1. **Definition:**
- The Calvin Cycle, also known as the Calvin-Benson cycle or dark reactions, is a series of
biochemical reactions that take place in the stroma of chloroplasts during photosynthesis.
2. **Location:**
- Occurs in the stroma of chloroplasts, the fluid-filled space surrounding the thylakoid
membranes.
3. **Purpose:**
- Converts carbon dioxide (CO2) into carbohydrates, primarily glucose, using the energy
derived from the light-dependent reactions (photosystem I and II).
4. **Initiation:**
- The cycle begins with the incorporation of carbon dioxide into a five-carbon sugar molecule
called ribulose-1,5-bisphosphate (RuBP).
5. **Enzyme Catalysis:**
- The enzyme responsible for carbon fixation is ribulose-1,5-bisphosphate
carboxylase/oxygenase (RuBisCO).
6. **Intermediate Molecules:**
- The initial product of carbon fixation is an unstable six-carbon compound that immediately
splits into two three-carbon molecules, 3-phosphoglycerate (3-PGA).
7. **Reduction Phase:**
- ATP and NADPH, produced during the light-dependent reactions, are used to convert 3-PGA
into glyceraldehyde-3-phosphate (G3P) through a series of chemical reactions.
8. **Regeneration of RuBP:**
- Some G3P molecules are used to regenerate RuBP through a complex series of reactions
that consume ATP.
9. **Net Result:**
- For every three molecules of CO2 entering the Calvin Cycle, one molecule of G3P is
produced. However, only one G3P exits the cycle to contribute to the synthesis of glucose.
10. **Connection to Photosynthesis:**
- The Calvin Cycle works in conjunction with the light-dependent reactions. The ATP and
NADPH produced in the light reactions provide the energy and reducing power needed for the
Calvin Cycle to fix carbon and produce sugars.
Understanding the Calvin Cycle is essential for comprehending how plants convert carbon
dioxide into organic molecules, playing a crucial role in the global carbon cycle and sustaining
life on Earth.