gas exchange in plants

Question 1

draw the structure of a plant leaf

Question 2

what is the function of the cuticle

Answer 2

the waxy covering the leaf which prevents water loss

Question 3

how is the leaf adapted for photosynthesis

Answer 3

• large surface area= captures as much light as possible
• Thin- allows light to penetrate leaf
• elongated palisade cells- can accommodate a large number
• palisade cells packed with chloroplasts- capture as much light as possible
• air spaces between spongey mesophyll- allows CO2 to diffuse to photosynthesising cells

Question 4

how is the lead adapted for gas exchange

Answer 4

• large surface area- room more many stomata
• thin= short diffusion path
• air spaces between spongey mesophyll - diffusion of gases between stomata and cells
• stomatal pores= gas exchange in and out of leaf

Question 5

outline how gas exchange occurs in the leaf

Answer 5

1) gases diffuse through the stomata down a conc gradient
2) once inside the leaf gases in substomatal air chambers diffuse through intercellular spaces between spongey mesophyll cells and into cells

Question 6

outline the structure of the stomata

Answer 6

• small pores most often found on the underside of the leaf
• each pore is bounded by two guard cells
• width of stomata can change allowing control of exchanges of gases between the atmosphere and plant tissue

Question 7

outline how stomata open

Answer 7

1) chloroplasts in the guard’s cell photosynthesis producing ATP
2) ATP provides energy for the active transport of potassium ions into guard cells from surrounding cells
3) this causes stored starch to be converted into malate
4) the K+ and malate lower the water potential in guard cells causing water to enter via osmosis
5) cells of guard cells are thinner in some places so when guard cells expand some areas are thinner- these areas are opposite each other
6) as the guard cells stretch a pore opens between thinner parts

Question 8

outline how stomata close

Answer 8

1) at night photosynthesis doesn’t occur
2) ATP is not produced so active transport of K+ doesn’t occur
3) starch isn’t converted to malate
4) water potential isn’t lowered
5) osmosis doesn’t occur
6) guard cells don’t stretch and remain closed

Question 9

why do stomata close

Answer 9

• prevent water loss