Chapter 9- Transport System And Water Transport In Plants Flashcards
Why do plants need transport systems
1) they are multicellular so they have a small surface area to volume ratio.
2) they also have high metabolic rate and simple diffusion would be too slow for metabolic demands
Why does the xylem tissue transport
Water and mineral ions in solution. These substances move up the plant from the roots to the leave’s.
What does the phloem tissue transport
It mainly transports sugars, both up and down the plant.
Where are the phloem and xylem located
In the roots, the xylem and phloem are in the centre for support
In the stem, they are near the outside (like a ring) to reduce bending
In the leaves, they make up a network of veins to support thin leaves.
Adaptations of xylem vessels
1) there are no end walls on the cells, making an uninterrupted tube that allows water to pass up through the middle easily.
2) cell walls are thickened with lignin to support the walls and stop them from collapsing.
3) lignin is deposited in different ways eg in a spiral or distinct rings to allow for flexibility.
4) vessels have small pits with allow mineral ions and water to be supplied to other cells.
What does the phloem contain
1) phloem fibres
2) phloem parenchyma
3) sieve tube elements
4) companion cells
What are sieve tube elements
They are living cells that are joined end to end to form sieve tubes. The end walls have lots of holes to allow solutes to pass through. They have no nucleus, a very thin cytoplasm and few organelles. The cytoplasm in adjacent cells is connected through the holes in the sieve plates.
What are companion cells
The lack of a nucleus and other organelles in sieve tube elements mean they cannot survive on their own. Companion cells carry out the living functions for both themselves and their sieve cells. For example, they provide energy for the active transport of solutes.
Examination of stained plant tissue
If stained with toluidine blue O, the lignin in the walls of the xylem cells become blue-green. The phloem and other cells appear shades of pink and purple.
Xylem vessel also tend to have a wider diameter than phloem vessels.
Plant dissection preparation
1) use a scalpel to cut a cross section of the stem. Cut the sections as thinly as possible.
2) use tweezers gently place the cut sections in water until you come to use them (stops it from drying out)
3) add a drop of water to a microscope slide, add the plant section and carefully add 1-2 drops of a stain eg toludine blue O and leave for one minute.
4) carefully apply a cover slip with a mounted needle for no air bubbles.
5) view specimen under light microscope.
How does water enter a plant
Water enters the root hair cells via osmosis and then passes through the root cortex, including the endodermis to reach the xylem. The water moves from an area of high water potential (roots) to low water potential (leaves).
Roots have high water potential because they are always surrounded by water and leaves have low water potential because water is always evaporating. This creates water potential gradients which keeps water moving through the plant in the right direction.
What is the symplast pathway
This is when the water goes through the cytoplasm of cells. The cytoplasm of neighbouring cells are connected through plasmodesmata. Water moves via osmosis.
What is the vacuolar pathway
Same as the symplast pathway, but water also goes through the vacuole as it passes through the cell. Makes this pathway the slowest.
What is the apoplast pathway
This is when water goes through the cell walls. The cell walls are very absorbent so water can diffuse through them. Water can carry solutes and move from areas of high hydrostatic pressure to areas of low hydrostatic pressure (mass flow).
When water reaches the endodermis cells, the water is blocked by the casparian strip so water now enters the symplast pathway. This is useful because this means water goes through the cell surface membrane so filters any impurities in the water.
How is water transported through the leaves
At the leaves, water leaves the xylem and moves into the cells mainly by the apoplast pathway. Water evaporated from the cell walls into the spaces between cells in the leaf. When the stomata open, water evaporates. It diffuses out of the leaf into surrounding air. This is known as transpiration.
