Grade 9 - Biological Diversity

Biological diversity refers to the number and variety of species and ecosystems on the Earth and the ecological processes of they are a part of. This should be differentiated from Earth's biodiversity, which is the entire collection of living organisms, each with their own unique characteristics.

Section 1: Diversity and Survival

A Species is a group of organisms that the same structures (characteristics) and can reproduce with each other (interbreed). There are over 1.5 million species of animals and 350,000 plant species identified so far.

Components of Biodiversity

The main components of biodiversity include:

  • Ecosystem diversity – the different types of living communities and the environments in which they are found, such as marshes, lakes, streams and forests, etc.
  • Community diversity – occurs within populations of organisms living within a particular ecosystem. Remember the word population refers to organisms of the same species living in the same area, while the term 'community' refers to members of different species that live in a specific area and share the same resources.
  • Species diversity – occurs within individual organisms of the same species.

    • Genetic diversity – occurs within organisms at a cellular level, as it describes the variety of genetic material in all living things.

  • Species Distribution – Not all plants and animal species are found in every part of the world, or even in every part of an eco-region. Most of the species of plants and animals can be found in tropical regions and, more specifically, in the rainforests. As you move closer to the poles of the Earth, there is less biological diversity.

Variations Influence Survival

Variations result in varying abilities for different organisms to survive in specific environments. This is called Adaptation. There are two types of adaptations. Physical features of an organism are structural adaptations, whereas, actions are behavioral adaptations.

Variation and Competition

In most ecosystems, resources such as water, food, sunlight, space, are scarce and so several species have to compete for these resources. The competition is not fair because one species may be better able to obtain the resource than another species. The species that is better able to obtain resources (outcompetes the other species) is at an advantage over other species resulting in better chances for survival. The species who does not win the resource may have to switch to a different, less desirable resource in order to survive.

Measuring Biological Diversity

To measure the biological diversity of an area, biologists use a measurement called a diversity index. This compares the diversity of species in a certain area with the total number of organisms in that same area, or ecosystem. The index is used to assess the health of an ecosystem, where a higher index indicates a healthier ecosystem.

Section 2: Habitat and Lifestyle

A habitat is the natural home or environment of an animal, plant, or other organism.

On the other hand, a niche is the role an organism has within a particular habitat or ecosystem. An organism's niche can be defined by describing what the organism eats, What eats the organism, physical description of its habitat, Nesting site, range and habits, What effect it has on the other populations, What effect it has on the environment etc. An organism's niche can change, depending on the environment in which it is located and the organisms with which it inter-relates.

Broad Niche: An organism that is adapted to an extensive range of environmental conditions for survival is said to have a broad niche. This wide range of adaption and survival skills indicates that the organism can live in various different conditions. The reverse side of this would be a narrow niche, in which the organism must have very specific environmental conditions to survive and only plays a limited role in its habitat. A broad niche organism may also be called a generalist, while a narrow niche organism may be called a specialist.

In the tropics, where the temperatures are relatively constant and food supply is stable, organisms are specialists. They efficiently survive in their environment, because they have relatively narrow niches with adaptations directed toward competing for one dependable food source, type of soil or level of light. This specialization allows many different species to coexist in the same area, preventing one species from becoming dominant. The result of this is high diversity with low populations. A specialist is well adapted to survive in one particular environment. This is considered to be the ‘trap of specialization’, because, as it is able to survive very well in one environment, it is not able to adapt to extreme change and may not survive when this occurs.

Some organisms have adaptations that enable them to live in extreme environments. These are called Extremophiles. These environments might have high pressure, high (or low) temperature, high radiation levels, high pH etc. Examples include: Antarctic springtail are arthrods that live in extreme cold, by producing a kind of antifreeze in its tissues, Tube worms live on the ocean floor, near black smokers, where volcanic vents make the temperature extremely hot etc.

Section 3: 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 sea 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.

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.

Sexual reproduction in plants involves gametes as well, male gametes and female gametes joining, during fertilization, to produce a zygote and then an embryo. Pollen contains the male gametes and is found on the stamen. Ovules contain the female gametes and are found in the pistil. Pollination occurs when pollen is transferred from the anther of the stamen to the stigma of the pistil. Cross-pollination occurs when pollen from one plant is carried to the stigma of another plant by wind, water or animals (bees or butterflies). Cross fertilization occurs when a grain of the pollen forms a long tube (pollen tube), which grows down the style into the ovary. The gametes unite to produce a zygote, which then develops into an embryo. This usually happens inside a seed, which protects the embryo and provides food (cotyledon) for the embryo when growing conditions are right. Plants which are produced, as a result of cross-fertilization, are not identical to either plant.

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.

Bacterial Conjugation: Bacteria are able to transfer genetic material directly from one cell to another through a process called bacterial conjugation. It is a primitive form of sexual reproduction, since two parent cells are involved. The benefit is that new combinations of inherited characteristics may result. Although this process is not actually reproduction, because there is no increase in the number of cells, it does result in genetic recombination. The newly created cell can then divide by binary fission, to create identical cells with the new genetic material.

Sexual Reproduction in Animals

Sexual reproduction in animals also involves gametes. The male gametes are called sperm cells, and the female gametes are called egg cells (ova). During mating, the sperm cell and the egg cell unite in a process called fertilization to form a zygote. The zygote undergoes several series of cell divisions and specializations resulting in the development of an embryo. This embryo develops further into a multi-cellular organism. This occurs inside the uterus of the female or outside (in an egg shell) in other animals.

Section 4: Inheritance

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.

Purebred VS Hybrid: To produce purebred organisms, a breeder would choose pure bred parents, ie., those parents whose ancestors have produced only the desired characteristic they want (true-breeding). If a breeder chooses two different 'true-breeds' then a hybrid would be produced.

Dominant Traits: Crossbreeding two different true-breeds will result in all of the offspring having the same characteristic, that is, the dominant trait. Only the DNA instructions for the dominant trait will be expressed.

Recessive Traits: When crossbreeding hybrids, the average results will produce 75% of the offspring with the dominant trait and 25% of the offspring with the recessive trait, because there are only 4 possible combinations. One trait is recessive and therefore the allele is recessive. A recessive trait only appears in the offspring if two recessive alleles are inherited.

Using Punnett Squares

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.

Nature Vs Nurture

Not all characteristics are inherited, some characteristics develop depending on the environment the organism is exposed to. Examples include: change in the pigmentation of skin color throughout the seasons due to the sun, height and weight can be influenced by diet. Scars, injuries, clothing, hairstyle, makeup, and cosmetic surgery may change a person’s characteristics, but they are not caused by genetics. One way that scientists study the relationship between genetics and the environment is to observe the similarities and differences between identical twins that have been separated at birth and raised in different environments.

Genetic Change

Factors in the environment, or random events can change genetic information contained in DNA. These changes are called mutations, and can cause changes in the structure of organisms, including people. Mutagens, such as X-rays, ultraviolet rays, cosmic rays and some chemicals can cause mutations to occur – some that have little visible effects and some that have dramatic effects. If mutations occur in the DNA of reproductive cells, the changes can be passed on from the parent to the offspring, increasing the variation within a species.

Section 5: 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.

Genes are located in the chromosomes and come in pairs. Each chromosome has numerous gene locations. Both genes in a pair carry DNA instructions for the same thing. Specific characteristic genes occupy matching locations on the two chromosomes. DNA code may not be exactly the same in both locations. Offspring inherit genes from both parents. The genes exist in an array of possible forms that differ as to their exact DNA sequence. These variations in forms are called alleles. The ultimate combination of the chromosome pair is what makes the variation possible - combining the different variations of different characteristics to create a unique variation.

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.

Section 6: Selection

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.

Artificial Selection in Agriculture

The process of intervention to produce more desirable organisms has been going on for some time. This process takes a long time to see results - usually many generations. Farmers, dog and horse breeders, along with scientists can now speed up the artificial selection process by using 'low-tech' or 'high-tech' technologies, such as;
1. Cloning
2. Artificial Insemination
3. In-Vitro Fertilization
4. Genetic Engineering

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.

Section 7: Preserving Biodiversity

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.

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.

Zoos were not originally started to preserve diversity. They were exotic collections for private collectors. They didn’t become public until the early 1800’s – in London. Today there are thousands around the world. Besides being home to a diverse group of animals and plants, Zoos can be educational institutions for students at all levels. Some zoos are part of a worldwide network that is attempting to protect and preserve endangered species. Animal exchange programs help to increase the genetic diversity essential to species survival. Support for research is also a large part of their program. Zoos are visible evidence of our attempt to preserve and maintain biological diversity.