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Classifying different types of organisms. A huge variety of organisms live on our planet. Scientists have categorized organisms to make them easier to identify. This is called classification.
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Classifying different types of organisms A huge variety of organisms live on our planet. Scientists have categorized organisms to make them easier to identify. This is called classification. Organisms can be classified into different species. A species contains individuals with the same physical characteristics and common ancestors. So far, scientists have identified around 290,000 species of plants, 1,250,000 species of animals and 5 million species of bacteria living on our planet.
animals vertebrates invertebrates Classifying animals Animals can be divided into two groups. Vertebrates have a backbone. They have a firm body because of the muscles that connect to their skeleton. Invertebrates do not have a backbone. They have soft inner bodies that are held in shape either by a flexible covering of outer cells or by a hard covering called an exoskeleton.
More about mammals Mammals are classified into three subgroups: • marsupials – They give birth to tiny underdeveloped young that develop in a pouch outside the mother's body, e.g. kangaroo. • monotremes – They lay eggs but suckle their young, e.g. platypus. • placentals – The young are attached to a placenta inside the womb. Newborns are already developed, e.g. bear. What type of mammal are humans?
More about arthropods Arthropods are divided into four subgroups: • crustacea – They have gills, more than six legs and two pairs of antennae, e.g. crab, barnacle, lobster, shrimp. • insects – They have six legs, and many have two pairs of wings, e.g. dragonfly, moth, ladybird, wasp. • arachnids – They have eight legs, no wings and their bodies are in two segments, e.g. spider, mite. • myriapods – They have many feet and long bodies of many segments, e.g. millipedes, centipedes.
Classifying plants Plants can be classified according to the structure of the vascular tissue (‘veins’) in their leaves. Monocotyledons are plants that have leaves with parallel veins. Maize plants are monocotyledons. Dicotyledons are plants that have wide leaves with branched veins. Horse chestnut trees are dicotyledons. Plants can also be classified according to whether they reproduce via seeds (like flowering plants) or spores (like mosses and liverworts).
Variation within a species Organisms of the same species are similar but not identical. Even though people are all from the same species, there are many ways in which they are different from each other. The differences that occur both between different species and within the same species are calledvariation.
Inherited characteristics The members of this family tree are related and so they share certain similar characteristics, such as hair colour and eye colour. Shared family characteristics are inherited from parents. So why don’t all family members look exactly alike? Why are identical twins more similar than brothers and sisters?
What is variation? Variation can come about for two reasons. What are they? Children inherit characteristics from their parents. Each child inherits a different combination of characteristics. This is called inherited variation. Other characteristics are affected by a person’s surroundings. This called environmental variation.
Inherited or environmental? Deciding if a characteristic is inherited or caused by environmental factors can cause a lot of discussion. Scientists have now decided that only four features are truly inherited and not affected by the environment at all. What are the four truly inherited characteristics? • natural eye colour • natural hair colour • blood group • certain inherited diseases.
Inherited or environmental? Most features are caused by a mixture of inheritance and environmentalfactors. Nose shape is inherited, but over time it may be affected by the environment. For instance, someone might have a nose that looks just like their mother’s. But if they were in an accident, they might break their nose and put a kink in it.
Continuous and discontinuous variation Characteristics can be classified in different ways. How would you categorize variation in eye colour? Could height be categorized in the same way? • A feature that can be measured and given a value from a range of values shows continuous variation. • A feature that cannot be measured but is one of a few distinct options shows discontinuous variation. Which type of variation are eye colour and height?
Where is the inherited information? An organism’s features can be inherited or caused by environmental factors. Inherited features are those that have been passed from the parents to their offspring. In all living things, inherited features are passed on in genetic material. Where is the genetic material found?
78.5 108.3 111.3 102.1 94.4 113.2 100.2 95.7 109.7 113.5 83.2 106.4 102.1 99.8 102.4 118.1 105.6 112.7 103.8 89.2 110.8 105.2 112.6 93.8 88.9 99.6 109.4 99.8 109.4 108.8 84.8 91.9 97.1 91.7 111.8 98.4 97.5 109.0 92.1 92.2 100.4 98.6 103.7 109.3 104.6 102.3 87.4 97.3 119.3 96.1 Masses of beefsteak tomatoes The mass of 50 beefsteak tomatoes was measured (in grams) and the results recorded in the following table:
Masses of beefsteak tomatoes The masses of the beefsteak tomatoes can be made into a frequency graph by counting how many tomatoes weigh between 78g and 82g, 82g and 86g and so on. What does this graph show? frequency mass of beefsteak tomatoes (grams)
Masses of plum tomatoes The mass of 50 plum tomatoes was also measured (in grams) and the results recorded in the following table: 40.0 62.2 65.3 58.1 73.0 74.4 61.3 71.0 48.1 71.6 59.0 63.9 64.4 44.9 59.8 60.5 71.1 62.0 64.4 65.7 56.3 55.7 50.2 55.6 52.3 59.4 68.3 61.8 54.7 59.4 49.7 71.9 71.2 46.5 42.0 58.6 60.6 63.7 64.5 59.6 43.1 58.2 60.1 68.3 72.5 57.2 63.1 48.5 64.5 47.7
Masses of plum tomatoes The masses of the plum tomatoes can be made into a frequency graph by counting how many tomatoes weigh between 40 g and 44 g, 44 g and 48 g and so on. What does this graph show? frequency mass of plum tomatoes (grams)
Comparing tomatoes Compare the frequency graphs for the masses of the tomatoes.Are there any differences between the two sets of results? Distribution of mass of beefsteak tomatoes. frequency mass (g) Distribution of mass of plum tomatoes. frequency mass (g)
Comparing tomatoes Other questions to consider when comparing the frequency graphs for the masses of the beefsteak and plum tomatoes: 1. What can you say about the variation of mass within each species of tomato and the variation between the two sets of results? 2. Are there any other measurements of the tomatoes that can be easily recorded and would show a similar set of results to the measurements of mass? 3. Some quantities cannot be measured immediately but are important to those who grow and those who buy a crop of tomatoes, e.g. disease resistance and time taken to ripen. Can you think of any more quantities like this?
Selecting desirable characteristics Farmers, horticulturalists and scientists may want to produce plants or animals with useful characteristics. There are several ways of doing this: • Selective breeding – this involves breeding individuals with desirable characteristics over generations to produce organisms with certain qualities. • Genetic engineering – this involves changing an organism’s genetic material to produce useful characteristics.
Selective breeding Selective breeding is a process humans use to produce animals or plants that have useful characteristics. Milk farmers choose cows with the highest milk yield to breed with a suitable bull. Continuing to do this over several generations can produce a whole herd of cows with a very high milk yield. Apple growers want to produce a type of apple that is tasty and resistant to disease. This can be done over several generations by crossing a variety of apple known for its taste with another variety that shows strong resistance to disease.
Genetic engineering Genetic engineering involves changing an organism’s genetic material. This can result in a change in the organism’s characteristics. Genetic engineering is used to produce genetically-modified (GM) organisms that have useful characteristics. For example, microbes can be genetically engineered to produce vaccines for human diseases. How are GM crops useful to humans?
Why use genetic engineering? Some cropsplants can be genetically engineered to be disease, herbicide or frost-resistant. These crops could produce larger crop yields. Crops, such as golden rice, have been engineered to contain extra vitamins. These could be useful in countries where malnutrition is a problem. Why do some people think that GM crops are unsafe?
Disadvantages of genetic engineering GM organisms have characteristics that do not occur naturally, so it’s very hard to predict the effect they may have on the environment and wildlife. It is possible that GM crops could cross-pollinate with naturally-occurring plants. For example, this could result in weeds with herbicide resistance, that would be very hard to get rid of. Also, GM crops could cause people to have unknown or unforeseen allergic reactions.
