AQA Combined Biology Notes Cell Strcuture Specialised Cells

Introduction to cells 

• You, as a human being, are made from trillions of cells, but only of about 250 different types
• A specialised cell is a cell that has a particular structure and composition of subcellular structures
• Structural differences between different types of cells enable them to perform specific functions within the organism
• Cells specialise by undergoing a process known as differentiation

The Nerve Cell 

• Function: conduction of impulses
• Adaptations:
  • Has a cell body where most of the cellular structures are located and most protein synthesis occurs
  • Extensions of the cytoplasm from the cell body form dendrites (which receive signals) and axons (which transmit signals), allowing the neurone to communicate with other nerve cells, muscles and glands
  • The axon (the main extension of cytoplasm away from the cell body) is covered with a fatty sheath, which speeds up nerve impulses. Axons can be up to 1m long in some animal.

Muscle Cells 

• Function: contraction for movement
• Adaptations:
  • There are three different types of muscle in animals: skeletal, smooth and cardiac (heart)
  • All muscle cells have layers of protein filaments in them. These layers can slide over each other causing muscle contraction
  • Muscle cells have a high density of mitochondria to provide sufficient energy (via respiration) for muscle contraction
  • Skeletal muscle cells fuse together during development to form multinucleated cells that contract in unison

A Sperm Cell

• Function: reproduction (pass on fathers genes)
• Adaptations:
  • The head contains a nucleus which contains half the normal number of chromosomes (haploid, no chromosome pairs)
  • The acrosome in…