gas exchange

Question 1

What are alveoli

Answer 1

Small air sacs where exchange of gas takes place during breathing

Question 2

Where has the blood passing next to the alveoli just returned from?

Answer 2

Just returned to the lungs from the rest of the body, so it contains lots of CO2 and very little oxygen.

Question 3

What happens to blood when passing alveoli?

Answer 3

Oxygen diffuses out of the alveolus (high concentration) into the blood (low concentration).

CO2 diffuses out of the blood (high concentration) into the alveolus (low concentration) to be breathed out.

Question 4

How are alveoli specialised for gas exchange

Answer 4

1. Huge number of microscopic alveoli gives the lungs an enormous SA.
2. Moist lining for gases to dissolve in
3. Alveoli have very thin walls - only one cell thick, so gases don’t have far to diffuse
4. Have blood great supply to maintain a high concentration gradient.
5. The walls are permeable - so gases can diffuse across easily.

Question 5

What are the effects of smoking to the lungs and circulatory system?

Answer 5

1. Damages walls inside alveoli, reducing SA for gas exchange and leading to diseases like emphysema.
2. Tar is cigarettes damages cilia in lungs and trachea, so chest infections are more likely
3. Tar irritates bronchi and bronchioles, encouraging mucus to be produced. which can’t be cleared very well by damaged cilia - causing smoker’s cough and chronic bronchitis
4. CO in cigarette smoke reduces amount of oxygen the blood can carry, so heart rate increases leading to higher blood pressure.
5. High blood pressure increases risk of coronary heart disease as artery walls are damaged, making formation of blood clots more likely.

Question 6

Describe the process of inhalation

Answer 6

1. The external intercostal muscles contract, pulling the ribs up.
2. The muscles of diaphragm contract, pulling diaphragm down into a more flattened shape.
3. Both these movements increase the pressure of the chest and cause a slight drop in pressure inside the thorax compared with the air outside.
4. Air then enters the lungs.

Question 7

Describe the process of exhalation

Answer 7

1. External intercostal muscles relax, and the internal intercostals contract, pulling the ribs down and in.
2. At the same time, the diaphragm muscles relax and diaphragm goes back to its normal dome shape.
3. Volume of thorax decreases, and pressure in thorax is raised slightly above atmospheric pressure.
4. Difference in pressure forces air out the lungs

Question 8

PRACTICAL: Investigate breathing in humans, including the release of carbon dioxide and the effect of exercise.

Answer 8

1. A person sits quietly for five minutes, making sure they are relaxed. They count the breaths they take in one minute, recording results in a table.
2. They wait a minute, and then count again, repeating if necessary until they get a steady value for the ‘resting rate’
3. Person then carries out some vigorous exercise, such as running on the spot for 3 mins.
4. Immediately after they finish, they sit down and record the breathing rate as before.
5. They then continue to record their breaths per minute, every minute, until they return to their normal resting rate.