Light independent

Question 1

Describe carbon fixation

Answer 1

First reaction: CO2 is added to ribulose 1, 5-bisphosphate (RuBP), a 5-carbon molecule, to form a 6-carbon intermediate
* This 6-carbon intermediate splits into two 3-carbon molecules of 3-phosphoglycerate (PGA)
* This first reaction occurs 3 times to produce 6 molecules of PGA
* All reactions in this phase are catalyzed by the enzyme rubisco.

Question 2

Describe reduction & oxidation reactions – for the ‘key players’

Answer 2

• P680: Gets oxidized (loses electrons) and needs new ones, so it splits water to get electrons.
• P700: Also gets oxidized and sends electrons to the primary electron acceptor, which eventually helps produce NADPH.
• Primary Electron Acceptors: Receive electrons from P680 and P700, helping start the electron transport chain (ETC).
• Cytc (Cytochrome complex): Acts like an electron shuttle, moving electrons along the ETC.
• PQ (Plastoquinone): Loses electrons (oxidizes) and transfers them along the ETC.
• NADP+ Reductase: Accepts electrons and reduces NADP+ into NADPH, which is used for energy.
• Ferredoxin: Transfers electrons in the ETC through redox (electron transfer) reactions.
• Water (H₂O): Splits and donates electrons to P680, releasing oxygen as a byproduct.
• Photons (Light): Excite P680 and P700, causing them to lose electrons and start the chain.

Question 3

Why is Rubisco considered one of the most important enzymes on Earth?

Answer 3

it helps in the making of organic molecules that are consumed by many of the world’s organisms

Question 4

Describe how RuBP is regenerated

Answer 4

1. G3P, a 3-carbon molecule, leaves the Calvin cycle.
2. The remaining 15 carbons are rearranged.
3. ATP and water help transform these carbons.
4. This process forms three molecules of RuBP.
5. RuBP is now ready to capture more CO₂ and keep the cycle going.