Cell Specialisation (AQA GCSE Biology: Combined Science)

• A specialised cell is a cell that has a structure that aids its specific function
  • 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

Nerve cells

Nerve cells (neurones) have an elongated structure which allows them to coordinate information from the brain and spinal cord with the rest of the body

• 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

Muscle cells contain layers of fibres which allow them to contract

• Function:
  • Contraction for movement
• Special features 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

Sperm cells are mobile – their tail helps propel them forward in search of an egg cell

• Function:
  • Transfer of genetic material to an egg cell for fertilisation
• Special features 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 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
  • 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

Root hair cells

The root hair is an extension of the cytoplasm, increasing the surface area of the cell in contact with the soil to maximise absorption of water and minerals

• Function:
  • Absorption of water and mineral ions from soil
• Special features 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 shorter diffusion distance
  • Mitochondria release energy for active transport of mineral ions

Xylem vessels

Xylem cells lose their top and bottom walls to form a continuous tube through which water moves from the roots to the leaves

• Function:
  • Transport of water and dissolved ions
• Special features that aid function:
  • No walls between cells to form continuous hollow tubes through which water is 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

Phloem cells are adapted for the transport of dissolved sugars and amino acids

• Function:
  • Transport of dissolved sugars and amino acids
• Special features that aid function:
  • Cells are joined end-to-end and contain holes in the end cell walls (sieve plates); this forms tubes which allow sugars and amino acids to flow easily
  • Cells have very few subcellular structures to aid the flow of materials