The stacked, fluid-filled sacs are called

Options

A. stroma
B. grana
C. thylakoids
D. lamellae

Answer

**Step-by-Step Solution:**

1. **Understanding the Structure of Chloroplasts:**
- Chloroplasts are organelles found in plant cells that are responsible for photosynthesis. They have a double membrane structure.

2. **Identifying the Components of Chloroplasts:**
- Inside the chloroplast, there are various structures, including thylakoids, grana, stroma, and lamellae.

3. **Defining Thylakoids:**
- Thylakoids are the stacked, disc-like structures within the chloroplast. They are arranged in stacks called grana.

4. **Understanding Grana:**
- Grana refer to a stack of thylakoids. Each individual stack is called a grana, but the term "thylakoids" refers to the entire stacked structure.

5. **Differentiating Between Stroma and Thylakoids:**
- Stroma is the fluid matrix surrounding the thylakoids, while thylakoids are the actual stacked structures where the light-dependent reactions of photosynthesis occur.

6. **Reviewing Other Options:**
- Lamellae are the thin membranes that connect thylakoids to each other but are not the stacked structures themselves.

7. **Conclusion:**
- Based on the definitions and structures discussed, the stacked, fluid-filled sacs in chloroplasts are called **thylakoids**.

**Final Answer: Thylakoids**

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