specialised cells

• cells specialise by undergoing differentiation - a process that involves the cell gaining new sub-cellular structures in order to be suited to its role.
• cells can either differentiate once early or have the ability to differentiate their whole life (these are stem cells). in animals, most cells only differentiate once, but in plants many cells retain the ability
• examples of specialised cells in animals:

  • sperm cells - specialised to carry the male's dna to the egg cell (ovum) for successful reproduction

  1. streamlined head and long tail to aid swimming
  2. many mitochondria (where respiration happens) which supply the energy to allow the cell to move
  3. the acrosome (top of the head) has digestive enzymes which break down the other layers of membrane of the egg cell
  4. haploid nucleus - the word haploid simply means that it has 23 chromosomes, rather than the 46 that most other body cells have
• examples of specialised cells in animals:

  • egg cell - specialised to accept a single sperm cell and develop into an embryo

  1. surrounded by a special cell membrane which can only accept one sperm cell (during fertilisation) and becomes impermeable following this
  2. lots of mitochondria to provide an engird source for the developing embryo
  3. large size and cytoplasm allow quick, repeated division as the embryo grows
• examples of specialised cells in animals:

  • ciliated epithelial cells - specialised to waft bacteria (trapped by mucus) to the stomach

  1. long, hair-like processes called cilia waft bacteria trapped by sticky mucus (produced by the nearby goblet cells) down to the stomach, where they are killed by the stomach acid. this is one of the ways our body protects against illness
• examples of specialised cells in plants:

  • root hair cells - specialised to take up water by osmosis and mineral ions by active transport from the soil as they are found in the tips of the roots

  1. have larger surface area due to root hairs, meaning more water can move in
  2. the large permanent vacuole affects the speed of movement from the soil to the cell
  3. mitochondria to provide energy from respiration for the active transport of mineral ions into the root hair cell
• examples of specialised cells in plants:

  • xylem cells - specialised to transport water and mineral ions up the plant from the roots to the shoots

  1. upon formation, a chemical called lignin is deposited which causes the cells to die. they become hollow and are joined end-to-end to form a continuous tube so water and mineral ions move through
  2. lignin is deposited in spirals which helps the cells withstand the pressure from the movement of water
• examples of specialised cells in plants:

  • phloem cells - specialised to carry the products of photosynthesis (food) to all parts of the plants

  1. cell walls of each cell form structures called sieve plates when they break down, allowing the movement of substances from cell to cell
  2. despite losing many sub-cellular structures, the energy these cells need to be alive is supplied by the mitochondria of the companion cells