Photosynthesis

Question 1

Light dependent reactions occur where?

Answer 1

In the thylakoid membranes

Question 2

Non-cyclic photophosphorylation

Answer 2

1) Light absorbed by PSII exciting 2 electrons
2) Electrons pass through ETC via redox reactions - lose energy used to produce ATP via chemiosmosis
3) Electrons passed to PSI
4) Light energy absorbed by PSI, exciting pair of electrons
5) Electrons move down ETC, generating more ATP
6) Electron pair gets added to NADP to make NADPH in stroma
7) Electrons replaced through photolysis of water

Question 3

Why is it called non-cyclic photophosphorylation?

Answer 3

Electrons don’t return back to PSII

Question 4

Cyclic photophosphorylation

Answer 4

1) Light energy absorbed by PSI, causing electron pair to be excited
2) Electrons pass through ETC, generating ATP
3) Electrons return to PSI
4) As electrons pass through ETC, energy lost is used to pump protons from stroma into thylakoid interior - can’t diffuse back as impermeable.
Creates proton gradient

Question 5

When does cyclic photophosphorylation take place?

Answer 5

When chloroplast needs increased amount of ATP

Question 6

Why is it called cyclic photophosphorylation?

Answer 6

Because the electrons return to PSI

Question 7

What is proton gradient enhanced by?

Answer 7

non-cyclic photophosphorylation: Proton added to NADP, so reduces conc. in stroma
Photolysis: Hydrogen ions produced in thylakoid interior

Question 8

What happens after non-cyclic and cyclic photophosphorylation?

Answer 8

• Enzyme ATP synthase has ion channel through centre that protons can diffuse into.
• Movement of protons used to generate ATP from ADP and Pi - chemiosmosis

Question 9

What occurs during light-independent reaction(calvin cycle)?

Question 10

Where does the light-independent reaction(calvin cycle) take place?