Gas Exchange (Edexcel GCSE Biology: Combined Science)

Figure 1 shows a section of an alveolus of the lungs. Certain parts and processes are labelled A-G.

Figure 1

Identify the parts and processes involved in the function of the alveolus as shown in Figure 1. Do not write in the greyed-out boxes.

Each adult lung is estimated to contain 520 million alveoli. 

The estimated overall surface area for gas exchange within the human breathing system is estimated to be 100 m² (100 million mm²).

Calculate the internal surface area of one alveolus from the human breathing system.

Give your answer to an appropriate number of significant figures.

One of the ways in which alveoli are adapted to their function is that they secrete a surfactant into the inner lining which also keeps the lining moist.

Give two reasons for secretions of this kind.

Maintaining a high concentration is important to maximise the rate of diffusion across the alveolar surface. 

Describe and explain how a high concentration gradient is maintained between the air in the alveolar space and the blood capillaries that surround an alveolus.

The presence of bronchioles, alveoli and blood capillaries within a lung all reduce its overall volume.

Explain how these structures actually improve the performance of the lung as a gas exchange organ. 

Figure 1 shows three air-breathing animals that evolved at different times of history. 

Figure 1

Place the three animals into a rank order, using the numbers 1-3, for their suggested lung surface area:volume ratios. 

Figure 2 represents Fick's Law of Diffusion.

Figure 2

Join the boxes with straight lines to illustrate which aspect(s) of lung structure and function allows each of the three variables in Fick's Law to be optimised.  

Select the row of the table in Figure 3 that gives the best adaptations for an air-breathing gas exchange system. 

State a reason for your answer. 

Row	Diffusion Pathway	Concentration Gradient	Surface Area
1	High	High	High
2	High	Low	High
3	Low	High	Low
4	Low	High	High

Figure 3

Figure 1 shows ciliated epithelial cells from the airways of a human as seen using a light microscope.

Figure 1

Draw the cell labelled A.

Label three parts of this cell on your diagram.

(4)

State the function of the ciliated epithelial cells in the airways of the human breathing system.

(1)

Figure 2 shows equipment used to investigate the rate of respiration in maggots.

Figure 2

As the maggots respire, the drop of coloured liquid moves towards the test tube.

Figure 3 shows the position of the drop of coloured liquid after ten minutes.

Figure 3

Use information from Figures 2 and 3 to calculate the mean rate of respiration of the maggots in mm per minute.

Explain how alveoli in human lungs are adapted for gas exchange.

Include the names of the gases that are being exchanged.