18 Questions
What is the primary function of cyclic electron flow in the light reactions of photosynthesis?
Generate more ATP without producing NADPH
In the context of the light reactions of photosynthesis, which process involves the formation of a proton gradient to synthesize ATP?
Photophosphorylation
Which type of plants utilize cyclic photophosphorylation as a significant source of ATP production?
C4 plants
What is the role of the oxygen evolving complex in the light reactions of photosynthesis?
Catalyze photolysis to release oxygen and electrons
Which photosystem is primarily involved in cyclic electron flow during photosynthesis?
Photosystem I
What is the main outcome of coupling PSII and PSI in the Z-scheme during photosynthesis?
Boosting electrons to produce NADPH
What is the primary function of bundle sheath chloroplasts in C4 plants?
Perform the Calvin cycle to fix carbon dioxide
In bacterial photosynthesis, where does the light-dependent reaction take place?
Thylakoid membrane
What is the main role of RuBisCO in the process of photosynthesis?
Fix carbon dioxide
Which photosystem in the thylakoid membrane is responsible for producing ATP in photosynthesis?
Photosystem I (PSI)
What is the main function of PSII (Photosystem II) in the light-dependent reactions of photosynthesis?
Generate oxygen
How do C4 plants differ from C3 plants in terms of photosynthesis?
C4 plants fix carbon dioxide into a 4-carbon molecule before entering the Calvin cycle
What is the primary function of carotenoids in photosynthesis?
Prevent oxidative damage of chlorophyll
In photosynthesis, which wavelength range is absorbed most effectively according to Engelmann's action spectrum?
Violet-blue and red
What is the structure of chlorophyll b compared to chlorophyll a?
The CH3 group is replaced by an aldehyde group (-CHO)
Which of the following is NOT a fate of the energy absorbed by pigments in photosynthesis?
Transferring energy to carotenoids
What is the role of carotenoids in photosynthesis?
Provide photoprotection
Which pigment acts as the primary photosynthetic pigment in plants?
Chlorophyll a
Study Notes
The Light Reactions
- Light energy drives the synthesis of both ATP and NADPH
- The oxygen evolving complex catalyzes the splitting of two water molecules (photolysis) to produce oxygen, protons, and electrons
- The proton gradient drives the ATP synthase to generate ATP (photophosphorylation)
The Z-Scheme
- The coupling of PSII and PSI boosts electrons to the energy level needed to produce NADPH
Cyclic Electron Flow
- Cyclic electron flow generates more ATP without producing NADPH
- Switches photosystem I into cyclic mode, also known as cyclic photophosphorylation
- Important as an ATP source in the bundle sheath chloroplasts of some C4 plants and used in bacterial photosynthesis
Non-Cyclic vs Cyclic Photophosphorylation
- Non-cyclic: involves both PSI and PSII, and photolysis occurs
- Cyclic: only involves PSI, and no photolysis occurs
Photosynthetic Pigments
- Chlorophyll a: absorbs light that powers photosynthesis through the excitation of electrons
- Chlorophyll b: has the same structure as chlorophyll a but with an aldehyde group (-CHO), absorbs at 500-640 nm (appearing olive green)
- Carotenoids: yellow, orange, red, or brown pigments that absorb strongly in the blue-violet range, pass absorbed light energy to chlorophyll a, and provide photoprotection
The Action Spectrum
- Demonstrated in 1883 by Theodor W. Engelmann
- Reveals which wavelengths of light are photosynthetically important
- The action spectrum resembles the absorption spectrum of chlorophyll a and the accessory pigments
Chloroplasts
- Where photosynthesis takes place
- Contain pigments that absorb light energy
- Site of the light-dependent reactions
Photosynthesis in General
- Life on earth ultimately depends on energy derived from the sun
- Photosynthesis is the only biological process that can harvest this energy
- Converts light energy into chemical energy
Test your knowledge on the light reactions of photosynthesis, including the production of ATP and NADPH, photolysis, and photophosphorylation. Questions may cover concepts from the electron transport chain, Fe-S proteins, and the oxygen evolving complex.
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