LEARNING OBJECTIVES
What you will be able to do
- compare plant, animal and bacterial cells
- link organelle structure to function
- explain specialised-cell adaptations
- describe levels of organisation
- calculate magnification and convert mm and μm
AT A GLANCE
INTRODUCTION · THE BIG IDEA
How cell structures support specialised functions and build tissues, organs and systems.
Every biological process begins with cells. Their internal structures divide work efficiently, while specialised cells combine to form tissues, organs and organ systems.
Use this chapter to connect visible cell features with function and to move confidently between microscope image size, actual size and magnification.
SECTION 01
Plant, animal and bacterial cells
Cells share basic machinery but differ according to their way of life. A membrane controls exchange, cytoplasm is the site of many reactions, ribosomes make proteins and DNA stores genetic information.
DETAILED EXPLANATION
- Animal cells have no cell wall or chloroplasts and may contain small temporary vacuoles.
- Bacteria have a wall, membrane, cytoplasm and ribosomes, but no nucleus or mitochondria. Circular DNA lies free in the cytoplasm and plasmids may carry additional genes.
- Mitochondria carry out aerobic respiration; the nucleus contains chromosomes and controls cell activities.
SECTION 02
Specialised cells and organisation
Specialisation produces cells whose shape and structures suit one main role. New cells arise from division of existing cells.
DETAILED EXPLANATION
- Neurones have long fibres for impulses; red blood cells contain haemoglobin and lack a nucleus; sperm have a flagellum and mitochondria; eggs contain nutrient reserves.
- A tissue is a group of similar cells working together. Several tissues form an organ; organs cooperate in an organ system; all systems together form an organism.
SECTION 03
Size and magnification
Magnification compares the size of an image with the specimen's real size. Both measurements must use the same units before division.
DETAILED EXPLANATION
- Rearrange the magnification formula using a formula triangle or ordinary algebra.
- A 48 mm drawing of a 120 μm cell uses 48 000 μm ÷ 120 μm = ×400 magnification.
STEP-BY-STEP EXAM EXAMPLE
Calculating the magnification of a cell drawing
- A drawing is 36 mm long; the real cell is 90 μm long.
- Convert the drawing to micrometres: 36 mm = 36 000 μm.
- Use magnification = image size ÷ actual size.
- Calculate 36 000 ÷ 90.
Answer: The drawing has a magnification of ×400.
QUICK CHAPTER SUMMARY
The ideas to carry forward
- Organelles have distinct functions.
- Plant, animal and bacterial cells have recognisable differences.
- Specialised structures improve cell function.
- Organisation runs from cell to organism.
- Convert units before using magnification.
QUICK REVISION CHECKLIST
Can you do each of these without your notes?
- compare plant, animal and bacterial cells
- link organelle structure to function
- explain specialised-cell adaptations
- describe levels of organisation
- calculate magnification and convert mm and μm