Chapter 5 · Biology
Unicellular and Multicellular Organisms
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An amoeba is one cell; you are about 37 trillion. In one, a single cell does everything; in the other, cells share the work.
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Key points
- Unicellular: the whole body is one cell, which carries out every life process (Amoeba, Paramecium, bacteria).
- Multicellular: many cells (fungi, plants, animals, humans).
- Division of labour: specialised cells do different jobs (muscle, nerve, red blood cells).
- Every multicellular organism starts as one cell, the zygote.
One cell vs trillions
In an Amoeba the single cell takes in food, respires, removes waste and reproduces by dividing. Your body has about 37 trillion cells (an estimate).
Division of labour
| Cell | Job |
|---|---|
| Muscle cell | Contracts to move body parts |
| Nerve cell | Carries messages |
| Red blood cell | Carries oxygen |
From one cell
A multicellular organism develops from a single cell, the zygote, which divides again and again (1 → 2 → 4 → 8 …); the cells then specialise.
Quick quiz
5 questions. Choose an answer for each, then submit to see your score and the explanations.
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