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8.2 Photosynthesis
8.2.1 Draw and label a diagram showing the structure of a chloroplast as seen in an electron micrograph
2D Representation
3D Representation
Electron Micrograph
8.2.2 State that photosynthesis consists of the light-dependent and light-independent reactions
Photosynthesis is a two-step process:
1. The light dependent reactions convert the light energy into chemical energy
2. The light independent reaction uses the chemical energy to make organic molecules
Overview of Photosynthesis
8.2.3 Explain the light dependent reactions
The light dependent reactions occur on the thylakoid membrane and may occur by either cyclic or non-cyclic processes
In both processes, light excites chlorophyll (clustered in photosystems) which release electrons that pass through an electron transport chain, making
ATP (photophosphorylation)
Non-Cyclic Photophosphorylation
Chlorophyll in photosystems I and II absorbs light, which triggers the release of high energy electrons (photoactivation)
The electrons from photosystem II pass along a series of carriers (electron transport chain), producing ATP via chemiosmosis
The electrons from photosystem I reduce NADP+ to generate NADPH + H+
Electrons lost from photosystem I are replaced by electrons from photsystem II
Electrons lost from photosystem II are replaced by electrons generated by the photolysis of water (oxygen is produced as a by-product)
Cyclic Photophosphorylation
Only photosystem I is involved in cyclic photophosphorylation
The high energy electrons released by photoactivation pass along an electron transport chain (producing ATP) before returning to photosystem I
Cyclic photophosphorylation does not produce NADPH + H+, which is needed for the light independent reactions
Thus while cyclic photophosphorylation can make chemical energy (ATP) from light, it cannot be used to make organic molecules
Standard Level
Higher Level
Options
Additional Resources
8.2 Photosynthesis
8.2.1 Draw and label a diagram showing the structure of a chloroplast as seen in an electron micrograph
2D Representation
3D Representation
Electron Micrograph
8.2.2 State that photosynthesis consists of the light-dependent and light-independent reactions
Photosynthesis is a two-step process:
1. The light dependent reactions convert the light energy into chemical energy
2. The light independent reaction uses the chemical energy to make organic molecules
Overview of Photosynthesis
8.2.3 Explain the light dependent reactions
The light dependent reactions occur on the thylakoid membrane and may occur by either cyclic or non-cyclic processes
In both processes, light excites chlorophyll (clustered in photosystems) which release electrons that pass through an electron transport chain, making
ATP (photophosphorylation)
Non-Cyclic Photophosphorylation
Chlorophyll in photosystems I and II absorbs light, which triggers the release of high energy electrons (photoactivation)
The electrons from photosystem II pass along a series of carriers (electron transport chain), producing ATP via chemiosmosis
The electrons from photosystem I reduce NADP+ to generate NADPH + H+
Electrons lost from photosystem I are replaced by electrons from photsystem II
Electrons lost from photosystem II are replaced by electrons generated by the photolysis of water (oxygen is produced as a by-product)
Cyclic Photophosphorylation
Only photosystem I is involved in cyclic photophosphorylation
The high energy electrons released by photoactivation pass along an electron transport chain (producing ATP) before returning to photosystem I
Cyclic photophosphorylation does not produce NADPH + H+, which is needed for the light independent reactions
Thus while cyclic photophosphorylation can make chemical energy (ATP) from light, it cannot be used to make organic molecules