Light - Dependent Stage

Question 1

What is photophosphorylation?

Answer 1

The addition of a phosphate group to ADP using energy from light

Question 2

Describe cyclic photophosphorylation.

Answer 2

PS1 absorbs photons which excites electrons in chlorophyll A, which passes them to an electron acceptor which then passes them down an ETC to PS1. The energy released as electrons transport phosphorylates ADP to ATP.

Question 3

Describe non-cyclic photophosphorylation.

Answer 3

PS1s electrons are accepted by NADP. PS11 absorbs photons and electrons are excited to the electron acceptor, which then passes them down an ETC to PS1. Electron passage down the ETC gives energy for phosphorylation of ADP to ATP. PS11 Receives electrons from the photolysis of water.

Question 4

Where does the photolysis of water occur and what is made?

Answer 4

In the thylakoid spaces, hydrogen oxygen and electrons.

Question 5

How is reduced NADP formed?

Answer 5

From the electrons from PS1 and protons from water.

Question 6

Describe how the protons get to reduced NADP.

Answer 6

1. The energy from electrons moving down proton pumps provides energy to pump protons from the stroma into the thylakoid space.
2. The protons join H+ ions from photolysis and accumulate, creating an electrochemical gradient
3. Chemiosmosis occurs. H+ ions diffuse down ATP synthase in the membrane, into the stroma. As they pass through ATP synthase, ADP is phosphorylated to ATP.
4. In the stroma, NADP accepts the H+ ions and with the electrons from PS1, is reduced.

Question 7

How is the proton gradient maintained?

Answer 7

1. The proton pump
2. The photolysis of water
3. The removal of protons from the stroma reducing NADP.