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© Edco 2007 Exploring Science Biology Photosynthesis is the way in which green plants make their food. Photosynthesis needs: –Carbon dioxide –Water –Light –Chlorophyll CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology Photosynthesis produces: –Glucose –Oxygen The word equation for photosynthesis is: carbon dioxide sunlight glucose + + water chlorophyll oxygen CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology To test a leaf for starch involves the following four steps: 1. Boil the leaf in water- this kills and softens the leaf. 2. Soak the leaf in hot alcohol – this removes the chlorophyll (green colour) 3. Place the leaf in boiling water- to re-soften the leaf 4. Add iodine — to test for starch CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology 1. 2. CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology 3. 4. CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology To show that starch is made by a plant in photosynthesis: –Put a plant into the dark for two days. –Cover some of the leaves with aluminium foil. –Leave the plant in bright light. CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology –Test the covered and uncovered leaves for starch. –The uncovered leaves turn blue-black (starch made in photosynthesis). –The covered leaves remain red-yellow (no starch made as photosynthesis does not happen in the dark). CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology A tropism is the change in growth of a plant in response to an outside stimulus. Phototropism is the way in which a plant changes its growth in response to light. The shoots of a plant grow towards light. CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology Phototropism can be investigated in the following way: Grow some seedings in lightproof boxes with holes cut in different positions. The shoots of the seedings are seen to always grow towards the light. CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology (H/L) Geotropism is the way in which a plant changes its growth in response to gravity: - The shoots of a plant grow away from gravity. - The roots of a plant grow towards gravity. CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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© Edco 2007 Exploring Science Biology (H/L) Geotropism can be investigated in the following way: - Plant some seeds in different positions. - The shoots always grow upwards (away from gravity) - The roots always grow downwards (towards gravity). CHAPTER 13 PHOTOSYNTHESIS AND PLANT RESPONSES
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