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)

• To explain how substances are transported around the plant. (B Grade)

• To describe the process of transpiration in plants and explain the factors that effect transpiration. (A Grade)

• Write out the word equation for photosynthesis!

• Symbol equation for A* / A http://www.youtube.com/watch?v=wj8TGhcCnxs

How do plants transport materials to where they are needed?

MOVING MATERIALS

WHICH CELLS TRANSPORT NUTRIENTS?

The cells are arranged in plants as vascular bundles.

Plants contain two types of cell adapted for transportation.

Phloem cells transport sugars produced in the leaves up and down the stem to growing and storage tissues.

Xylem cells transport water and minerals up the stem from the roots to the shoots and leaves. This transport occurs in one direction only.

Both phloem and xylem form continuous systems connecting roots, stems and leaves.

What are the vessels that transport water around the plant?

What are the vessels that transport food around the plant?

In what direction do these vessels carry the substances around the plant?

Xylem

Phloem

Phloem – both directionsXylem – from roots to leaves

WATER LOSS DURING PHOTOSYNTHESISThe 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?

LEAF ADAPTATIONSIf the stomata were permanently open, the plant would continue to lose water until it dried up.

In order to prevent excess water loss, leaves have developed an outer waxy cuticle that prevents evaporation from cells.

Most stomata are located on the underside of leaves, keeping them in the shade. This prevents excess evaporation when the stomata are open.

When a plant does not have enough water to spare, guard cells cannot become turgid and open the stomata.

stoma

waxy cuticle

HOW DO TALL TREES GET ENOUGH WATER?Redwoods are the tallest species of tree in the world.

How does a plant this size get water from its roots to the branches at the top?

What experiment could show that water travels up stems?

The tallest redwood ever measured was 120 metres tall. That is six times the height of the Angel of the North!

The water will travel up the stem, or trunk, of the tree.

WHAT IS TRANSPIRATION?

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?

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.

Transpiration is the loss of water from plants by evaporation.

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.

Air around the plant usually contains less water than the cells of the plant, so water evaporates into the air.

Transpiration can be measured using a potometer.

A cut plant stem is sealed into the potometer using a rubber bung.

This gives an indirect measurement of the rate of transpiration.

An air bubble is introduced to the capillary tube.

The distance the bubble travels shows how much water the stem has taken up.

HOW IS THE RATE OF TRANSPIRATION MEASURED?