The protophloem has (A)____ sieve tubes whereas metaphloem has (B)___ sieve tubes.

Answer

To answer the question regarding the characteristics of protophloem and metaphloem sieve tubes, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Types of Phloem**:
- The phloem is divided into two main types: protophloem and metaphloem.

2. **Identify Protophloem**:
- Protophloem is the first formed phloem. It develops during the early stages of plant growth and is primarily found in the growing parts of the plant.

3. **Characteristics of Protophloem**:
- The sieve tubes in protophloem are narrower. This is because they are designed to function in actively growing regions where the plant is still elongating.

4. **Identify Metaphloem**:
- Metaphloem is formed later than protophloem and is found in the mature parts of the plant.

5. **Characteristics of Metaphloem**:
- The sieve tubes in metaphloem are larger in diameter compared to those in protophloem. This allows for more efficient transport of nutrients in mature plant tissues.

6. **Fill in the Blanks**:
- Based on the characteristics identified:
- (A) for protophloem: **narrow**
- (B) for metaphloem: **bigger**

### Final Answer:
The protophloem has (A) **narrow** sieve tubes whereas metaphloem has (B) **bigger** sieve tubes.

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