1.1. Table 1 compares the features of the human gas exchange system. 

Complete the table by putting a tick (✓) in each box if the feature is present and a cross (×) if the feature is absent in each structure. 

The first row has been done for you. 

Table 1

1.2. Complete the following sentences about the gas exchange system. 

Choose the correct words from the list below.

Ciliated epithelial cells have projections called ............... .

The role of these projections is to sweep ............... , dust and mucus out of the ............... .

The dust and mucus are swept towards the ............... where they can be ............... and destroyed by stomach acid. 

1.3. Fig. 1 shows different structures in the human airways viewed in cross section under a light microscope.

Fig. 1

Identify the structures labelled B in Fig. 1 and name the process that takes place here.

1.4. Explain one function of structure A in Fig. 1.