6.5 Limiting water loss

Question 1

What is the problem for all terrestrial organisms

Answer 1

That water easily evaporates from the surface of their bodies and they easily become dehydrated

Question 2

What adaptations have insects evolved to reduce water loss

Answer 2

1. Small surface area to volume ratio - this minimises the area over which water is lost
2. Waterproof coverings over their body surfaces. In the case of insects this is a rigid outer skeleton of chitin that is covered with a waterproof cuticle
3. Spiracles - openings of the tracheae and can be closed to reduce water loss.

Question 3

How do plants limit water loss

Answer 3

By having a waterproof covering over parts of the leaves and the ability to close stomata when necessary

Question 4

What are xerophytes

Answer 4

Plants that are adapted to living in areas where water is in short supply

Question 5

What is the main way of surviving in habitats where there is a high rate of water loss and limited water supply

Answer 5

Reducing the rate at which water can be lost through evaporation

Question 6

Why do leaves have the most modifications

Answer 6

Because that is where most water is lost

Question 7

What are some examples of modifications

Answer 7

1. A thick cuticle - Waxy cuticle on leaves forms a waterproof barrier
2. Rolling up of leaves - Protects the lower epidermis from the outside, helps trap a region of still air which becomes saturated with water. therefore no gradient forms and water isnt lost from the leaf
3. Hairy leaves - a thick layer of hairs on leaves, these trap still and moist air next to the leaf surface. The water potential gradient between the inside and the outside of the leaves is reduced and therefore less water is lost by evaporation
4. Stomata in pits or grooves. These again trap still, moist air next to the leaf and reduce the water potential gradient.
5. A reduced surface area to voume ratio of the leaves. Leaves that are thin and circular in cross-section. This is balanced with photosynthesis needs