Gas exchange in small organisms

• Unicellular organism: Amoeba

  Adaptions to increase SA:V : Pseudopodia

  method of O2 delivery: Simple diffusion

  Habitat: Freshwater ponds - stagnant water with low oxygen concentration. The dissolved oxygen freely diffuses across the cell membrane

  Other: short diffusion pathway
• Small multicellular organism: Flatworm

  Adaptions to increase SA:V : Very thin and flat

  method of O2 delivery: Simple Diffusion

  Habitat: Mostly aquatic (fresh or salt water) - dissolved oxygen freely diffuses across the cell membrane. Large active flatworms have basic gills

  Other: Short diffusion pathway
• Small multicellular organism: Earthworm

  Adaptions to increase SA:V : Diffusion across moist skin. Closed circulation and haemoglobin to carry oxygen to each cell

  Habitat: Damp skin so oxygen dissolves and diffuses across the body surface