Gas Exchange in Humans: B11

IGCSE biology

Label the following

What is the human breathing system?

Organ system that allows the body to obtain oxygen needed for aerobic respiration (needs O₂) and allows the body to remove the carbon dioxide (releases CO₂) produced as waste

Where are the alvioli located?

At the end of the bronchides

What is the pathway of air through the lungs? 

Nose/mouth —> larynx — treachea —> bronchi —> bronchioles —> alveoili 

Describe the pathway of air through the lungs? 

1. Nose/mouth: air enters the body through here

2. Larynx: directs air into the trachea

3. Trachea: windpipe carries air into the lungs

4. Bronchi: trachea splits into two main bronchi (one for each lung)

5. Bronchioles: bronchi branch off into smaller tubes called bronchioles

6. Alveoli: tiny air sacs surrounded by capillaries located at the end of bronchioles, where gas exchange happens

Where does gas exchange occur?

Oxygen diffuses from the alveolus into the capillary through diffusion following the concentration gradient

Describe the gas exchange process in more detail

1. Air is inhaled through the nose or mouth, filling alveoli with air

2. There is a high concentration of oxygen in the alveolus, and a low concentration in the capillaries

3. Oxygen diffuses from a high concentration in the alveolus to a low concentration in the capillaries

4. Oxygen binds with haemoglobin and is released in cells with low oxygen concentration

What are some features of gas exchange surfaces?

Have a large surface area: more space for gases to diffuse across

Thin: reduces diffusion distance, making gases like oxygen and carbon dioxide diffuse more quickly

Good blood supply: each alveolus has lots of capillaries surrounding it, which transport blood

Good ventilation with air: a good supply of air supplied through breathing

What is inspired air?

The air you breathe in

What is the composition of inspired air?

More oxygen, less carbon dioxide, and water vapour vary

What is expired air?

The air you breathe out

What is the composition of expired air?

Less oxygen, more carbon dioxide, and more water vapour because moisture evaporates from the cells of the gas exchange surface

What is the effect of exercise on breathing?

1. Cells in the body respire more during periods of physical activity to provide the muscles with the energy needed

2. Since there’s more respiration, more carbon dioxide is produced as a waste product

3. The brain detects an increasing carbon dioxide rate in the blood

4. This triggers the body to respond by increasing the rate and depth of breathing to expel carbon dioxide from the body

5. These changes also increase the amount of oxygen obtained, which is needed for aerobic respiration to continue