The cell as a unit of life
Every living organism is made of cells — the basic structural and functional unit of life. Cells can be prokaryotic (no nucleus) or eukaryotic (nucleus present).
Key organelles
- Nucleus — stores DNA, controls cell activity
- Mitochondria — site of aerobic respiration, produces ATP
- Ribosomes — synthesize proteins
- Endoplasmic reticulum — transports materials; rough ER has ribosomes attached
- Golgi apparatus — packages and modifies proteins for export
- Chloroplasts — (plant cells only) site of photosynthesis
- Cell wall — (plant cells only) rigid support made of cellulose
- Vacuole — storage; large and central in plant cells
Plant vs animal cells
| Feature | Plant cell | Animal cell | |---|---|---| | Cell wall | Present | Absent | | Chloroplasts | Present | Absent | | Vacuole | Large, central | Small, if present | | Shape | Fixed, rectangular | Variable, round |
Diagram checklist for exams
When labelling a cell diagram, always include: nucleus, cell membrane, cytoplasm, and — depending on cell type — cell wall, chloroplasts, and vacuole. Examiners commonly deduct marks for missing the cell membrane, since it's easy to overlook next to a cell wall.
Quick recap questions
- Why do only plant cells have chloroplasts?
- Which organelle would you expect to find in unusually high numbers in a muscle cell, and why?