M8. (a) (gills have) lamellae on filaments; lots of both; 2 (b) (i) all 3 go up; Accept converse 1 (ii) more oxygen can be supplied; for more respiration; Accept answer relating to CO2 2 [5] (a) 1. Large surface area provided by lamellae / filaments increases diffusion / makes M9. diffusion efficient;; Q Candidates are required to to lamellae or filaments. Do not penalise for confusion between two 2. Thin epithelium / distance between water and blood; 3. and blood flow in opposite directions / countercurrent; 4. (Point 4) maintains concentration gradient (along gill) / equilibrium not reached / as water always next to blood with lower concentration of oxygen; 5. Circulation replaces blood saturated with oxygen; 6. Ventilation replaces (as oxygen removed); 6 (b) Mixing of air and water (at surface); Air has higher concentration of oxygen than water; Diffusion into water; Plants / seaweeds near surface / in Produce oxygen by photosynthesis; 2 max (c) Not much oxygen near sea bed; Toadfish haemoglobin (nearly) saturated / loads readily at / has higher affinity for oxygen at low partial pressure (of oxygen); 2
M8. (a) (gills have) lamellae on filaments; lots of both; 2 (b) (i) all 3 go up; Accept converse 1 (ii) more oxygen can be supplied; for more respiration; Accept answer relating to CO2 2 [5] M9. (a) 1. Large surface area provided by lamellae / filaments increases diffusion / makes diffusion efficient;; Q Candidates are required to to lamellae or filaments. Do not penalise for confusion between two 2. Thin epithelium / distance between water and blood; 3. and blood flow in opposite directions / countercurrent; 4. (Point 4) maintains concentration gradient (along gill) / equilibrium not reached / as water always next to blood with lower concentration of oxygen; 5. Circulation replaces blood saturated with oxygen; 6. Ventilation replaces (as oxygen removed); 6 (b) Mixing of air and water (at surface); Air has higher concentration of oxygen than water; Diffusion into water; Plants / seaweeds near surface / in Produce oxygen by photosynthesis; 2 max (c) Not much oxygen near sea bed; Toadfish haemoglobin (nearly) saturated / loads readily at / has higher affinity for oxygen at low partial pressure (of oxygen); 2
CounterCurrentFlow.doc.docx