Cell Structure & Size of Specimens

Revise Cell Structure & Size of Specimens for Biology 0610 (O Level) — revision notes and instant AI marking.

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✓ What You'll Master

The structure of animal, plant, and bacterial cells and what each part does
How to identify cells under different magnifications
How cells specialise and develop unique features for their jobs
How to calculate magnification using the key formula
How to convert between millimetres and micrometres confidently
The hierarchy from cells → tissues → organs → systems

1. Cell Structure

All living things are made of cells. Understanding their structure is the foundation of biology. Think of a cell like a tiny factory—every part has a specific job, and they all work together to keep the cell alive.

Animal Cells vs Plant Cells

While both animal and plant cells have a nucleus and cell membrane, they have some critical differences:

Key Difference: Plant cells have rigid cell walls (cellulose) that give them shape and support, while animal cells have only flexible membranes. This is why plant cells are rectangular and animal cells are round. Plant cells also have chloroplasts for photosynthesis and permanent vacuoles for storage, which animal cells lack.

Feature	Animal Cell	Plant Cell
Cell Wall	Absent	Present (cellulose)
Chloroplasts	Absent	Present
Permanent Vacuole	Absent	Large and permanent
Carbohydrate Storage	Glycogen	Starch or sucrose
Shape	Rounded	Rectangular

Universal Cell Structures (Found in ALL Cells)

Nucleus: The control centre. Contains DNA (genetic instructions) that tells the cell what to do. Think of it as the cell's brain.

Cell Membrane: The bouncer. It's a selective barrier that lets some things in and keeps others out. Controls what enters and leaves the cell.

Cytoplasm: The jelly. A gel-like substance where most of the cell's chemical reactions happen (including respiration). Supports all the internal structures.

Mitochondria: The powerhouse. The site of aerobic respiration—where energy is released for the cell to use.

Ribosomes: The protein factory. Tiny structures scattered throughout the cytoplasm where proteins are made (protein synthesis).

Plant Cell Only Structures

Cell Wall: Made of cellulose. Rigid and tough—gives the plant cell its rectangular shape and extra support.

Chloroplasts: Green factory. Contains chlorophyll pigment that absorbs light for photosynthesis. This is why plants are green.

Permanent Vacuole: The water tank. Large, permanent sac in the centre containing cell sap (sugars and salts). Stores materials and helps support the cell's shape.

Bacterial Cells: Prokaryotes

2. Organisation of Cells

Producing New Cells

New cells are produced by the division of existing cells.

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3. Magnification Formula
4. Converting Between Units (Extended Tier)
📚 What to Memorise
✓ Concepts Checklist
🎯 Exam Tips & Common Mistakes
Specialised Cells (Differentiation)
Levels of Organisation
The Magnification Equation

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Cell Structure & Size of Specimens