Animal, plant and bacterial cells
Two kinds of cell
Every living thing is made of cells, and there are two kinds.
- Eukaryotic cells keep their genetic material (DNA) inside a nucleus. Animals, plants, fungi and protists are made of them.
- Prokaryotic cells are bacteria. They are much smaller, about a tenth of the size of a typical animal cell, and have no nucleus: their DNA is one loop floating in the cytoplasm, often with extra small rings called plasmids.
The parts and their jobs
Animal and plant cells have:
- nucleus: holds the genetic material that controls the cell
- cytoplasm: a jelly where most chemical reactions happen
- cell membrane: controls what goes in and out
- mitochondria: where aerobic respiration releases energy
- ribosomes: where proteins are made
Plant cells also have a cell wall of cellulose (strength), chloroplasts (absorb light for photosynthesis) and a permanent vacuole full of cell sap (keeps the cell firm). Bacteria have a cell wall too, but it is not made of cellulose. Many also have a flagellum, a tail that turns to move them along.
Not every plant cell has chloroplasts: root cells get no light, so they have none.
How big is a cell?
Cells are measured in micrometres (μm) and their smallest parts in nanometres (nm).
1 mm = 1000 μm
1 μm = 1000 nm
To compare two sizes, put them in the same unit and divide the bigger by the smaller. Each power of ten is one order of magnitude.
- Plant cell 100 μm; virus 100 nm = 0.1 μm
- 100 ÷ 0.1 = 1000 times bigger
- 1000 = 10³: three orders of magnitude
Going to a smaller unit, the number gets bigger (0.05 mm = 50 μm). If yours got smaller, you divided instead of multiplying.
Loading the question
This question is in Brainlag Plus