Plant Mass Transport Flashcards
What does the xylem transport
Water and mineral ions
What do the phloem vessels transport
Sugars
What are xylem tubes made from
Dead cells (vessel elements)
Give an adaption of the xylem vessel
No end walls
= uninterrupted tube = no resistance to water
Explain the cohesion-tension theory of water
- Water evaporates at the leaf
- Creates tension pulling more water up
- Water molecules are cohesive. So the whole colum of water is pulled up
- Water Exeter’s stem by roots
What is transportation.
The evaporation of water from the stomata Down the Conc grad
How does light affect transportation rate
High light intensity = increased rate
Stoma open for photosynthesis
How does temp affect transpiration rate
High temp = high rate
Water molecules have more energy
Evaporate faster
Increases concentration grad
How does humidity affect transpiration rate
High humidity = low rate
More water molecules surrounding stoma
Low conc grad
How does wind affect transpiration rate
High wind = high rate
Wind blows water molecules away from leaf
Maintains conc grad
What are the 2 structures in the phloem
Sieve tube elements
Companion cell
Adaption of serve tube elements
No nucleus and few organelles = less resistance to transported materials
What is the function of companion cells
Carry out living function s of rice tube elements
Eg. Respiration for active transport
What is the structure between sieve tube elements
Sieve Plates
Define translocation
Movement of solutes to where they are needed
Is translocation passive or needs energy
Needs energy
Where does translocation move molecules to
Source to sink
How is a conc grad Maintained for translocation
Enzymes break down solutes at the sink into something else
Explain the mass flow hypothesis
Source: 1. Active transport moves solutes from companion cells of sieve tubes 2. Lower water potential in sieve tube 3. Water whether sieve tube 4. Increases p Sink: 5. Solutes removed from sieve tubes 6. Increases water potential 7. Water leaves 8. Lowers pressure Overall: Pressure gradient from source to sink
Give 4 pieces of Evidence for mass flow
- If a ring of bark is removed (including phloem Not xylem) A bulge forms above the ring, and has a higher conc than the fluid below = shows downward flow
- Radioactive tracers can be tracked eg. C14
- Sal flows out faster at the leaves than at the roots = pressure gradient
- If a metabolic inhibitor is used = translocation stops = uses active transport
Give 2 pieces of evidence against mass flow hypothesis
- Sugar travels to many different sinks not just the one with the higher water potential.b
- Sieve plates would create a barrier so a lot of p would be needed
How do you use radioactive tracers to show mass flow
- Supply plant with C14
- Taken in by photosynthesis and used to make sugars
- Miovement of sugars tracked by autoradiography
- Kill plant by liquid N
- Place on photographic film
- Radioactive substances turn black
What do potomètres measure
Water uptake by a plant
What is assumed when using a potomètre
The water uptake by roots is directly proportional to water loss by the leaves
