Exam-style questions

Question 1

Explain why fish require a specialised gas exchange surface

Answer 1

• fish have a higher metabolic rate, so have a higher oxygen demand and energy demand
• their scales are impermeable, so gases can’t diffuse through them
• fish have a small surface area to volume ratio

Question 2

Describe and explain how the gill is adapted for gas exchange

Answer 2

• gills contain gill filaments, which have a high surface area to increase rate of oxygen diffusion
• gill filaments have a thin wall, so small diffusion distance
• have countercurrent exchange system, where blood and water flow over gill lamellae in opposite directions to maintain a steep conc. gradient
• have a rich blood supply, to maintain a steep conc. gradient

Question 3

The gill itself has a series of gill rakers on the outer edge of the gill. What do these do

Answer 3

they protect the gill filaments and lamellae from debris and small pebbles

Question 4

Give two differences between the structure of a vein and the structure of a capillary

Answer 4

• veins have a larger lumen than capillaries
• veins have valves, whilst capillaries don’t

Question 5

Infection of the lungs with Mycobacterium tuberculosis can result in a range of symptoms. These symptoms can include severe breathing problems, a persistent
cough and coughing up blood.
A tubercle is a solid mass of dead tissue, macrophages and bacteria.

Suggest why this infection can result in these symptoms.

Answer 5

as alveoli is replaced by tubercle, the surface area of the lungs is reduced, thus less gas exchange occurs. Coughing resulted by the tubercle causing irritation
Coughing up blood caused by damaged vessel, due to high pressure & stress on vessels

Question 6

Describe and explain how the lungs of a mammal are adapted for rapid gas
exchange.

Answer 6

• alveoli are one cell thick, so small diffusion distance
• alveoli provide large surface area
• alveoli are covered in capillaries, which provide rich blood supply to maintain a high concentration gradient
• ventilation provides high concentration gradient

Question 7

In mammals, blood passes through the heart twice for each circulation of the
body.
Suggest how this type of circulation enables mammals to carry out effective
gas exchange.

Answer 7

• one side of the heart transports oxygenated blood, whilst the other side transports deoxygenated blood
• the deoxygenated and oxygenated blood is separated by the septum
• this maximises the supply of oxygen to the respiring cells, as mammals need good oxygen supply to meet high energy demand and metabolic rates