Grade 6
Life Sciences

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.

Chapters covered in this course

Chapter 1: Classifying Living Organisms Chapter 2: Cells Chapter 3: Genetics Chapter 4: Ecoystems

Chapter 1 Chapter 1: Classifying Living Organisms

Lesson 1: Classifying Plants and Animals Lesson 2: Plants Lesson 3: Animals Lesson 4: Animal Systems Lesson 5: Adaptations in Plants and Animals

Lesson 1: Classifying Plants and Animals

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.

Characteristics of Living Things

There are 5 basic functions that can be used to define living things:

Livivng things are made of cells: Cells are the building blocks of life, they carry out all basic life processes such as convrting food molecules into energy and getting rid of waste. Some organisms are only made up of one cell while others have multiple cells.
Living things can obtain and use energy: All living things require energy to carry out their life functions. Plants capture energy from the sun. Animals obtain energy by consuming plants or other animals.
Living things reproduce: Reproduction is the process where an organism can produce more of itself. Some living things made of one cell can undergo cell division and form more one-celled organisms. Multicellular organisms may have a more complex way or reproducing. In some cases, they need two individuals to contribute special cells that combine together to form a single cell that then develops into an organism. When two cells combine to form an organism, the daughter organism (offspring) will have features/characteristics that combine those from both parent organisms.
Living organisms grow and develop: Each organism has a life cycle that involves changes in its size, shape and ability to move. A human baby may take 12 months before they learn how to walk. A calf takes only a few minutes to be able to stand up and walk. Seeds germinate and grow into full size trees/plants.
Living things respond to their environment: When its cold, living things find a way to keep warm, and vice versa. Living things will avoid environments that may harm them.

Classifying Organisms

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.

Naming Organisms

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.

Kingdoms

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:

Bacteria
Archaea
Protozoa
Chromista
Plantae
Fungi
Animalia

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: 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

Protozoa: 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.

Chromista: 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.

Plantae: 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.

Fungi: 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.

Animalia: 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.

Lesson 2: Plants

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

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

Reproduction can either be classified as sexual or asexual. Sexual reproduction is the production of new organisms by the union of a male and female sex cells. Asexual reproduction is the production of a new organism using only one cell type. Some organisms can reproduce through both sexual and asexual processes.

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.

Self pollination occurs when pollen is transferred from the anthers to the stigma on the same flower. Cross pollination is when the pollen is transferred to the stigma of a different flower. Pollinators are organisms that transfer pollen from flower to flower, such as bees, butterflies, birds etc.

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.

Some plants use spores instead of seeds. Spores are cells that can develop into new organisms. Spores do not contain stored food. Mosses and ferns use spores to reproduce.

Life Cycles of Plants

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.

Below is an illustration of alternation of generations:

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.

Lesson 3: Animals

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:

Amphibians: They have jaws, smooth skin and hard bony skeletons. Most breath through gills in the water when they are young and then through lungs when they become adults.

Birds: Birds have jaws, feathers and hard bony skeletons. They breathe through lungs. Most birds can fly.
Reptiles: Some reptiles live in water and some live on land. They have jaws, scales and a hard bony skeleton. They breath through lungs.

Mammals: mammals have hair or fur. They have jaws and a hard bony skeleton. They breathe through lungs and feed their young on mother's milk. Most mammals live on land.
Jawless fish: They have soft skeletons and gills. There are about 70 species including hagfish.

Bony fish: They have a hard, nony skeleton and breath through gills.

Cartilagenous fish: They have a skeleton made of cartilage. They breathe through gills. There are about 750 species including sharks and rays.

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.

Crustaceans: Include crabs, shrimps and lobsters. They are the most abundant animals in the ocean. They can live in fresh water or in salty water.

The largest group of arthropods are the insects with over 1 million species. The insect body has a head, thorax and abdomen. Three pairs of legs are attached to the thorax. They have eyes and antennae that help the insect to sense its environment.

Arachnids: They include spiders, ticks and scorpions. They have 4 pairs of appendages, one or two body segments and no antennae.

Lesson 4: Animal Systems

You have learnt previously that living things are made of cellsand 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.

Digestive System

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.

Respiratory System

Alhtough 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.

Circulatory System

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.

Regulation of Body temperature

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.

Lesson 5: Adaptations in Plants and Animals

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.

Structural Adaptations

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.

Mimicry

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. The example below 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.

Behavioral Adaptations

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.

Chapter 2 Chapter 2: Cells

Lesson 1: Cell Theory Lesson 2: Plant and Animal Cells Lesson 3: Cell Division Lesson 4: Microorganisms

Lesson 1: Cell Theory

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.

Biological Organization

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:

Muscle tissue: Cells and fibers that move bones, pump blood and push substances through the digestive system.
Connective tissue: The tissue present in bone, cartilage, tendons, fat and blood.
Nerve tissue: Responsible for carrying messages throughout the body.
Epithelial tissue: Include the outer layer of the skin and the cells lining the digetive system.

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.

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.

Lesson 2: Plant and Animal Cells

Plant and animal cells differ in:

Plant cells contain chloroplasts, which are necessary for energy metabolism.
Plant cells contain a large central vacuole.
Plant cells contain a cell wall, which gives the cells a regular shape.
Animal cells contain lysosomes, plant cells do not.
Animal cells have centrioles, which are necessary for cell division.

Cell Organelles

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).

The structure of a mitochondria. (Source: genome.gov)

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.

Structure of the Plasma Membrane

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.

Chemical structure of a phospholipid and the phospholipid bilayer. (Source: Wikipedia-CC BY-SA 3.0)

Functions of the Cell Membrane

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.

Cellular Transport

Transport across the cell membrane is either Active (requires energy) or Passive (does not require energy to occur).

Passive transport include Diffusion and Osmosis.

Diffusion

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.

Diffusion across a membrane

Membranes can be classified as:

Impermeable: does not let anything pass through the membrane

Permeable: allows all materials to pass through the membrane

Semi-permeable: allows some particles to pass through the membrane while excluding other particles

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.

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.

Factors that influence rate of diffusion

Concentration Gradient: The difference in concentration between two locations. Molecules of substances move from high concentration to low concentration, so the larger the concentration gradient the faster the diffusion rate.

Temperature: Higher temperature results in faster diffusion rate.

Particle size: The larger the particle the slower the movement.

Facilitated 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.

Osmosis

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.

Plants rely on a process called photosynthesis to obtain their energy. They utilize energy from the sun to produce food in form of glucose. The main ingredients (reactants) needed for photosynthesis to occur are carbon dioxide and water. The process produces glucose and oxygen.

Photosynthesis takes place inside chloroplasts. These organelles in plant cells contain the green pigment called chlorophyll. Chlorophyll captures energy from the Sun and the energy powers photosynthesis. The glucose produced in the process is stored within the plant. Oxygen, a waste product of photosynthesis, is released into the atmosphere.

Plants and animals use glucose as an energy source to perform various biological processes through a process called cellular respiration. Cellular respiration is like burning fuel to produce energy. It takes place in the mitochondria, an organelle found in the cell.

Cellular respiration can either be aerobic (requiring oxygen) or anaerobic (not requiring oxygen). Aeorbic respiration is more common when the oxygen supply to the cells meets the demand. Anaerobic respoiration (also called fermentation) occurs when the cells are not receiving sufficient oxygen for the needs. For example, during strenous exercise, the cells are utilizing energy much faster than can be produced by aerobic respiration.

Lesson 3: Cell Division

Cell 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

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.

Interphase

Interphase is when the cell is not dividing. It is the stage between cell divisions. Most of the cell's time in the cell cycle is spent in interphase.

Prophase

Chromatin condenses into distinct duplicated chromosomes.
Nuclear membrane begins to disintegrate.
In animal cells organelles called the centrioles move to opposite sides of the cell ('poles').
Astral rays (microtubules) form around centrioles.

A detailed illustration of the Cell Cycle and Prophase. (Source: Wikipedia-CC BY-SA 3.0 / Public Domain)

Metaphase

Chromosomes line up at equatorial plate (metaphase plate) and centromere attaches to spindle fibers that formed from elongated astral rays.
At the end of this phase the centromere splits separating the sister chromatids.
Nuclear membrane disappears.

An illustration of Metaphase, and most specifically the formation of the metaphase plate. (Source: Wikipedia-CC BY-SA 3.0)

Anaphase

The spindle fibers contract, pulling the chromosomes (sister chromatids) to the opposite poles of the cell.
Centromeres divide.

An illustration of Anaphase. (Source: Wikipedia-CC BY-SA 3.0)

Telophase

Chromatids reach opposite poles; spindle and astral rays disappear.
Chromosomes unwind back into chromatin.
Nuclear membrane begins to reform.
Cell membrane pinches in the middle to divide the cell - Cytokinesis.

An illustration of Telophase. Nuclear membranes begin to form around two separate sections of what will become two separate cells. (Source: Wikipedia-CC BY-SA 3.0)

Cytokinesis

The Cytoplasm begins to divide by forming a cleavage furrow at the equator and pinches off forming 2 daughter cells, with genetic information identical to each other. These cells will become the new parent cells for the next cell division cycle.

An illustration of Cytokinesis with two cells formed, marking the end of Mitosis. (Source: Wikipedia-CC BY-SA 3.0)

Mitosis - Animals versus Plants

There are 2 main differences between animal and plant cell division:

Plants do not contain centrioles. They contain microtubules that create many of the same proteins (spindles), they just don’t have the centrioles
Plants do not undergo cytokinesis. Instead, a cell plate forms at the equator of the cell to form a new cell wall.

A detailed illustration of the differences between Cytokinesis in animals and in plants. (Source: Wikipedia-CC BY-SA 3.0)

Technologies related to Mitosis

Cloning

Cloning is the process in which identical offspring are formed from a single cell or tissue. Many plants have the ability to naturally clone themselves; this is called totipotent (i.e. strawberries, aspen trees). Most animal cells are not totipotent (except salamanders) but technology has advanced to allow us to clone (i.e. Dolly the sheep).

Cloning techniques include nuclear transfer from blastula, nuclear transfer with electrical or chemical shock, identical twins.

Nuclear transfer from blastula:The nucleus of a cell from a blastula is removed and transplanted into an enucleated unfertilized egg. Enucleated cells are cells that do not contain a nucleus. The egg begins to divide by mitosis, eventually forming an organism.

Identical twins: Occur when a zygote divides into two and each undergoes successive mitotic cycles to form the multicellular embryos The genetic information between the two embryos is identical

Meiosis

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).

An overview of Meiosis. In general, Meiosis occurs in two stages, Meiosis I and Meiosis II. (Source: Wikipedia-CC BY-SA 3.0)

Stages of Meiosis

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

Chromatin coils tightly to form chromosomes.
Homologous chromosomes pair up side by side in a process called synapsis.
When 2 homologous chromosomes are paired, the structure is called a bivalent.
Chromosomes shorten & thicken - the homologous chromosomes (bivalents) pair up to form tetrads.
Each tetrad contains 2 homologous chromosomes and 4 chromatids.
Crossing Over: As the homologous chromosomes come close together, they often intertwine. Sometimes chromatids break & exchange segments. This process is called crossing over. The area(s) where the chromatids overlap is called a chiasma. Here homologous chromosomes exchange genetic material.

Metaphase I

The tetrads line up on the equatorial plate.
The homologous pairs line up randomly- There is a 50-50 chance for the daughter cells to get either pair from each chromosome.
Spindle fibers attach to the centromeres of the chromosomes.
Each pair of sister chromatids from each homologous chromosome is ready to move to opposite poles of the cell.

Anaphase I

Homologous chromosomes separate and move to opposite poles.
This process is known as segregation-the separation of paired genes.
At this point, reduction division has occurred!
Each chromosome remains double stranded

Telophase I

Cytoplasm divides i.e. Cytokinesis.
A nuclear membrane begins to form.
Chromosomes unwind into chromatin.
The two new daughter cells contain 2 chromosomes each.

An overview of Meiosis I. (Source: Wikipedia-CC BY-SA 3.0 - Edited by Foundations Learning Hub staff to optimize the screen)

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

Begins with the 2 daughter cells from meiosis I.
DNA replication does NOT occur.
Nuclear membrane dissolves, spindle fibers form.

Metaphase II

The chromosomes, each with two sister chromatids, align on the equatorial plate.
The centromeres attach to spindle fibers.

Anaphase II

The centromeres separate and chromatids move towards opposite poles.

Telophase II

Four new cells will be formed.
Each of the new cells will contain only one member from each homologous pair i.e. haploid (n).

An overview of Meiosis II. (Source: Wikipedia-CC BY-SA 3.0 - Edited by Foundations Learning Hub staff to optimize the screen)

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.

Comparing Mitosis and Meiosis

Meiosis takes place in 2 stages involving 2 successive divisions.
Meiosis occurs in germ line cells to generate gametes (ova and sperm) while mitosis occurs in body / somatic cells.
The chromosomes arrange themselves in homologous pairs (pair up with another chromosome of the same size and shape).
In meiosis, the four daughter cells are not necessarily identical mostly because of the crossing over that occurs. In addition, the daughter cells in meiosis are haploid i.e. have only half the number of chromosomes present in the original parent cell. Daughter cells arising from mitosis are diploid.

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).

Lesson 4: Microorganisms

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.

Chapter 3 Chapter 3: Genetics

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 Change

Lesson 1: Control of Traits

Living 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.

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.

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.

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.

Lesson 2: Human Genetics

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 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

Circles represent female. Squares represent males.
A horizontal line connecting a circle and a square represents two parents. A vertical line connects parents to offspring.
Horizontal lines connects the children in a family. The oldest child is always on the left and the youngest on the right.
Dark shaded circles or squares represent individuals who show the trait of interest.
Lighter shaded circles or squares represent individuals that do not express the trait of interest.

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.

Lesson 3: Modern Genetics

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.

Lesson 4: Genetic Change

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'.

Chapter 4 Chapter 4: Ecosystems

Lesson 1: Earth's Ecosystems Lesson 2: Food Chains, Webs and Pyramids Lesson 3: Comparing Ecosystems Lesson 4: Changes In Ecosystems

Lesson 1: Earth's Ecosystems

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 specieis) are considered together, it is called a community. So a community will include the number of giraffes, lions, cheetahs and all other species in the national park.

Cycles in Ecosystems

The Water Cycle

The water cycle is made up of three manin processes.

Evaporation
Condensation
Precipitation

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.

The Carbon Cycle

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 Nitrogen Cycle

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

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

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

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.

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.

Lesson 2: Food Chains, Webs and Pyramids

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.

Lesson 3: Comparing Ecosystems

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:

Desert
Tundra
Aquatic
Forest
Grassland

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.

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.

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.

Lesson 4: Changes In Ecosystems

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.

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.

Comparing Changes in Organisms

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.

Life Sciences

Grade 6 Life Sciences