Gas exchange in flowering plants

Question 1

How do plants exchange gases

Answer 1

By diffusion

Question 2

What are the main gases that move in and out of plants?

Answer 2

CO2 and O2 (photosynthesis and respiration)

Question 3

How does diffusion take place during photosynthesis?

Answer 3

• When a plant is photosynthesising it uses up lots of CO2 inside the plant making more CO2 move into the leaf by diffusion.
• Lots of O2 is being made as a waste product of photosynthesis. Some is used in respiration ans rest diffuses out through the stomata

Question 4

What does the net exchange of gases depend on?

Answer 4

Light intensity

Question 5

When does photosynthesis take place?

Answer 5

During the day when there is light available

Question 6

When do plants respire?

Answer 6

They need to all the time - night and day - to get the energy they need to live

Question 7

What happens during the day when light intensity is high?

Answer 7

• Oxygen is released and carbon dioxide is taken in

Plants make more oxygen by photosynthesis than they use in respiration and use up more carbon dioxide than they produce

Question 8

What happens during the night when there is no light?

Answer 8

• Oxygen is taken in and carbon dioxide is released

Plants only respire as there is not enough light for photosynthesis to take place

Question 9

What are adapted for efficient gas exchange?

Answer 9

Leaves

Question 10

Give some adaptions of leaves?

Answer 10

• Broad - large sa for diffusion
• Thin - gases travel short distance only
• Air sacs inside leaf - increase sa, gases move easily between cells
• Lower epidermis have stomata - they let gases diffuse out and allow water to escape via transpiration

Question 11

Why do the stomata close when its dark?

Answer 11

Photosynthesis cannot happen in the dark so they do not need to let in CO2. Also water cannot escape when the stomata are closed to this stops the plant drying out

Question 12

When else do the stomata close other than when its dark?

Answer 12

When supplies of water from the roots start to dry up - this stops the plant from photosynthesising and drying up and dying

Question 13

What is the opening and closing of the stomata controlled by?

Answer 13

The guard cells that surround them

Question 14

What does hydrogen-carbonate indicator show?

Answer 14

Changes in CO2 concentration

Question 15

What colour is the hydrogen-carbonate indicator in air with normal CO2 concentration?

Answer 15

Orange

Question 16

What happens to the hydrogen-carbonate indicator when CO2 concentration of air increases?

Answer 16

It changes colour to yellow - more CO2 will dissolve

Question 17

What happens to the hydrogen-carbonate indicator when CO2 concentration of air decreases?

Answer 17

It changes colour to purple - CO2 will come out of solution

Question 18

Describe an experiment to show how light effects gas exchange

Answer 18

• Add the same volume of hydrogen-carbonate indicator to four boiling tubes
• Put similar sized healthy leaves into three of the tubes and seal with a rubber bung
• Leave the forth tube empty (control tube)
• Wrap one tube in aluminium foil and the other in a gauze
• Place all tubes in bright light and leave for an hour

Question 19

What would you expect in the control tube?

Answer 19

No change in the colour of hydrogen-carbonate indicator (stays orange)

Question 20

What would you expect in the tube with aluminium wrapped around it?

Answer 20

Hydrogen-carbonate indicator should change to yellow - respiration is still taking place but no photosynthesis so the CO2 concentration increases

Question 21

What would you expect in the tube with gauze wrapped around it?

Answer 21

The hydrogen-carbonate indicator would stay a similar colour (so orange) - with a little photosynthesis and some respiration taking place as equal amounts of CO2 are being taken up and produced by the leaf

Question 22

What would you expect in the tube with nothing covering it?

Answer 22

The hydrogen-carbonate indicator should change to purple - there will be some respiration but lots of photosynthesis leading to a net uptake of CO2 by the leaf meaning a lower CO2 concentration in the tube