C3: Gas Exchange in plants

Question 1

describe the structure of an angiosperm leaf

10 points

Answer 1

waxy cuticle
upper epidermis
palisade mesophyll layer
spongy mesophyll layer
xylem
phloem
praenchyma
stomata
guard cells
lower epidermis

Question 2

how is a leaf adapted for phtosynthesis

4 points

Answer 2

thin
transparent cuticle and upper epidermis
stomata to supply co2
large surface area
palisade mesophyll are long and packed with chloroplasts

Question 3

what cells open and close the stomata

Answer 3

guard cells

Question 4

describe the mechanism for the opening of the stomata

Answer 4

Guard cells have chloroplasts which produce ATP through photosynthesis
this is used to pump K+ ions into the cell via active transport
stored starch is converted into malate
the K+ ions and malate lower the water potential in the cell so water moves in by osmosis
the inner cell wall of the guard cell is thicker so when the cell becomes turgid it curves outward leaving a pore in the middle ( the stoma)

at night the reverse happens

Question 5

when are stomata mainly closed and why

Answer 5

at night to reduce water loss as no photosynthesis is occuring
in very bright and therefore hot conditions to reduce water loss
if there is excessive water loss they are closed