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Cells

Plant, animal, bacterial cells & organelles

Three Types of Cells

Plant cells: Have cell wall (cellulose), vacuole, chloroplasts. Eukaryotic.

Animal cells: No cell wall, no permanent vacuole, no chloroplasts. Eukaryotic.

Bacterial cells: No nucleus, no membrane-bound organelles, circular DNA. Prokaryotic. Much smaller (~1 μm vs 10-100 μm).

Plant Cell Structures

Cell wall: Rigid cellulose layer outside membrane. Provides support & strength.

Vacuole: Fluid-filled sac containing cell sap. Maintains turgor (keeps cell rigid). Regulates water.

Chloroplasts: Site of photosynthesis. Contains chlorophyll (green pigment). Found in green parts of plant.

Organelles — Their Functions

Organelle	Function	Animal	Plant
Mitochondria	Aerobic respiration — energy release	✓	✓
Nucleus	Contains DNA — controls cell	✓	✓
Ribosome	Protein synthesis	✓	✓
ER (rough)	Protein synthesis & transport	✓	✓
Golgi apparatus	Modifies & packages proteins	✓	✓
Chloroplast	Photosynthesis	✗	✓

Magnification Formula

Magnification = Image Size ÷ Actual Size

Example: Actual cell = 20 μm. Magnified image = 2 cm.
Convert: 2 cm = 20,000 μm
Magnification = 20,000 ÷ 20 = ×1000

Higher magnification = smaller structures visible, but narrower field of view

Specialised Animal Cells

Red blood cell (RBC): No nucleus. Biconcave shape. Carries oxygen via haemoglobin.

Neurone (nerve cell): Long axon for electrical signal transmission. Dendrites receive signals. Synapse connects to next cell.

Sperm cell: Tail (flagellum) for movement. Mitochondria power tail. Acrosome enzyme penetrates egg.

Egg cell: Large with food reserves (yolk). Nucleus in centre. Zona pellucida (membrane) protects.

Specialised Plant Cells

Root hair cell: Long hair-like projection. Large surface area for water absorption. Thin walls allow osmosis.

Palisade cell: Elongated, packed with chloroplasts. In upper leaf layer. Maximises light absorption for photosynthesis.

Guard cell: Controls stomata opening. High starch → low osmotic potential → cell swells → stoma opens. Allows gas exchange.

Bacterial Cells

No membrane-bound nucleus or organelles

Nucleoid: Region containing circular DNA (not surrounded by nuclear membrane)

Plasmids: Small circular DNA pieces. Used in genetic engineering (antibiotic resistance genes)

Flagella: Whip-like structures for movement (plural flagellum)

Pili: Hair-like projections for attachment or DNA transfer

Size Comparison

Eukaryotic cells: 10–100 μm

Prokaryotic cells: 0.5–5 μm

Bacteria are much smaller than plant/animal cells

1 μm = 0.001 mm = 1 × 10⁻⁶ m

Exam Tips

✓ Know which organelles are in animal vs plant cells

✓ Learn magnification formula and how to rearrange it

✓ Bacterial cells have NO nucleus — prokaryotic, not eukaryotic

✓ Specialised cells have structure matched to function

✓ Cell wall, vacuole, chloroplasts = PLANT cells only

Key Takeaways

✅ Plant cells: wall, vacuole, chloroplasts

✅ Animal cells: no wall, no large vacuole

✅ Bacterial cells: prokaryotic, no nucleus

✅ Magnification = Image Size ÷ Actual Size

✅ Specialised cells: structure = function

Get the drawings right on exam day! 🔬✓