Chapter 8 Respiration in Humans I

Question 1

Explain the effect of carbon monoxide on the normal functioning of the body [2] (2014/A5)

Answer 1

1. Carbon monoxide binds with haemoglobin irreversibly to form carboxyhaemoglobin [1]
2. Reduces the oxygen carrying capacity of red blood cells, thus the amount of oxygen per unit vol of blood. Reduces respiration by body tissues, reducing energy released. [1] (R: no oxygen reaches the cells)

Question 2

Suggest why the number of deaths from lung cancer in smokers is much greater than it is in non-smokers [1] (2014/A5)

Answer 2

Cigarette smoke contains carcinogenic substances such as tar which increases the risk of lung cancer. [1]

Question 3

Explain how air is made to enter the lungs [6] (2014/B10 E)

Answer 3

When breathing in,
1. Diaphragm muscle contracts and diaphragm flattens [1];
2. external intercostal muscles contract while internal intercostal muscles relax; [1]
3. ribs swing upwards and
outwards; [1]
4. hence increases the volume of the thoracic cavity; [1]
5. decreasing the pressure in the lungs; [1]
6. the atmospheric pressure is now higher than the pressure in the lungs, causing air to be forced into the lungs. [1]

Question 4

Describe how a molecule of oxygen present on the air breathed in reaches a muscle cell in the wall of the left atrium [4] (2014/B10 E)

Answer 4

1 Molecule of oxygen dissolves in the thin film of moisture lining the inner surface of the alveolar wall and diffuses through the one-cell thick alveolar wall down a concentration gradient into the blood capillaries across the one-cell thick endothelial wall [1]
2. and into blood plasma and diffuses into the red blood cell, combining with haemoglobin to form oxyhaemoglobin. [1]
3. It is then carried by the blood from the blood capillaries through the pulmonary veins into the left atrium and into the left
ventricle, then into the aorta [1]
4. before entering the coronary arteries which branch into arterioles and then network of blood capillaries. Oxygen molecules dissociate from oxyhaemoglobin in red blood cells, diffuse from the blood capillaries into the tissue fluid and then finally into the muscle cells in the wall of the left atrium. [1]