Limiting Water Loss

Question 1

Where can problems arise in creating efficient gas exchange systems?

Answer 1

Features that make gas exchange systems efficient also make organisms efficient at losing water

Question 2

Why is the air at exchange surfaces saturated with?

Answer 2

About 100% saturated with water vapour so less water evaporates from exchange surfaces

Question 3

What adaptions do insects have that allow them to reduce water loss?

Answer 3

• small surface area to volume ratio
• waterproof coverings
• spiracles

Question 4

How does a small surface area to volume ratio limit water loss?

Answer 4

It minimises the area over which water is lost

Question 5

What is the waterproof covering that covers insects?

Answer 5

The rigid chitin outer skeleton is covered with a waterproof cuticle

Question 6

How do spiracles reduce water loss?

Answer 6

They open and close to reduce water loss

Question 7

What do the features that reduce water in insects mean for their ability to diffuse gases?

Answer 7

They cannot use their body surface respiratory gases, they use their trachea instead

Question 8

How do plants limit water?

Answer 8

• they have a waterproof covering covering parts of the leaves
• they have the ability to close and open their stomata

Question 9

What can xerophytes do?

Answer 9

Limit loss through transpiration

Question 10

What are xerophyte?

Answer 10

They are plants adapted to living in areas where water is in short supply

Question 11

What is the main way in which xerophytes limit water loss?

Answer 11

Limit loss of water through evaporation

Question 12

What modifications do xerophytes have that allow them to limit water loss?

Answer 12

• a thick cuticle
• rolling up of leaves
• hairy leaves
• stomata in pits or grooves
• a reduced surface area to volume ratio in leaves

Question 13

How does a thick cuticle limit water loss in xerophytes?

Answer 13

The waxy cuticle on leaves forms a waterproof barrier and the thicker the leaves, the more effective the barrier

Question 14

How does rolling leaves up limit water loss in xerophytes?

Answer 14

Most leaves have the stomata on the the lower epidermis, the rolling of leaves protects the lower epidermis and traps a layer of still air within the leaf, this region have a very high water potential so their is no loss of water because their is no water potential gradient

Question 15

How do hairy leaves limit water loss in xerophytes?

Answer 15

It traps moist air next to the leaf surface reducing the concentration gradient between the inside and the outside of the leaf therefore reducing water loss

Question 16

How do stomata in pits or grooves limit water loss in xerophytes?

Answer 16

They trap moist air next to the leaf reducing the water potential gradient

Question 17

How does a reduced surface area to volume ratio limit water loss in xerophytes?

Answer 17

The smaller the surface area to volume ratio the slower the rate of diffusion, the reduction in surface area has to be balanced against the need for sufficient area for photosynthesis to meet the requirements of the plant

Question 18

What is the main problem insects and plants face when living on land?

Answer 18

Efficient gas exchange requires a thin, permeable surface with a large area and on land these features can lead to a considerable loss of water by evaporation

Question 19

State one modification to reduce water loss that is shared by plants and animals

Answer 19

Waterproof covering to the body and ability to close and open their gas exchange systems

Question 20

How do insects limit water loss and why is this method not feasible in plants?

Answer 20

By having a small surface area to volume ratio this is not feasible in plants because plants photosynthesise and need a large surface area to capture light

Question 21

Explain how the rolling of leaves helps to reduce water loss?

Answer 21

Water evaporation from the leaf is trapped making the region within the rolled up leaf saturated with water vapour there is then no water potential gradient and no water will diffuse out

Question 22

Explain why rolling leaves with the upper epidermis on the outside is not feasible

Answer 22

Almost all stomata are on the underside of the leaf therefore they will be exposed to air currents what will reduce the water potential immediately outside the leaf increasing the water potential gradient and maximising water loss