Classifying Organisms
Compare broad biological groups, including plants, animals and fungi, using shared characteristics. Recognise that micro-organism describes very small organisms and can overlap biological groups.
What a learner can do afterwards
- Name plants, animals and fungi as broad biological groups, and explain that these are not a complete list of all life
- Compare characteristics such as food methods, and explain why movement or size alone does not identify a biological group
- Give examples of plants, animals, fungi and micro-organisms, including bacteria and microscopic fungi such as yeast
1 · Read
Scientists compare shared characteristics to place organisms in biological groups. Plants, animals and fungi are examples, not a complete list of all life. Micro-organism describes very small organisms. It is a size description that can overlap biological groups.
Most plants make food using sunlight. Grass, daisies and ferns are examples. Animals obtain food by eating organisms or material from them. Birds, snails and grasshoppers are animals. A grasshopper can eat grass: the grass makes food using sunlight, while the grasshopper eats it. Many animals move to find food, but movement alone does not identify an animal.
An oak tree and a cactus are plants that make food using sunlight. A rabbit eats grass, and a seagull eats food it finds. Both are animals. A rock is nonliving. Compare known examples and several characteristics instead of deciding from colour or movement alone.
Mushrooms, moulds and yeasts are fungi. Fungi absorb nutrients from their surroundings and do not make food using sunlight. Many break down dead material; others obtain nutrients from living things. Bread mould can break down bread. A fungus on dead wood can get nutrients from that wood. Compare it with a daisy: the daisy makes food using sunlight; this fungus absorbs nutrients from wood. Their shared stillness does not make their food methods the same.
Micro-organisms are very small organisms, usually studied with a microscope. A typical individual bacterium needs a microscope to be seen clearly. Bacteria are living things, but they are neither plants nor animals. Some bacteria move. Yeasts are microscopic fungi, and some animals are microscopic too. A microscopic animal is still an animal.
Size, movement and food provide useful evidence, but no single clue sorts every organism. Some micro-organisms move or use sunlight. If an unknown pond organism moves, eats and is microscopic, you can describe its small size. You need more evidence to settle its biological group.
Compare specified individuals when ordering sizes. A seedling and a full-grown tree can differ greatly. Use the stated size relationships: if one organism is larger than another, place it earlier in a biggest-to-smallest list. A microscopic individual comes after much larger examples that you can see without a microscope.
Compare shared characteristics to identify biological groups. Micro-organism describes small size and can overlap groups such as fungi and animals.
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More to read
Two descriptions can fit
An organism can have a biological group name and a size description. Yeast belongs to fungi. An individual yeast is microscopic, so it is also a micro-organism. Those descriptions do not compete.
The same distinction matters for animals. Some animals are microscopic. Their size does not remove them from the animal group.
Plants, animals and fungi are examples of broad biological groups, not a complete list of all life. Bacteria are living organisms outside those three groups. Micro-organism is useful when discussing very small organisms, but it does not name one exclusive biological group.
Compare food methods
Grass makes food using sunlight. A grasshopper eats grass. Living in the same field does not mean they obtain food in the same way.
Fungi absorb nutrients from their surroundings. Many help break down dead material, such as fallen wood. Others obtain nutrients from living things. Do not assume that every fungus feeds in exactly the same setting.
Food methods give useful evidence for comparison. They are not a complete identification test. Some micro-organisms use sunlight, while others move and feed on other organisms. An unknown organism may need several observations before its biological group can be identified.
Test a grouping rule
Suppose someone proposes that every moving organism is an animal. A moving rabbit agrees with that rule, but it does not prove the rule works for everything. A moving bacterium challenges it: bacteria are not animals.
Now consider the claim that microscopic things cannot be alive. A typical bacterium is microscopic and living. It challenges that claim too.
When testing a rule, look for an example that meets one part of the claim but does not fit its conclusion. Keep the observation separate from the conclusion. Movement is an observation; animal is a biological group.
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