Section 3- Mass Transport Plants Flashcards
What are water and mineral ions transported through in plants?
Xylem
Why does xylem have no end walls?
So water flow is uninterrupted
Why are side walls lignified?
To increase strength, preventing collapse under pressure
What does the latent heat of vaporisation being high allow for leaves?
Allows a cooling effect
So enzymes do not denature
What does cohesion of water form?
Continuous column of water
What is the cohesion-tension theory?
Transpiration stream occurs when water evaporates from surface of mesophyll cells in leaf
What is transpiration?
When water vapour diffuses out of the stomata.
What does transpiration cause in the leaf?
Tension which pulls more water up the xylem into the cell
Why is a potometer not best for determining transpiration rate?
Due to photosynthesis occuring
What does a plant being used with a potometer need to be cut on a slant?
To increase surface area
Why does a plant need to be cut underwater?
Keeps a continuous column of water
What is the method of using a potometer?
- Leafy shoot cut under water
- Potometer filled with water
- Leafy shoot fitted to potometer
- Air bubble introduced into capillary tube
- Distance moved by air bubble recorded
- Calculate volume of water lost
What are the 3 components of phloem vessles?
Sieve tube elements: tube to transport sucrose in dissolved sap
Companion cells: involved in ATP production for active loading of sucrose into sieve tubes
Sieve plates: gaps between cell walls where cytoplasm links, allowing substances to flow
What is the process where organic materials are transported around the plant?
Translocation
What is the source and sink in plants?
Source: site of production of sugar
Sink: places where they will be used or stored
How can ringing experiments be used to investigate transport in plants?
Bark and phloem of tree are removed in ring leaving behind xylem
Tissues above missing ring swell = accumulation of sucrose
-Therefore tissues must be transported in phloem
How can tracing experiments be used to investigate transport in plants?
Plants grown in presence of radioactive carbon dioxide
Using autoradiography, areas exposed to radiation correspond to where phloem is can be seen
How can aphids be used to investigate transport in plants?
When noses of aphids removed, phloem sap seeps out
Show phloem is under pressure
Why is less water lost from the upper surface of a leaf?
More stomata at the lower surface
Waxy cuticle on the upper surface
How would covering a leaf in epidermal hairs help xerophytes survive in their habitat?
Reduces water potential gradient
Hair trap water vapor
More humid air around leaf so less transpiration
What is translocation at the source?
Sucrose is actively transported into the phloem
Reduces water potential
Water moves in by osmosis
Increases pressure at the source
What is translocation at the sink?
Sucrose is actively transported out of phloem
Increases water potential
Water moves out by osmosis
Reduces pressure at the sink
What is one way in which companion cells are adapted for the transport of sugars between cell?
Mitochondria: release energy for active transport
Ribosomes to produce proteins for protein carriers
Describe the mass flow hypothesis for the mechanism of translocation in plants.
At the source sucrose is actively transported into the phloem by companion cells
Lowers water potential of sieve tube
Water enters by osmosis
Increasing pressure causes mass movement towards sink
What are two features of root hair cells which adapt them for water uptake?
Large surface area
Low water potential
What are two features why xylem vessels are adapted for water transport?
No end walls - allows for continuous column of water
Lignin in side walls - stops collapse
No cytoplasm - ease of flow
Why can transpiration in plants not be avoided?
Open stomata
Large surface area
Water potential gradient
