speclised cells

• red blood cells 


  -contain haemoglobin, which carries oxygen

  -no nucleus to maximise space for oxygen

  -biconcave as surface area is maximised to carry as much oxygen as possible
• sperm cell


  -many mitochondria to produce enough energy for movement

  -tail moves them towards egg

  -pointy head to "brake" into egg

  -nucleus contains genetic material for fertilisation
• muscle cells 


  -heart muscles contact and relax to pump blood around body. never get tired

  -skeletal muscle is joined to bones. its cells contract to make bones move and joints bend.