Photosynthesis

Question 1

What is the process of light-dependent reactions?

Answer 1

1. Photoactivation
2. Photolysis
3. Electron transport chain
4. Chemiosmosis
5. ATP synthesis
6. NADP reduction

Question 2

Where does the light dependent reaction take place?

Answer 2

Thylakoids, a special membrane structure found within the chloroplast.

Question 3

Where does the light independent reaction take place?

Answer 3

In the stroma

Question 4

What are the steps in light independent reactions?

Answer 4

1. Carbon fixation
2. Carboxylation of RuBP
3. Triose phosphate production

Question 5

Explain what happens in photosystem 2.

Answer 5

• Chlorophyll molecules are activated by light photons.
• This energy is taken to the reaction center, which provides 2 electrons.
• They go up in energy level and are taken in by an electron carrier known as plastoquinone.
• Plastoquinone carries those electrons to another carrier which takes them to photosystem 1.
• This process is repeated so that there is a total of 4 electrons.

Question 6

Explain the process of photolysis.

Answer 6

• Because the reaction center lost 4 electrons, it becomes a powerful oxidising agent.
• Therefore, water molecules are split, and the electrons are given for use in the light-dependent reaction.

Question 7

Explain what happens in the light-dependent reaction.

Answer 7

1. Light energy is absorbed by PSII. Light energy excites electrons in chlorophyll. Electrons move to a higher energy level. These electrons move along the electron transport chain to PSI.
2. Photolysis takes place to produce more electrons.
3. Excited electrons lose energy as they move along the ETC. This energy is used to transport protons into the thylakoid so that it has a higher concentration of protons than the stroma, which forms a proton gradient across the membrane. Protons move into the stroma through ATP synthase, which forms ATP(used for the Calvin cycle).
4. Light energy is absorbed by PSI which excites electrons to a higher energy level. Electrons are transferred to NADP, along with a proton from the stroma to form reduced NADP for the Calvin cycle.

Question 8

Where does the Calvin cycle take place?

Answer 8

Stroma of the chloroplast

Question 9

What are the 4 phases of the Calvin cycle?

Answer 9

1. Carbon fixation
2. Reduction of 3-PGA to triose phosphate.
3. Release of one molecule of triose phosphate to make glucose and other compounds.
4. Regeneration of Ribulose Bisphosphate.

Question 10

Explain what happens in the Calvin cycle.

Answer 10

• CO2 reacts with Ribulose Bisphosphate to form two molecules of glycerate 3-phosphate.
• ATP and reduced NADP are required for the reduction of GP to triose phosphate.
• Ribulose Bisphosphate is regenerated.

Question 11

What is the function of rubisco?

Answer 11

It is an enzyme that catalyzes the reaction between CO2 and RuBP.

Question 12

What is the function of the thylakoid and grana?

Answer 12

Thylakoids and grana offer a large surface area where photosystems, ETC, and ATP synthase are embedded and light-dependent reactions occur.

Question 13

What is the function of the small thylakoid membrane space?

Answer 13

Allows the fast generation of the H + gradient needed for chemiosmosis.

Question 14

What is the function of the Stroma?

Answer 14

This contains rubisco, as well as other enzymes, substrates, NADPH and ATP molecules to keep the Calvin cycle turning.

Question 15

What is the function of 70s ribosomes?

Answer 15

Synthesize some of the proteins and enzymes needed within the chloroplast.