Auxin synthesis occurs in

Options

A. Root/shoot tips
B. Cortex
C. Xylem
D. Phloem cells.

Answer

### Step-by-Step Solution:

1. **Understanding Auxin**: Auxin is a type of plant hormone that plays a crucial role in plant growth and development.

2. **Location of Synthesis**: Auxin synthesis primarily occurs in young meristematic tissues. These tissues are responsible for the growth of plants.

3. **Identifying Meristematic Tissues**: The young meristematic tissues where auxin is synthesized are located at the tips of roots and shoots.

4. **Amino Acid Source**: Auxin is synthesized from the amino acid tryptophan, which is essential for its production.

5. **Functions of Auxin**: Auxin is involved in various physiological processes, including stimulating apical dominance (the growth of the main stem over lateral branches) and influencing phototropism (the growth of plants towards light).

6. **Final Answer**: Therefore, the synthesis of auxin occurs in the root and shoot tips.