LEARNING OBJECTIVES
By the end of this chapter, you should be able to:
- 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
THE BIG IDEA
How cell structures support specialised functions and build tissues, organs and systems.
This chapter builds each process from its structures, inputs and outputs. Follow the connections rather than memorising isolated facts, then use precise biological terms when explaining cause and effect.
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
- Plant cells also have a cellulose cell wall, a permanent vacuole and chloroplasts in photosynthetic tissues.
- 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
- Ciliated cells move mucus; root hair cells provide a large absorption surface; palisade cells contain many chloroplasts.
- 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
- 1 mm = 1000 μm. Multiply millimetres by 1000 to obtain micrometres; divide micrometres by 1000 to obtain millimetres.
- 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.
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.