Topic 3B: Gas Exchange In Humans

Question 1

Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake. [2]

Answer 1

1. Large(r) organisms have a small(er) surface area:volume;
2. Overcomes long diffusion pathway

Question 2

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them. [3]

Answer 2

1. Many alveoli provide a large surface area so diffusion is fast;
2. Many capillaries provide a large surface area so diffusion is fast;
3. Alveolar epithelium and capillary endothelium are both one cell thick and these cells are flattened so short diffusion pathway;
4. Ventilation of air and circulation of blood maintain oxygen concentration gradient.

Question 3

If alveolar epithelium cells die inside a human body they are replaced by non-specialised, thickened tissue.

Explain why death of alveolar epithelium cells reduces gas exchange in human lungs. [3]

Answer 3

1. Reduced surface area;
2. Increased diffusion pathways;
3. Reduced rate of gas exchange

Question 4

Describe the gross structure of the human gas exchange system. [2]

Answer 4

1. Trachea, bronchi, bronchioles, alveoli.
2. Above structures named in correct order

Question 5

Describe how humans breathe in and out. [5]

Answer 5

Breathing in:
1. Diaphragm (muscles) contract and diaphragm flattens;
2. External intercostal muscles contract and rib cage pulled up/out;
3. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric pressure);

Breathing out:
4. Diaphragm (muscles) relaxes and diaphragm moves up;
5. External intercostal muscles relax and rib cage moves down/in;
6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric pressure).

Question 6

Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange. [2]

Answer 6

1. Flattened cells;
2. Reduces diffusion pathway

Question 7

Tidal volume is the volume of air inhaled or exhaled during a single breath when a person is resting.

Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveoli. [3]

Answer 7

1. Less carbon dioxide exhaled;
2. (So) reduced concentration gradient (between blood and alveoli);
3. More carbon dioxide stays in the blood.

Question 8

Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Details of breathing are not required. [4]

Answer 8

1. Trachea, bronchi, bronchioles;
2. Oxygen moves down pressure gradient;
   .
3. Diffuses down concentration gradient;
4. Across alveolar epithelium;
5. Across capillary endothelium.

Question 9

Describe the pathway taken by an oxygen molecule from an alveolus to the blood. [2]

Answer 9

1. (Across) alveolar epithelium;
2. Endothelium of capillary.

Question 10

Describe and explain the mechanism that causes lungs to fill with air. [3]

Answer 10

1. Diaphragm (muscle) contracts and intercostal muscles contract;
2. (Causes volume increase and) pressure decrease;
3. Air moves down a pressure gradient.

Question 11

Scientists who investigate disease may look at risk factors. What is a risk factor? [1]

Answer 11

1. Something that increases the probability of getting a disease.

Question 12

Suggest two precautions that need to be taken when finding a sample for an experiment. [2]

Answer 12

1. Large sample size;
2. Individuals chosen at random;
3. Are healthy;
4. Equal number of males and females

Question 13

The volume of air a person can breathe out in 1 second decreases after the age of 30.

Use your knowledge of ventilation to suggest why. [1]

Answer 13

1. Internal intercostal muscles less effective