8.3 Photosynthesis
Energy Transfer
Write a chemical equation for the process of photosynthesis
6CO2 +
12H O
sunlight
C H O
+
6O
+
6H O
6 12 6
2
2
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2
chlorophyll
Outline the organisation of photosynthetic pigments into photosystems
Photosynthetic pigments absorb different wavelengths of light, so to maximise light absorption they are
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grouped into photosystems (with accessory pigments passing electrons to a central reaction centre)
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Identify the two stages of photosynthesis
Light dependent reactions
1. …………………………………………………………………………………………………………………………………………………...
Light independent reactions (i.e. Calvin cycle)
2. …………………………………………………………………………………………………………………………………………………..
Chloroplasts
Label the different parts of a chloroplast
3
1
Outer membrane
1. …………………………………………………………………………
4
Stroma
2. …………………………………………………………………………
Inner membrane
3. …………………………………………………………………………
5
2
Thylakoid
4. …………………………………………………………………………
Granum
5. …………………………………………………………………………
Explain the relationship between the structure of the chloroplast and its function
Structure
Function
Thylakoid
Disc shaped with small lumen (small volume maximises proton gradient)
Grana
Thylakoids organised into stacks (increases SA:Vol ratio)
Stroma
Contains appropriate enzymes and suitable pH for the Calvin cycle to occur
Photosynthesis Stages
Describe the key events in the light dependent reactions (non-cyclic photophosphorylation)
Light photoactivates chlorophyll within photosystem II (P680) and photosystem I (P700)
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Electrons released from PSI are taken up by hydrogen carriers (forms NADPH)
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Electrons released from PSII go through an electron transport chain (causing proton accumulation in thylakoids)
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Protons return to the stroma via chemiosmosis through ATP synthase (producing ATP via photophosphorylation)
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Electrons lost from PSI are replaced by PSII electrons, while PSII electrons are replaced by photolysis of water
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Compare cyclic and non-cyclic photophosphorylation
Cyclic Photophosphorylation
Non-Cyclic Photophosphorylation
Photosystems
PSI only
PSI AND PSII
Products
ATP only
ATP AND NADPH
Purpose
Cannot be used to make organic molecules
Used to make organic molecules via
light independent reactions (Calvin cycle)
Describe the key events in the light independent reactions (Calvin cycle)
Carbon fixation: RuBP is carboxylated by carbon dioxide to form two 3C compounds (GP)
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Reduction: GP is reduced by NADPH and reacts with ATP to form triose phosphate (TP)
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Regeneration: One TP molecule is used to make organic compounds, the rest are reacted with ATP to reform RuBP
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Outline how Calvin established the stages of the Calvin cycle via the ‘lollipop’ experiment
Calvin treated algae with radioactive carbon (14C) in a ‘lollipop’ apparatus
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Algae was then subjected to light to promote photosynthesis
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Algae was then killed (with alcohol) at different time periods and the carbon compounds were extracted
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(via 2D chromatography) and then visualised (via autoradiography)
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This allowed Calvin to elucidate the order in which carbon compounds occurred (i.e. RuBP to GP to TP to RuBP)
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