Carbon dioxide joins the photosynthetic pathway in

Options

A. PS I
B. PS II
C. light dependent reaction
D. light Independent reaction

Answer

To solve the question "Carbon dioxide joins the photosynthetic pathway in," we need to understand the two main stages of photosynthesis: the light-dependent reactions and the light-independent reactions (also known as the dark reactions).

### Step-by-Step Solution:

1. **Understanding Photosynthesis**: Photosynthesis consists of two main stages:
- **Light-dependent reactions**: These occur in the thylakoid membranes of the chloroplasts and require light to produce ATP and NADPH.
- **Light-independent reactions (Calvin Cycle or Dark reactions)**: These occur in the stroma of the chloroplasts and do not require light directly. This is where carbon dioxide is fixed into organic molecules.

2. **Role of Carbon Dioxide**: Carbon dioxide is a crucial component that enters the light-independent reactions. During these reactions, CO2 is incorporated into organic molecules through a process known as carbon fixation.

3. **Identifying the Correct Option**:
- **Photosystem I and II**: These are involved in the light-dependent reactions and are responsible for capturing light energy. They do not directly involve carbon dioxide.
- **Light-dependent reactions**: As mentioned, these reactions do not incorporate carbon dioxide; they produce energy carriers (ATP and NADPH) that are used in the next stage.
- **Light-independent reactions**: This is where carbon dioxide is fixed into carbohydrates. Therefore, this is the correct answer.

4. **Conclusion**: The correct answer to the question is that carbon dioxide joins the photosynthetic pathway in the **light-independent reaction**.

### Final Answer:
Carbon dioxide joins the photosynthetic pathway in the **light-independent reaction**.

---