Photosynthesis

Question 1

Where do the light depedndent and light independent reactions occur in plants?

Answer 1

Dependent: thylakoids of chloroplasts

Independent: stroma of chloroplasts

Question 2

What process takes place to start the ETC?

Answer 2

Light E is absorbed by chlorophyll

Light E excites e-s in the chlorophyll (raises them to a higher E level) so they’re released from the chlorophyll molecule.

The chlorophyll has been photoionised.

Question 3

Describe part I of the LDR.

Answer 3

ETC:

Elelctrons released from the chlorophyll move down a seeries of carrier proteins embedded in the thylakoid membrane and undergo a series of redox reactions that release energy.

Question 4

How does the ETC effect chemiosmosis?

Answer 4

It helps establish a concerntration gradient of protons for chemiosmosis.

Some E released from the ETC is coupled to the active transport of H+ ions (protons) from the stroma into the thylakoid space.

Question 5

Describe part 2 of the LDR.

Answer 5

Chemiosmosis

• some E released from the ETC is used to actively transport protons from the stroma to the thylakoid space.
• these protons move back into the stroma, down their conc. gradient via ATP synthase.
• the movemnt down the concerntration gradient catalyses the reaction: ADP + Pi -> ATP

Question 6

State the roles of ATP and reduced NADP in the light independent reaction.

Answer 6

ATP: reduction of GP to TP and provides phosphate group to convert RuP into RuBP.

Reduced NADP: coenzyme transports electrons needed for reduction of GP to TP.

Question 7

What is the purpose of the LDR?

Answer 7

To capture light energy to:

• make ATP
• split water into H+ ions (protons) and OH- ions (photolysis).

(remeber PS is the making of glucose (to be converted into ATP?E) and oxygen from CO2 and water.
This is where water comes from and why O2 is produced from the LDR.

Question 8

Diagram of how the LIR and LDR reaction interact.

Question 9

Where do the H+ ions and electrons used to reduce NADP come from?

Answer 9

H+ ions: photolysis of water

Electrons: NADP acts as as the final electron acceptor of the elctron transfer chain.

Question 10

Name the 3 stages of the calvin cycle.

Answer 10

1. carbon cycle
2. reduction
3. regeneration

Question 11

Outline the sequence of events in the light independent reaction (Calvin cycle).

Question 12

Describe the calvin cycle.

Answer 12

carbon fixation: Raaction between RuBP (ribulose bisphosphate) and CO2 catalysed by rubisco.

reduction:
2 x GP are reduced to 2 x TP
requires 2 x reduced NADP and 2 x ATP.
Forms 2 x NADP and 2 x ADP.

regeneration:
- after 1C leaves the cycle to form useful organic molecules, the 5C compound RuP forms.
- RuBP is regenerated from RuP leaving 1 x ATP.
- forms 1 x ADP

Question 13

How are the products of the LDR used in the LIR?

Answer 13

ATP and reduced NADP from the LDR supply the energy and hydrogen needed to make simple sugars from CO2.

Question 14

How and wher is reduced NADP produced in the light- dependent reaction?

Question 15

What happens to the products of the photolysis of water?

Answer 15

H+ ions: move out of the thylakoid space vis ATP synthase and are used reduce the coenzyme NADP.

e- : replace the electrons lost from chlorophll

O2: used for respirationor diffuses out of the leaf as a waste gas.

Question 16

State the no. of carbon atoms in RuBP, GP and TP.

Answer 16

RuBP: 5
GP: 3
TP: 3

Question 17

How does the light-independent reaction result in the production of useful organic substances?

Answer 17

1C leaves the cycle (ie. some of the Tp is converted into organic molecules).

Question 18

How is a proton concerntration gradient established during chemiosmosis?

Answer 18

In order for there to be higher concerntration of H+ ions in the thylakoid space, more must enter the thylakoid.

Energy from the ETC is coupled with te active transport of H+ ions from the stroma to the space.

Question 19

Explain the role of light in photolysis.