9.1 The Gas Exchange System

Describe the pathway taken by a molecule of oxygen from the outside air to the blood of a human.

Premature babies can suffer from a deficiency of a substance called pulmonary surfactant. This can lead to a condition known as respiratory distress syndrome (RDS). Fig. 1 below shows the possible appearance of the lung tissue of an RDS patient and the appearance of normal lung tissue.

Fig. 1

Image courtesy of Atlas of Pulmonary Pathology, licensed under the Creative Commons Attribution-ShareAlike 2.0 Generic license, and adapted and redistributed under conditions found at https://creativecommons.org/licenses/by-sa/2.0/ 

Identify and label on Fig. 1 healthy lung tissue.

[2]

[2]

RDS can be treated by the administration of an alternative form of pulmonary surfactant to the lungs. The graph shown in Fig. 2 gives the effect of different variations of pulmonary surfactant on the lung volume of rabbits at different pressures. The variations include pulmonary surfactant isolated from sheep lungs, as well as synthetic versions of pulmonary surfactant that contain its separate lipid and protein components. Note that cm H₂O is a unit of pressure.

Fig. 2

Use the information provided to explain why each of the following statements is incorrect:

Pulmonary surfactant is essential for lung expansion.

[1]

(ii)

Phospholipids are the active component of pulmonary surfactant.

[1]

(iii)

Pulmonary surfactant from sheep is the most effective treatment for RDS in premature babies.

[2]

The form of pulmonary surfactant produced in mammalian lungs contains proteins known as SP-A and SP-D, which are known to be involved with the activation of phagocytes.

Suggest, with a reason, a symptom that would result from a deficiency of SP-A and SP-D proteins.

Fig. 1 shows a tissue sample taken from a human lung. Two cells are labelled A and B.

Fig. 1

Identify cell A and cell B and describe their function.

Cell A is adapted for its function. 

Describe and explain one feature of cell A that makes it well adapted as part of the gas exchange system. 

Scientists grew alveolar epithelium cells in culture for 10 days. The cells were exposed to hydrogen peroxide. Hydrogen peroxide is a toxin that is found in cigarette smoke. Each day the scientists calculated the mass of cells that died each hour. Their results are shown in Table 1 below. 

Table 1

For each day, calculate the rate of cell death per minute. Record the rates in standard form and give an appropriate unit.

[2]

Plot a suitable graph of your processed data on the grid in Fig. 2.

Fig. 2

[3]

Alpha-1-antitrypsin is a protein that reduces the activity of enzymes that can damage lung tissue. Hydrogen peroxide reduces the activity of alpha-1-antitrypsin. Scientists investigated the effect of different concentrations of hydrogen peroxide on the activity of alpha-1-antitrypsin.
Fig. 3 shows their results.

Fig. 3

Use Fig. 3 and the information from part (c) to explain why long term smokers suffer with shortness of breath.

Fig. 1 is an image of an electron micrograph showing a cross section through the lining of part of the human gas exchange system. The magnification of Fig. 1 is x5000.

Fig. 1

The line marked Z in Fig.1 measures 3.1 cm.

Calculate the actual length of the structure measured by line Z. Give your answer in µm.

For Fig.1:

[2]

(iii)

Name one location in the gas exchange system where the structures identified in part ii) would be found.

Explain the functions of structures X and Y in Fig.1.

Certain lung conditions can lead to remodelling of the lining of the airways and an increase in the numbers of structure Y from Fig.1. This is known as cell metaplasia and can lead to damaging symptoms.

Suggest three symptoms that may result from metaplasia of structure Y from Fig.1.

Fig. 1A is a photomicrograph of healthy lung tissue.

Fig. 1B is a photomicrograph of lung tissue from a person with emphysema, a chronic obstructive pulmonary disease (COPD). The images are both at magnification ×40.

Fig. 1

Name the structure labelled H in Fig. 1A.

Calculate the actual diameter of the alveolus at X–Y.

Write down the formula and use it to make your calculation.

When measured with a ruler on the page, the image of alveolus X-Y would appear as follows:

Give your answer to the nearest whole micrometre (μm).

Gas exchange in the lungs occurs in the alveoli.

Describe the process of gas exchange in healthy lungs and suggest how this compares with gas exchange in the diseased lung shown in Fig. 1B.