Photosynthesis 光合作用

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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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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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Xerophyte is a kind of plants adapted in desert habitat.

Try again...

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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 ?


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Experiments :

Aim : To show that chlorophyll is necessary for

photosynthesis.


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.


Any Criticism on the set-up ?

(Think about Variables.)

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Is it better ?


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Experiments :

Aim : To show that oxygen is produced during

photosynthesis.


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LogicsIn an experiment, think about :Aim and objectiveControl experimentDependent variablesIndependent variablesAssumptionsLimitations

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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 oxygenDark 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

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Photosynthesis 光合作用