Features that make a good gas exchange system increase water loss:(
Insects:
Water can leave insects through their spiracles. They have evolved the following adaptations to combat water loss:
- Insects are covered in a rigid outer skeleton of chitin that is covered with a waterproof cuticle
- Small surface area to volume ratio to reduce the area over water which can be lost
- Spiracles can be closed to reduce water loss. This occurs mainly at rest as it conflicts with the insects need for gas exchange
Plants:
Water can leave plant leaves through their stomatal pores. They also have waterproof coverings (a waxy cubicle) but cannot have a small surface area to volume ratio as they need a lot of light for photosynthesis. To help reduce water loss plants have the ability to close their stomatal pores when water loss would be excessive. Xeryphytic plants (xerophytes, plants which live in areas where water is in short supply, e.g deserts) have evolved the ability to limit water loss through transpiration by limiting the rate at which water can be lost through evaporation:
- Rolled leaves protect the (lower) epidermis from the outside, trapping a region of highly saturated still air within the rolled leaf. This still air has the same water potential as the inside of the leaf therefore no water loss occurs. - marram grass
- Stomata in pits of grooves again traps still air resulting in no water loss - pine trees
- Thick cuticle means less water can escape - holly
- Hairy leaves trap still, moist air next to the leaf surface meaning less water is lost by evaporation - a type of heather plant
- By having leaves with a circular cross sectional area (reducing the surface area to volume ratio of the leaves) greatly reduces the rate of water loss. However this reduction in surface area is balanced against the need for a sufficient area for photosynthesis. - pine needles
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