Mass transport in plants Flashcards
What is transpiration?
The loss of water vapor from stomata via evaporation
Factors that effect transpiration
- Light intensity
- Temperature
- Humidity
- Wind
How does light intensity affect transpiration?
- More light intensity = more transpiration
- More light = more stomata open = larger SA for evaporation
How does temperature affect transpiration?
- Increase temperature = more transpiration
- More heat = more KE = faster moving molecules = more evaporation
How does humidity affect transpiration?
- More humidity = less transpiration
- More water vapor outside will increase WP outside compared to inside = reduced WP gradient = less evaporation
How does wind affect transpiration?
- 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
Describe cohesion
- Water is dipolar = H-bonds form between adjacent H+O = cohesion
- Water molecules stick together = travel up xylem as continuous column
Describe adhesion + capillarity
- Water is adhesive to other molecules = adheres to xylem walls
- Narrower xylem = more capillarity
Describe root pressure
- Water moves into roots via osmosis = increase volume of liquid = pressure increases
- Increase in root pressure forces water above it upwards
Explain movement of water up the xylem
- 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
Functions of a potometer
- 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
Describe how to use a potometer
- 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
Why must plant be cut and equipment be set underwater?
Cohesion tension causes negative pressure in xylem so cut in air = draw air into xylem = break continuous water column = prevent transpiration
Why are all the joints covered in petroleum jelly?
Petroleum jelly is water proof = prevent water leaking out = all water only leaves through transpiration
How to calculate rate of transpiration
πr2 * distance travelled by bubble / time taken
What variables should you control when comparing 2 different plant species
Same SA = same number of stomata
What is translocation?
Transport of organic substances in a plant via phloem through active transport
Parts of a phloem tissue
SIEVE CELLS:
- Have holes for the flow of sugar solution
- Living cells
- No nucleus
- Few nucleus
COMPANIAN CELLS:
- Provide ATP needed active transport
Describe the mass flow hypothesis
- Mass flow from source of production (leaves) to sink site where organic substances are used up (respiring tissue)
- Flow from source to sink
Explain the process of translocation
- 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
Use of tracers to prove phloem transports sugars
- 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
Use of ringing to prove phloem transports sugars
- 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
