Gas exchange in humans

Question 1

What is the function of the trachea? (2 points)

Answer 1

The trachea is lined with ciliated epithelial cells that:

• Secrete mucus to trap dust and bacteria.
• Have cilia that sweep the mucus out of the airways

Question 2

How does oxygen diffuse in the alveoli?

Answer 2

Oxygen diffuses from the alveoli into the blood because:

• High concentration of O₂ in the alveoli
• Low concentration of O₂ in the blood

Question 3

How does carbon dioxide diffuse in the alveoli?

Answer 3

Carbon dioxide diffuses from the blood into the alveoli because:

• High concentration of CO₂ in the blood
• Low concentration of CO₂ in the alveoli

Question 4

What are the adaptations of the alveoli for gas exchange? (4 points)

Answer 4

• Thin walls – Short diffusion distance for rapid gas exchange.
• Large number of alveoli – Increases surface area for faster diffusion.
• Surrounded by blood capillaries – Maintains a steep concentration gradient.
• Moist surface – Helps dissolve gases for diffusion.

Question 5

What happens during breathing in (inhalation)? (3 points)

Answer 5

• External intercostal muscles contract – Ribcage moves up and out, increasing thorax volume.
• Diaphragm contracts and flattens, increasing thorax volume.
• Increased thorax volume → decreased pressure, so air enters the lungs.

Question 6

What happens during breathing out (exhalation)? (3 points)

Answer 6

• Internal intercostal muscles contract – Ribcage moves down and in, decreasing thorax volume.
• Diaphragm relaxes – Returns to dome shape, decreasing thorax volume.
• Decreased thorax volume → increased pressure, so air exits.

Question 7

Why does breathing rate increase during exercise? (2 points)

Answer 7

• More oxygen is needed for aerobic respiration in muscle cells to release energy for muscle contraction.
• Helps remove excess CO₂ produced during respiration.

Question 8

Why does breathing rate remain high after exercise? (2 points)

Answer 8

• Oxygen is needed to oxidize lactic acid produced during anaerobic respiration.
• This is called oxygen debt repayment.

Question 9

What harmful substances does tobacco contain?

Answer 9

Tobacco contains nicotine, tar, and carbon monoxide.

Question 10

How does nicotine affect the body? (2 points)

Answer 10

• Raises blood pressure
• Increases risk of heart attacks

Question 11

How does carbon monoxide affect the body? (2 points)

Answer 11

• Binds with haemoglobin in red blood cells, forming carboxyhaemoglobin.
• Reduces the concentration of oxygen in the blood.

Question 12

How does tar affect the lungs? (3 points)

Answer 12

• Causes lung cancer.
• Damages cilia, preventing the removal of mucus, leading to chronic bronchitis.
• Damages alveoli, reducing surface area for gas exchange, causing lung emphysema.