Ch 7 Gas exchange in humans

Question 1

Mucus-secreting cells, ciliated epithelial cells

Answer 1

• secrete mucus
• the mucus traps dust particles and microorganisms in the inhaled air
• cilia of ciliated epithelial cells in the lining beat to sweep the mucus towards the pharynx
• the mucus is then coughed up or swallowed into the stomach where most of the microorganisms will be killed by hydrochloric acid

Question 2

Pneumothorax

Answer 2

• the pressure inside the pleural cavity is normally lower than the atmospheric pressure
• if the pleural membrane of a lung is ruptured, air leaks into the pleural cavity and the negative pressure cannot be maintained. The lung collapses due to its own elasticity

Question 3

Uptake of oxygen by the blood

Answer 3

During inhalation, atmospheric air flows into air sacs. Oxygen in inhaled air dissolves in the water film lining the air sacs. Since the oxygen concentration of the water film is higher than that of the deoxygenated blood, dissolved oxygen in the water film diffuses across the walls of the air sacs and the capillaries into the blood.

Question 4

Removal of carbon dioxide from the blood

Answer 4

Since the carbon dioxide concentration of the deoxygenated blood is higher than that of the water film, carbon dioxide in the blood diffuses across the walls of the capillaries and the air sacs into the air in the air sacs. Carbon dioxide is then removed from the body during exhalation.

Question 5

Adaptations of air sacs for gas exchange

Answer 5

1. There are a large number of air sacs. This provides a very large surface area for diffusion of gases
2. The epithelia making up the walls of the air sacs are very thin, only one-celled thick. This reduces the diffusion distance for gases
3. The inner surfaces of air sacs are moist. Oxygen in inhaled air dissolves in the water film lining the inner surfaces of the air sacs before diffusion takes place.
4. There are numerous capillaries surrounding the air sacs. This allows rapid transport of gases to and away from the air sacs. A steep concentration gradient of gases between the air sacs and the blood can be maintained for efficient diffusion of gases
5. The walls of air sacs are very close to the capillaries surrounding the air sacs. This reduces the diffusion distance of gases

Question 6

Asthma attack

Answer 6

The bronchioles constrict. This reduces the amount of atmospheric air reaching the air sacs. The concentration gradient of gases between the air sacs and the blood is less steep. Gas exchange is less efficient.

Question 7

Emphysema

Answer 7

The walls of the air sacs break down. This reduces the area of respiratory surface for gas exchange.

Question 8

SARS

Answer 8

Fluid accumulates in the air sacs. This increases the diffusion distance of gases and reduces the surface area of the respiratory surface for gas exchange. Gas exchange is less sufficient.

Question 9

Adaptations of red blood cells for carrying oxygen

Answer 9

1. Red blood cells are packed with haemoglobin. This increases the oxygen-carrying capacity of blood
2. Mature red blood cells have no nucleus. This provides space for more haemoglobin
3. Red blood cells have a biconcave disc shape. This provides a large surface area to volume ratio and short distance for diffusion of oxygen

Question 10

Inhalation

Answer 10

Intercostal muscles contract. The rib cage moves upwards and outwards. Diaphragm muscles contract. The diaphragm becomes flattened. The volume of the thoracic cavity is increased. The volume of the lungs is increased. The air pressure in the lung decreases and becomes lower than the atmospheric pressure. Air rushes into the lungs.

Question 11

Exhalation

Answer 11

Intercostal muscles relax. The rib cage moves downwards and inwards. Diaphragm muscles relax. The diaphragm returns to its dome shape. The volume of the thoracic cavity is decreased. The volume of the lungs is decreased. The air pressure in the lungs increases and becomes higher than the atmospheric pressure. Air is forced out of the lungs,