التفاعلات اللاضوئية Light-Independent Reactions (Calvin Cycle)

Light-Independent Reactions of Photosynthesis (Calvin Cycle)

The video explains the light-independent reactions of photosynthesis, also known as the Calvin cycle, which take place in the stroma of the chloroplast and do not require light.

Key Concepts and Steps

• The cycle begins with a five-carbon compound called ribulose bisphosphate (RuBP), which reacts with carbon dioxide (CO₂) to form a six-carbon compound.
• This six-carbon compound quickly splits into twelve three-carbon molecules known as 3-phosphoglycerate.
• Using energy from ATP and high-energy electrons from NADPH (both produced during the light-dependent reactions), these three-carbon molecules are converted into high-energy forms.
• Two of these three-carbon molecules exit the cycle and combine to form glucose, the plant’s food.
• The remaining ten three-carbon molecules are rearranged, using ATP energy, to regenerate the original six five-carbon molecules, allowing the cycle to continue.
• The Calvin cycle is named after Melvin Calvin, who elucidated these reactions through extensive research.

Photosynthesis Overview

Photosynthesis consists of two main stages:

• Light-dependent reactions

  • Occur in the thylakoid membranes
  • Require light
  • Produce ATP, NADPH, and oxygen

• Light-independent reactions (Calvin cycle)

  • Occur in the stroma
  • Do not require light
  • Use ATP, NADPH, and CO₂ to produce glucose

Summary of the Calvin Cycle Steps

1. CO₂ fixation: 5-carbon compound (RuBP) + CO₂ → 6-carbon compound

2. Splitting: 6-carbon compound → twelve 3-carbon molecules (3-phosphoglycerate)

3. Energy input: ATP and NADPH convert 3-carbon molecules into high-energy forms

4. Glucose formation: Two 3-carbon molecules combine to form glucose

5. Regeneration: Ten 3-carbon molecules are rearranged to regenerate six 5-carbon molecules

Researchers Featured

• Melvin Calvin — discoverer of the Calvin cycle through extensive research