Mass transport in plants

Question 1

Define transpiration

Answer 1

the loss of water vapour from the stomata by evaporation

Question 2

What are the 4 factors affecting transpiration

Answer 2

light intensity
humidity
temperature
wind

Question 3

How does light intensity affect transpiration?

Answer 3

Positive correlation
light causes more stomata to open = larger surface area for evaporation

Question 4

How does temperature affect the rate of transpiration?

Answer 4

Positive correlation
more heat → more kinetic energy → molecules move faster → more kinetic energy

Question 5

How does humidity affect the rate of transpiration?

Answer 5

Negative correlation
More water vapour in the air than leaf →water potential more positive outside leaf → reduces water potential gradient → less water can evaporate out

Question 6

How does wind affect the rate of transpiration

Answer 6

Positive correlation
More wind blowing away water vapour → maintains water potential gradient

Question 7

cohesion

Answer 7

water is a dipolar molecule (slight negative oxygen and slight positive hydrogen)
enables hydrogen bonds to form
causes water molecules to stick
the narrower the xylem

Question 8

Capillarity (adhesion)

Answer 8

adhesion of water is when water sticks to other molecules
water sticks to the xylem walls
narrower the xylem the bigger the impact of capillarity

Question 9

root pressure

Answer 9

water moves into the roots by osmosis → increases the volume of liquid in the root → pressure inside the root increases → forces the water to move upwards

Question 10

cohesion tension theory

Answer 10

cohesion
adhesion
root pressure

Question 11

How can we move water up a tree?

Answer 11

1) water vapour evaporates out of the stomata leave, loss in water volume creates a lower pressure

2) when this water is lost by transpiration, water is pulled up by the xylem to replace it

3) due to hydrogen bonds between water molecules, they are cohesive → creates a column of water

4) water molecules stick to the walls on xylem to help pull the water column up

5) as the column is being pulled up the xylem it creates tension, pulling xylem in to become narrower

Question 12

phloem

Answer 12

transports organic substances to cells

Question 13

what are the 2 key cells in the phloem tissue

Answer 13

sieve tube elements
companion cells

Question 14

companion cell

Answer 14

provide ATP required for active transport of sucrose

Question 15

sieve tube elements

Answer 15

living cells
no nucleus
few organelles

Question 16

how does sucrose transport from the source to the sieve tube element?

Answer 16

1) photosynthesis occurring in the chloroplasts of leaves create sucrose
2) sucrose is actively transported into the sieve tube from the source cell using the companion cell

Question 17

How does the sucrose get transported within the phloem of the sieve tube element?

Answer 17

1) the increase of sucrose in the sieve tube lowers the water potential
2) water enters the sieve tube elements from the surrounding xylem vessels via osmosis
3) this creates water volume in the sieve tube and creates an increase in hydrostatic pressure → causing the liquid to be forced towards the sink

Question 18

at the source

Answer 18

-high concentration of solute
-active transport loads solutes from the companion cells to the sieve tube of the phloem
-lowers water potential inside the sieve tube
-water enters the sieve tube by osmosis from the xylem and companion cells
-increase pressure inside sieve tubes at the end of the source

Question 19

at the sink

Answer 19

-low concentration of solute
-solutes are used up
-increase water potential in sieve tube
-water leaves tube via osmosis
-lowering pressure inside sieve tube

Question 20

mass flow in phloem

Answer 20

-pressure gradient from the souce to sink
-pushes solutes from the source to the sink
-solutes are used or stored at the sink e.g. respiration