AQA GCSE Combined Science: Trilogy

## Eukaryotic and prokaryotic cells Plant and animal cells are **eukaryotic**: their genetic material is enclosed in a nucleus, along with a cell membrane and cytoplasm. Bacteria are **prokaryotic**. A bacterial cell is much smaller and has no nucleus; its DNA is a single loop lying free in the cytoplasm, and it may also carry one or more small rings of DNA called **plasmids**. Outside the membrane it has a cell wall. | Feature | Animal cell | Plant cell | Bacterial cell | |---|---|---|---| | Nucleus | yes | yes | no, a single DNA loop | | Cell membrane and cytoplasm | yes | yes | yes | | Mitochondria | yes | yes | no | | Ribosomes | yes | yes | yes | | Cell wall | no | cellulose | yes, not made of cellulose | | Chloroplasts | no | often | no | | Permanent vacuole | no | yes | no | | Plasmids | no | no | sometimes | ## Sub-cellular structures and what they do Each part of a cell is there because the cell needs a job doing, and the structure fits the job. - The nucleus holds the chromosomes, so it carries the instructions that control what the cell does. - The cytoplasm is a watery gel in which most chemical reactions of the cell take place, and it contains the enzymes that control them. - The cell membrane controls which substances go into and out of the cell. - Mitochondria are where aerobic respiration takes place, releasing the energy the cell uses. Cells that use a lot of energy, such as muscle cells, have many. - Ribosomes are where proteins are made, by joining amino…