Specialised cells
Specialised cells (specialized cells in the US) are cells whose structure is adapted to carry out one particular job. A sperm cell has a tail to swim, a nerve cell is long to carry impulses over a distance, and a root hair cell has a long extension to take in water. Cells become specialised by a process called differentiation.
What is cell specialisation?
All the cells in your body came from one fertilised egg. Early on, the cells are all alike. As the embryo develops, they differentiate: each one gains the sub-cellular structures it needs for a certain job, and becomes a specialised cell. Groups of specialised cells then work together as tissues, tissues make organs, and organs make organ systems.
Animals and plants differ here. AQA's GCSE Biology specification says most types of animal cell differentiate at an early stage, while many types of plant cell keep the ability to differentiate throughout life. In mature animals, cell division is mainly for repair and replacement.
Which cells do I need to know?
- AQA GCSE Biology: sperm, nerve and muscle cells in animals, and root hair, xylem and phloem cells in plants. You should also be able to explain the structure of a cell you haven't met when given information about it.
- Edexcel GCSE Combined Science: Pearson's scheme of work lists sperm cells, egg cells and ciliated epithelial cells.
Specialised animal cells
| Cell | Job | Adaptations |
|---|---|---|
| Sperm cell | Reach the egg and fertilise it | Tail to swim; many mitochondria for energy; acrosome with enzymes to digest the egg's outer layer; haploid nucleus with half the genetic material |
| Egg cell | Be fertilised and feed the early embryo | Nutrients stored in the cytoplasm; haploid nucleus; membrane changes after fertilisation so only one sperm gets in |
| Nerve cell (neurone) | Carry electrical impulses around the body | Long axon to carry impulses a long way; branched dendrites to connect with many other cells; nerve endings that pass the impulse on |
| Muscle cell | Contract to cause movement | Protein filaments that slide over each other; many mitochondria to release energy; can store glycogen |
| Ciliated epithelial cell | Move substances along a surface | Tiny hair-like cilia that beat together, such as wafting mucus out of the airways |
Nerve cell adaptations
A nerve cell's job is to carry messages quickly. Its axon can be very long, so one cell can carry an impulse from your spinal cord to your foot. Its dendrites branch out to receive impulses from many other nerve cells. Many axons are wrapped in a fatty myelin sheath that insulates them and speeds up the impulse. At the far end, nerve endings pass the message on to the next cell across a gap called a synapse.
Muscle cell adaptations
Muscle cells contract by protein filaments sliding over each other, which shortens the cell. That needs a lot of energy, so muscle cells are packed with mitochondria for respiration. They can also store glycogen, which can be broken down to glucose for respiration when the muscle is working hard.
Specialised plant cells
| Cell | Job | Adaptations |
|---|---|---|
| Root hair cell | Absorb water and mineral ions from the soil | Long hair-like extension gives a large surface area; thin wall; many mitochondria for active transport of mineral ions; no chloroplasts, as it is underground |
| Xylem cell | Carry water and mineral ions up from the roots | Dead cells joined end to end with no end walls, making hollow tubes; walls strengthened with lignin |
| Phloem cell | Carry dissolved sugars around the plant | Sieve tube cells joined end to end, with sieve plates (pores) between them; companion cells beside them provide energy |
| Palisade cell | Photosynthesis | Packed with chloroplasts; near the upper surface of the leaf, where the light is |
| Guard cell | Open and close stomata | Change shape to open or close the pore, controlling gas exchange and water loss |
Root hair cell diagram: the labels
Drawn, a root hair cell looks like an ordinary box-shaped plant cell with a long, thin finger reaching out sideways into the soil. These are the parts to label:
| Label | What it does |
|---|---|
| Root hair | The long extension: greatly increases the surface area for absorbing water and mineral ions |
| Cell wall | Made of cellulose; supports the cell and lets water through |
| Cell membrane | Controls what enters and leaves; carries out active transport of mineral ions |
| Cytoplasm | Where most chemical reactions happen |
| Nucleus | Contains the genetic material that controls the cell |
| Permanent vacuole | Filled with cell sap |
| Mitochondria | Release energy by respiration for active transport |
Notice what is missing: no chloroplasts. Root hair cells are underground in the dark, so they can't photosynthesise. That is a favourite exam question.
Test yourself on matching cells to their adaptations, then press Mark to check your answers in the course.
Match each specialised or stem cell to the feature that suits its job.
Press Mark to have your answer marked in the Cell Biology course.
Specialised cells and stem cells
A stem cell is an undifferentiated cell that can divide to make more cells and can become different types of cell. Embryonic stem cells can become almost any cell. Adult stem cells, such as those in bone marrow, can form only some types, such as blood cells. In plants, meristem tissue at the tips of roots and shoots keeps making new cells that can become every kind of plant cell, for as long as the plant lives. The Cell Biology course covers specialised cells and stem cells, with plant, animal and bacterial cells before them.
How to answer a specialised cell question
"Explain how a cell is adapted" questions want each feature linked to what it does for the cell. Give the feature, then say so or which and the benefit:
Listing "long hair, mitochondria" without the reasons usually only earns part of the marks. If the question gives you an unfamiliar cell, use the same method: spot the unusual feature, and say how it helps that cell do its job.
Common mistakes
- Saying root hair cells photosynthesise. They have no chloroplasts.
- Calling xylem cells alive. Mature xylem is made of dead cells forming hollow tubes.
- Mixing up xylem and phloem. Xylem carries water and mineral ions up. Phloem carries dissolved sugars up and down.
- Saying the tail gives the sperm energy. The mitochondria release energy; the tail uses it to swim.
- Naming a feature without its benefit. Always add what the feature does.
To test cell biology under time pressure, try today's GCSE Biology Higher or GCSE Combined Science Higher short timed paper. Each paper mixes topics, so specialised cells won't come up every day.
Common questions
What are specialised cells?
How do cells become specialised?
How is a nerve cell adapted to its function?
How is a muscle cell adapted?
Why don't root hair cells have chloroplasts?
What is the difference between a specialised cell and a stem cell?
Revision cards
Say the answer first, then flip the card to check it.
Where to go next
- Learn it
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