Gas Exchange Plants

Question 1

What does the amount and type of gasses that plants exchange depend upon?

Answer 1

Rate of:
• Photosynthesis
• Respiration
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• Plants require CO2 for photosynthesis, and produce oxygen
• Plants require O2 for respiration, and produce Carbon Dioxide
This also reduces gas exchange with atmosphere, as gasses produced in one process can be used in another

Question 2

What happens to the oxygen & carbon dioxide in plants?

Answer 2

• During photosynthesis, some of the CO2 comes from the respiration of cells, but most of it is from the external air
• Some oxygen from photosynthesis is used in respiration, however most of it diffuses out of the plant

Question 3

Where is the oxygen & dioxide supplied from when photosynthesis is not occurring?

Answer 3

• oxygen diffuses into the leaf because it is being constantly used by cells during respiration
• Carbon dioxide produced during respiration diffuses out, because there is no photosynthesis occurring

Question 4

In what ways is gas exchange in plants similar to insects?

Answer 4

• Diffusion takes place in gas phase ( air / gas ), which makes rate of diffusion faster than if it were in water
• No living cell is far from the external air ( a source of oxygen and carbon dioxide )
• No specific transport system for gasses, they move in through the plant via diffusion

Question 5

How long is the diffusion pathway of leafs?

Answer 5

Short

Question 6

What is the surface area to volume ratio of leaf compared to tissue?

Answer 6

• Large surface area to volume ratio compared to the volume of tissue

Question 7

What is the site of gas exchange in plants?

Answer 7

Leaves

Question 8

What adaptations do leaves have for diffusion?

Answer 8

• Many stomata ( small pores ), no cell is far from stomata, and therefore the diffusion pathway is short
• Numerous interconnecting air spaces that occur throughout the mespophyll so gases can readily come in contact with mesophyll cells
• Large surface area of mesophyll cells for rapid diffusion

Question 9

What are stomata?

Answer 9

• Stomata are small pores, that mainly appear on the leaves ( typically the underside ).
• Each stoma is surrounded by a pair of guard cells

Question 10

What is the purpose of the guard cells?

Answer 10

• Can open and close the stomatal pore

* They can then control the rate of gaseous exchange

Question 11

How can plants control the rate of gas exchange?

Answer 11

• They have special guard cells which can open and close the stomatal pore
• They can therefore then control the rate of gas exchange

Question 12

Why is it important to control the rate of gas exchange?

Answer 12

• Organisms can lose water by evaporation, too much water lost can damage/harm the organism

Question 13

What do most exchange surfaces have in common

Answer 13

• They have a large surface area

* They are thin

Question 14

How do plants balance the conflicting needs of gas exchange and control of

Answer 14

Close stomata at times when water loss would be excessive