Topic 11 (Gas exchange in humans)

Question 1

How do organisms obtain oxygen for aerobic respiration?

Answer 1

Organisms obtain oxygen for aerobic respiration through the process of gas exchange.
Unicellular organisms 🡪 large surface area to volume
ratio: gas exchange by diffusion
Large animals 🡪 smaller surface area to volume
ratio: use special organs for gas exchange

Question 2

How does air enter our body?

Answer 2

1) The nose - Air usually enters through the two external nostrils.
2) Pharynx
3) Larynx
4) Trachea - The trachea is supported by C-shaped rings of cartilage.
5) Bronchi and bronchioles - The trachea divides into two tubes called bronchi (singular: bronchus ). Each bronchus branches into bronchioles.
6) Alveoli (air sacs) - Gas exchange takes place through the walls of the alveoli.

Question 3

How are the lungs adapted for efficient gas exchange?

Answer 3

*Numerous alveoli in the lungs provide a large surface area.
*Wall of the alveolus is only one cell thick.
*Walls of the alveoli are richly supplied with blood capillaries.
*Thin film of moisture covers the surface of the alveolus.

Question 4

How is oxygen transported around the body?

Answer 4

*High oxygen concentration (in the lungs): oxygen combines with haemoglobin, forming oxyhaemoglobin.
*Low oxygen concentration (in organs/ tissues): oxyhaemoglobin releases oxygen to respiring cells.

Question 5

What are the two phases of the breathing movement.

Answer 5

*Taking in of air inspiration or inhalation
*Giving out of air expiration or exhalation

Question 6

Diagram of inspiration/inhalation and expiration/exhalation.

Answer 6

Slides 13 and 14.

Question 7

How does inspired air differ from expired air? (inspired air)

Answer 7

Inspired air:-
Oxygen: About 21.0%
Carbon dioxide: About 0.03%
Water vapor: Variable (rarely saturated)
Nitrogen: About 78.0%
Temperature: Variable
Dust particles: Variable but usually present

Question 8

How does inspired air differ from expired air? (expired air)

Answer 8

Expired air:-
Oxygen: About 16.4%
Carbon dioxide: About 4.0%
Water vapor: Saturated
Nitrogen: About 78.0%
Temperature: About body temperature (37°C)
Dust particles: Little, if any

Question 9

What is the stimulus for breathing?

Answer 9

The stimulus for breathing is a high concentration of carbon dioxide in the blood or alveolar air.