ITS A GREEN WORLD WATER WATER EVERYWHERE Starter

IT’S A GREEN WORLD WATER, WATER EVERYWHERE

Starter How do tall trees get enough water? 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.

Water, water everywhere Learning objectives § Describe how water travels through a plant. § Explain that transpiration is a consequence of the way leaves are adapted for photosynthesis. § Explain how the cellular structure of a leaf is adapted to reduce water loss Success criteria § Student should be able to draw a plant showing the direction of flow of water. § Successfully complete a stomatal peel.

Plants and condensation Look at the demonstration (Worksheet. B 4 b 7) § Where has the condensation in bell jar A come from? § How do you know that it has not come from the air? § The condensation is tested with dry cobalt chloride paper, which is blue. Why is the cobalt chloride paper dried? § When the dry cobalt chloride paper is put against the condensation, what colour does it become? § What does this prove?

Movement of water up a stem

What is transpiration? Transpiration is the loss of water by evaporation from plants. Although it may seem bad for plants, transpiration actually moves water from the roots to the top of the plant, without using energy. How does this work?

Transpiration Draw a diagram of a tree showing the process of transpiration – use the textbook fig 8 p 60 to help you.

Transpiration Evaporation of water from a leaf creates a suction effect. This pulls the water up through the stem. This movement of water is useful because: § Evaporation of water cools the plant § Photosynthesis needs a supply of water § A cell full of water gives support § The water carries useful dissolved minerals

Balancing water loss with water uptake Plant adaptations to reduce water loss § Leaves have a waxy cuticle covering the upper epidermis § Most stomata are found on the lower surface of the leaf where it is darker and cooler.

Controlling water loss How do plants reduce water loss? § § Stomata mainly on lower epidermis Few stomata Small leaves The ability to close stomata

Balancing water loss with water uptake The stomata open and close automatically when supplies of water from the roots start to dry up. Open stomata allow gases in and out for photosynthesis Stomata are sensitive to light and close at night to conserve water. Guard cells turgid Guard cells flaccid Stoma opens Stoma closes

Stomatal peel experiment § Paint the upper and lower surfaces of a leaf with nail polish. § Allow to dry. § Gently peel off and mount on a microscope slide. § Place a cover slip on top and examine under the microscope. § How many stomata can you see? § Which side of the leaf has the most stomata?

Plenary

Water, water everywhere Learning objectives § Describe how water travels through a plant. § Explain that transpiration is a consequence of the way leaves are adapted for photosynthesis. § Explain how the cellular structure of a leaf is adapted to reduce water loss Success criteria § Student should be able to draw a plant showing the direction of flow of water. § Successfully complete a stomatal peel.