Biosynthetic Phase (Dark reactions) of photosynthesis is

Options

A. production of assimilatory power
B. reduction of carbon to carbohydrates
C. assimilation of `CO_(2)`
D. both 2 and 3

Answer

### Step-by-Step Solution:

1. **Understanding Photosynthesis**: Photosynthesis in higher plants consists of two main phases: the Light Reactions and the Dark Reactions (or the Biosynthetic Phase). The Light Reactions occur in the presence of light and produce energy molecules, while the Dark Reactions do not directly require light.

2. **Light Reactions**: In the Light Reactions, energy is captured from sunlight and converted into chemical energy in the form of ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). These energy carriers are essential for the subsequent reactions in the dark phase.

3. **Dark Reactions (Biosynthetic Phase)**: The Dark Reactions utilize the ATP and NADPH produced in the Light Reactions to convert carbon dioxide (CO2) into glucose (C6H12O6). This phase is also known as the Calvin Cycle.

4. **Steps of the Dark Reactions**:
- **Carbon Fixation**: The first step involves the fixation of carbon dioxide into a 5-carbon sugar called ribulose bisphosphate (RuBP), catalyzed by the enzyme RuBisCO. This results in a 6-carbon compound that quickly splits into two 3-carbon molecules (3-phosphoglycerate or 3-PGA).
- **Reduction Phase**: In this phase, ATP and NADPH from the Light Reactions are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), a 3-carbon sugar. This step involves the reduction of 3-PGA.
- **Regeneration Phase**: The final step involves regenerating RuBP from G3P, allowing the cycle to continue. Some G3P molecules are used to form glucose and other carbohydrates, while others are used to regenerate RuBP.

5. **Conclusion**: The Dark Reactions are crucial for synthesizing carbohydrates from carbon dioxide and are driven by the energy produced in the Light Reactions. The overall process can be summarized as the conversion of CO2 into glucose, which is a vital source of energy for the plant.