Gas Exchange In A Leaf

Question 1

Is the rate of photosynthesis higher or lower than the rate of respiration?

Answer 1

Higher so carbon dioxide must be gained from the external environment

Question 2

What happens in regards of gas exchange during the day in a plant?

Answer 2

• lost of light so lots of photosynthesis
• needs lots of CO2 for photosynthesis and producing lots of O2
• CO2 in and O2 out

Question 3

What happens in regards to gas exchange during the night?

Answer 3

• not a lot of light so not a lot of photosynthesis
• needs lots of O2 for respiration and producing lots of C02
• C02 out 02 in

Question 4

What is the structure of a dicotyledonous plant leaf?
(Top to bottom)

Answer 4

1.Waxy cuticle - prevents water loss
2. Upper epidermis layer
3. Palisade mesophyll cells - contain chloroplasts for photosynthesis
4. Spongy mesophyll cells (has lots of air spaces)
5. Sub- stomata air spaces
6. Lower epidemics cells
7. Guard cells
8. Stoma - how the gases enter and exit the leaf
9. Vascular bundle: xylem, phloem , sheath

Question 5

How are gases transported through leaf?

Answer 5

Simply diffuse down diffusion gradients as there is not transport system.

Question 6

What are adaptations of the leaf for efficient gas exchange?

Answer 6

1. Many small pores so no cell is far from air = short diffusion pathway
2. Large surface area of mesophyll cells for rapid diffusion
3. Numerous interconnecting air spaces to connect all the different mesophyll cells
4. Most stomata on underside of leaf to reduce water loss
5. Guard cells help control water loss by closing the stomata when necessary eg during night