waste
The garbage produced by people and industries is disposed depending on the type of waste. Most garbage ends up in landfills. Landfills are usually covered in soil when they are full. Under the right conditions, the garbage deposited in landfills decomposes slowly and safely. In other areas in the world, garbage is deposited in open pits and left to rot slowly. While in other areas, garbage is burnt in incinerators that produce large amounts of smoke.
Household garbage like left over food, fruits and vegetables, garden waste may be biodegradable. These can be used to make compost, which can be reused in gardens to plant various crops.
Toxic waste from industries may be poisonous and must be disposed off according to the regulations or manufacturer's guidelines.
Common household items such as batteries, paint, cleaners, oils should be disposed off according to the regulations/directions.
Some countries have recycling programs where some materials such as food grade plastic bottles, packaging boxes and glass bottles are purchased and recycled.
Resources are scarce and precious and must be protected so as to benefit multiple generations. People have developed many ways to protect soil. For example, after harvest, farmers add humus or decomposed organic material to replace the nutrients that were removed by the previous crop. Farmers can also add animal manure or compost. This adds organic matter to the soil to help crops grow. Crop rotation is a practice where farmers grow different crops every year. This way, the crops are not utilizing the same nutrients from the soil every year. Planting legumes such as peas and beans on the land helps the land to obtain nitrogen from the air reducing the need to provide nitrogen through fertilizers. Some farmers plant grass between the roas of cash crops as a way to prevent soil from staying bare. If the farm is on a slope, farmers can build terraces to reduce soil erosion and allow planting crops.
Alternative Energy Sources
Alternative energy sources include sources of energy other than fossil fuels. These can include:
Geothermal energy: This energy source relies on the heat in the Earth's interior. The heat in the Earth's interior heats water and the steam or hot water provides geothermal energy. This type of energy can be used in some areas to heat homes and produce electricity.
Wind energy has now become an important alternative to fossil energy. Windmills use moving air to spin wind turbines that then generate electricity. Many windmills can be installed to generate electricity for homes and businesses.
Bioenergy utilizes biomass such as corn, sugarcane and other biological waste in a process called biomass conversion to generate alcohol based biofuels such as ethanol, or heat. Some organic matter produces methane (biogas), which can be burned for cooking or heating homes.
(Source TILLEY et al. (2014))
Running water can also be used to produce 'hydroelectricity'. Many dams all over the world have hydroelectric plants.
The Sun provides the largest amount of energy for Earth. Plants use energy from the Sun to produce food. People harness the power of sunlight by using solar cells, devices that use sunlight to produce electricity.
Recycling
We can help protect Earth’s land, water, and air by following the 3 Rs of conservation: reduce, reuse, and recycle.
We can reduce the amount of natural resources we use. We can reduce the fuel used for heating and air conditioning by adjusting indoor temperatures to use less heat in cold weather and less air conditioning in hot weather. We can also design cars that need less fuel for the same driving distance (more fuel efficient).
Reusing materials saves resources. We can reuse many products. We can use washable tableware instead of disposable cups, dishes, and plates.
Recycling reduces the amount of energy needed to make things and also reduces the amount of garbage we produce.
Air is a mixture of gases that surrond the earth like a blanket. This layer is called the Atmosphere The air on earth consists of three main gases, Oxygen, Nitrogen, Carbon dioxide and water vapor. Without these gases, there would be no life on earth. Air that moves from place to place is called Wind. wind can be gentle and can also be strong and destructive. The earth's atmosphere is made up of several layers. The layer closest to the earth surface is called the Troposphere. This is a thin layer but all of life lives in this layer. The Stratosphere is located above the troposphere. Temperatures here are a bit warmer than the troposphere.
Weather
Jet airplanes normally fly within the stratosphere, just above the troposphere, because it is very stable. The stratosphere contains the ozone layer. The ozone layer absorbs harmful rays from the Sun. Rock fragments from space often burn up in the next layer, the mesosphere. The coldest temperatures in Earth’s atmosphere are found at the top of the mesosphere. The outermost layer, the thermosphere, is where space shuttles orbit.
Properties of Weather: Weather is the condition of the atmosphere at an given time and place. Some of the properties of weather include:
Temperature: describes how hot or cold it is. When the suns energy hits the ground, the surface warms the air above it and the air temperature increases. A thermometer is used to measure temperature.
Humidity: is a measure of how much water vapor is in the air. Deserts have low humidity while rain forests have high humidity. Areas close to an ocean or large lakes also have high humidity due to evaporation from the ocean. Humidity is measured using a hygrometer.
Air pressure: Air pressure is the force that air pushes on the surface of the earth. Air pressure is measured by an equipment called Barometer.
Precipitation: Any form of water that falls from clouds is called precipitation. This includes rain, snow, sleet and hail. A rain gauge is used to measure the amount of rainfall.
Wind: Wind is air in motion. The wind speed if an important property of weather. It can influence how cold it feels (wind chill). It can result in faster evaporation of water from oceans and lakes. The direction of wind is measured using a wind vane and the speed of wind can be measured using an Anemometer.
Insolation is the amount of the Sun's energy that reaches Earth at a given time and place. The angle of insolation is the angle at which sunlight hits Earth's surface. The larger the angle, the more intense the Sun's rays. Insolation also varies during the course of a day.
Air Pressure:
Air particles have mass, and so Earth’s gravity attracts them. Air pressure is the force exerted on a given area by the impacts of gas particles in constant motion. Standard air pressure, or the air pressure at sea level, is about 1 kilogram per square centimeter.
Earth's air pressure varies. As you move higher in the atmosphere, there is less air above you. Because there are fewer air particles above you that are being pulled toward Earth by gravity, there is less air pressure. Air pressure is an important weather variable. Air pressure variations help produce wind.
A convection cell is a circular pattern of rising air, sinking air, and wind.
Sea breeze is wind that blows from the sea to the land. At night, air over land cools faster than air over water.
A land breeze is wind that blows from the land to the water.
The direction of wind is measured using a wind vane or weather vane and the speed of wind can be measured using an Anemometer. A weather vane is a movable arrow which points in the direction that the wind is blowing.
Global Winds
Generally, wind blow from areas of higher pressure to areas of lower pressure. However, the Earth's rotation also pushes the winds to either the right or the left. This shift is called the Coriolis effect. The Coriolis effect causes winds in the Northern Hemisphere to curve to the right, or clockwise. In the Southern Hemisphere, the Coriolis effect causes winds to curve to the left, or counterclockwise.
Trade Winds
Trade winds are winds that blow toward the equator and are curved to the west by the Coriolis effect. These winds are referred to by the direction from which they come—northeast or southeast. The winds that blow toward the poles are curved to the east. Because they seem to come from the west, these winds are called westerlies.
Humidity
Water vapor may be measured as humidity, the actual amount of water vapor in the air.
Relative humidity measures the amount of water vapor in the air compared to the total amount the air could hold at that temperature. A relative humidity of 50 percent means that the air contains half the water vapor it could possibly hold at that particular temperature. When the relative humidity is 100%, the air is saturated i.e., cannot hold any more water vapor. Any additional water vapor condenses into a liquid. The temperature at which this occurs is called dew point.
Clouds
There are different kinds of clouds and each type means a different type of weather may be coming.
Cumulus clouds are small, white puffs. They may also appear in long rows.
Cirrus clouds are thin clouds very high in the sky. They are made of ice.
Stratus clouds are often low in the sky. They come in sheets and cover the entire sky.
How much of the sky is covered by clouds? Terms such as clear, scattered clouds, partly cloudy, mostly cloudy, and overcast are all used to describe the amount of cloud cover. You can record cloud cover using symbols such as those shown below. An empty circle indicates clear skies. Circles with different shaded portions indicate varied amounts of cloud cover.
Snow
Water freezes at 0°C. When it is cold in the atmosphere and the water vapor freezes and becomes heavy, they fall as snow. The snow may melt as it falls on the ground. Melting means changing from solid (ice) to liquid (water).
Hail
When rain falls as a liquid but freezes along the way, it turns into small chunks of ice called sleet. When these chunks of ice are larger, they are called hail. Usually, hail occurs together with a thunderstorm. Hail ranges form the size of a pea to large chunks the size of a baseball.
Thunder is the loud sound you hear during a thunderstorm and is made when lightning heats the air around it quickly. If thunderstorms are predicted in the weather, stay away from water and trees. If tornadoes are predicted, stay in a sturdy shelter such as a basement. In any storms, always listen and follow the directions provided by your local authorities.
A Tornado is a rotating column of air that touches the ground during a thunderstorm. it can be dangerous so when you see a tornado, or suspect a tornado may be approaching, you need to take cover.
Hurricanes form over warm water in the ocean. They result in heavy rains and strong winds.
Weather Maps
Weather maps show a region's air pressure. They include isobars, which are lines that connect places with equal air pressure. Isobars help make air-pressure patterns easier to see. Air pressure is commonly measured in millibars. Isobars give scientists an idea of wind speed. Air moves fastest where pressure differences are greatest. Isobars spaced closely together show a large change of pressure over a small area. They indicate that wind speeds will be high. Isobars spaced wide apart indicate gentle winds.
Different types of weather develop in highs than in lows. In general, areas of high pressure have fair weather. Cumulus clouds might be present, but there would generally be little or no rain. A low-pressure area usually has clouds and precipitation. Storms and rain often follow a drop in air pressure. When the barometer reading drops suddenly, there is a good chance that precipitation will occur.
Air Masses: An air mass is a region or an area where the air has the same properties. The weather in these regions is also the same and the air mass behaves as one unit. Air masses usually form at the poles of the equator and move across the earth covering it like a blanket. As air masses move, they bring weather along with them. When two air masses meet, the area where they meet is called a front. A front, therefore, is the boundary between two air masses that have different temperatures. Because of the temperature difference, fronts result in a change of weather where they occur.
There are three types of moving fronts. At a cold front, cold air moves in under a warm air mass. Cold fronts often bring brief, heavy storms. After these storms, the skies become clear, and the weather is usually cooler and drier. At a warm front, warm air moves in over a cold air mass. Warm fronts often bring light, steady rain or snow. Afterward, the weather is usually warmer and more humid. When a cold front catches up with a warm front, an occluded front forms.
Interpreting Weather Maps
Many factors combine to influence weather. These factors include air pressure, humidity, and temperature. To predict the weather, information about these and many other factors must be compiled from points of research all over the world. Scientists use computers to analyze all this information. This information is then summarized on weather maps.
The information on weather maps is obtained from various sources. On the ground, weather stations record temperature, wind direction, wind speed, and humidity. Weather balloons to take measurements from high up in Earth’s atmosphere. In some cases, satellites can perform similar functions. The satellites orbit Earth, taking photographs and relaying them to computers. Another important tool for weather scientists is radar. Radar uses radio signals to detect precipitation. By combining information from ground measurements, weather balloons, satellites, and radar, scientists can form detailed pictures of weather conditions.
Climate is the pattern of weather that can be observed in a specific place year after year. Different parts of the earth have different climates. Climate can be described using words like warm and dry, cold and snowy, cool and wet, etc. Farmers depend on climate to decide which crop to grow and when to grow. Some crops do well in dry areas and others need a lot more rainfall to grow.
Climate Regions: Climate areas are areas which have similar patterns of temperature, humidity, precipitation and wind. For example, Polar regions tend to be cold, and have low precipitation. Tropical regions lie close to the equator and are warm, humid and rainy. Temperate regions are in between polar and tropical. Temperate regions have four seasons (Summer - Fall - Winter - Spring). Other temperate regions have more like two seasons, a wet and a dry season.
Factors that affect Climate
Latitude: Latitudes are a measure of how far a place is from the equator. The equator's latitude is 0 degrees (0°). The highest latitudes are at the North and South poles. Both are 90°. The climate is very cold at the poles, while the climate is warm and rainy at the equator. The regions between the equator and the poles are temperate and the climates vary but is mostly mild.
Global Winds: Temperature differences between latitudes cause global winds. These are winds that move air between the equator and poles. Warm air at the equator rises and moves toward the poles. Cold air near the poles sinks and moves toward the equator.
Ocean Currents: Ocean currents indicate the direction of flow. Some ocean currents may result in movement of warm water from the equator to the poles. There are also currents that move along the latitudes. Togetehr, these currents result in circular patterns in the oceans.
Distance from water bodies: More than 70% of the earth surface is covered by water. Climates near lakes and oceans are cloudier and rainier than regions farther inland. Summers are cooler. Winters are warmer. Nearness to water reduces temperature extremes. It also increases moisture in the air.
Altitude: Altitude is a measure of of the height of a place above the sea level. The climate at the base of a mountain is usually warmer than at the peak. Warm air rises up the side of the mountain and as the alititude increases, the temperature reduces. Water vapor in the air condenses to form clouds. As the cloud moves up the side of the mountain, the water droplets become heavy and they fall as precipitation. By the time the air passes to the other side of the mountain, it is dry and cannot cause significant precipitation. so the climate on the other side of the mountain tends to be dry. (Picture credit: Eileen Chontos.)
Each planet in the solar system is drawn toward the sun by gravity. Gravity is a force of attraction between two objects. The strngth of the force depends on the mass of the two objects, and the distance between the two objects. The strength of the force decreases as the mass decreases and as the objects are positioned further apart.
The Earth is larger than the Moon so the expectation is that the strength of gravity will be higher on the Earth than on the Moon. In fact, the Moon's gravity is only about one sixth of the Earth's gravity.
Two objects do not have to touch each other to produce a force of gravity between them. The pull of gravity between Earth and the Sun acts across about 150 million kilometers of space. Gravity also acts across roughly 6 billion kilometers of space between the Sun and Pluto. However, because Pluto is located farther away from the Sun, the strength of gravity bwteen the Sun and Pluto is much lower than the gravity between the Sun and the Earth.
The force of gravity between the planets and between the planets and the Sun results in a path that the planets take around the Sun. These paths are called orbits.
As the Earth orbits around the Sun, it is pulled toward the Sun because of gravity but at the same time, inertia makes the planet move away from the Sun. Inertia is defined as the tendency of a moving object to continue moving in a straight line. The combination of gravity and inertia results in planets moving in a nearly cirvular orbit around the Sun called an ellipse.
When Earth is closest to the Sun, it is about 147,000,000 kilometers away. When Earth is furthest from the Sun, it is about 152,000,000 kilometers away.
The Earth moves aroudn the sun at a staggering 30km per second. The Earth's orbit is around 942,000,000 km long, so it takes the Earth about 365 1/4 days for the earth to make a complete trip around the Sun. This is called a Revolution and it is equal to one year.
An imaginary line drawn from the Earth's North to the South pole is called the Earth's axis. The Earth axis is tilted at an angle of about 23o. As the Earth revolves around the Sun, sunlight strikes different parts of the Earth at different angles. The changes in the angle result in seasons. When the Northern Hemisphere is tilted away from the Sun, the ground does not receive much heat energy and temperatures are low. In the Northern Hemisphere, this is the beginning of winter. At the same time, summer begins in the Southern Hemisphere. The Southern Hemisphere is tilted toward the Sun, the ground receives more heat energy and temperatures are warmer. In spring and in fall/autumn, both hemispheres receive equal warmth from sunlight, which makes temperatures mild.
The solar energy that reaches the Earth is called insolation. Insolation does not warm all places on the Earth equally. Because of the shape of the Earth, (sphere) and with an imaginary line (the equator) dividing the earth into two equal hemispheres, the sun strikes with the most vertical angle at or near the equator.
The atmosphere forms layers of gases around the earth. The layer of gsases cloest to the earth is called the trophosphere. This layer is thickest at the equator and thinnest at the poles. Above the trophosphere are the stratosphere, mesosphere, thermosphere, and exosphere.
Gases are more dense closer to the earth surface and become less dense as you move toward the exosphere. Tha gas particles press on the Earth's surface and on everything they surround. The force put on a given area by the weight of the air above it is called Air pressure or Atmospheric pressure. You do not feel this weight because atmospheric pressure pushes in all directions and these pushes balance each other.
The Moon
The Moon has no atmosphere. Because there is no atmosphere, there are no winds and there is no weather on the Moon. There is no air to block radiation from the Sun or for astronauts to breathe. As a result, the temperatures on the moon can be as high as 123oC or as low as -233oC. Astronauts going to the moon need to wear spacesuits to protect them from the changes in temperature and from radiation. They also need containers of oxygen to breathe.
The cheese like craters on the moon are as a result of rocks traveling through space and hitting the Moon.
As the Moon revolves around Earth, different amounts of light reflect from the Moon’s surface and the Moon appears to change shape. A phase of the Moon is the appearance and shape of the Moon as you see it at a particular time. The phase depends on the location of the Moon in relation to Earth and the Sun.
An eclipse occurs when one object moves in front of another object in space.
A solar eclipse occurs when the Moon passes directly between the Sun and Earth. When this happens, the Moon casts a shadow on Earth. People on Earth see darkness move across the Sun.
A lunar eclipse occurs when the Moon moves into Earth’s shadow and is no longer reached by direct sunlight. This happens when Earth is between the Sun and the Moon.
If you are on Earth in the umbra during a solar eclipse, darkness covers the entire face of the Sun. This is called a total solar eclipse. If you are on Earth in the penumbra during a solar eclipse, darkness covers only part of the Sun. This is called a partial solar eclipse.
In lunar eclipses, Earth’s shadow causes the umbra and penumbra. Lunar eclipses may also be total or partial depending on whether or not the Moon is in the umbra or penumbra.
The pull of gravity between the Moon and Earth and between the Sun and Earth causes a bulge in the surface of Earth. On the part of Earth’s surface that is rocky, we do not notice this pull. However, the pull can be seen in the oceans and other large bodies of water. This pull causes the tide, or the rise and fall of the ocean’s surface.
When the Sun and the Moon line up and pull in the same direction. This causes higher high tides and lower low tides, called spring tides. The tides with the smallest range between high and low tides occur between these two spring tides. These more moderate tides are called neap tides. They take place when the Sun and the Moon pull in different directions and their pulls partly cancel each other.
Until 1610, when the telescope was developed by the Astronomer Galileo Galilei, people used to observe the sky using only their eyes. As you learnt in the previous topic that the air in the atmosphere has different densities. As light from stars travels through the air, the changes in density make the faint light of the stars appear fuzzy. Looking through a telescope makes dim objects seem brighter and also makes objects appear larger so more details can be observed.
Telescopes can be placed in space to avoid the interference caused by variations in air density in the atmosphere. In 1990, the Hubble Space Telescope was placed into orbit around the Earth. This and other space telescopes gather more than visible light from objects in space, they can detect heat given off by stars and other space objects.
Radio telescopes are located on Earth and record data from radio waves given off by objects in space. Several dishes focus the waves so the radio waves data can be recorded and computers covert the data into images. Radio waves are not affected by air densities so they can move through the atmosphere without interference.
A solar system is made up of a star and the objects that orbit around it. In our solar system, there are eight planets orbiting the Sun. A planet is a large object that orbits a star. Form neares to the sun, the planets in our solar system include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The planets travel around the sun in elliptical or nearly circular orbits.
The inner planets are closer to the Sun than the asteroid belt and have surfaces made of rock. These planets are Mercury, Venus, Earth, and Mars. The outer planets are beyond the asteroid belt and have surfaces made of gases. These planets are Jupiter, Saturn, Uranus, and Neptune. Pluto was once known as the ninth planet. Pluto’s elongated orbit and small size were different from the other planets. Because of this, scientists debated whether Pluto should be classified as a planet. In Aug 2006, the International Astronomical Union officially reclassified Pluto as a dwarf planet. Other dwarf planets include Ceres and 2003 UB313, which is larger than Pluto but farther from the Sun.
Planet's unique features:
Jupiter: has the great red spot (aka red eye), which is a huge storm that has been blowing for over 400 years. It is believed that combination of sulfur and phosphorus are in Jupiter's atmosphere gives this storm its red color.
Saturn rings: First observed by Galileo in 1610. They are made of ice and rocks ranging in size from pea size to rocks larger than a house. Jupiter, Uranus and Neptune also have faint rings that are more difficult to observe.
Venus: The surface of Venus shows evidence of violent volcanic activity in the past. Venus has shield and composite volcanoes similar to those found on Earth. Long rivers of lava have also been observed on Venus.
Mars rocks! The dark boulders on the surface of Mars are volcanic rock fragments that have been found on Mars. These rocks look similar to rocks found near lava flows on Earth.
A moon is a natural object (natural satellite) that orbits a planet. Different planets have different numbers and sizes of moons. Generally, the outer planets have more moons. The Earth has only one moon while Jupiter has at least 63 moons. Saturn has 47 moons, Uranus has 27 and Neptune has 13.
An artificial satellite is an object that is put in space by man to orbit around the earth or other planets. These may be to monitor weather or conduct various forms of communication.
Moons vary in size. Ganymede is the largest moon in the solar system. In fact Ganymede is larger than Pluto and Mercury. The Earth's moon is also larger than Pluto and is clearly visible without a telescope.
When small objects in space collide with larger objects, a crater is formed. Craters are bowl-shaped holes on the larger object.
A comet is a mixture of frozen gases, ice, dust, and rock that moves in an elliptical orbit around the Sun.
An asteroid is a rock that revolves around the Sun. Most of the thousands of asteroids in the solar system are located between Mars and Jupiter in the asteroid belt.
An object that crosses paths with Earth and enters the atmosphere is called a meteor. Most meteors burn up before they reach the ground. When a meteor lands on the ground, it is called a meteorite.
Chelyabinsk meteor - 2013
A star is an object that produces its own heat and light energy. Stars go through stages from beginning to ending depending on how much hydrogen tha star contains. The star's cycle ends when it stops giving off energy.
All stars form out of a nebula. A nebula is a cloud of gases and dust. Gravity pulls the mass of nebula, which contains a lot of hydrogen atoms and as the atoms move closer they collide with each other producing heat. The temperature increases and when the temperature reaches 10 million degrees Celcius, the hydrogen atoms combine to form Ehlium. This process produces huge amounts of heat and light. This marks the beginning of the formation of a star.
The sun is a star, like other stars, it uses hydrogen as the source of energy. As the heat in the sun increases, it forces the hydrogen at the endge of the sun to expand into space, as the hydrogen moves further away from the center of the sun, it cools slightly and turns red. This stage of the star is called a red giant.
Eventually, all the helium is gone and the star begins to cool off and shrink becoming a white dwarf. A white dwarf is a small dense star that sines with a cooler white light. This is the end of the cycle for medium sized stars.
Stars that start with larger amounts of hydrogen (larger stars) end their cycle differently. After they become red giants the atoms at the core become so hot that they combine to form iron atoms. Eventually the iron gets so hot and explodes into a supernova. Supernovas shine brightly for days or weeks then they fade away.
If a star is very massive, it may end its life as a black hole. A black hole is an object that is so dense and has such powerful gravity that nothing can escape from it,not even light.
The sun is a medium sized star with a temperature of around 6000 degrees celcius. Giant stars are about 100 times larger than the sun and super giant stars are 1000 times larger. Neutron stars are the smalles stars.
Stars that form patterns are called constellations. Constellations were often named after animals, characters from stories, or familiar objects. Some constellations have been extensively useful to both ancient and modern travelers. For example, if you can see either the Big Dipper or the Little Dipper in the night sky, you can follow the line that their stars make to find Polaris, the North Star. If you travel in the direction of Polaris, you will be moving north. If you ever become lost in the woods or at sea, look for Polaris (North star) in the night sky. It will help guide you to safety.
The ancient Greeks divided the sky into 12 sections. They named some constellations after characters from Greek myths, such as Orion, a hunter, and Hercules, a hero.
Light Years
After the sun, the next closest star is called Proxima Centauri and is about 40,000,000,000,000 km away. This distance is so huge and becomes difficult to remember and comprehend. We can use the unit light year, which is equal to the distance that light travels in a year, and is equal to 9.5 billion kilometers. Proxima Centauri is 4.2 light years away from the earth.
Clusters and Binary Stars
Some stars form clusters that may contain more than 100,000 stars. Clobular clusters are shaoed like a sphere. When two stars are close to each other, or somehow overlap and are seen as though they were only one star, they are called binary stars. the prefix -bi stands for 'two'. A star that seems to be blinking might actually be a binary star where one of the stars, the dimmer one, blocks the light from the brighter star.
Galaxies
A galaxy is a huge very distant collection of stars. Each galaxy holds billions of stars.
Galaxies differ in size, age, and structure. Astronomers place them in three main groups based on their shapes: spiral, elliptical, and irregular.
A spiral galaxy looks like a whirlpool. The spiral arms can be tightly or loosely wound around the galaxy’s core, and they often contain a great deal of dust. Some spiral galaxies are barred galaxies. A barred galaxy has a “bar” of stars, gas, and dust through its center. The spiral arms emerge from this bar.
An elliptical galaxy is shaped a bit like a football. It has no spiral arms and little or no dust.
An irregular galaxy has no recognizable shape. The amount of dust and gas varies. The irregular shape may have been caused by collisions with other galaxies.
Our solar system is part of the galaxy called the Milky Way. The stars you see in the sky are part of the Milky Way galaxy. The Milky Way is a spiral galaxy. The stars are grouped in a bulge around a core. All of the stars in the Milky Way, including our Sun, orbit this core. The closer a star is to the core, the faster its orbit is. Several spiral arms extend out from the core. Our solar system is located on one of these spiral arms. The arms contain most of the Milky Way’s gas and dust. We cannot see the center of the Milky Way, because there is dust between us and the core. However, from Earth we can see more stars when we look in the direction of the galaxy’s center than when we look in other directions.
The Big Bang Theory
The Big Bang Theory hypothesizes that the universe started with a big bang a single point and has been expanding ever since. Scientific evidence indicates that the big bang happened 13.7 billion years ago.
Astronomers think the galaxies must have been closer to each other in the past. The early universe was very dense, and its temperature was high. At the beginning moment, the universe was extremely tiny, hot, and dense. From this tiny beginning, the universe expanded rapidly. This expansion sent matter out in all directions.
The galaxies continue to move outward. Evidence for the big bang comes from background radiation. Background radiation comes from all directions in space. This radiation is left over from the beginning moments of the universe.
How did Earth form?
Scientists think that Earth is about 4.6 billion years old and theorise that the Earth and its atmosphere developed in a series of stages. The process began in the nebula that formed the Sun. Dust and ice particles moved within the nebula, occasionally colliding. They merged and stuck together. The clumps of particles grew until they became the young Earth, or proto-Earth. Over time, proto-Earth became large enough that its gravity could hold an atmosphere. Scientists believe that the atmosphere did not initially contain oxygen, as it does today. Atmospheric oxygen developed as a waste product of photosynthesis.
Aerospace Engineer
Aerospace engineers complete a degree program in aerospace engineering from a recognized university. As an aerospace engineer, you could make flights into space possible by helping build highspeed spacecraft. You could also make travel closer to Earth faster and safer by improving aircraft design. Therefore, aerospace engineering is for those interested in designing spacecraft, missiles, helicopters, or military jets.
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