Gas Exchange Exam Questions

Question 1

Explain the advantage of a higher ventilation rate of fish when temperature of water increases.

Answer 1

Higher temperature decreases solubility of oxygen in water so less oxygen flows over gills.
So blood oxygen concentration decreases
An increase in ventilation rate increases the flow of oxygen across gills.
So this maintains a diffusion gradient of oxygen in gills.
So maintains oxygen supply to tissues for respiration.

Question 2

Explain the movement of oxygen into the gas exchange system of an insect when it is at rest. (3)

Answer 2

Oxygen is used up in aerobic respiration in cells due to metabolic processes.
So concentration of oxygen in cells and tracheoles decreases
So oxygen moves from the air down a diffusion gradient to the tracheoles

Question 3

Describe how the gas exchange system of an insect:
Provides cells with sufficient oxygen
Limits water loss.
Explain your answers

Answer 3

Spiacles lead to tracheae which lead to tracheoles
Open spircales allow diffusion of oxygen from air
Tracheoles have thin surface so short diffusion distance to cells
Tracheoles are very branched and extend out to all respiring cells so large surface area and short diffusion distance of oxygen to cells.
Tracheoles walls are permeable to oxygen so allow oxygen to diffuse to cells
Spiracles close during inactivity to limit water loss by evaporation
Chitin in trachea are impermeable so limit water loss

Question 4

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

Answer 4

Many gill lamellae are located on many hill filaments so increase surface area for diffusion of oxygen.
Epithelium of gill lamellae are very thin so reduce diffusion distance of oxygen between water and blood.
Counter current flow, where blood in capillaries flow in opposite direction to water
Maintains a diffusion gradient across entire length of lamellae/ water is always next to blood with a lower oxygen concentration
Ventilation replaces water as oxygen is removed
Circulation replaces blood with a higher oxygen concentration. This maintain diffusion gradient of oxygen.

Question 5

How does anaerobic respiration in insects increase gas exchange?

Answer 5

Lactic acid builds up in respiring cells so the water potential of the cells decreases.
So water moves from tracheoles to cells via osmosis.
So volume inside tracheoles increase so pressure decreases so air moves down pressure gradient/ surface area inside tracheoles increase so faster rate of diffusion of oxygen/ diffusion is faster in air than water.

Question 6

How does abdominal movement in insects increase gas exchange?

Answer 6

Adnominal muscles contract and relax and move gases on mass by mass transport
So this speeds up movement of gases as larger volume of gases move through insect
So more ventilation of oxygen so maintains diffusion gradient of oxygen between atmosphere and tracheoles

Question 7

How does carbon dioxide move into the leaves of plants?

Answer 7

Carbon dioxide is used up in photosynthesis by palisade cells.
This increases diffusion gradient of CO2 between spongy mesophyll and atmosphere as CO2 concentration in spongy mesophyll decreases.
So CO2 moves in by diffusion down a diffusion gradient through open stomata

Question 8

Explain why the air breathed out of the lungs may sometimes have the same concentration of oxygen as the air outside. (2)

Answer 8

Air must be exhaled out of trachea without reaching alveoli.
Gas exchange of oxygen, where oxygen diffuses into blood only happens in alveoli, not trachea.

Question 9

Explain why there may still be carbon dioxide in the blood that reaches the heart from the lungs. (2)

Answer 9

The muscles in the lungs, such as external intercostal muscles, contract during inspiration.
Contraction means muscles in the lungs respire and produce carbon dioxide, which reaches the blood and travels into the heart

Question 10

Describe and explain how fish maintain a flow of water over their gills. (4)

Answer 10

1. mouth opens, operculum / opercular valve shuts;
2. floor of mouth lowered;
3. water enters due to decreased pressure / increased volume;
4. mouth closes, operculum / opercular valve opens;
5. floor raised results in increased pressure / decreased volume;
6. high / increased pressure forces / pushes water over gills;