Zigzag Paper 1

• Not all fish rely on gills for gas exchange. Some young fishes have high proportion of oxygen through their skin. Suggest why this is useful?

  • Skin is PERMEABLE to oxygen
  • In small fish, surface area is large compared to their volume
  • In small fish no cell is ever far from the skin surface / diffusion distance to any tissue is short
• An African lung fish is primitive species of fish - used to have lungs before developing gills. Suggest which conditions this adaptation is likely to have evolved.

  • SPECIFICATION = "Changes to body shape and the development of systems in larger organisms as adaptations that facilitate exchange as this ratio reduces"
  • Water with low oxygen concentrations, lungs allow the fish to obtain oxygen from the atmosphere
  • OR small pools that temporarily dry out - lungs allow fish to survive temporarily out of water
• Explain how cell membrane of immune cells is adapted to recognize pathogens

  • Receptors on cell surface membrane for antigens
  • Has antigen recognition sites / unique sites that recognise possible antigens