6.5: Limiting water loss

Question 1

The features that make a good gas exchange system are the same features that do what?

Answer 1

The features that make a good gas exchange system are the same features that increase water loss

Question 2

The features that make a good gas exchange system are the same features that increase water loss.
In order to survive, what does terrestrial organisms do?

Answer 2

In order to survive, terrestrial organisms must limit their water loss without compromising the efficiency of their gas exchange systems

Question 3

Examples of terrestrial organisms

Answer 3

Examples of terrestrial organisms are:

1. Insects
2. Plants

Question 4

Most insects are terrestrial (do what)?

Answer 4

Most insects are terrestrial (live on land)

Question 5

Most insects are terrestrial (live on land).
The problem for all terrestrial organisms is that water easily evaporates from the surface of their bodies and they can become dehydrated.
They have evolved adaptations to conserve water.
However, efficient gas exchange requires a thin, permeable surface with a large area.
What do these features conflict with?

Answer 5

These features conflict with the need to conserve water

Question 6

Insects have evolved the following adaptations that reduce water loss, what?

Answer 6

Insects have evolved the following adaptations that reduce water loss:

1. A small SA:V ratio
2. Waterproof coverings over their body surfaces
3. Spiracles

Question 7

Insects have evolved the following adaptations that reduce water loss - A small SA:V ratio, waterproof coverings over the body surfaces and spiracles.
1. A small SA:V ratio to do what?

Answer 7

A small SA:V ratio to minimise the area over which water is lost

Question 8

Insects have evolved the following adaptations that reduce water loss - A small SA:V ratio, waterproof coverings over the body surfaces and spiracles.
1. A small SA:V ratio to minimise the area over which water is lost.
2. Waterproof coverings over their body surfaces.
In the case of insects, what is this covering?

Answer 8

In the case of insects, this covering is a rigid outer skeleton of chitin

Question 9

Insects have evolved the following adaptations that reduce water loss - A small SA:V ratio, waterproof coverings over the body surfaces and spiracles.
1. A small SA:V ratio to minimise the area over which water is lost.
2. Waterproof coverings over their body surfaces.
In the case of insects, this covering is a rigid outer skeleton of chitin that is covered with what?

Answer 9

In the case of insects, this covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle

Question 10

Insects have evolved the following adaptations that reduce water loss - A small SA:V ratio, waterproof coverings over the body surfaces and spiracles.
1. A small SA:V ratio to minimise the area over which water is lost.
2. Waterproof coverings over their body surfaces.
In the case of insects, this covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle.
3. Spiracles are the openings of the tracheae at the body surface and these can be closed to reduce water loss.
What does this conflict with?

Answer 10

This conflicts with the need for oxygen

Question 11

Insects have evolved the following adaptations that reduce water loss - A small SA:V ratio, waterproof coverings over the body surfaces and spiracles.
1. A small SA:V ratio to minimise the area over which water is lost.
2. Waterproof coverings over their body surfaces.
In the case of insects, this covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle.
3. Spiracles are the openings of the tracheae at the body surface and these can be closed to reduce water loss.
This conflicts with the need for oxygen and so largely occurs when?

Answer 11

This:

1. Conflicts with the need for oxygen
2. So largely occurs when the insect is at rest

Question 12

Insects have evolved the following adaptations that reduce water loss - A small SA:V ratio, waterproof coverings over the body surfaces and spiracles.
1. A small SA:V ratio to minimise the area over which water is lost.
2. Waterproof coverings over their body surfaces.
In the case of insects, this covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle.
3. Spiracles are the openings of the tracheae at the body surface and these can be closed to reduce water loss.
This conflicts with the need for oxygen and so largely occurs when the insect is at rest.
These features mean that insects cannot use the body surface to diffuse respiratory gases in the way a single-celled organism does.
Instead, they have an internal network of tubes called tracheae that carry air containing oxygen directly to what?

Answer 12

Instead, they have an internal network of tubes called tracheae that carry air containing oxygen directly to the muscle tissues

Question 13

While plants also have waterproof coverings, they cannot have a small SA:V ratio.
Why is this?

Answer 13

This is because:

1. Plants photosynthesise
2. Photosynthesis requires a large leaf surface area for the capture of light and for the exchange of gases

Question 14

Xerophytes

Answer 14

Xerophytes are plants that are adapted to living in:

1. Hot and dry environments
2. Areas where water is in short supply

Question 15

Xerophytes are plants that are adapted to living in hot and dry environments and in areas where water is in short supply.
Without these adaptations, what would happen to these plants?

Answer 15

Without these adaptations, these plants would:

1. Become desiccated
2. Die

Question 16

What has leaves with a thick waxy cuticle that reduces water loss?

Answer 16

Holly has leaves with a thick waxy cuticle that reduces water loss

Question 17

What have needle-like leaves to reduce water loss?

Answer 17

Conifers have needle-like leaves to reduce water loss

Question 18

Xerophytes have special adaptations to reduce the rate of transpiration:
1. Reduced leaf area as what?

Answer 18

Reduced leaf area as the leaves are reduced to spines

Question 19

Xerophytes have special adaptations to reduce the rate of transpiration:

1. Reduced leaf area as the leaves are reduced to spines.
2. What to hold water?

Answer 19

Thick, fleshy stems to hold water

Question 20

Xerophytes have special adaptations to reduce the rate of transpiration:

1. Reduced leaf area as the leaves are reduced to spines.
2. Thick, fleshy stems to hold water.
3. What to reflect the Sun?

Answer 20

A silver surface to reflect the Sun

Question 21

What is the scientific name for cacti?

Answer 21

Xerophytes is the scientific name for cacti

Question 22

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
What do examples of these modifications include?

Answer 22

Examples of these modifications include:

1. A very thick waxy cuticle to reduce evaporation
2. Rolling up of leaves
3. Hairy leaves
4. Stomata in pits or grooves
5. A reduced SA:V ratio of the leaves

Question 23

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
1. A very thick waxy cuticle to reduce evaporation:
Although the waxy cuticle on leaves forms a waterproof barrier, up to 10% of water loss can still occur by this route.
The thicker the cuticle, what?

Answer 23

The thicker the cuticle, the less water can escape by this means

Question 24

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
1. A very thick waxy cuticle to reduce evaporation:
Although the waxy cuticle on leaves forms a waterproof barrier, up to 10% of water loss can still occur by this route.
The thicker the cuticle, the less water can escape by this means, for example what?

Answer 24

The thicker the cuticle, the less water can escape by this means, for example holly

Question 25

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
2. Rolling up of leaves:
What does the rolling up of leaves do?

Answer 25

The rolling up of leaves:

1. Reduces the area exposed to the air
2. Keeps the stomata on the inside

Question 26

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
2. Rolling up of leaves:
The rolling up of leaves reduces the area exposed to the air and keeps the stomata on the inside, so increasing what?

Answer 26

The rolling up of leaves:
1. Reduces the area exposed to the air
2. Keeps the stomata on the inside
,so increasing the water vapour inside the roll

Question 27

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
2. Rolling up of leaves:
The rolling up of leaves reduces the area exposed to the air and keeps the stomata on the inside, so increasing the water vapour inside the roll.
What does increasing the water vapour around the stomata do?

Answer 27

Increasing the water vapour around the stomata reduces the water potential gradient

Question 28

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
2. Rolling up of leaves:
The rolling up of leaves reduces the area exposed to the air and keeps the stomata on the inside, so increasing the water vapour inside the roll.
Increasing the water vapour around the stomata reduces the water potential gradient and so does what?

Answer 28

Increasing the water vapour around the stomata:

1. Reduces the water potential gradient
2. So slows water loss

Question 29

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
3. Hairy leaves:
A thick layer of hairs on leaves, especially on the what, traps what air next to the leaf surface?

Answer 29

A thick layer of hairs on leaves, especially on the lower epidermis, traps:
1. Still
2. Moist
3. Saturated
air next to the leaf surface

Question 30

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
3. Hairy leaves:
A thick layer of hairs on leaves, especially on the lower epidermis, traps still, moist, saturated air next to the leaf surface.
What is reduced?

Answer 30

The water potential gradient between:
1. The inside
2. The outside
of the leaves is reduced

Question 31

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
3. Hairy leaves:
A thick layer of hairs on leaves, especially on the lower epidermis, traps still, moist, saturated air next to the leaf surface.
The water potential gradient between the inside and the outside of the leaves is reduced and therefore what?

Answer 31

The water potential gradient between:
1. The inside
2. The outside
of the leaves is reduced and therefore less water is lost by evaporation

Question 32

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
3. Hairy leaves:
A thick layer of hairs on leaves, especially on the lower epidermis, traps still, moist, saturated 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.
What plant has this modification?

Answer 32

One type of heather plant has this modification

Question 33

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
4. Stomata in pits or grooves.
What do stomata in pits or grooves do?

Answer 33

Stomata in pits or grooves again:

1. Trap still, moist air next to the leaf
2. Become saturated or sunken
3. Reduce the water potential gradient

Question 34

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
4. Stomata in pits or grooves.
Stomata in pits or grooves again trap still, moist air next to the leaf, become saturated or sunken and reduce the water potential gradient.
Examples of plants using this mechanism include what?

Answer 34

Examples of plants using this mechanism include pine trees

Question 35

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
5. A reduced SA:V ratio of the leaves.
The smaller the SA:V ratio, the slower the rate of diffusion.
By having leaves that are what, rather than leaves that are what, the rate of water loss can be considerably reduced?

Answer 35

By having:
1. Leaves that are small and roughly circular in cross-section
,rather than
2. Leaves that are broad and flat
,the rate of water loss can be considerably reduced

Question 36

The main way of surviving in habitats where there is a high rate of water loss and a limited water supply is to reduce the rate at which water can be lost through evaporation.
As the vast majority of water loss occurs through the leaves, it is these organs that usually show most modifications.
Examples of these modifications include a very thick waxy cuticle to reduce evaporation, rolling up of leaves, hairy leaves, stomata in pits or grooves and a reduced SA:V ratio of the leaves.
5. A reduced SA:V ratio of the leaves.
The smaller the SA:V ratio, the slower the rate of diffusion.
By having leaves that are small and roughly circular in cross-section, rather than leaves that are broad and flat, the rate of water loss can be considerably reduced.
Examples

Answer 36

For example:

1. Spines
2. Pine needles

Question 37

What does climate change affect?

Answer 37

Climate change affects:

1. Rainfall
2. The rate of evaporation of water

Question 38

Climate change affects rainfall and the rate of evaporation of water.
As a result, what changes?

Answer 38

As a result, the distribution of plant species changes

Question 39

Climate change affects rainfall and the rate of evaporation of water.
As a result, the distribution of plant species changes.
As regions become drier, so what increases?

Answer 39

As regions become drier, so the number of xerophytic plants in them increases