1One cell does it all
A unicellular organism is made of one cell, which must move, feed, respire, remove waste, grow and reproduce. Paramecium, from a pond, swims by beating tiny hairs called cilia.
unicellular
Lesson 1.3 notes
Single-celled organisms
Some living things are just one cell. See how an amoeba, Euglena, yeast and bacteria are adapted to move, feed and survive.
2Amoeba on the move
An amoeba moves by pushing out parts of its cell called pseudopodia (false feet). The rest of the cell flows after them, so it changes shape as it goes.
amoebapseudopodia
3Amoeba feeding
An amoeba flows its pseudopodia around a bit of food and traps it in a food vacuole. The food is digested there, and the useful substances pass into the cytoplasm.
food vacuole
4Getting rid of water
Pond water keeps moving into the amoeba. Its contractile vacuole collects the extra water and squeezes it out, so the cell doesn't swell up and burst.
contractile vacuole
5Euglena swims to the light
Euglena swims by lashing a whip-like flagellum. A red eyespot detects light, so it can swim towards the light.
Euglenaflagellumeyespot
6Euglena makes food
Euglena has chloroplasts, so in the light it makes its own food by photosynthesis, like a plant. In the dark it can take in food from the water instead, like an animal.
7Yeast and bacteria
Yeast is a single-celled fungus, used to make bread rise. Bacteria are much smaller single cells with no nucleus: their genetic material is loose in the cytoplasm.
yeastbacteria
Explore: Pond lab
Watch an amoeba and some Euglena in a drop of pond water. Feed the amoeba, switch off its contractile vacuole, and move a lamp to see where the Euglena swim.
Common mistake: Single-celled doesn't mean simple
One cell has to do every job that your body shares out between trillions of cells: moving, feeding, respiring, getting rid of waste and reproducing. Its parts are adapted for all of them.
Remember
- A unicellular organism is a living thing made of just one cell, which carries out every life process.
- An amoeba moves and traps food with pseudopodia, digests it in a food vacuole and pumps out extra water with a contractile vacuole.
- Euglena swims with a flagellum, detects light with its eyespot and makes food in its chloroplasts.
Going further at GCSE