Transport in plants Flashcards
What is the function of the xylem in plants?
The xylem transports water and dissolved minerals from the roots to the rest of the plant.
Also provide structural support
What is the function of the phloem in plants?
The phloem transports organic nutrients, particularly sucrose, from the leaves to other parts of the plant.
What is transpiration?
Transpiration is the loss of water vapor from the aerial parts of the plant, mainly through the stomata in the leaves.
What are the main factors affecting the rate of transpiration?
- light intensity
- temperature
- humidity
- wind
- leaf SA
- stomatal density
Light
Increases transpiration by opening stomata.
Temperature
Higher temperatures increase evaporation rates.
Humidity
Lower humidity increases the rate of transpiration.
Wind
Removes water vapor, increasing transpiration.
Leaf SA
Larger areas increase transpiration.
Stomatal density
More stomata increase transpiration rates.
What is the process of water uptake by plant roots?
Water is taken up by plant roots primarily through osmosis, where water moves from an area of higher water potential in the soil to an area of lower water potential in the root cells.
What is the cohesion-tension theory?
The cohesion-tension theory explains how water moves up through the xylem.
Cohesion refers to the attraction between water molecules, and tension is the pulling force generated by evaporation at the leaf surface.
How does water move through the xylem?
Water moves through the xylem via bulk flow, driven by negative pressure (tension) generated by transpiration and the cohesive properties of water.
What are stomata and their function?
Stomata are small openings on the leaf surface that allow gas exchange.
They play a critical role in transpiration and photosynthesis by regulating the movement of gases and water vapour
What is the role of guard cells?
Guard cells surround stomata and regulate their opening and closing, thus controlling gas exchange and water loss.
Define the term ‘root pressure.’
Root pressure is the osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.
What is the significance of the Casparian strip?
The Casparian strip is a band of cell wall material in the roots that blocks passive flow of water and solutes, forcing them to cross the plasma membrane of endodermal cells, ensuring selective uptake.
Describe the process of translocation.
Translocation is the movement of organic compounds (mainly sucrose) from sources (like leaves) to sinks (like roots, fruits, and growing tissues) via the phloem.
What is the pressure-flow hypothesis?
The pressure-flow hypothesis explains the mechanism of phloem transport. It involves the generation of high pressure at the source end and low pressure at the sink end, causing sap to flow from source to sink.
Explain the term ‘capillary action’ in plants.
Capillary action is the ability of water to flow in narrow spaces without the assistance of external forces, essential for the movement of water through the tiny pores in the cell walls of xylem vessels.
Cohesion
Water molecules stick together due to hydrogen bonding.
Adhesion
Water molecules stick to the walls of xylem vessels.
Phloem translocation of sucrose mechanism
- loading
- mass flow
- unloading
Loading
Active transport of sucrose into phloem sieve tubes at the source.
