Cell Specialisation (AQA GCSE Biology): Revision Note

Specialised cells

• A specialised cell is a cell that has a structure that aids its specific function within a tissue, an organ or organ system, or the whole organism

  • This could relate to cell shape or the combination of cellular structures present within the cell

• Cells specialise by undergoing a process known as differentiation

Specialised cells in animals

Nerve Cells

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• Function:

  • Conduction of electrical impulses

• Special features that aid function:

  • Nerve cells are long, meaning that they can conduct nerve impulses between different areas of the body 

  • Extensions of the cytoplasm known as dendrites allowing nerve cells to communicate with other nerve cells, muscles and glands

  • The axon is covered with a fatty sheath which speeds up nerve impulse transmission

Muscle cells

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• Function:

  • Contraction for movement

• Structures that aid function:

  • Muscle cells have many mitochondria to release energy for contraction

  • All muscle cells contain protein filaments that can slide over each other to allow muscle contraction

Sperm cells

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• Function:

  • Transfer of genetic material to an egg cell for fertilisation

• Structures that aid function:

  • The mid-piece is packed with mitochondria to release energy (via respiration) for the tail

  • The tail rotates, propelling the sperm cell forward and allowing it to move

  • The head contains a nucleus with half the normal number of chromosomes, allowing the sperm cell to fuse with an egg cell to restore the normal chromosome number

  • The acrosome in the head contains digestive enzymes that can break down the outer layer of an egg cell so that the haploid nucleus can enter to fuse with the egg’s nucleus

Specialised cells in plants

Root hair cells

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• Function:

  • Absorption of water and mineral ions from soil

• Structures that aid function:

  • Root hairs increase surface area (SA) so the rate of water uptake by osmosis is greater

  • Thinner walls than other plant cells so that water can move through easily due to a shorter diffusion distance

  • Mitochondria release energy for active transport of mineral ions

Xylem vessels

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• Function:

  • Transport of water and dissolved ions

• Structures that aid function:

  • Xylem is made of dead cells

  • No end walls between cells to form continuous hollow tubes through which water is passively drawn upwards towards the leaves

  • Cells contain no organelles or cytoplasm, allowing free passage of water

  • Outer walls are thickened with a substance called lignin, strengthening the tubes and providing support for the plant

Phloem cells

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• Function:

  • Transport of dissolved sugars and amino acids via active transport

• Structures that aid function:

  • Phloem is made of living cells

  • Cells are joined end-to-end and contain pores in the end walls (sieve plates); this forms tubes which allow sugars and amino acids to flow easily

  • Cells have very few sub-cellular structures to aid the flow of materials