Mass transport in plants Flashcards
What transport is the xylem responsible for?
Transporting water and mineral ions.
(Transpiration)
Describe the structure of the xylem.
Vessel elements - which are the cells that make up the xylem and are dead.
No end walls - continuous tube for water to flow through.
Lignin lined walls - provides structural support
What are the steps involved in water transport in the xylem?
(Cohesion-Tension)
- Water is evaporated from the leaves through transpiration
- Loss of water from the leaves creates tension in the xylem
- Water is pulled upwards in the xylem by tension
- Water molecules also form hydrogen bonds with each other via cohesion
- The bonded water molecules are pulled upwards in the xylem by cohesion
- Water diffuses into the roots to replace the water lost from the bottom of the stem
What is the first step in investigating transpiration rate?
1.) Assemble the potometer
- The potometer is filled with water and a cutting of the shoot is placed inside
- The shoot must be cut and placed into the potometer while underwater to ensure no air enters the xylem.
Why must the shoot be placed into the potometer while underwater?
To ensure no air enters the xylem
What is the second step in investigating transpiration rate?
2.) Form the air bubble
- Remove the end of the capillary tube from the water beaker
- Wait for a bubble of air to form in the capillary tube
- Place the capillary tube back into the water
The air bubble is then used to record the volume of water used by the shoot.
What is the first part of the second step (form the air bubble) of investigating transpiration rate?
Remove the end of the capillary tube from the water beaker
What is the second part of the second step (form the air bubble) of investigating transpiration rate?
Wait for a bubble of air to form in the capillary tube
What is the third part of the second step (form the air bubble) of investigating transpiration rate?
Place the capillary tube back into the water
What is the fourth and final part of the second step (form the air bubble) of investigating transpiration rate?
The air bubble is used to record the volume of water used by the shoot
What is the third step in investigating transpiration rate?
3.) Record bubble movement
- Mark the starting position of the air bubble
- Use a stopwatch to record the distance moved by the air bubble in a given time period
What is the fourth step in investigating transpiration rate?
4.) Calculate transpiration rate
- Calculate the rate of movement of the bubble per hour
- The rate of bubble movement is equal to the transpiration rate
What is the fifth step in investigating transpiration rate?
5.) Change the variable
- Experiment can be repeated by changing a different variable each time e.g. temperature or light
- This allows the effects of an environmental factor on transpiration rate to be compared.
What transport is the phloem responsible for?
Transporting dissolved sugars.
(Translocation)
Describe the structure of the phloem.
Sieve tube elements - the cells that make up the phloem vessel. They are living cells that have a cytoplasm but no nucleus.
Companion cells - connected to STE via plasmodesmata. Companion cells have a nucleus
Sieve plates - at either end of STE. They have large pores that allow sap to move through STE. They allow sugars to be transported through the phloem.
What are the walls of sieve tube elements made of?
Cellulose
What is the role of sieve plates?
Allow sap movement
What is translocation?
The process where sugars produced in photosynthesis are transported from the leaves to other parts of a plant.
What are the 5 steps in translocation?
- Active transport of sucrose
- Diffusion of sucrose
- Water diffusing into the phloem by Osmosis
- Unloading of sucrose
- Water diffusing out the phloem by Osmosis
Explain the active transport of sucrose step of translocation.
- Sucrose produced during photosynthesis (leaves are the source)
- Sucrose actively transported into companion cells in phloem
- Energy for active transport from mitochondria in companion cells
- H+ ions actively transported out of companion cells
- Co-transport of H+ ions with sucrose into companion cells
Explain the diffusion of sucrose step of translocation.
- Loading of sucrose into phloem causes the concentration of sucrose to increase
- Sucrose diffused from companion cells into STE
Explain the osmosis into the phloem step of translocation.
- Increase concentration of sucrose in the phloem causes water potential in phloem to decrease.
- Water potential gradient between outside of phloem and inside
- Water diffuses into phloem by osmosis
Explain the unloading of sucrose step of translocation.
- At bottom of phloem, sucrose concentration is low because it is being used up in the cells (the sink)
- Sucrose diffuses out of phloem and into sink cells
- This lowers water potential of sink cells
Explain the osmosis out of the phloem step of translocation.
- Water diffuses down water potential gradient and out of the phloem by osmosis.
- Diffusion of water into phloem at the source and out the phloem at the sink creates hydrostatic pressure gradient.
- Hydrostatic pressure gradient allows mass transport of sucrose from source to sink
- This is mass flow
