3.4.2 Mass Transport in Plants Flashcards
What enviromental factors INCREASE the rate of transpiration
- Increasing temperature
- Decreasing humidity
- Increasing light intensity
- Increasing wind speed
What enviromental factors DECREASE the rate of transpiration
- Decreasing temperature
- Increasing humidity
- Decreasing light intensity
- Decreasing wind speed
Why does the rate of transpiration increase with increasing light intensity
Causes stomata to open
Why does the diameter of the xylem decrease as the rate of transpiration increases
- Water lost from the leaf in transpiration
- Creates more tension and pulling force on water molecules in xylem
What does water lost from the leaf in transpiration creating more tension and pulling force on water molecules in xylem create
The diameter of the xylem to decrease
What device is used to measure the rate of transpiration
Potometers
What are the vital procedures to setting up a potometer
- Cut stem underwater, and at a slant
- Ensure no air bubbles are present
- Seal joints with vasaline to ensure airtight
Why do potometers not truly measure the rate of transpiration
- Water used for support
- Water used in photosynthesis
- Water produced in aerobic respiration
- Apparatus not fully sealed
What is the benefit of xylem cells being dead, and therefore empty with no cytoplasm contents
Allows water to flow easier
What xylem specialisation allows water to flow easier
Cells are dead, and therefore empty with no cytoplasm contents
What is the benefit of xylem cells being long, forming tubes, with no end walls, meaning it’s hollow
Allows for continuous columns of water
What xylem specialisation allows continuous columns of water to flow
Cells are long, forming tubes, with no end walls meaning thay are hollow
What is the benefit of xylem cells having a thickened cell wall with cellulose and lignin
Support, and waterproofing
What xylem specialisation allows for support, and waterproofing
Thickened cell walls with cellulose and lignin
What is the benefit of xylem cells have pits in walls
Allows lateral movement of water
What xylem specialisation allows for lateral movement of water
Pits in walls
Describe and explain the cohesion-tension theory
- Water lost from the leaves by evaporation, due to transpiration
- Lowers the water potential of mesophyll cells, so water drawn out of xylem
- Water pulled up xylem creating tension
- Due to cohesive forces between water molecules, caused by hydrogen bonding
- Allows a continous column of water to be pulled
- Water molecules adhere to the xylem walls
In the cohesion-tension theory how is water lost from the leaves
By evaporation, due to transpiration
In the cohesion-tension theory why is water drawn out of the xylem
The water potential of mesophyll cells has been lowered
In the cohesion-tension theory what creates tension
Water being pulled up xylem
In the cohesion-tension theory what causes cohesive forces between water molecules
Hydrogen bonding
In the cohesion-tension theory what allows a continous column of water to be pulled
Cohesive forces between water molecules, due to hydrogen bonding
In the cohesion-tension theory what do water molecules adhere to
Xylem walls
In the phloem solution, what key molecules are transported
Sucrose and amino-acids
What key component are within the sieve tube element of the phloem
Sieve plates
What is the specialisation of companion cells in the phloem
Have lots of mitochondria, to actively transport sucrose into phloem from source
What is the most general way of describing route of mass-flow hypothesis
From source to sink
Describe and explain the Mass-Flow Hypothesis
- Sucrose actively transported into sieve tube element, from source, by companion cells
- This lowers the water potential in the sieve tube element, so** water moves in by osmosis** from the xylem
- Produces a high hydrostatic pressure
- Mass flow of sucrose from source to sink
- At sink, sucrose is unloaded and used or converted to starch for storage
In the Mass-Flow Hypothesis what actively transports sucrose into sieve tube element from source
Companion cells
In the Mass-Flow Hypothesis what does a low water potential in the sieve tube element allow
Water to move in by osmosis from the xylem
In the Mass-Flow Hypothesis what does the movement of water into the sieve tube element by osmosis from the xylem create
High hydrostatic pressure
In the Mass-Flow Hypothesis where is the mass flow
From source to sink
In the Mass-Flow Hypothesis what happens at the sink
Sucrose is unloaded and used or converted to starch for storage
Explain how the following provides evidence for the Mass-Flow Hypothesis: Translocation slows if respiration inhibitors used
No active transport of sucrose from companion cells at source
Explain how the following provides evidence for the Mass-Flow Hypothesis: If phloem punctured, contents flows out
Occuring at high pressure
Explain how the following provides evidence for the Mass-Flow Hypothesis: Plants can be supplied with radioactive CO2 and traced
Sucrose moves from source, up and down stem, to sinks
Explain how the following provides evidence for the Mass-Flow Hypothesis: ring of bark removed, so that xylem remains, but phloem removed
- Bulging above ring due to build-up of fluid in phloem
- Tissues die below, as no sucrose for respiration
