Plant Transport Flashcards
(43 cards)
What does the vascular tissue of plants consist of?
The vascular tissue of plants consists of xylem and phloem.
What do xylem vessels transport?
Xylem vessels transport water and inorganic ions from the roots to the leaves.
What do phloem tubes transport?
Phloem tubes transport organic molecules (sucrose and amino acids) from the leaves to growing points and to the roots.
What is the process called when phloem transports organic molecules?
This process is known as TRANSLOCATION.
Where are vascular tissues found in a root?
Xylem and phloem are found in the centre of a root as a central stele.
What surrounds the stele in a root?
The stele is surrounded by a single layer of cells known as the endodermis.
What are the general undifferentiated cells between the endodermis and the epidermis in a root called?
These cells are known as the cortex (parenchyma).
Where are the vascular tissues found in a stem?
Vascular tissue is arranged as vascular bundles around the outside of the stem.
What is the function of the cortex in a stem?
The cortex may be used for starch storage or maintaining turgidity.
How is the xylem adapted for transport of water and ions?
The xylem has no end walls and no cell contents, allowing unrestricted transport. The walls are thickened with impermeable lignin and cellulose, which prevents leakage of water and provides strength to prevent collapse due to tension from the transpiration stream, as well as structural support for the plant.
What patterns of lignification are found in the more immature protoxylem?
Annular and spiral lignification allow expansion and elongation during growth.
What patterns of lignification are found in the more mature metaxylem?
Reticulate and pitted lignification allows movement of water between adjacent vessels and surrounding cells.
What is TRANSPIRATION?
Transpiration is the evaporation of water from the spongy mesophyll cells followed by the diffusion of water through the stomata and into the atmosphere.
What are the 3 main stages in the transport of water and ions through a plant?
- Movement into root hairs and across the root
- Transport up the stem in the xylem
- Transport through the leaf and evaporation from the leaf.
How do water and ions enter the plant?
Water is taken up by root hair cells by osmosis (high water potential to lower water potential). Mineral ions are taken up by root hair cells by active uptake or facilitated diffusion. The root hair cells provide a thin surface membrane, a permeable wall and a large surface area for this.
Describe the APOPLAST pathway.
In the apoplast pathway, water moves along the cellulose microfibrils of the cell walls of the cortex cells. This is aided by the parallel arrangement of the microfibrils and the mesh-like arrangement of the walls. Cohesion between the water molecules (due to hydrogen bonds) helps pull the water column along.
Describe the SYMPLAST pathway across the root cortex.
In the symplast pathway, water moves by osmosis from cell to cell via the cytoplasm and plasmodesmata of each cell of the cortex.
It moves by osmosis along the water potential gradient
Which partner is faster, apoplast or symplast?
Apoplast pathway.
What is the endodermis?
A layer of cells just outside the stele of the root with walls embedded with a waxy layer of suberin called the Casparian strip.
What happens at the Casparian strip?
Water is forced out of the apoplast pathway and into the symplast pathway, crossing the plasma membrane.
What is the importance of the Casparian Strip?
It provides metabolic control over which ions enter the xylem.
What provides the force needed to transfer water and ions from the endodermis into the xylem?
Energy is used to pump ions into the xylem from the endodermis, creating a water potential gradient to draw in water by osmosis. This creates a root pressure from below to help push water up through the xylem
