OCR A-level biology - chapter 7 | Questions with 100% correct Answers | Verified

Why is gas exchange important? - -the metabolic reaction is low in small organisms -surface area is small in large organism How are concentration gradients of gases maintained? - By transport of gases away from the gas exchange surface. Cellular respiration takes place in all cells in the body so creates constant O2 demand and need to eliminate CO2. Why do waste products need to be removed? - So they don't build up and become toxic. Why don't small organisms need exchange systems? - large sa:v Short diffusion distance. Why do large organisms need an exchange system? - small sa:v longer diffusion pathway How does size effect the need for an exchange system? - Small organisms - Single celled - Cytoplasm close to the environment. -oxygen through Diffusion is enough to keep the organism alive. Multicellular organisms - Several layers of cells - Diffusion too slow to supply innermost cells - O2 & nutrients no longer have a diffusion pathway. How does SA:V effect the need for an exchange system? - Small organisms - small SA, small volume, large SA:V, sufficient to supply all cells with oxygen.Large organisms - large SA, large volume, small SA:V. main features of any efficient gas exchange - -increased surface area (overcomes small sa:v ratio) -thin layer -(short diffusion pathway) -good blood supply(steep concentration gradient,faster diffusion rate) -ventilation to maintain diffusion gradient