3.3.2 Gas exchange

Question 1

Describe a method you could use to find the surface area of a leaf.

Answer 1

1. Draw around leaf on graph paper;
2. Count squares (however described);
3. Multiply by 2 (for upper and lower leaf surface)
4. Cut out and weigh;
5. Multiply by 2 (for upper and lower leaf surface).

Question 2

Other than the features of leaves in the table above, give two features of leaves of xerophytes.
For each feature explain how it reduces water loss.

Answer 2

Thick(er) cuticle
so
increase in diffusion

Sunken stomata
so
reduction in air movements / increase in humidity / decrease in water potential gradient.

Question 3

Describe and explain the mechanism that causes forced expiration.

Answer 3

1. Contraction of internal intercostal muscles;
2. Relaxation of diaphragm muscles / of external intercostal muscles; 3. Causes decrease in volume of chest / thoracic cavity;
3. Air pushed down pressure gradient.

Question 4

Describe and explain the mechanism that causes forced expiration.

Answer 4

Muscle walls of bronchi / bronchioles contract; Walls of bronchi / bronchioles secrete more mucus; Diameter of airways reduced;
(Therefore) flow of air reduced.

Question 5

Describe and explain how the countercurrent system leads to efficient gas exchange across the gills of a fish.

Answer 5

Water and blood flow in opposite directions;

Maintains concentration / diffusion gradient / equilibrium not reached / water always next to blood with a lower concentration of oxygen;

Along whole / length of gill / lamellae

Question 6

Amoebic gill disease (AGD) is caused by a parasite that lives on the gills of some species of fish. The disease causes the lamellae to become thicker and to fuse together.
AGD reduces the efficiency of gas exchange in fish. Give two reasons why.

Answer 6

(Thicker lamellae so) greater / longer diffusion distance / pathway;

(Lamellae fuse so) reduced surface area;

Question 7

The volume of water passing over the gills increases if the temperature of the water increases. Suggest why.

Answer 7

increased metabolism 
Less oxygen (dissolved in water);

Question 8

Describe two adaptations of the structure of alveoli for efficient gas exchange.

Answer 8

Thin walls / cells;

(Total) surface area is large;

Question 9

The photograph shows a fire-breather creating a ball of fire. Fire-breathers do this by blowing a fine mist of paraffin oil onto a flame. Some of this mist can be inhaled and may eventually lead to fibrosis.
People who have been fire-breathers for many years often find they cannot breathe out properly. Explain why.

Answer 9

Loss of elasticity / elastic tissue / increase in scar tissue;

Less recoil;

Question 10

The people in group B were recovering from an asthma attack.

Explain how an asthma attack caused the drop in the mean FEV shown in the figure below.

Answer 10

Muscle walls of bronchi / bronchioles contract; Walls of bronchi / bronchioles secrete more mucus; Diameter of airways reduced;
(Therefore) flow of air reduced.

Question 11

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Details of breathing are not required.

Answer 11

Trachea and bronchi and bronchioles; Down pressure gradient;
Down diffusion gradient;
Across alveolar epithelium.