6.5 Limiting Water Loss

Question 1

How do insects limit their water loss?

Answer 1

1. Small SA: volume ratio
2. Waterproof coverings consisting of rigid outer skeleton of chitin covered with a waterproof cuticle
3. Spiracles that can open and close (although closing them conflicts with need for oxygen so mostly occurs when the insect is at rest)

Question 2

Why do insects need to limit water loss?

Answer 2

Insects are terrestrial, thus water easily evaporates from the surface of their bodies and they can get dehydrated. Need for a thin, permeable surface for gas exchange conflicts with limiting water loss so a balance has to be found

Question 3

Why can plants not have a small SA to limit water loss?

Answer 3

They require a large SA for photosynthesis

Question 4

What are xerophytes?

Answer 4

Plants that have adapted to limit water loss by transpiration due to a restricted supply

Question 5

What are some ways in which xerophytes conserve water?

Answer 5

1. A thick cuticle to stop water ecsaping
2. Rolling up of leaves as stomata (located mostly on the lower epidermis) have still hair that becomes saturated with water and gains a high water potential next to them. This means there’s no water potential gradient thus water does not diffuse out of the plant
3. Hairy leaves trap still, moist air next to the leaf, especially the underside, lowering water potential gradient
4. Stomata in pits and grooves to trap still, moist air and lower the water potential gradient
5. Reduced SA to volume ratio of leaves to reduce water loss. An example is pine needles as leaves on cacti