Suggest why the frog’s skin must be moist for gaseous exchange to occur.

Frogs respire through their skin, a process known as cutaneous respiration. For this process to occur, the skin must be moist. Here's why:

1. Permeability: The skin of a frog is permeable to gases. This means that gases can pass through it. However, for this to happen, the skin must be moist. The moisture helps in the diffusion of gases.

2. Dissolution of gases: Gases like oxygen and carbon dioxide dissolve in water. When the frog's skin is moist, these gases can dissolve in the thin layer of water on the skin. This dissolved gas can then be absorbed into the frog's bloodstream.

3. Facilitates diffusion: The moisture on the frog's skin also facilitates the diffusion of gases. Gases move from an area of high concentration to an area of low concentration. The moisture helps in this movement of gases.

4. Protection: The moisture on the frog's skin also protects it from drying out. If the skin dries out, it can become less permeable to gases, hindering the frog's ability to respire.

In conclusion, the moisture on a frog's skin is crucial for gaseous exchange because it aids in the permeability of the skin, the dissolution and diffusion of gases, and it helps to keep the skin from drying out.