Water Loss

Question 1

What is the main gas exchange surface of plants?

Answer 1

Surface of mesophyll cells in the leaf, they have a large surface area.

Question 2

What do plants require CO2 for?

Answer 2

• Photosynthesis, which produces O2

* O2 is used in respiration

Question 3

How can gas exchange be detrimental to plants and insects?

Answer 3

Exchanging gasses causes insects and plants to lose water.

Question 4

What does efficient gas exchange require?

Answer 4

Thin permeable surface with a large area, this feature however also can cause water loss

Question 5

What adaptations have insects evolved to reduce water loss?

Answer 5

• Small surface area to volume ratio, this minimises the area over which water is lost
• water proof coverings, this covering is a rigid outer skeleton of chitin that is covered with a waterproof cuticle
• Spiracles, these openings of the tracheae at the body surface can be closed to reduce water loss, this however can conflict with the need for oxygen and is used when the oxygen is at rest.

Question 6

How is waterproofing present in insects?

Answer 6

Rigid outer skeleton of chitin that is covered with a waterproof cuticle

Question 7

How do spiracles prevent water loss?

Answer 7

• Spiracles, these openings of the tracheae at the body surface can be closed to reduce water loss.
• This however can conflict with the need for oxygen and is used when the oxygen is at rest.

Question 8

What is a disadvantage to the features that insects have evolved for water loss prevention?

Answer 8

• They can not use their body surface to diffuse respiratory gasses in the way a single celled organism can.
• They have had to evolve an internal networks of tracheae that carry air containing oxygen directly to the tissues

Question 9

Why can plants not have a small surface area to volume ratio?

Answer 9

• Plants undergo photosynthesis

* For photosynthesis to be effective, it requires a large leaf surface area for the capture of light and gas exchange

Question 10

How do plants reduce water loss?

Answer 10

• Plants have a waterproof covering over parts of the leaves

* Ability to close stomata when necessary

Question 11

What are xerophytes?

Answer 11

• Plants that are specially adapted for life in warm, dry or windy habitats where water loss is a problem, and water is in short supply
• Plants that have evolved adaptations to limit water loss through transpiration

Question 12

What is required for plants to survive in habitats where there is a large amount of water loss, and low water supply?

Answer 12

Reduce the rate of water loss

Question 13

What part of the plant does most water loss occur through?

Answer 13

Leaves, and therefore most of the adaptations occur here

Question 14

What are some examples of adaptations of xerophytes?

Answer 14

• Thick Cuticle
• Rolling Up of Leaves
• Hairy Leaves
• Stomata in pits/grooves
• Reduce surface area to volume ratio of leaves

Question 15

How does a thick cuticle prevent water loss?

Answer 15

• Waxy, and waterproof cuticles on leaves and stems reduce evaporation
• The thicker the cuticle, the less water can escape

Question 16

How does rolling up of leaves reduce water loss?

Answer 16

• Rolling up of leaves in a way that protects the lower epidermis helps to trap a region of air within the rolled leaf
• This region becomes saturated with water vapour and so has a very high water potential. this traps moist air around the stomata.
• There is no water potential gradient between the inside and outside of the leave, and therefore no water loss can occur

Question 17

How do hair leaves reduce water loss?

Answer 17

• Thick layer of hairs on leaves, on the lower dermis traps moist air next to the leaf surface
• The water potential gradient between the inside and outside of the leaves is reduced, and less water is lost by evaporation

Question 18

How do grooved stomata reduce water loss?

Answer 18

• Trap moist air next to the leaf and reduce the water potential gradient, this reduces the amount of water diffusing out of the leaf and evaporating away

Question 19

How does a reduced surface area to volume ratio reduce water loss?

Answer 19

• Smaller the surface area to volume ratio, the slower the rate of diffusion
• Small circular leaves reduces the surface area to volume ratio, which reduces the rate of water loss
• The reduction in surface area is balanced against the need for a sufficient area for photosynthesis to meet the requirements for the plants

Question 20

How does a reduced number of stomata reduce water loss?

Answer 20

• Fewer places for water to escape

Question 21

Why are stomata kept open during the day?

Answer 21

To allow gas exchange to take place

Question 22

How are the stomata opened?

Answer 22

• Water enters the guard cells making them turgid
• This will open the stomatal pore
• If the plant starts to get dehydrated, the guard cells lose water and become flaccid, which closes the pore