cell specialisation

• Sperm cells have a streamlined head and long tail to aid swimming, there are many mitochondria which supply energy to allow the cell move and the acrosome ( head) has digestive enzymes to break down outer layers of egg membrane.
• Nerve cells have a long axon so impulses can be carried along long distances, lots of extensions from the cell body for branched connections with other nerves and the nerve endings have many mitochondria to make neurotransmitters (chemicals).
• Muscle cells have special proteins (myosin and actin) which slide over each other for muscle contraction, lots of mitochondria to provide energy for contraction and they can store glycogen, used in respiration.
• Sperm cells are specialised to carry the male‘s DNA to the egg cell (ovum) for successful reproduction.
• Nerve cells are specialised to transmit electrical signals quickly from one place in the body to another.
• Muscle cells are specialised to contract quickly to move bones or simply to squeeze (blood pressure variation), therefore causing movement.
• xylem cells are specialised to transport water and mineral ions up the plant from roots to shoots:

  • lignin is deposited which cause the cells to die, become hollow and join end to end to form a continuous tube that water and mineral ions can move through
  • lignin is deposited in spirals to help the cells withstand the pressure from water movement.
• phloem cells are specialised to carry the products of photosynthesis to all parts of the plant:

  • cell walls of each cell form sieve plates when they break down to allow the movement of substances from cell to cell
  • despite losing many sub-cellular structures, the energy they need to be alive is supplied by mitochondria of the companion cells
• cell differentiation in animals:

  • almost all cells differentiate at an early stage and then lose this ability
  • most specialised cells can make more of the same cell by mitosis
  • others like rbc cannot divide and are replaced by stem cells
  • in mature animals, mitosis only happens to repair or replace damaged cells
• cell differentiation in plant cells:

  • many types of cells retain ability to differentiate
  • only differentiate when reach final position in plant
  • they can still re-differentiate when moved to a different position