exchange EQ

Question 1

the adult damselfly uses a tracheal system for gas exchange.
explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange. (3)

Answer 1

1. tracheoles have thin walls so short diffusion distance to cells;
2. highly branched/large number of tracheoles so large surface area for gas exchange;
3. fluid at end of the tracheoles that move out (into tissue) during exercise so this maintains diffusion/concentration gradient for oxygen/carbon dioxide;

Question 2

explain two ways in which the structure of fish gills is adapted for efficient gas exchange. (2)

Answer 2

1. many lamellae/filaments, so large surface area;
2. thin surface so short diffusion pathway;

Question 3

explain the counter current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills. (3)

Answer 3

1. water and blood flow in opposite directions;
2. blood always passing water with a higher concentration;
3. diffusion gradient maintained throughout length (of gill);
   OR
   if water and blood flowed in the same direction equilibrium would be reached;

Question 4

a fish uses its gills to absorb oxygen from water. explain how the gills of a fish are adapted for efficient gas exchange. (6)

Answer 4

1. large surface area provided by lamellae which increases diffusion (make it more efficient);
2. thin epithelium distance between water and blood;
3. water and blood flow in opposite directions = counter current;
4. maintains concentration gradient (along gill) as equilibrium not reached as water always next to blood with lower concentration of oxygen;
5. circulation replaces blood saturated with oxygen;
6. ventilation replaces water (as oxygen is removed);

Question 5

abdominal pumping increases the efficiency of gas exchange between the tracheoles and muscle tissue of the insect. explain why. (2)

Answer 5

1. more oxygen enters quicker;
2. so maintains greater diffusion or concentration gradient;

Question 6

abdominal pumping is an adaptation not found in many small insects. these small insects obtain sufficient oxygen by diffusion.
explain how their small size enables gas exchange to be efficient without the need for abdominal pumping. (1)

Answer 6

large surface area: volume/shortens diffusion distance (to tissues).