AQA GCSE Biology

All living things are made of cells, and the cells of plants, animals and bacteria share some features while differing in others. Knowing which structure does which job lets you explain why a particular cell looks the way it does. ## Eukaryotic and prokaryotic cells Plant and animal cells are **eukaryotic cells**. Each has a nucleus that holds its genetic material, as well as a cell membrane and cytoplasm. **Prokaryotic cells** are the bacteria, and they are far smaller. A bacterial cell has a cell wall outside its membrane and no nucleus; its DNA is one loop lying free in the cytoplasm, and it may also carry one or more little rings of extra DNA called **plasmids**. | Feature | Eukaryotic cell | Prokaryotic cell | |---|---|---| | Size | larger | much smaller | | Genetic material | in a nucleus | a single DNA loop, free in the cytoplasm | | Plasmids | none | one or more may be present | | Cell wall | cellulose in plants, none in animals | present | ## Structures in animal and plant cells The parts found in most animal cells are a nucleus, cytoplasm, a membrane, mitochondria and ribosomes. Plant cells commonly have those too, with chloroplasts and a large permanent vacuole full of cell sap in addition. A plant or algal cell is also enclosed by a cellulose cell wall. | Structure | What it does | |---|---| | Nucleus | contains the genetic material (DNA in chromosomes) and controls the activities of the cell | | Cytoplasm | a watery gel where most chemical reactions take place…