1.1Unit 1 — Cell Biology
Cell Structure — SQA National 5 Biology — SQA National 5 Biology Revision Notes & Topical Questions
5 min read 2 parts Lesson 1 of 6
Section 1 of 2Ultrastructure of different cell types
| Organelle / Structure | Animal Cell | Plant Cell | Fungal Cell | Bacterial Cell | Function |
|---|---|---|---|---|---|
| Nucleus | Present | Present | Present | Absent | Controls cell activities and stores genetic information (chromosomes/DNA) |
| Cytoplasm | Present | Present | Present | Present | Site of most chemical reactions (metabolism) |
| Cell Membrane | Present | Present | Present | Present | Selectively permeable barrier controlling entry and exit of substances |
| Mitochondria | Present | Present | Present | Absent | Site of aerobic respiration and ATP production |
| Ribosomes | Present | Present | Present | Present | Site of protein synthesis |
| Cell Wall | Absent | Present (Cellulose) | Present (Chitin/glucan) | Present (Peptidoglycan) | Provides rigid structural support; prevents bursting from osmotic pressure |
| Vacuole (permanent) | Absent | Present | Present | Absent | Contains cell sap; maintains cell turgidity |
| Chloroplasts | Absent | Present (green parts) | Absent | Absent | Site of photosynthesis (contains green chlorophyll pigment) |
| Plasmids | Absent | Absent | Absent | Present | Small circular rings of DNA carrying non-essential useful genes |
| Circular chromosome | Absent | Absent | Absent | Present | Single loop of genetic material free in cytoplasm (no nuclear envelope) |
Section 2 of 2Cell size calculations and magnification
1Units of measurement3 points
:
- 1 millimetre (mm) = 1,000 micrometres (µm).
- To convert mm to µm, multiply by 1,000.
- To convert µm to mm, divide by 1,000.
2Calculating cell size across field of view1 point
:
- Cell length = Field of view diameter / Number of cells fitting across
- Example: If field of view is 2 mm (2,000 µm) and 8 cells fit end-to-end: Average cell length = 2,000 µm / 8 = 250 µm.
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