Plant Homeostasis - Xerophytes

Question 1

What are xerophytes?

Answer 1

A plant that has adapted to live in arid environments. It has developed specialised features that minimise water loss, while maintain gas exchange.

Question 2

Where is water gained in plants?

Answer 2

Through root hairs.

Question 3

How is water lost in plants?

Answer 3

By the evaporation from surfaces and through transpiration through stomata.

Question 4

Describe the 7 steps of the uptake of water in plants.

Answer 4

1. Water moves into root cells’ hairs by osmosis.
2. From a low solute concentration to a high solution concentration.
3. Across a semi-permeable cell membrane.
4. Passive process.
5. Water moves along a concentration gradient.
6. Concentration gradient is due to higher cell solute concentration than in soil.
7. Solutes move into roots by active transport.

Question 5

Why do plants need water?

Answer 5

Photosynthesis.

Question 6

What is the equation for photosynthesis?

Answer 6

CO2 + H2O > C6H12O6 + O2

Question 7

Define transpiration.

Answer 7

The evaorative loss of water from plants usually through small pores called stomata found on the inside of leaves.

Question 8

Describe the 5 points of why transpiration is important.

Answer 8

1. Transpiration supplies photosynthesis with the water it needs.
2. The evaporation from mesophyll cells in the leaves that accompanies transpiration requires energy and therefore cools the plants.
3. Transpiration stream is necessary for distributing mineral salts throughout the plant.
4. Dissolving gases for exchange.
5. Gaurd cells control water and gas exchange.

Question 9

Describe gas exchange in guard cells

Answer 9

When turgid thin walls stretch more than thicker ones causing them to open. When they lose water they begin to close up reducing gas exchange. They need to take in carbon dioxide for photosynthesis and need to get rid of oxygen.

Question 10

List 6 factors affecting the rate of transpiration.

Answer 10

1. Temperature.
2. Wind.
3. Humidity.
4. Light.
5. Surface area.
6. Soil water.

Question 11

Describe temperature as a factor affecting transpiration.

Answer 11

An increase in temperature increases the evaporation rate because of an increase in the water vapour concentration gradient between the air at the surface and outside the leaf.

Question 12

Describe wind as a factor affecting transpiration.

Answer 12

An increase in winds leads to an increase in evaporation, which leads to an increase in the rate of transpiration because air is being carried away.

Question 13

Describe humidity as a factor affecting transpiration.

Answer 13

A decrease in humidity leads to a higher water vapour concentration gradient between the air at the surface and outside the leaf. This increases the diffusion of water vapour out of the leaf.

Question 14

Describe light as a factor affecting transpiration.

Answer 14

An increase in sunlight leads to an increase in transpiration. Warming the leaf can open the stomata causing transpiration.

Question 15

List 6 structural adaptations of xerophytes.

Answer 15

1. Reduction in leaf surface area.
2. Sunken stomata.
3. Deep roots.
4. Rolled leaves.
5. Thick waxy leaf cuticle.
6. Shallow spreading roots.

Question 16

List 2 physiological adaptations of xerophytes.

Answer 16

1. Stomata opening at night.
2. Storage of water in succulent tissues.

Question 17

Describe a reduction in leaf surface area as a structural adaptation.

Answer 17

Leaves may be reduced to spines or be long and narrow reducing the area of transpiration. There may be a reduced number of stomata. Small leaf surface reduces evaporation and water loss.

Question 18

Describe sunken stomata as a structural adaptation.

Answer 18

Prevent water loss by increasing the relative humidity near each stoma. It decreases concentration gradient, evaporation and diffusion. This creates a microclimate.

Question 19

Describe deep roots as a structural adaptation.

Answer 19

Reach water resources underground such as a water table. This increases water uptake preventing dehydration.

Question 20

Describe rolled leaves as a structural adaptation.

Answer 20

Rolled leaves and hair both serve to trap moist air. This reduces the concentration gradient and diffusion rate of water vapour and the evaporation and transpiration rate.

Question 21

Describe a thick waxy leaf cuticle as a structural adaptation.

Answer 21

Is impermeable to water, preventing evaporation and water loss. The cuticle can reflect light, reducing the amount of light absorbed and preventing an increase in the transpiration rate.

Question 22

Describe shallow spreading roots as a structural adaptation.

Answer 22

Collect occasional rainfall and increase water uptake. Reduce the risk of dehydration of the plant.

Question 23

Describe stomata opening at night as a physiological adaptation.

Answer 23

Assists in water loss because stomata are closed during the hottest part of the day reducing transpiration and evaporation.

Question 24

Describe the storage of water in succulent tissues as a physiological adaptation.

Answer 24

Plants store water in fleshy stems or leaves for use during dry periods. This reduces water loss during hot dry periods.