Photosynthesis

Question 1

What are the main differences between cyclic and non-cyclic photophosphorylation?

Answer 1

Non-cyclic photophosphorylation: Photosystem I and II are involved and reduced NADP and ATP are the products formed.

Cyclic photophosphorylation: Only Photosystem I is involved and ATP is the only product formed.

Question 2

What happens in non-cyclic photophosphorylation?

Answer 2

1. Electrons of P680 of Photosystem II are excited by light energy and donated to the primary electron acceptor.
2. Meanwhile, H2O is split to release electrons to replace the donated electrons, producing O2 in photolysis of water.
3. The excited electrons are passed along electron carriers in the Electron Transport Chain and the energy released is harnessed to produce ATP via chemiosmosis.
4. Electrons enter Photosystem I and replace the electrons that are lost from P700 and are also excited and donated from P700 to the primary electron acceptor.
5. The excited electrons from P700 are passed along another ETC to produce ATP. They are eventually passed to the final electron acceptor NADP to produce reduced NADP.

Question 3

Where are the photosystems located in the chloroplast?

Answer 3

Thylakoid membrane.

Question 4

What is the difference between Photosystem I and Photosystem II?

Answer 4

The reaction center pigment in Photosystem I is called P700 which absorbs light best at the wavelength of 700nm while the reaction center pigment in Photosystem II is called P680 which absorbs light best at the wavelength of 680nm.

Question 5

What is the function of a primary electron acceptor?

Answer 5

It accepts and traps energised electrons from the special chlorophyll a molecule.

Question 6

What is the function of the reaction center?

Answer 6

Chlorophyll a molecules found in the reaction center trigger the light reaction by donating their excited electrons to a primary electron acceptor which traps the high energy electrons and passes the electrons to the electron transport chain.

Question 7

What are the advantages of having the light harvesting antenna complex?

Answer 7

• Increases the range of wavelengths of light the photosystem can absorb
• Increases the amount of light energy the photosystem can absorb

Question 8

What does the light harvesting antenna complex consist of?

Answer 8

It consists of clusters of chlorophyll a, chlorophyll b and carotenoid molecules.

Question 9

What are the components of a photosystem?

Answer 9

1. Light harvesting antenna complex
2. Reaction center
3. Primary electron acceptor