Ways of getting food

Food from others

Animals and fungi cannot make their own food. They are heterotrophs: they take food that other living things have made. How they do it depends on the food and on where they live. Some eat grass, some eat meat, some take in tiny particles, and some live on or inside another living thing.

Three ways of getting food

• A saprophyte lives on dead and decaying matter. It releases digestive juices onto the food, and absorbs the small molecules that form. Saprophytes clean up dead plants and animals.
• A parasite lives on or inside a living host. Cuscuta (amar-bel) is a yellow plant without chlorophyll. It winds around a green plant and sucks food from it. Lice and ticks feed on the blood of animals; a tapeworm lives in the intestine.

You should find that Cuscuta is parasitic even though it is a plant. It does not make its own food, and it feeds on a living host.

Amoeba: food in a bag

Amoeba is a single cell, and it has no mouth. It takes in food with its whole surface.

1. The cell pushes out finger-like flows called pseudopodia (false feet) around a food particle.
2. The pseudopodia meet and close, and the particle is now inside the cell in a food vacuole.
3. Juices in the vacuole break the food into simple molecules, which pass into the cell.
4. The waste that is not digested moves to the surface and is thrown out.

Paramecium: a fixed spot for food

Paramecium is also a single cell, but it has a fixed shape, like a slipper. So it cannot flow around its food. It takes food in at one fixed spot, a groove on one side. Its body is covered with fine hair-like cilia. The cilia beat and sweep water with food particles into the groove.

Bigger animals

In bigger animals, food goes through a long tube, the alimentary canal, with a part for each job: taking food in, digesting it, absorbing it and removing waste. A cow and a lion both eat whole food, but the cow's food is grass, which is hard to digest. You will follow the human canal in the next lesson.

Try it in Python

This program decides the kind of nutrition of seven living things from three answers.

Practise with new numbers

Common mistakes

• Thinking every plant makes its own food. Cuscuta has no chlorophyll and is a parasite.
• Thinking a parasite kills its host at once. It needs the host alive, to keep feeding on it.
• Saying fungi eat their food. They digest it outside, and then absorb it.
• Thinking Amoeba has a mouth. It takes food in at any point of its surface.

Remember these

• Heterotrophs take food from others: holozoic, saprophytic and parasitic nutrition.
• Saprophytes digest dead matter outside the body and absorb it.
• Parasites feed on a living host without killing it.
• Amoeba traps food with pseudopodia in a food vacuole. Paramecium sweeps food into a fixed spot with cilia.

Check yourself

Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.

1. Bread left in a damp box grows a fluffy mould. Which kind of nutrition does the mould have?

2. Cuscuta is a plant. Why does it not make its own food?

3. How does Amoeba take in a food particle?

4. Why can Paramecium take in food only at one spot?

5. Why do all heterotrophs depend on autotrophs in the end?