Plant Transport- Module 3: Exchange and Transport

Question 1

Define the term transpiration

Answer 1

Loss of water vapour from the leaf
Through the stomata

Question 2

Explain the mechanism by which water is transported from the root cortex to the leaves. (9)

Answer 2

Water cross the root cortex by osmosis
Apoplast pathway through the cell walls
Symplast pathway through the cytoplasm and plasmodesmata
Minerals ions actively transported into the xylem
Reduces water potential in xylem
Water enters by osmosis
Increases hydrostatic pressure at bottom of xylem
Water vapour lost from the leaves
Reduces hydrostatic pressure at top of xylem
Water moves up xylem by mass flow
From high to low hydrostatic pressure

Question 3

State two adaptations that hydrophytes can have to their environment

Answer 3

Stomata on the upper surface of the leaf
Air spaces in the tissues
Flexible leaves and stems

Question 4

State three adaptations that xerophytes can have to reduce water loss by transpiration

Answer 4

Sunken stomata / pits
Rolled leaves with the lower epidermis on the inside
Hairs around stomata
Thicker waxy cuticle

Question 5

Describe how a potometer is used to estimate transpiration rates. (6)

Answer 5

Cut the shoot at a slant to increase the surface area
Ensure the apparatus is water/air tight
Remove the capillary tube from the beaker of water to add an air bubble
Wait for the air bubble to reach 0 on the scale
Leave the potometer for a set time
Record the distance the bubble has moved
Calculate a rate (distance / time)
Repeat twice more
Spot and discard anomalous results
Calculate a mean rate

Question 6

Describe and explain how light intensity affects the rate of transpiration

Answer 6

As the light intensity increases the rate of transpiration increases.
More stomata open to let in CO2 for photosynthesis
Water vapour can diffuse out of the leaf more quickly

Question 7

Describe and explain how humidity affects the rate of transpiration

Answer 7

As the humidity increases the rate of transpiration decreases
More water vapour in the air
Lower water vapour potential gradient
Slower rate of diffusion of the water vapour

Question 8

Describe and explain how wind speed affects the rate of transpiration.

Answer 8

As the wind speed increases the rate of transpiration increases
Any water vapour outside the stomata is blown away
This increases the water vapour potential gradient
Faster rate of diffusion of the water vapour

Question 9

Describe and explain how temperature affects the rate of transpiration

Answer 9

As temperature increases the rate of transpiration increases
Molecules of water vapour gain kinetic energy
Therefore faster rate of diffusion of the water vapour molecules

Question 10

Explain why transpiration is a consequence of gaseous exchange

Answer 10

Stomata have to open to let in CO2
For photosynthesis
As the stomata are open water vapour diffuses out.

Question 11

what is a hydrophyte?

Answer 11

plants that live in aquatic habitats

need adaptions to cope with oxygen levels

Question 12

what are xerophytes?

Answer 12

-Plants adapted to live in dry conditions
-adapted to reduce water loss by transpiration

Question 13

What is Translocation

Answer 13

The movement of assimilates from the source to the sink

Question 14

What are Assimilates?

Answer 14

Products of photosynthesis, mainly sucrose

Question 15

What is the Source in a plant?

Answer 15

Where the assimilates are made e.g: leaves

Question 16

What is the sink in a plant?

Answer 16

Tissue that use the assimilates e.g: roots

Question 17

What is the Process of the mass flow hypothesis?

(translocation)

Answer 17

1)In the leaf cells (the source), glucose is converted to sucrose

2)Hydrogen ions are pumped out of the companion cell by active transport into the surrounding tissue cells

3)This creates a high concentration of hydrogen ions outside the companion cell so they diffuse back into the companion cell through a co-transport protein

4)At the same time, sucrose binds to and is carried through the co-transport protein

5)Sucrose then diffuses through the plasmodesmata into the sieve tube element

6)This lowers the water potential inside the sieve tubes so water enters from the xylem through osmosis

7)This increases the hydrostatic pressure in the source end of the phloem

8)The sucrose diffuses out of the phloem at the sink to be used or stored. This increases the water potential at the sink end of the phloem

9)Water leaves the sieve tubes by osmosis, reducing the hydrostatic pressure at the sink

10) THis results in a pressure gradient so the solution in the phloem moves by mass flow, from high hydrostatic pressure to low hydrostatic pressure