Gas Exchange: Plants

Question 1

What is the relationship between photosynthesis and respiration in plants?

Answer 1

The oxygen produced by photosynthesis can be used by respiring cells and the carbon dioxide produced by respiration can be used in photosynthesis.

Question 2

Why must gas exchange occur with external air aswell as those produced in respiration or photosynthesis?

Answer 2

Because the rates of photosynthesis change throughout the day based on conditions such as light level.

Question 3

What happens to the rate of photosynthesis compared to respiration in plants at night?

Answer 3

It is lower than respiration.

Question 4

When is external gas exchange necessary?

Answer 4

When the rates of photosynthesis and respiration are different.

Question 5

When are the rates of photosynthesis and respiration the same?

Answer 5

They are only the same for a very small time, (maybe a few minutes).

Question 6

How are the leaves adapted for rapid diffusion of gases?

Answer 6

1) Many stomata - short diffusion distance.
2) Many interconnecting air spaces - in spongy mesophyll so gases are in contact with mesophyll.
3) Large surface area of mesophyll cells - allows rapid diffusion.

Question 7

At what part of the plant does gas exchange occur in mostly?

Answer 7

The leaves.

Question 8

What happens to the rate of photosynthesis compared to respiration in plants in the day?

Answer 8

It is higher than respiration.

Question 9

What are stomata?

Answer 9

Small pores found on the underside of a leaf.

Question 10

What surrounds the stomata?

Answer 10

Guard cells.

Question 11

Where can you find stomata?

Answer 11

They are located in the lower epidermis.

Question 12

What is the function of the stomata?

Answer 12

Their openings control the rate of gas exchange and limit the water loss through transpiration.

Question 13

What controls the stomatal openings?

Answer 13

Guard cells.

Question 14

What is the relationship between the cuticle and water loss?

Answer 14

The waxier the cuticle, the less water escapes.

Question 15

What is the function of a thick, waxy cuticle?

Answer 15

It forms a waterproof barrier to reduce water loss.

Question 16

What adaptations do the plants have to limit water loss?

Answer 16

• Thick, waxy cuticle.
• Rolling up the leaves.
• Hairy leaves.
• Stomata in pits and grooves.
• Reduced leaf SA:V.

Question 17

What does a reduced SA:V ratio mean for water loss?

Answer 17

The slower the rate of diffusion, thus the rate of water loss.

Question 18

How does rolling up the leaves aid water retention?

Answer 18

The stoma are found in the lower epidermis, rolling the leaves helps to trap a region of still air full of water vapour and thus a very high water potential, causing no water potential gradient meaning less water loss.

Question 19

How is the SA:V ratio reduced by the leaf?

Answer 19

This is achieved through small circular leaves rather than broad, flat leaves.

Question 20

How do hairy leaves help water loss?

Answer 20

The hairy leaves trap still, moist air next to the leaf surface, this reduces water potential gradient which reduces water loss.

Question 21

How do stomata in pits and grooves help water loss?

Answer 21

This traps still, moist air outside the leaf which again reduces water potential gradient.

Question 22

Where is the main gas exchange surface within the leaf?

Answer 22

The surface of mesophyll cells.

Question 23

What key feature of gas exchange is held in the lower epidermis?

Answer 23

Stomata.

Question 24

What happens to the guard cells when the cell is losing too much water?

Answer 24

They get dehydrated, lose water and come flaccid, closing the pore.

Question 25

What happens to the guard cells when the cell needs to lose water?

Answer 25

Water enters the guard cells and causes them to become turgid, opening the stomatal pores.