Lesson 1.5 · AQA Combined Science

Specialised cells

Built for a job

A specialised cell has structures suited to its function. Explain an adaptation by linking a feature → how it helps the cell do its job.

Animal cells

Sperm cell

Fertilises an egg.
A tail helps it swim. Many mitochondria release energy for movement. Enzymes in the head help it enter the egg.

Nerve cell

Carries electrical impulses.
A long fibre carries impulses over a distance. Branched ends connect with other cells. An insulating sheath helps impulses travel quickly.

Muscle cell

Contracts to cause movement.
Protein fibres slide past one another so the cell can shorten. Many mitochondria release energy by aerobic respiration.

Plant cells

Root hair cell

Absorbs water and mineral ions.
The long extension gives a large surface area for absorption from the soil. Water enters by osmosis; mineral ions can enter by active transport.

Xylem vessel

Transports water and mineral ions up a plant.
Dead cells join to form hollow tubes with no end walls. Lignin strengthens the walls and supports the plant. Bands in the diagram represent lignin.

Phloem tissue

Transports dissolved sugars around a plant.
Living sieve tube cells join end to end, with pores in their end walls. Companion cells provide energy for transport. The diagram shows a tube and companion cell. Different tubes can carry sugars in different directions.

Becoming specialised

Differentiation is when a cell develops structures that allow it to do a particular job.

Most animal cells differentiate early in development. In mature animals, cell division mainly replaces or repairs cells.

Many plant cells can differentiate throughout life, allowing new roots, shoots and other structures to grow.

One unspecialised cell can give rise to specialised cells.

Build an explanation

Feature: a root hair cell has a long extension.
Effect: this increases surface area.
Job: more water and mineral ions can be absorbed.

For an unfamiliar cell, use the structures you are shown and link them to its stated job.

Remember

Feature → effect → function. Differentiation is the process of becoming specialised.