transport in plants - xylem

Question 1

Explain how water is lost from the
leaf

Answer 1

diffusion from higher water vapour potential (in air space) to
lower water vapour potential (in atmosphere) through
stomata

Question 2

Explain how water is lost from
mesophyll cells

Answer 2

evaporation from mesophyll cell into air space of leaf

Question 3

Define cohesion

Answer 3

attraction of water molecules to each other due to their polar
nature - forming hydrogen bonds

Question 4

Define transpiration pull

Answer 4

the continuous column of water is pulled up the xylem due to
transpiration

Question 5

Explain why there is negative
pressure in the xylem during
transpiration

Answer 5

Transpiration causing the movement of the water column
puts the xylem under pressure

Question 6

Transpiration is a passive process
but needs energy, where does this
energy come from?

Answer 6

sun light

Question 7

Define what
transpiration is

Answer 7

The process where evaporation of water from the leaves pulls a
stream of water through the xylem vessels of the stem

Question 8

Explain how water
moves through the
leaf

Answer 8

Water evaporates from the cell walls of the mesophyll cells into the
air spaces in the leaf.
This lowers water potential in mesophyll cell and water moves by
osmosis from neighbouring cells
The process is repeated through the cells
Replaced by water from the xylem

Question 9

Explain how water
moves up the
xylem

Answer 9

Cohesion-tension theory
Water evaporates from mesophyll cells
Water molecules form hydrogen bonds between each other -
cohesion
Water forms continuous, unbroken column through mesophyll cells
and xylem - transpiration pull
This causes a negative pressure within the xylem
No energy required other than that from the sun which drives
evaporation

Question 10

Define cohesion tension theory

Answer 10

Transpiration pull puts the xylem under tension so there is negative pressure within the xylem