Dark reactions of carbon assimilation occur in

Options

A. Cytoplasmic matrix
B. Mitochondria
C. Leucoplasts
D. Chloroplasts.

Answer

**Step-by-Step Solution:**

1. **Understanding Photosynthesis**: Photosynthesis is the process by which plants synthesize their own food using sunlight. It consists of two main reactions: light reactions and dark reactions.

2. **Identifying the Types of Reactions**:
- **Light Reactions**: These are light-dependent reactions that occur in the presence of sunlight. They take place in the thylakoid membranes of the chloroplasts, where water is split (photolysis) to produce ATP and NADPH.
- **Dark Reactions**: Also known as light-independent reactions, these do not require light directly. They utilize the ATP and NADPH produced in the light reactions to assimilate carbon dioxide into glucose.

3. **Locating the Dark Reactions**:
- The dark reactions occur in the **stroma** of the chloroplasts. The stroma is the fluid-filled space surrounding the thylakoids in the chloroplast and is where the Calvin cycle (the process of carbon fixation) takes place.

4. **Evaluating the Options**:
- **Cytoplasmic Matrix**: Incorrect, as dark reactions do not occur here.
- **Mitochondria**: Incorrect, as this organelle is primarily involved in cellular respiration, not photosynthesis.
- **Leucoplast**: Incorrect, as leucoplasts are involved in storage, not in the photosynthetic process.
- **Chloroplast**: Correct, specifically in the stroma of the chloroplast.

5. **Conclusion**: The dark reactions of carbon assimilation occur in the **stroma of the chloroplast**.

**Final Answer**: The dark reactions of carbon assimilation occur in the stroma of the chloroplast.

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