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112/04/12
Photosynthesis光合作用香港道教聯合會青松中學吳友強
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Leaf 葉片X-section橫切面 :Palisade mesophyll柵狀葉肉
Chloroplast葉綠體
Quick Revision :Where does photosynthesis occur ？
電子顯微鏡下的葉綠體
Chloroplast under electron microscope
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Warm-up QuestionsWarm-up QuestionsThe following microphotograph is a transverse section of a
A. stem.
B. leaf.
C. root.
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Sorry, you’ve got the wrong answer!!!
Can you find cortex ( 皮層 ), which is very obvious in a cross-section
of a stem ?
Try again...
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Sorry, you’ve got the wrong answer!!!
Are the vascular bundles( 維管束 ) concentrated in the centreof the section ?
Try again...
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Congratulations!!!
You’ve got the correct answer!!!
Go to next question...
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Warm-up QuestionsWarm-up QuestionsHere is a transverse section of a leaf. It is a leaf of
A. monocotyledonous xerophyte
B. dicotyledonous hydrophyte
C. dicotyledonous mesophyte
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Sorry, you’ve got the wrong answer!!!
Xerophyte is a kind of plants adapted in desert habitat.
Try again...
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Sorry, you’ve got the wrong answer!!!
Hydrophyte is a kind of plants adapted in aquatic habitat.
Try again...
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Congratulations!!!
You’ve got the correct answer!!!
Bonus …….
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Bonus :
Give two reasons to support your answer.
??????
??????
??????
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Definition of Photosynthesis
Photosynthesis is a process by which green plants use sunlight trapped by chlorophyll to produce organic compounds (carbodyrate) from carbon dioxide and water, oxygen is released as by-product.
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Summary of Photosynthesis
Carbon dioxide二氧化碳
Water水
Oxygen氧
Glucose葡萄糖
Chlorophyll葉綠素
Sunlight陽光
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Experiments :
1.To show that starch is produced during Photosynthesis.
light6CO2 ＋ 6H2O C6H12O6 + 6O2 chlorophyll
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Four steps :
1.Boil the leaf in water, why ?
2.Boil the leaf in alcohol, why ?
3.Wash the leaf in warm water, why ?
4.Add iodine solution to the leaf, what is the expected result ?
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Experiments :
Aim :
To show that light is necessary for Photosynthesis.
Control :
Do we need a Control for this experiment ?
light6CO2 ＋ 6H2O C6H12O6 + 6O2 chlorophyll
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Experiments :
Aim :
To show that chlorophyll is necessary for photosynthesis.
light6CO2 ＋ 6H2O C6H12O6 + 6O2 chlorophyll
Control :
Do we need a Control for this experiment ?Any Assumption ?
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Experiments :
Aim :
To show that carbon dioxide is necessary for photosynthesis.
light6CO2 ＋ 6H2O C6H12O6 + 6O2 chlorophyll
Any Criticism on the set-up ?
(Think about Variables.)
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Is it better ?
light6CO2 ＋ 6H2O C6H12O6 + 6O2 chlorophyll
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Experiments :
Aim :
To show that oxygen is produced during
photosynthesis.
light6CO2 ＋ 6H2O C6H12O6 + 6O2 chlorophyll
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LogicsIn an experiment, think about :
Aim and objective
Control experiment
Dependent variables
Independent variables
Assumptions
Limitations
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Limitations of the summary equation :
1.Photosynthesis is a two phase process, which cannot be shown in the equation.
2.Source of oxygen cannot be shown.
3.Glucose is not the first product of photosynthesis.
6CO2 ＋ 6H2O C6H12O6 + 6O2
light
chlorophyll
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Photosynthesis involves two stages :
Light reaction• light is necessary• light split water into hydrogen and oxygen
Dark reaction• light is not necessary• hydrogen is used to reduce carbon dioxide
to carbodyrate
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Water水
Light陽光
Chlorophyll葉綠素
Oxygen氧
Hydrogen 氫（原子）
Released fromthe plant
Dark reaction
Light reaction
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Hydrogen 氫（原子）
Carbon dioxide
二氧化碳
Carbohydrate碳水化合物
Dark reaction
