1.1.3: Cell specialisation
Not started yet — this one needs some love.
A specialised cell has a structure adapted to its specific function — a particular shape, or a particular combination of sub-cellular structures.
Cells become specialised by a process called differentiation.
Sperm cell:
long flagellum (tail) for swimming
many mitochondria to release energy for movement
acrosome containing enzymes to penetrate the egg
streamlined head
Nerve cell (neurone):
very long axon to transmit impulses over long distances
many dendrites to connect with other neurones
myelin sheath to speed up conduction
Muscle cell:
protein myofibrils for contraction
many mitochondria to release energy for contraction
Root hair cell:
long extension → large surface area for absorbing water and mineral ions
no chloroplasts (underground, so no light for photosynthesis)
close to xylem vessels
Xylem cell:
made of dead cells, hollow (no cytoplasm)
lignified walls for strength
forms a continuous tube for water transport
Phloem cell:
made of living cells
pores (sieve plates) in the end walls let dissolved sugars flow through
Common exam mistakes
Always link the structural feature to its function — just naming the specialised cell is insufficient.
Root hair cells have no chloroplasts — they are underground and receive no light.
Nerve cells transmit electrical impulses, not chemical signals along the axon (though they use chemicals at synapses).
Do not say muscle cells 'use' energy — they need energy from respiration for contraction.