Question

1.evaginated gas exchange surface - a thin flap of the body wall extends outward for gas exchange. This is only found in water living animals. Why? 2. invaginated gas exchange surface - the gas exchange surface is within the body but connected by passages to the outside environment. This is the usual respiratory system for a terrestrial animal. Why? Observe the demonstration of crayfish gills. Note their feathery appearance. This feathery nature greatly increases their surface area. Why is this important?

Answer 1

1.In the aquatic environment, there is no difficulty of drying of the respiratory surfaces. Because they are always surrounded by water.The respiratory surfaces of the body are always moist and help in gas exchange. Water also is important in keeping the thin respiratory surfaces separate , so that they do not stick to one another. This allows the water to pass through all the layers of the respiratory surface for beteer exchange of gases.

2.The respiratory surfaces always need to be thin, moist and should have more surface area. In the terrestrial environment, the respiratory surfaces are internalised in to the body. This is because, in the terrestrial environment, there is the danger of the surfaces getting completely dried. Dry surfaces can't help in exchange of gases. So the respiratory surfaces are internalised deep inside, so that they are not exposed to environment and moisture is conserved on the surfaces. This helps in exchang eof gases.

Respiratory surfaces always should have large surface area. More surface area will allow more exchange of gases.

Less surface area will result in less exchange of gases. That is the reason why the cray fish gills are feathery as it increases the gill surfaces to increase the area for gas exchange.