6.4 Gas Exchange

Question 1

Define ventilation

Answer 1

The movement of air to and from a gas exchange surface (alveoli).

Question 2

Define gas exchange

Answer 2

The diffusion of respiratory gasses across a gas-exchange surface.

Question 3

Define cell respiration

Answer 3

Reaction within cells which uses oxygen and produces carbon dioxide. Released energy is captured within ATP molecules for use within the cell.

Question 4

Explain the need for a ventilation system

Answer 4

The body needs oxygen to make ATP via cell respiration. The body needs to get rid of carbon dioxide which is a product of cell respiration. The ventilation system passes oxygen over the alveoli, so it can diffuse into the blood stream, and exhales carbon dioxide.

Question 5

Outline the features of alveoli that adapt them to gas exchange

Answer 5

Thin wall
Rich capillary network
High SA:V ratio
Moist

Question 6

Explain how the thins walls of alveoli adapt them to gas exchange

Answer 6

Made up of single layer of flattened cells and so are the walls of the capillaries so diffusion distance is small, allowing rapid gas exchange.

Question 7

Explain how the rich capillary network helps alveoli with gas exchange

Answer 7

Alveoli are covered by a dense network of capillaries that help to maintain a concentration gradient.

Question 8

Explain how a high SA:V ratio helps alveoli with gas exchange

Answer 8

Great numbers of spherically-shaped alveoli optimise surface area for gas exchange.

Question 9

Explain how the moistness of alveoli helps them with gas exchange

Answer 9

Some cells in the lining secrete fluid to allow gases to dissolve and to prevent alveoli from collapsing (through cohesion).

Question 10

Describe what happens during inspiration

Answer 10

Diaphragm muscles contract and flatten downwards. External intercostal muscles contract, pulling ribs upwards and outwards
This increases the volume of the thoracic cavity (and therefore lung volume). The pressure of air in the lungs is decreased below atmospheric pressure. Air flows into the lungs to equalise the pressure.

Question 11

Describe what happens during expiration

Answer 11

Diaphragm muscles relax and diaphragm curves upwards. Abdominal muscles contract, pushing diaphragm upwards. External intercostal muscles relax, allowing the ribs to fall. Internal intercostal muscles contract, pulling ribs downwards. This decreases the volume of the thoracic cavity (and therefore lung volume). The pressure of air in the lungs is increased above atmospheric pressure. Air flows out of the lungs to equalise the pressure.