Transport in Plants Flashcards
Module 3
Where are transport vessels generally located?
They are located in stems, roots, leaves.
List reasons why plants need a transport system.
They have a low surface area to volume ratio.
Diffusion is not sufficient to help them meet their high metabolic demands.
Substances need to be moved over long distances.
Was is a vascular bundle composed of?
It contains xylem vessels and phloem vessels.
What do xylem vessels transport?
They transport water and mineral ions.
Is the flow in xylem vessels unidirectional or bidirectional?
It is unidirectional meaning that it is transport up the plant from the roots to the leaves.
What do phloem vessels transport?
They transport assimilates - e.g. sucrose and amino acids/nutrients. - Transpiration
Describe the flow in phloem vessels?
The assimilates can be transport up and down in a bidirectional flow. - Translocation
What are xylem vessels composed of?
They are composed of dead cells that align to form a continuous end-to-end tube.
Why are xylem tubes narrow?
It prevents the water column from breaking easily and allows capillary action to be effective.
What other structural features are present in xylem vessels?
The contain deposits of lignin which help to strengthen the cell wall (helps to prevent the walls from collapsing) and they contain pits/pores which allows for the sideways movement of water.
How is the xylem vessel adapted to ensure that the water flow is not impeded?
The xylem vessels do not contain any cell contents and end walls since they are dead cells.
True of false - mature xylem vessels are not almost completely impregnated with lignin and contain pits/pores.
False - they are impregnated almost completely with lignin and the pits/pores allow for the movement of water.
What are phloem vessels composed of?
They are composed of sieve tube elements and companion cells.
Give some general examples of assimilates.
Sucrose.
Amino acid - sap.
List some adaptations of the phloem vessels.
They are elongated cells positioned end to end to form a tubular structure and contain very little cytoplasm within the tubes providing little obstruction to movement.
They also do not contain a nucleus to prevent obstruction.
They also have perforated walls (sieve plates) to allow the movement of sap/assimilates.
The companion cells carry out the metabolic processes.
Why is water important for a plant?
Turgor pressure - allows the plant to drive roots through soil and other surfaces.
Water can be lost from the plant through evaporation which is a process that helps to cool the plant. - transpiration.
Water can also help to transport assimilates in aqueous solutions (dissolved in water).
It is a reactant needed in photosynthesis.
How does water move in a root cell from the soil water.
The water potential in the root cell is lower compared to the soil water whilst the concentration of minerals and other solutes is higher in the cytoplasm. So water moves into the root cells down its water potential gradient.
What are the 3 ways water movement can occur?
Apoplast, symplast, vacuolar.
Describe the distribution of vascular tissue in roots.
Xylem forms a central cylinder that is surrounded by phloem.
Vascular bundles are arranged in the centre which allows them to withstand tugging strains and can provide support as they grow through the soil and water is transported upwards.
Describe the arrangement of vascular tissue in stems.
The xylem and phloem are present in the outer region.
Vascular bundles are located around the edge which helps to provide strength and support.
It forms similarly to scaffolding which helps the stem to resistant bending.
Xylem tissue is found on the inside whilst phloem tissue is present on the outside. There a layer between known as the cambium - a layer of unspecialised cells that promote growth/contains meristematic tissue.
