Section 4 - Respiration and Gas Exchange P2

Question 1

Gas exchange in plants happen by what process?

Answer 1

Diffusion

Question 2

What does diffusion do to carbon dioxide and oxygen when a plant is photosynthesising?

Answer 2

• lower concentration of carbon dioxide inside the plant that outside (so carbon dioxide diffuses in)
• higher concentration of oxygen inside the plant than outside (so oxygen diffuses out)

Question 3

What does the net exchange of gases in plants depend on?

Answer 3

Light intensity

Question 4

When do plants photosynthesise?

Answer 4

In the day (when there’s light)

Question 5

When do plants respire?

Answer 5

All the time (because they need energy to live)

Question 6

Describe the net exchange of gases during the day in plants:

Answer 6

(light intensity is high)
-plants make more oxygen than they use
(release oxygen and take up carbon dioxide)

Question 7

Describe the net exchange of gases during the night in plants:

Answer 7

(light intensity is low)
-plants only respire
(take in oxygen and release carbon dioxide)

Question 8

How are leaves adapted for efficient gas exchange?

Answer 8

• leaves are broad (large surface area for diffusion)
• leaves are thin (short diffusion distance)
• there are air spaces within a leaf (increase surface area for gas exchange
• lower surface full of stomata (let gases diffuse and water to escape)
• stomata close when it’s dark (stops plant drying out)
• stomata close when water supply dries up (stops photosynthesis, more importantly stops drying out

Question 9

What controls the opening and closing of the stomata?

Answer 9

Guard cells

Question 10

How do guard cells open and close the stomata?

Answer 10

By changing their shape and volume

• increase in volume to open stomata
• decrease in volume to close the stomata

Question 11

What are the colour changes of Hydrogen-carbonate indicator? (in terms of carbon dioxide concentration)

Answer 11

• normal carbon dioxide concentration - ORANGE
• high carbon dioxide concentration - YELLOW
• low carbon dioxide concentration - PURPLE

Question 12

Describe an experiment for how you can use Hydrogen-carbonate indicator to investigate the effects of light on gas exchange:

Answer 12

• add the same volume of indicator to 4 boiling tubes
• put a leaf in 3 of the tubes and seal all 4 with bungs
• tube 1 is just the control (no leaf) [stay orange]
• tube 2 wrapped in foil [yellow, more carbon dioxide]
• tube 3 wrapped in gauze [orange, no net change]
• tube 4 uncovered [purple, less carbon dioxide]