Transpiration

Question 1

What is transpiration?

Answer 1

loss of water by evaporation from the aerial parts of a plant

Question 2

How does water get to the mesophyll cells?

Answer 2

water enters the leaves in the xylem and passes by osmosis into the mesophyll cells

Question 3

What happens to the water in the mesophyll cells?

Answer 3

water evaporates from the surface of the cells to form water vapour

Question 4

What happens to the water vapour?

Answer 4

Spongy mesophyll cells have large air spaces where the water vapour can diffuse through, as the vapour collects here the water vapour potential rises

Question 5

What happens when the water vapour potential inside the leaf is higher than outside?

Answer 5

Water mols will diffuse out of leaf, open stomata are easy way to leave, open during day for gas exchange

Question 6

What 3 processes does transpiration involve?

Answer 6

osmosis from xylem to mesophyll cells, evaporation from surface of mesophyll cells into intercellular spaces, diffusion of water from intercellular spaces through stomata

Question 7

What are the 5 ways that water movement up the stem is useful?

Answer 7

water needed in leaves for photosynthesis, needed for cells to grow/elongate, keeps cells turgid, carries useful minerals up plant, evaporation keeps plant cool

Question 8

How is the rate of transpiration measured?

Answer 8

potometer, measures rate of water uptake by a cut shoot, 99% water lost is transpiration so reasonable estimate,

Question 9

How must the potometer be set up? How is the rate calculated?

Answer 9

no air bubbles, water lost by the leaf is replaced by water in the capillary tube, movement of meniscus measured

Question 10

How does number of leaves affect rate of water loss?

Answer 10

More leaves = larger SA, more vapour can be lost

Question 11

How does number, size and position of stomata affect rate of water loss?

Answer 11

many, large stomata = vapour lost quicker, on lower surface = vapour lost slower

Question 12

How does the presence of cuticle affect the rate of water loss?

Answer 12

A waxy cuticle reduces evaporation from the leaf surface

Question 13

How does light affect the rate of water loss?

Answer 13

In light, stomata open so more vapour is lost

Question 14

What are the 3 ways that a higher temperature affect the rate of water loss?

Answer 14

increase evaporation so water vapour potential in leaf rises, water mols more kinetic energy so diffusion through stomata increases, decrease water vapour potential of air so more rapid diffusion out of leaf

Question 15

How does relative humidity affect the rate of water loss?

Answer 15

Higher humidity decrease rate of water loss due to smaller water vapour potential gradient between air in leaf and outside

Question 16

How does air movement/wind affect the rate of water loss?

Answer 16

air moving outside the leaf will carry away vapour that has just diffused maintaining a high water vapour diffusion gradient

Question 17

How does water availability affect the rate of water loss?

Answer 17

Little water in the soil means the water lost cant be replaced

Question 18

What happens when plants loose too much water?

Answer 18

Plant cells will lose turgidity, non-woody plants will wilt and die, leaves of woody plants will wilt and the plant dies