Gas exchange in plants and limiting water loss

Question 1

Explain why plants have a reduced need for gas exchange with the air than animals

Answer 1

they produce oxygen during photosynthesis which can be used in respiration

Question 2

Describe gas exchange in a plant when photosynthesis is taking place

Answer 2

CO2 moves into the leaf (for photosynthesis) and O2 moves out (some of it, the rest is used in respiration)

Question 3

Describe gas exchange in a plant when photosynthesis is not taking place

Answer 3

oxygen diffuses into the leaf for respiration, carbon dioxide diffuses out

Question 4

How do plants ensure a large surface area:volume?

Answer 4

air spaces inside the leaf

Question 5

Describe 3 adaptations of a leaf for rapid diffusion

Answer 5

many stomata - short diffusion pathway
air spaces in mesophyll - gases in close contact with cell
large surface area of mesophyll cells

Question 6

Describe the conflict between gas exchange and water loss in plants

Answer 6

plants need stomata open to exchange gases during photosynthesis but also lose more water when stomata are open

Question 7

How does a thick cuticle limit water loss in plants?

Answer 7

Less water can escape the leaf (via transpiration)

Question 8

How do hairy leaves and stomata in pits/grooves limit water loss in plants?

Answer 8

hairs on leaves trap moist air next to the leaf surface. This reduces the water potential gradient and therefore limits the water lost

Question 9

How does the rolling up of leaves limit water loss in plants?

Answer 9

Stomata are on the lower epidermis- the leaves roll up in a way which protects the lower epidermis and traps still air. This reduces water potential gradient, limiting water loss

Question 10

How does a reduced SA to volume ratio limit water loss in plants?

Answer 10

Smaller surface area leads to limited diffusion. This has to be balanced with the need for a larger surface area for light absorption for photosynthesis

Question 11

Give 2 ways gas exchange is similar in insects and plants?

Answer 11

• no living cell is far from external air
• diffusion takes place in gas phase (more rapid)

Question 12

Give 2 ways gas exchange is different in insects and plants?

Answer 12

• insects have smaller SA to volume ratio
• insects do not interchange gases from photosynthesis
• insects have trachae, plants do not

Question 13

How are plants adapted for efficient gas exchange?

Answer 13

• numerous air spaces throughout mesophyll cells
• large SA of mesophyll cells
• many stomata

Question 14

Why is gas exchange needed in all organisms (not just plants)?

Answer 14

• some substances from the environment are needed in processed within cells
• waste products need to be removed, or else they could be harmful

Question 15

What is a xerophyte?

Answer 15

a plant that is adapted to survive in environments with little water

Question 16

Why is no CO2 taken in by plants in the dark?

Answer 16

• no photosynthesis that uses CO2
• so diffusion gradient isn’t maintained