Adaptions for gas exchange - Plants

Question 1

During the day

Answer 1

Photosynthesis and respiration occur

Question 2

During the night

Answer 2

Only respiration occurs

Question 3

Leaf structure

Answer 3

• Waxy cuticle
• Upper epidermis
• Palisade mesophyll (with chloroplasts)
• Spongy mesophyll (with chloroplasts)
• Air spaces
• Lower epidermis
• Stomata
• Guard cells

Question 4

Adaptions for photosynthesis (7)

Answer 4

-Large surface area:
Captures as much light as possible

-Thin:
Light penetrates through leaf

-Cuticle and epidermis are transparent:
Light penetrates to the mesophyll

-Palisade cells are elongated:
Can accommodate a large number

-Palisade cells have many chloroplast:
Captures as much light as possible

-Chloroplast rotate and move within mesophyll cells:
They move into the best positions for light absorption

-Air spaces in the spongy mesophyll:
Allows CO2 to diffuse to photosynthesising cells

Question 5

Adaptions for gas exchange (4)

Answer 5

-Large surface area:
Room for many stomata

-Thin:
Diffusion pathway for gases entering and leaving is short

-Air spaces in the spongy mesophyll:
Allow O2 and CO2 to diffuse between the stomata and the cells

-Stomatal pores:
Facilitates gas exchange in and out of leaf

Question 6

The malate theory

Answer 6

If water enters the guard cell they become turgid and the pore opens

If water leaves the guard cell they become flaccid and the pore closes

Stomatal opening:
1) In the light, chloroplasts in the guard cells photosynthesis and produce ATP

2) ATP provides energy for active transport of K+ ions into guard cells from surrounding epidermal cells
3) Stored starch is converted to malate ions
4) Water potential in guard cells is lowered by malate and K+ so water enters by osmosis
5) Due to uneven thickness of the guard cells, as the cell increases in size the stomatal por opens