Sieve tubes are constituent of
(a) Wood
(b) Vascular cambium
(c) Phellem
(d) Bast

Options

A. Wood
B. Vascular cambium
C. Phellem
D. Bast

Answer

To determine the correct answer to the question regarding the constituents of sieve tubes, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Function of Sieve Tubes**:
- Sieve tubes are specialized structures in plants that are primarily involved in the transport of food (sugars and nutrients) from the leaves (source) to other parts of the plant (sink).

2. **Identify the Tissue Type**:
- Sieve tubes are components of phloem tissue. Phloem is responsible for the translocation of food in plants.

3. **Analyze the Given Options**:
- (a) Wood: Wood is primarily composed of xylem, which is responsible for water and mineral transport.
- (b) Vascular cambium: This is a layer of tissue that produces new xylem and phloem cells but does not contain sieve tubes.
- (c) Phellem: Also known as cork, this is a protective tissue and does not contain sieve tubes.
- (d) Bast: Bast is another term used to refer to the phloem, which includes sieve tubes.

4. **Select the Correct Option**:
- Since sieve tubes are part of the phloem, and "bast" is synonymous with phloem, the correct answer is (d) Bast.

### Final Answer:
(d) Bast

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