Mrs Abrey Lesson 4 exchange in plants
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Transcript of Mrs Abrey Lesson 4 exchange in plants
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Exchange in plants
Lesson objectives
• All will be able to state substances to be exchanged in plants
• Most will be able to describe and explain how plants maximise exchange
• Some will be able to suggest reasons why plants do not need to exchange carbon dioxide from the air continuously
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Stick the leaf diagram in books and label
• Key words:
– Stomata
– Guard cell
– Upper epidermis
– Lower epidermis
– Waxy cuticle
– Palisade cells
– Spongy mesophyll
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Exchange in plants
• What substances do plants need to exchange?
• Where do they exchange these substances?
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How are leaves adapted for efficient gas exchange?
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1. Surface area
• The flattened shape of a leaf (and internal air spaces) increases surface area for diffusion
• Thin to reduce the distance for diffusion
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2. They only take in carbon dioxide when they need to
• Why don’t leaves need carbon dioxide all the time?
• All over the surface of a leaf are small openings known as stomata. They can be opened or closed (by guard cells). Only open when carbon dioxide is needed so prevents too much water loss.
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Exchange in Plants
• Are there more stomata on top of the leaf or under it?
• Make a prediction
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Exchange in plants
• Apply a thin layer of clear nail varnish to the lower surface of the leaf.
• Allow to dry• Carefully peel off the dry nail varnish with a pair of
tweezers• Place peel in a drop of water on a microscope slide• Cover with a coverslip • View sample under microscope first under low
magnification and then high.• Count and record the number of stomata you see.• Repeat - coating the upper surface of the leaf.
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One Stoma
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On the underside of leaves are small holes, or pores, called stomata. A single hole is called a stoma.
Each stoma is surrounded by two guard cells, which control the opening and closing of the stoma.
What would happen if the stomata were permanently open?
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Exchange in plants
• Now look under the microscope at the cress roots – what do you notice
• How does this help the plant?
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How are roots adapted for water/mineral uptake?
1. Thin
2. Divided into many tubes (increases surface area)
3. The cells of the roots are made up of tiny projections called root hair cells (increases SA)