Gas Exchange in Humans

Question 1

Inspiration/Inhalation

Answer 1

External intercostal muscles contract and raise ribs. The diaphragm muscle contracts and flattens. The volume of the thorax increases. The air pressure in the thoracic cavity falls below that of atmospheric air. Air rushes into lungs along a pressure gradient

Question 2

Expiration/Exhalation

Answer 2

External intercostal muscles relax and ribs move down and inwards. The diaphragm relaxes and becomes dome-shaped. the volume of that thorax decreases. Air rushes out of the lungs along a pressure gradient

Question 3

How are alveoli suited for gas exchange?

Answer 3

• They are a large surface area
• Walls are very thin, only 1 cell thick
• A strong blood supply maintains a high concentration gradient

Question 4

What does smoking cause?

Answer 4

Lung cancer, bronchitis and emphysema

Question 5

What are the chemicals in cigarette smoke?

Answer 5

Tar - a sticky brown substance that is deposited in the lungs. It is a carcinogen (causes cancer)
Nicotine - an addictive drug
Carbon Monoxide - reduces the blood’s capacity to carry oxygen

Question 6

How does smoking cause bronchitis?

Answer 6

In the trachea and bronchi of a smoker, the cilia are destroyed by chemicals in the cigarette smoke. The reduced number of cilia means that mucus is not swept away from the lungs, but remains to block the air passages. This is made worse by the fact that the smoke irritates the lining of the airways, stimulating cells to produce more mucus. Irritation of the bronchial tree, along with bacterial infections in the mucus can cause bronchitis

Question 7

How does smoking cause emphysema?

Answer 7

Smoking damages the walls of the alveoli, which break down and fuse together, greatly reducing the surface area and making gas exchange inefficient meaning that the blood carries less oxygen

Question 8

Investigating the effect of exercise on breathing in humans

Answer 8

1. A person sits quietly for 5 minutes then count the number of breaths they take in one minute
2. Record, then repeat and average
3. The person then does vigorous exercise
4. Immediately record their breath rate after and then every minute until they return to their normal resting rate