Transport in plants 4.4 Flashcards
Why does the xylem contain pits?
To allow water to move sideways between the vessels
What tissue is the xylem made up of?
Dead tissues
What is the xylem thickened with?
Lignin
How is lignin deposited?
Spiral patterns to maintain flexibility
What is translocation?
The movement of nutrients to storage organs
What cells does the phloem consist of?
Companion cells
Sieve tubes
What is the plasmodesmata?
Gaps between cell walls allowing flow of substances between cells
How does water move through the symplast pathway?
Water moves through the cytoplasm via the plasmodesmata
How does water move through the apoplastic pathway
Water moves through cell walls and intercellular spaces which are permeable
Through what cells does water move into the plant?
Root hair cells
How is the column of water maintained?
Through cohesion and adhesion
What is cohesion?
Attraction between like molecules, water forming hydrogen bonds with other molecules of water
What is adhesion?
Attraction between unlike molecules
What causes hydrostatic pressure in the xylem?
Evaporation
What does hydrostatic pressure in the xylem cause?
The tension moves the whole column upwards due to cohesion, this is the cohesion-tension model
What does sucrose move from-to?
Moves from the source (produces more sugar than required) to the sinks (eg, root and shoot)
How does light intensity affect transpiration?
Increases the number of stomata that are open for gas exchange
How does air movement affect transpiration?
Removes still air from around the leaf and increases the concentration gradient, increasing diffusion
What is the mass flow hypothesis?
Explains the movement of assimilates in the phloem
What is one bit of evidence to support the mass flow hypothesis?
-You can use radioactive isotopes to mark glucose and trace sucrose through the phloem
What are two weaknesses of the mass flow hypothesis?
-Doesn’t explain why there can be bidirectional movement in the sieve tube
-Doesn’t explain different speeds of movement in the phloem
