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Published byDerek Burke Modified over 6 years ago
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Photosynthesis In these lessons we will: Revise photosynthesis Use a practical activity to look at the conditions needed for photosynthesis to happen Investigate photosynthesis using algae
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Revising photosynthesis
What is photosynthesis? Why do plants do it? How would a person tell if a plant is photosynthesising?
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Photosynthesis light energy Carbon dioxide Water Glucose Oxygen
Chlorophyll
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So photosynthesis makes oxygen and glucose.
How could a plant be tested for these? An alternative is to test for a substance that plants make from glucose. What do plants make from glucose? STARCH ! So the plant could be tested for starch to show it had been photosynthesising.
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Photosynthesis light energy Carbon dioxide Water Glucose Oxygen
Chlorophyll
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Now the class will carry out some practical work
on some destarched Geranium plants. Each pair is trying to find out which leaves have been photosynthesising Starch will be present if the plant has been able to photosynthesise. Iodine is used to test for Starch.
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Collect the following apparatus:
Bunsen burner, tripod, heat mat, test tube rack, 4 boiling tubes, 1 large beaker, 1 white tile, glass rod, 1 bottle of iodine and dropper, a marker pen
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Testing leaves for Starch
Step Boil leaf in water for a few minutes Boil leaf in alcohol for a few minutes Place leaf in hot water for 30 seconds Add Iodine to leaf Reason To soften cells in leaf To remove green pigment (chlorophyll) To re-soften cells in leaf To stain any starch in leaf
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Use a white tile to collect and record the results
Leaf A Leaf B Leaf C Leaf D
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What have you learned? Which leaves had starch present? What is necessary for photosynthesis? So for photosynthesis plants need? light energy Carbon dioxide Water Glucose Oxygen Chlorophyll
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Write – up your practical.
Describe what you did Describe your results Explain what the results mean.
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Practicals Using algal cells to investigate photosynthesis The class will now carry out some practicals to investigate photosynthesis using algal cells. Initially the algal cells will need to be immobilised using a simple immobilisation technique that your teacher will show you. Refer to guide as necessary
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Investigations into photosynthesis
The immobilised algal cells can be used to investigate the effects of a variety of factors on photosynthesis. When completing an investigation it would be good practice to complete it in the standard format. The teacher will advise you on this.
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You should by now have a good understanding of
the factors that affect the rate of photosynthesis. Write down what they are and what affect they have on a plants rate of photosynthesis.
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Practical using algal balls
Does changing the light intensity affect the amount of photosynthesis? Design an experiment to answer this question and carry it out!!!!!
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