Gas Exchange

Question 1

Smaller organisms have a ….

Answer 1

Large surface area to volume ratio

Question 2

Larger organisms have a …..

Answer 2

Smaller surface area to volume ratio

Question 3

Ficks law

Answer 3

Surface area × concentration gradient/ diffusion distance

Question 4

Gas exchange in single celled organisms

Answer 4

They have a large surface area to volume ratio so use simple diffusion.
Oxygen diffused into the organism to produce ATP during aerobic respiration.
Carbon dioxide diffused out the organism as a waste product.
This produces a large surface area which increases rate of diffusion.

Question 5

What makes a good exchange surface?

Answer 5

Large surface area
Large concentration gradients
Thin exchange surface (few membrane or thin walls)

Question 6

Gas exchange in insects

Answer 6

Oxygen enters through the spiracles which are tiny pores in the surface membrane and open when carbon dioxide levels are high and are opened and closed to control evaporation of water by insects.
2. Spiracles close
3. Oxygen the diffuses into the trachea which is a network of tubes supported by strengthened rings.
4. Oxygen then diffuses into the tracheoles which are highly brached for an a large surface area and they are thin so diffusion distance is reduced, this therefore increases the rate of diffusion
5. Oxygen is then delivered directly to the respiring cells to produce ATP

Question 7

Features that limit water loss in insects

Answer 7

1. Spiracles that are tiny pores on the large permeable exoskeleton
2. The exoskeleton is covered with waterproof cuticle.
3. Relatively small surface area to volume ratio to minimise water loss.

Question 8

Why diffusion happens in the gas exchange systems (tracheal system) of insects?

Answer 8

Respiring cells use the oxygen which lowers the concentration of gas within the trachea so oxygen diffuses into the cells from the trachea to the tracheoles into the cells to meet their requirements from an area of high to low concentration.

Question 9

Fight for flight for an insect

Answer 9

When an insect is at rest water builds up in the tracheoles near the muscle cells.
2. During flight or fight, insects respire anaerobically and produce lactate, this lactate is dissolved in the water that was built up in the tracheoles producing lactic acid.
3. This lowers the water potential of the muscle cells, so water passes from the tracheloes into muscle cells.
4. This allows air into the tracheoles and therefore reduces diffusion distance for oxygen when needed at most.