Arrangement of thylakoids like piles of coin is known as-

Answer

### Step-by-Step Solution:

1. **Identify the Structure**: The question asks about the arrangement of thylakoids, which are structures found in chloroplasts.

2. **Understand Thylakoids**: Thylakoids are flattened, membrane-bound sacs that are involved in the process of photosynthesis. They are stacked in a specific arrangement.

3. **Recognize the Arrangement**: The arrangement of thylakoids resembles piles of coins. This specific stacking is crucial for their function in photosynthesis.

4. **Define the Term**: The term used to describe a stack of thylakoids is "granum" (plural: "grana"). Each individual stack is referred to as a granum.

5. **Conclusion**: Therefore, the arrangement of thylakoids like piles of coins is known as "grana".

### Final Answer:
The arrangement of thylakoids like piles of coins is known as **grana**.

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