Answer:
The correct answer is - option a. root cap.
Step-by-step explanation:
Roots of the plants are developed from the structure called radical in seed during germination of seed.The tip of the root is tender due to the present of the apical meristem that is the precursor of the new cells of the root and protected by the root cap and penetrate in to the soil with the help of mucigel. Mucigel is the which protects the extending roots from developing friction.
Thus, the correct answer is : option a. root cap.