Mass Transport in Plants Flashcards
What is the role of xylem in plants?
Xylem transports water and mineral ions from the roots to the rest of the plant.
What is the role of phloem in plants?
Phloem transports the products of photosynthesis (mainly sugars) from the leaves to other parts of the plant.
What is the structure of the xylem?
Xylem consists of dead cells that form long tubes. It has no end walls, and the cells are reinforced with lignin for strength.
What is the structure of the phloem?
Phloem consists of living sieve tube elements, companion cells, and phloem fibers. Sieve plates allow for the flow of sap.
What is the function of companion cells?
Companion cells provide metabolic support to sieve tube elements and are involved in loading and unloading sugars into phloem.
Describe the cohesion-tension theory.
The cohesion-tension theory explains how water moves through the xylem. Water molecules stick together (cohesion) and to the walls (adhesion), creating tension to pull water upwards.
How does the root hair cell absorb water?
Root hair cells absorb water by osmosis due to a lower water potential inside the cell compared to the surrounding soil water.
What is the pressure flow hypothesis?
The pressure flow hypothesis suggests that phloem transport is driven by pressure differences between source (high concentration of sugars) and sink regions.
What are stomata and their function?
Stomata are pores in the leaf epidermis that allow gas exchange. They are surrounded by guard cells that control their opening and closing.
What is the role of the Casparian strip?
The Casparian strip in the root endodermis prevents the apoplast pathway (through cell walls) and forces water into the symplast pathway (through cells).
How does water move through the plant?
Water moves through the plant via the xylem through capillary action, cohesion, adhesion, and transpiration pull.
What is transpiration?
Transpiration is the loss of water vapor from plant leaves, primarily through stomata, which helps to create the suction needed to draw water up through the plant.
What is the role of lignin in xylem vessels?
Lignin strengthens xylem vessels, making them less prone to collapsing under the pressure of water flow, and also helps in waterproofing the vessels.
What factors affect the rate of transpiration?
Factors include temperature, humidity, wind speed, light intensity, and the number of stomata on the leaf surface.
What is the apoplast pathway?
The apoplast pathway is the movement of water through the plant cell walls and intercellular spaces, avoiding the cytoplasm.
What is the symplast pathway?
The symplast pathway is the movement of water through the cytoplasm of plant cells, connected by plasmodesmata (cell-to-cell channels).
How does the cohesion-tension theory support water transport?
It suggests that as water evaporates from the leaves (transpiration), a pull is created, drawing water up through the plant due to cohesion between water molecules.
What is the difference between xylem and phloem?
Xylem carries water and minerals upwards and is made of dead cells, while phloem transports sugars and other products of photosynthesis in both directions and is made of living cells.
What is the source-sink model of phloem transport?
The source-sink model explains that sugars are actively transported from a source (usually leaves) to a sink (such as roots or fruits), creating a pressure gradient for phloem transport.
How does water potential affect water movement in plants?
Water moves from areas of higher water potential (less negative) to areas of lower water potential (more negative), driving the movement of water into roots and through the plant.
