Gas Exchange in the Leaf of a Plant

Question 1

What do plant cells require and remove in respiration?

Answer 1

Oxygen is required and carbon dioxide is removed

Question 2

What reduces gas exchange in plant cells?

Answer 2

Some of the products of respiration/photosynthesis are used in photosynthesis/respiration

Question 3

What does the rate of gas exchange in fish rely on?

Answer 3

The balance between the rates of respiration and photosynthesis

Question 4

When photosynthesis is occurring what happens to gas exchange?

Answer 4

• some carbon dioxide comes from respiration but most comes from external air
• some oxygen is used in respiration but most of it diffuses out of the plant

Question 5

When photosynthesis is not occurring what happens to gas exchange?

Answer 5

• oxygen diffuses into the leaf because of the constant need from respiration
• carbon dioxide that is produced in respiration diffuses out

Question 6

Why can plants have rapid gas exchange?

Answer 6

• Because no living cell is far from the external air therefore there is a constant source of both carbon dioxide and respiration
• Diffusion takes place in the gaseous stage which is the most rapid
• Short diffusion pathway

Question 7

How are leaves adapted for gas exchange?

Answer 7

• Many small pores (stomata) so no cell is far away from a stomata keeping diffusion distances small
• Numerous interconnecting air-spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells
• Large surface area of mesophyll cells for rapid diffusion

Question 8

What are the stomata?

Answer 8

Minute pores that occur mainly on the leaves, especially on the underside

Question 9

What is each stoma surrounded by?

Answer 9

A pair of guard cells

Question 10

What do guard cells do?

Answer 10

They open and close the stomatal pore therefore controlling the rate of gas exchange

Question 11

What can guard cells control?

Answer 11

The amount of water loss

Question 12

How do terrestrial organisms lose water?

Answer 12

By evaporation

Question 13

How do guard cells limit water loss?

Answer 13

By closing stomata at times when water loss would be excessive

Question 14

State two similarities between gas exchange in plants and that of a terrestrial insect?

Answer 14

• no living cell is far from the external air
• diffusion takes place in the gas phase
• need to avoid excess water loss
• diffuse air through pores in their outer coverings (they can control the opening and closing of these pores)

Question 15

State two differences between the gas exchange in a plant leaf and that of a terrestrial insect?

Answer 15

• Insects may create mass air flow
• insects have a smaller surface area to volume ratio
• insects have trachea in which gas can diffuse through
• insects do not photosynthesise so cannot interchange gases between respiration and photosynthesis

Question 16

Explain an advantage of a plant being able to open and close the stomata

Answer 16

Helps them control water loss through transpiration and evaporation