7. Light dependent Reactions

Question 1

What are the two goals of light reactions

Answer 1

1. Capturing light energy
2. Using the light energy to create chemical energy (ATP or NADPH [electron carriers in plants])

Question 2

What happens in light reactions

Answer 2

• Pigments don’t absorb light independent
• Photosystems are embedded in the thylakoid membrane

Question 3

What are the names of the 2 photosystems

Answer 3

Photosystem 2 is called P680 (absorbs 680mn)
Photosystem 1 is called P700 (absorbs 700nm)

Question 4

What do photosystems consist of and contain

Answer 4

A photosystem consists of antenna complex and a reaction center. They contain chlorophyll and accessory pigments that are associated with proteins.

Question 5

Explain the excitation of electrons in regards to light reactions

Answer 5

Excitation: The photon hits the chlorophyll and the electrons are energized to a higher energy level

Question 6

Why do electrons loose heat and light

Answer 6

Electrons in a chlorophyll molecule are normally at their ground state. Outside a living organism, excited electrons want to return to their ground state and loose potential energy as heat and light.

Question 7

What are excited electrons captured by

Answer 7

In the cell the excited electron is captured by a special molecule called the primary electron acceptor, pheophytin (then this happens there is no fluorescing).

Question 8

What is the energy from electrons used to make

Answer 8

The energy of the electrons is used to produce ATP and NADPH

Question 9

How is ATP and NADPH made from electrons

Answer 9

In a two part process called non-cyclic electron flow

Question 10

What is the non-cyclic Electron flow

Answer 10

A ONE WAY flow of electrons

Question 11

Explain the first step of the non-cyclic electron slow

Answer 11

1. PS680 (Photosystem II) absorbs light causing an electron to become energized
   a. This energized electron makes its way to the primary electron acceptor.
   b. The energized electrons are replaced by electrons that come from the splitting of water (photolysis).
   c. Process produces Oxygen and H+

Question 12

Explain the second step of the non-cyclic electron slow

Answer 12

2. Electrons are passed along through the electron transport chain (ETC) to PS700 (photosystem I)
   a. ETC consists of proteins (in order): plastoquinone (PQ), cytochrome (Cyto or n6-f) and plastocyanin (PC)
   b. As e- flow through chain, H+ ions are pumped across thylakoid membrane into the thylakoid space (lumen)
   c. Creates a concentration gradient to produce ATP (photophosphorylation and chemiosmosis with ATP synthesis)

Question 13

Explain the third step of the non-cyclic electron slow

Answer 13

3. PS700 (photosystem I) absorbs light causing an electron to become energized
   a. Energized electron makes it way to the primary electron acceptor
   b. The energized electrons are replaced by electrons from PS680 and ETC

Question 14

Explain the forth step of the non-cyclic electron slow

Answer 14

4. Electrons are passed to another ETC
   a. ETC consists of proteins (in order): Ferredoxin (Fd), and NADP to reductase
   b. Electrons use NADP+ to be reduced to NADPH
   c. 2e- are required to produce 1 NADPH

Question 15

Explain Photophosphorylation

Answer 15

The attachment of a phosphate group to a molecule or an ion

Question 16

Explain Cyclic Photophosphorylation

Answer 16

No NADPH made, only ATP - when abundance of NADPH, but shortage of ATP