IP Biology Notes: Cell Structure and Organisation (Upper Sec 01)
26 Nov 2025, 00:00 Z
Reviewed by
Ezekiel Tan·Academic Advisor (Biology)
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Use this as a free IP Biology notes chapter on cell structure and organisation for Year 3 to Year 4. It keeps the IP pacing while reinforcing the 6093 biology foundations most schools test through DBQs, diagrams, and practical explanations.
Status: SEAB O-Level Biology 6093 syllabus (exams from 2026) checked 2025-11-30 - scope unchanged; remains the reference for this note.
What you must know
- Key structures in plant vs animal cells: cell wall (plant, fully permeable), membrane (partially permeable), cytoplasm, nucleus, vacuoles (large central in plant; small temporary in animal), chloroplasts (plant only), centrioles (animal).
- Organelle functions: rough ER (protein transport), smooth ER (lipid synthesis, detox), Golgi (modifies/packages), mitochondria (aerobic respiration, ATP), ribosomes (protein synthesis).
- Specialised cells: root hair (long extension, large SA, thin wall), red blood cell (biconcave, no nucleus, haemoglobin), muscle cell (long, many mitochondria), xylem vessel (lignified, hollow).
Detailed notes
- Ultrastructure links: rough ER + ribosomes for protein synthesis and export; smooth ER for lipids/detox; Golgi modifies/packages into vesicles; lysosomes (animal) for digestion; tonoplast surrounds vacuole; plasmodesmata connect plant cells.
- Membrane as fluid mosaic: phospholipid bilayer with proteins; selectively permeable; transport via diffusion, osmosis, active transport, endo/exocytosis (qualitative).
- Turgor vs plasmolysis: plant cells in hypotonic solutions become turgid (wall prevents bursting); in hypertonic solutions cytoplasm pulls from wall (plasmolysis), reversible if rehydrated.
- Specialised cells: ciliated epithelium (cilia + mucus movement), palisade mesophyll (many chloroplasts, elongated), nerve cell (long axon, many mitochondria), sperm (flagellum, enzymes in acrosome).
Worked walkthroughs
- Predict appearance of plant cells in distilled water vs concentrated salt: turgid vs plasmolysed; relate to water potential.
- Trace a secreted protein: gene → mRNA → ribosome on rough ER → vesicle → Golgi → vesicle → exocytosis at membrane.
- Explain why muscle cells have many mitochondria and why red blood cells lack nucleus/mitochondria.
Pitfalls and fixes
- Calling cell wall “partially permeable”-it is fully permeable and non-living.
- Mixing chloroplasts (photosynthesis) with mitochondria (respiration).
- Using “diffusion” for water movement-use “osmosis” across partially permeable membranes.
- Forgetting animal cells lack large central vacuole, chloroplasts, and cell wall.
