Plant transport. How would you make a rainbow rose?. Lesson Objective: To show how the substances needed by the plant are transported around the plant. Success ! To relate the structure of xylem and phloem to their function (A Grade)
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How would you make a rainbow rose?
To show how the substances needed by the plant are transported around the plant.
Symbol equation for A* / A
How do plants transport materials to where they are needed?
Plants contain two types of cell adapted for transportation.
Xylem cells transport water and minerals up the stem from the roots to the shoots and leaves. This transport occurs in one direction only.
Phloem cells transport sugars produced in the leaves up
and down the stem to growing and storage tissues.
The cells are arranged in plants as vascular bundles.
Both phloem and xylem form continuous systems connecting roots, stems and leaves.
Phloem – both directions
Xylem – from roots to leaves
The underside of leaves have small holes called stomata. Each stoma is surrounded by two guard cells.
During photosynthesis, low carbon dioxide levels inside the plant cause guard cells to gain water and become turgid. They curve out, opening the stoma and allowing gases in and out. Water also evaporates through the stomata.
High carbon dioxide levels cause the guard cells to lose water, closing the stoma and preventing further water loss.
What would happen if the stomata were permanently open?
If the stomata were permanently open, the plant would continue to lose water until it dried up.
When a plant does not have enough water to spare, guard cells cannot become turgid and open the stomata.
Most stomata are located on the underside of leaves, keeping them in the shade. This prevents excess evaporation when the stomata are open.
In order to prevent excess water loss, leaves have developed an outer waxy cuticle that prevents evaporation from cells.
Redwoods are the tallest species of tree in the world.
The tallest redwood ever measured was 120 metres tall. That is six times the height of the Angel of the North!
How does a plant this size get water from its roots to the branches at the top?
The water will travel up the stem, or trunk, of the tree.
What experiment could show that water travels up stems?
Plants lose water when they open the stomata in their leaves to let in carbon dioxide. A stoma can only open if there is enough water in its guard cells. This helps to prevent excessive water loss.
Transpiration is the loss of water from plants by evaporation.
Water always moves from an area of high concentration to an area of low concentration. This movement of water is a type of diffusion called osmosis.
Air around the plant usually contains less water than the cells of the plant, so water evaporates into the air.
Although transpiration may seem bad for plants, it actually moves water from the roots to the top of the plant, without using energy. How does this work?
Transpiration can be measured using a potometer.
A cut plant stem is sealed into the potometer using a rubber bung.
An air bubble is introduced to the capillary tube.
The distance the bubble travels shows how much water the stem has taken up.
This gives an indirect measurement of the rate of transpiration.