Light Reaction

Question 1

What is photosystem

Answer 1

Photosystem is a process which absorbs energy from photons and converts it into ATP and NADPH.

Question 2

What is antenna complex

Answer 2

The antenna complex is a web of chlorophyll molecules, which transfer the energy absorbed through the photons to the reaction centre chlorophyll and

Question 3

What is the reaction centre

Answer 3

The reaction centre is a where the energy absorbed reaches the it’s chlorophyll molecule, causing its electrons to become excited, which the primary electron acceptor captures and starts the ETC

Question 4

What happens to an electron when it becomes excited

Answer 4

Due to additional energy (energy absorbed from the photons), molecules electrons gain enough energy to jump to an higher energy level, causing them to be transferred to the primary electron acceptor

Question 5

Photosystem 2 (PSII)

Answer 5

• Absorbs wavelengths of 680 nm, exciting electrons
• Z proteins split water molecules (photolysis)
• H+ (proton gradient for ATP synthesis) and electrons are released to replace excited ones, and oxygen is formed as byproduct
• excited electrons are captured by the PEA and moved to plastoquinone

Question 6

Plastiquinone (PQ)

Answer 6

• An electron acceptor, which accepts the electrons from photosystem 2 (PSII)
• Take the excited electrons from PSII to B6-f complex

Question 7

Cytochrome (B6-f) complex

Answer 7

• The B6-f complex is a enzyme complex that pumps protons (H+)
• In the thylakoid membrane
• Pumps H+ from the stroma to the lumen
• Active transport, requires energy to move protons against their concentration gradient, creating an electrochemical gradient, which is used for ATP synthase

Question 8

Plastocyanin (PC)

Answer 8

• Electron carrier protein
• carries electrons from b6-f complex to PSI

Question 9

Photosystem 1 (PSI)

Answer 9

• wavelength of 700nm is absorbed
• Reaction centres chlorophyll molecule gets excited, allowing electrons to jump to the primary electron acceptor
• passes electrons on to ferredoxin

Question 10

Ferredoxin (Fd)

Answer 10

• electron carrier
• takes the electrons from PSI through the stroma (which contains NADP+)
• donates electrons to the NADP reductase (FNR), reducing NADP+ to NADPH

Question 11

NADP reductase (FNR)

Answer 11

• Ferredoxin donates electrons to NADP+ reductase, which reduce NADP+ to NADPH

Question 12

ATP Synthase

Answer 12

• Protons pass down gradient into stroma
• Synthesize ATP by photophosphorylation (creating ATP
using light energy)

Question 13

Proton gradient

Answer 13

• PSII and B6-f complex contribute to proton pump
• pump from the stroma to lumen, on the thylakoid membrane
• as pump continues, concentration increases, creating a gradient
• to balance gradient, ATP synthase allow protons to flow back (stroma to lumen)
• ATP synthase, uses phosphorylation to create ATP. As protons flow back, the energy released is used to bind inorganic phosphate group (Pi) to ADP

Question 14

Non cyclic electron flow vs cyclic electron flow