Stomata

Question 1

How do stomata control transpiration?

Answer 1

opening and closing of pores

this is a turgor-driven process

when tugor is low, the asymmetric configuration of the guard cell walls close the pore

Question 2

What do guard cells do in favourable conditions?

Answer 2

guard cells actively pump solutes by active transport, increasing their turgor

cellulose hoops prevent cells from swelling in width so they swell lengthways

becayse the inner wall of the cell is less flexible than the outer wall, they become bean shaped and open the pore

Question 3

What other ways is stomata turgor controlled?

Answer 3

when water is scarce, hormone signal from the roots can trigger turgor loos in the guard cells which close the pore

Question 4

How does light affect the rate of transpiration?

Answer 4

light is required for photosynthesis, and stomata need to be open for gas exchange

in the dark most of the stomata will close

increasing light intensity gives increasing numbers of open stomata

this increasing transpiration

Question 5

How does humidity affect the rate of transpiration?

Answer 5

lowers transpiration because there is a reduced water vapour potential gradient between the inside of the leaf and the outside air

dry air has the opposite effect

Question 6

How does temperature affect the rate of transpiration?

Answer 6

increase in temperature increases KE of the water molecules and therefore increases the rate of evaporation from the spongy mesophyll cells into the air and the spaces in the leaf

increases the concentration of water vapour that the external air can hold, before it becomes saturated

both increase the diffsuion gradient between the air inside and outside the leaf

Question 7

How does air movement affect the rate of transpiration?

Answer 7

each leaf has a layer ofstill air around it, trapped by the shape of the leaf and features such as hairs on its surface

the water vapour accumulates next the leaf so the water vapopour potential around the stomata increases, reduces the diffsuion gradient

air movement will increase the rate of transpiration because it increases the gradient

Question 8

What other factor affects the rate of transpiration?

Answer 8

soil-water availability

if it is very dry the plan wqill be under water stress and the rate of transpiration will reduced

stomata will close

Question 9

how are the guard cells adapted to their role?

Answer 9

wall thicker on one side

can change shape

transport proteins

mitochondria

Question 10

Name a part other than the stomata where water may be lost

Answer 10

cuticle/epidermis