Edexcel GCSE Biology

## Eukaryotic and prokaryotic cells Living things are built from cells, and cells come in two basic designs. **Eukaryotic** cells, which make up animals, plants, fungi and protists, keep their genetic material inside a nucleus. **Prokaryotic** cells, the bacteria, have no nucleus, and their DNA lies free in the cytoplasm. Prokaryotic cells are also much smaller, often only a thousandth of a millimetre or two across, whereas a typical animal cell is around ten to a hundred times wider. Every structure inside a cell has a job, and the shape of a cell usually tells you what it does. ### Animal cells | Structure | What it does | |---|---| | Nucleus | contains the chromosomes, so it holds the genetic information and controls the activities of the cell | | Cell membrane | a thin, partly permeable layer that controls which substances enter and leave | | Cytoplasm | a watery gel where most chemical reactions of the cell take place | | Mitochondria | the site of aerobic respiration, which releases the energy the cell uses | | Ribosomes | where amino acids are joined together to make proteins | Cells that use a lot of energy, such as muscle cells, contain many mitochondria. Cells that make a lot of protein, such as those of the pancreas that produce digestive enzymes, contain many ribosomes. ### Plant cells A plant cell has all of the structures above, plus three more. | Structure | What it does | |---|---| | Cell wall | made of cellulose; it is rigid, so it supports the cell and…