Cell Differentiation

• Cell differentiation is an important process by which a cell changes to become specialised.

  Cells that have not differentiated are therefore unspecialised. As an organism develops, cells differentiate to form different types of cells.
• As a multicellular organism develops, its cells differentiate to form specialised cells.
• In an animal, most cells differentiate at an early stage of its development. Cell division is mainly restricted to repair and replacement in mature animals.

  
  

  • Animal cells therefore lose their ability to differentiate after they have become specialised early in the life of the animal.
  • Some cells in various locations throughout the body of an animal retain the ability to differentiate throughout the life of the animal. These cells are called adult stem cells and are mainly involved in replacing and repairing cells (such as blood or skin cells)
• Plants differ from animals in that many types of plant cell retain the ability to fully differentiate throughout the life of a plant, not just in the early stages of development.
• Animals and plants produced by sexual reproduction begin life as a single cell – a fertilised egg or zygote.

  
  

  This cell must divide to produce a multicellular organism. It must also

  differentiate so that its cells develop features that enable them to fulfil specific roles.
• Cells of the circulatory system are specialised to transport substances, defend the body, and regulate temperature.
• Cells of the excretory system are specialised to remove waste products and unwanted substances, and regulate the water content of the body.
• Cells of the muscular system are specialised to bring about movement.
• Cells of the nervous system are specialised to respond to internal and external stimuli and conditions, and carry messages for the body work as a coordinated whole.
• Cells of the respiratory system are specialised to deliver oxygen for respiration and remove waste.
• Cells of the reproductive system are specialised to bring about fertilisation to produce new offspring.
• Cells of the skeletal system are specialised to bring about movement, support and protect internal structures, produce blood cells, and store and release calcium.
• In the leaf, cells of the palisade mesophyll, are specialised to carry out photosynthesis.
• In the leaf, cells of the spongy mesophyll are specialised to allow gases to circulate for the exchange of gases between the leaf and the environment, and to carry out some photosynthesis.
• In the leaf, cells of the guard cells are specialised to open and close to control the exchange of gases - carbon dioxide, water vapour, and oxygen.
• In the phloem, cells of the sieve tubes are specialised to transport products of photosynthesis, including sugars and amino acids, from the leaf to where they are needed.
• In the phloem, cells of the companion cells are specialised to provide the energy required for transporting substances in sieve tubes.
• In the xylem, cells of the xylem vessels are specialised to transport water and dissolved minerals from the roots, up the plant.
• In the growing points, cells of the meristem are specialised to produce new cells as they divide.