Final answer:
During secondary growth in a dicot root, the cork cambium is formed by the activity of the pericycle. This process contributes to the increase in girth of the plant and produces suberin-rich cork cells which replace the original epidermis. The correct answer to the question is the pericycle (option 3).
Step-by-step explanation:
Formation of Cork Cambium During Secondary Growth in Dicot Roots
The process of secondary growth is typical in woody plants and some herbaceous dicots. The cork cambium, also known as phellogen, is responsible for producing the protective outer layer of the stem or root known as the bark. During secondary growth in a dicot root, the cork cambium is primarily formed by the activity of the pericycle, which is present just inside the endodermis. This cambium generates tissue that contributes to an increase in the girth of the plant, whereas the cork cells it creates replace the original epidermal layer of the root.
The cork cambium produces substances like suberin in cork cells to repel water, aiding in the protection of the plant from physical damage and reducing water loss. The persistent addition of new layers by the cork cambium and vascular cambium contributes to the increasing diameter of roots and stems over time. As the growth progresses, older layers of cork are replaced by newer ones, allowing the plant to adapt and maintain its protective layer.
The correct option for the formation of cork cambium during secondary growth in a dicot root is (3) pericycle.