Starch formation during dark phase is observed in these regions

Options

A. Chloroplasts
B. Amyloplasts
C. Cytosol of mesophyll cells
D. 1 & 3

Answer

To answer the question regarding where starch formation during the dark phase occurs, we can break down the solution into several steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the regions where starch formation occurs during the dark phase of photosynthesis.

2. **Identifying Key Terms**: The key terms in the question are "starch formation," "dark phase," and the specific regions mentioned: chloroplasts, amyloplasts, and the cytosol of mesophyll cells.

3. **Role of Chloroplasts**: Chloroplasts are the sites of photosynthesis in plant cells. During the light phase, they capture sunlight and convert it into chemical energy, which is then used to form glucose. During the dark phase (Calvin cycle), glucose can be converted into starch.

4. **Role of Amyloplasts**: Amyloplasts are specialized organelles that store starch. However, they do not play a role in the formation of starch. Their primary function is to store the starch that has already been synthesized.

5. **Role of Cytosol in Mesophyll Cells**: The cytosol of mesophyll cells is also involved in the dark phase of photosynthesis. It provides the environment for the enzymatic reactions that convert glucose into starch.

6. **Conclusion**: Since starch formation occurs in chloroplasts and the cytosol of mesophyll cells, but not in amyloplasts (which are for storage), the correct answer is option D, which includes both chloroplasts and the cytosol of mesophyll cells.

### Final Answer:
The correct regions where starch formation during the dark phase is observed are **both chloroplasts and the cytosol of mesophyll cells (Option D)**.