Mass transport in plants

Question 1

What is transpiration?

Answer 1

The loss of water vapor from stomata via evaporation

Question 2

Factors that effect transpiration

Answer 2

• Light intensity
• Temperature
• Humidity
• Wind

Question 3

How does light intensity affect transpiration?

Answer 3

• More light intensity = more transpiration
• More light = more stomata open = larger SA for evaporation

Question 4

How does temperature affect transpiration?

Answer 4

• Increase temperature = more transpiration
• More heat = more KE = faster moving molecules = more evaporation

Question 5

How does humidity affect transpiration?

Answer 5

• More humidity = less transpiration
• More water vapor outside will increase WP outside compared to inside = reduced WP gradient = less evaporation

Question 6

How does wind affect transpiration?

Answer 6

• More wind = more transpiration
• More wind blows away humid air/water vapor in the air = WP inside is more than outside = maintain WP gradient = more evaporation

Question 7

Describe cohesion

Answer 7

• Water is dipolar = H-bonds form between adjacent H+O = cohesion
• Water molecules stick together = travel up xylem as continuous column

Question 8

Describe adhesion + capillarity

Answer 8

• Water is adhesive to other molecules = adheres to xylem walls
• Narrower xylem = more capillarity

Question 9

Describe root pressure

Answer 9

• Water moves into roots via osmosis = increase volume of liquid = pressure increases
• Increase in root pressure forces water above it upwards

Question 10

Explain movement of water up the xylem

Answer 10

• Water evaporates out the stomata = decreases in volume = decreases pressure
• Water lost by transpiration = replaced by pulling water up the xylem
• H-bonds = cohesion = water creates a column of water
• Adhesion to walls = pulls water column upwards
• water pulled up = tension = pulls xylem narrower = increase capillarity

Question 11

Functions of a potometer

Answer 11

• Measures rate of uptake of water by plant
• It is impossible to measure rate of water evaporated = uptake proportional to rate of transpiration
• Can be used to see the effect of named variable on rate of transpiration

Question 12

Describe how to use a potometer

Answer 12

• Cut plant underwater
• Fill potometer with water until no air bubbles
• Plant attached to potometer underwater
• Rubber seals and petroleum jelly to make it air tight
• 1 air bubble is introduced and distance moved by air bubble recorded
  -Apparatus can be reset by opening tap
• Lamp can replicate effect of sunlight
• Fan can replicate effect of wind
• Plastic bag on top can replicate effect of humidity

Question 13

Why must plant be cut and equipment be set underwater?

Answer 13

Cohesion tension causes negative pressure in xylem so cut in air = draw air into xylem = break continuous water column = prevent transpiration

Question 14

Why are all the joints covered in petroleum jelly?

Answer 14

Petroleum jelly is water proof = prevent water leaking out = all water only leaves through transpiration

Question 15

How to calculate rate of transpiration

Answer 15

πr2 * distance travelled by bubble / time taken

Question 16

What variables should you control when comparing 2 different plant species

Answer 16

Same SA = same number of stomata

Question 17

What is translocation?

Answer 17

Transport of organic substances in a plant via phloem through active transport

Question 18

Parts of a phloem tissue

Answer 18

SIEVE CELLS:
- Have holes for the flow of sugar solution
- Living cells
- No nucleus
- Few nucleus
COMPANIAN CELLS:
- Provide ATP needed active transport

Question 19

Describe the mass flow hypothesis

Answer 19

• Mass flow from source of production (leaves) to sink site where organic substances are used up (respiring tissue)
• Flow from source to sink

Question 20

Explain the process of translocation

Answer 20

• Photosynthesis = organic substance at site
• High concentration of sucrose at site = diffuses down concentration gradient to companion cells via facilitated diffusion
• Active transport of H+ from companion cells to cell wall using ATP = H+ moves down concentration gradient to sieve cells via carrier protein = co-transport of sucrose
• Increase of sucrose in sieve cells = decrease WP
• Water enters from xylem via osmosis = increase water volume in sieve cells = increase hydrostatic pressure = liquid forced to sink
• Sucrose is already being used to respire/stored by sink = more sucrose actively transported into sink = WP decrease
• Osmosis of water from sieve tubes into sink + xylem
• Decreased water in sieve cells = hydrostatic pressure decreases = pressure gradient maintained

Question 21

Use of tracers to prove phloem transports sugars

Answer 21

• Plants provided with radioactively labelled CO2 = absorbed by plants and used in photosynthesis = radioactively labelled sugars produced
• When stems are put on X-ray film parts containing sugar = black = highlighting placement of phloem and that sugars are transported by it

Question 22

Use of ringing to prove phloem transports sugars

Answer 22

• Ring of bark + phloem is removed from tree trunk = swelling of trunk above removed ring
• Proves that since phloem is removed sugar cannot be transported