Gas Exchange in Plants

Question 1

Properties of gas exchange

Answer 1

• Large surface area
• Thin (one layer of epithelial cells) - provide short diffusion pathway across gas exchange surface

Question 2

What does the organism do for gases across exchange surface?

Answer 2

Maintain concentration gradient

Question 3

How does single-celled organisms utilise diffusion?

Answer 3

Absorb and release gases by diffusion through their outer surface

Question 4

Why does single-celled organisms not need gas exchange?

Answer 4

• Large surface area
• Short diffusion pathway
  *

Question 5

Why do plants need O2?

Answer 5

For respiration

produces CO2 as a waste product

Question 6

What is the main gas exchange surface for leaf?

Answer 6

Surface of mesophyll cells in leaf

-well adapted for their function

Large surface area

Question 7

How do gases move in mesophyll cells?

Answer 7

They are found inside the cells

Gases move in and out of pores in epidermis called stomata

Question 8

What can stomata control?

Answer 8

They can open to allow exchange of gases and close if the plant is losing too much later

Guard cells control the opening and closing of stomata

Question 9

What is the unfortunate consequence of exchanging gases?

Answer 9

Lose water

Question 10

How are insects specialised if they are losing too much water through exchanging gases?

Answer 10

• They close their spiracles using muscles
• Waterproof waxy cuticles all around body and tiny hairs around spiracles to reduce evaporation

Question 11

Are plants stomata open during gas exchange?

Answer 11

Yes

Question 12

How does water enter through plants stomata?

Answer 12

Water entering guard cells making them turgrid which opens stomatal pore

Question 13

What happens if the plant is dehydrated with gas exchange?

Answer 13

If plants start to dehydrate, the guard cells lose water and become flaccid - close pore

Question 14

What plants is this a problem for water loss?

Answer 14

Xerophytes- plants live in dry/windy habitats

Question 15

Following adaptations for xerophytic plants

Answer 15

• Stomata
• Layer of hairs on epidmeris
• Curled leaves
• Reduced number of stomata
• Waxy , waterproof cuticles

Question 16

How is stomata adapted for xerophytic plants?

Answer 16

Sunk in pits trap moist air - reducing concentration gradient of water between leaf and air

Reduce the amount of water diffusing out of the leaf and evaporating away

Question 17

How is their layer of hair around epidermis adapted for xerophytic plants?

Answer 17

Trap moist air around the stomata

Question 18

How is curled leaves with stomata inside the xerophytic plants adapted?

Answer 18

Protecting them from wind

windy conditions increase rate of diffusion and evaporation

Question 19

How is the reduced number of stomata adapted for xerophytic plants?

Answer 19

Fewer places for water to escape

Question 20

How having waxy, waterproof cuticles on leaves adapted for xerophytic plants?

Answer 20

reduce evaporation

Question 21

Species C has a high number of stomata per mm²

Despite this it loses a small amount of water

Use this data to explain why:

Answer 21

It is thick so huge diffusion distance pathway

Question 22

Suggest an appropriate units the student should use to compare the distribution of stomata on leaves

Answer 22

Stomata per millimetre per squared

Question 23

The pieces of leaf were very thin. Explain why this was important.

Answer 23

This allows the light to pass through

This means you can view it properly under the optical microscope

Question 24

Give two reasons why it was important to count the number of stomata in several parts of each pieces of leaf tissue

Answer 24

• Very accurate
• It won’t be the same number of stomata

Question 25

Suggest two reasons why the rate of water uptake by plants might not be the same as the rate of transpiration

Answer 25

• Water used in photosynthesis
• Water is produced in respiration

Question 26

Treatment 2 shows that even when the lower surface of the leaf is sealed there is still some uptake of carbon dioxide

Suggest how this uptake of carbon dioxide continues

Answer 26

CO2 uptake through the upper surface

Question 27

In both treatment 1 and 2 , the uptake of carbon dioxide falls to zero when the light is turned off

Answer 27

CO2 used in photosynthesis

it is not anymore

Question 28

What happens when the plant has a lot of H20?

Answer 28

Guard cells are turgid

Question 29

State the two similarities between gas exchange in plants leaf and gas exchange in an insect

Answer 29

• Diffusion takes place in gas phase
• Need to avoid excessive water loss

Question 30

State two differences between gas exchange in leaf and insect

Answer 30

• Insects has smaller surface area to volume raito
• Insects do not interchange gases between respiration and photosynthesis - plants do
• Insects has trachae along which gases diffuse - plants do not

Question 31

Explain the advantage of a plant of being able to control the opening and closing of the stomata

Answer 31

Helps to control the water loss by evaporation/transpiration