Key Terms
- Organelle — specialised structure within a cell with a specific function
- Nucleus — membrane-bound organelle containing DNA; controls all cell activity
- Mitochondria — site of aerobic respiration; release energy (ATP) for the cell
- Ribosome — site of protein synthesis; present in ALL cells (prokaryotic and eukaryotic)
- Chloroplast — site of photosynthesis; contain chlorophyll; plants only
- Cell wall — made of cellulose; provides structural support; plants only
- Permanent vacuole — contains cell sap; maintains turgor pressure; plants only
Must-Know Facts
- All cells (prokaryotic and eukaryotic) share: cell membrane, cytoplasm, ribosomes, DNA
- Plant cells ONLY: chloroplasts, cell wall (cellulose), permanent vacuole
- Prokaryotic cells: NO nucleus, NO membrane-bound organelles, but DO have ribosomes
- Mitochondria and chloroplasts have their own DNA — evidence they evolved from ancient bacteria
- Cells doing aerobic respiration need MORE mitochondria (e.g. muscle cells, sperm cells)
- Red blood cells have no nucleus or mitochondria — more space for haemoglobin, no aerobic respiration
- Grade 7+: link structure to function — the more an organelle is needed, the more copies the cell has
Organelle Function Quick Reference
| Nucleus | Controls cell activity; contains genetic information (DNA) |
| Mitochondria | Site of aerobic respiration — transfers energy to ATP |
| Ribosomes | Site of protein synthesis (in ALL cell types) |
| Chloroplast | Site of photosynthesis (plants only) |
| Cell wall | Structural support; prevents bursting when turgid (plants) |
| Vacuole | Stores cell sap; maintains turgor pressure (plants) |
| Cell membrane | Controls movement of substances in and out of the cell |
Common Exam Mistakes
- Writing "cell wall controls what enters the cell": It is the cell membrane that controls entry and exit — the cell wall is fully permeable and provides only structural support.
- Writing "plant cells do not respire because they photosynthesise": Plant cells respire constantly (in all cells, day and night). Photosynthesis and respiration are separate processes. Plant cells have mitochondria.
- Writing "only animal cells have ribosomes": All living cells — including bacterial cells — have ribosomes. They are the site of protein synthesis in every cell type.
- Writing "mitochondria produce glucose": Mitochondria transfer energy from glucose during aerobic respiration. Glucose is produced during photosynthesis in chloroplasts — a completely different organelle and process.
- Saying red blood cells have mitochondria: Mature red blood cells have no nucleus and no mitochondria. They rely on anaerobic respiration (glycolysis in cytoplasm) to meet their energy needs.
This topic summary covers Knowledge Organiser: Cell Organelles within Cell Organelles for GCSE Biology. Revise Cell Organelles in Cell Biology for GCSE Biology with 12 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 14 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Cell Organelles
Scientists studying mitochondria use electron microscopes rather than light microscopes. Which statement correctly explains why electron microscopes are more useful for studying cell ultrastructure?
The diameter of a ribosome is approximately 0.00002 mm. (a) Write this diameter in standard form, in millimetres. (b) Convert this diameter into nanometres (nm).
Quick recall flashcards
What is the difference between magnification and resolution?
Magnification: how many times larger the image is than the real object. Resolution: the ability to distinguish two nearby points as separate. A high-resolution image shows fine detail; high magnification of a low-resolution image just produces a blurry enlargement.
What is the formula for calculating magnification?
Magnification = image size ÷ real size (both measurements must be converted to the same units before dividing). For example, if an image measures 6000 μm across and the real object measures 2 μm across, the magnification is 6000 ÷ 2 = ×3000.