3.3.4.2 Mass transport in plants

Question 1

Transpiration

Answer 1

The loss of water vapour from the stomata by evaporation

Question 2

rate of transpiration is affected by:

Answer 2

temperature
humidity
wind
light intensity

Question 3

how does light intensity, affect transpiration?

Answer 3

Positive Correlation

More light causes more stomata to open = larger S.A for evaporation

Question 4

how does temperature affect the rate of transpiration?

Answer 4

positive correlation

More heat = more kinetic, energy and faster moving molecules = more evaporation

Question 5

How does humidity affect the rate of transpiration?

Answer 5

Negative correlation

More water vapour in air makes water potential more positive outside of leaf, reducing water potential gradient

Question 6

How does wind affect the rate of transpiration?

Answer 6

Positive correlation

More wind blows away humid air containing water vapour which maintains water potential gradient

Question 7

what are three things are involved in cohesion tension theory?

Answer 7

• Cohesion
• Capillarity/adhesion
• Root pressure

Question 8

Adhesion

Answer 8

the sticking of water molecules to the xylem wall which creates capillarity

Question 9

Cohesion

Answer 9

Sticking together of water molecules due to hydrogen bonding creating a continuous water column

Question 10

Outline the movement of water up the xylem

Answer 10

1. Water vapour evaporates out of stomata creating lower pressure
2. Water lost by transpiration is replaced by more water pulled up the xylem due to negative pressure
3. Hydrogen bonding between water molecules creates cohesion which creates a column if water within the xylem
4. Water molecules also adhere to the walls of the xylem which helps to pull tge water column upwards
5. Tension is creted which pulls xylem in to become narrower

Question 11

Potometer

Answer 11

Measures the rate of uptake of water from a plant as water uptake is believed to be proportional to transpiration

Question 12

Outline the steps in the potometer practical

Answer 12

1. Cut sample of plant underwater to prevent any air from entering the xylem
2. Potometer is filled with water and air bubbles are removed
3. Cut leafy plant is attached to the potometer using rubber seals and petroleum jelly
4. One air bubble is purposely introduced into equipment and the distance that this air bubble has moved towards the plant is recorded

Question 13

Phloem

Answer 13

Responsible for transporting organic substances to all cells in a plant

Question 14

Translocation

Answer 14

the movement of dissolved substances from from an area of high concentration to an area of low concentration

Question 15

What two parts does a phloem cell contain?

Answer 15

• Sieve tube elements
• Companion cells

Question 16

What are the properties of a sieve tube element ?

Answer 16

• Living cells
• Perforated end walls for continuous flow of sugar solution
• Contains no nucleus
• Contains few organelles

Question 17

What are the properties of a companion cell ?

Answer 17

Provides ATP required for active transport of organic substances

Question 18

Mass flow hypothesis

Answer 18

mass flow from the source of production (the leaves) to the sink, the site were organic substances such as glucose and sucrose are used up in respiring tissues.

Question 19

1. How sucrose transports from the source to the sieve tube element

Answer 19

1. photosynthesis occurring in the chloroplast of leaves, creates organic substances e.g. sucrose
2. Sucrose is actively transported into the sieve tube element, using companion cell

Question 20

2. Movement of sucrose within phloem sieve tube element

Answer 20

1. Increase of sucrose in the sieve tube element, lowers water potential.
2. Water enters sieve element from surroundings xylem
   vessel via osmosis
3. Increase in water volume in tube element increases hydrostatic pressure causing liquid to be forced towards sink.

Question 21

3. transport of sucrose to the sink (respiring cells)

Answer 21

1. Sucrose is used in respiration at the sink or stored as in insoluble starch
2. More sucrose is actively transported into sink cell which causes water potential to decrease.
3. Resulting in osmosis of water from sieve tube element to sink cell.
4. Removal of water decreases volume in sieve tube element and hydrostatic pressure decreases.
5. movement of soluble organic substances is due to the difference in hydrostatic pressure in sieve and sink.

Question 22

how do tracers investigate translocation?

Question 23

how does ringing investigate translocation?