Correct option is D
The correct answer is option (4): Dicots and gymnosperms.
Explanation:
In plants, secondary growth refers to the increase in the thickness or girth of the plant, which occurs through the activity of the vascular cambium. This process involves the production of additional vascular tissues, such as xylem and phloem, which contributes to the thickening of the stem.
Gymnosperms (e.g., conifers like pines and firs) and dicotyledons (dicots) both undergo secondary growth through the activity of the vascular cambium. This results in the production of additional xylem and phloem tissues, contributing to the overall increase in plant girth.
Monocots, on the other hand, generally do not undergo secondary growth. They lack a vascular cambium, so they do not increase their vascular tissue through secondary growth. Examples of monocots include grasses, lilies, and palms.
Why the other options are incorrect:
Option (1) Gymnosperms only: While gymnosperms do undergo secondary growth through the vascular cambium, dicots are also known to undergo this process. Therefore, this option is not correct as it excludes dicots.
Option (2) Dicots only: While dicots undergo secondary growth through the vascular cambium, gymnosperms also undergo secondary growth, so this option is incomplete.
Option (3) Dicots and monocotyledons: Monocots generally do not undergo secondary growth because they lack a vascular cambium. This makes this option incorrect.
Additional Information:
Vascular cambium: This is a lateral meristem found between the xylem and phloem in dicots and gymnosperms. It divides to produce new cells, leading to the formation of secondary xylem (wood) and secondary phloem. The increase in girth due to this growth is an important feature of many woody plants.
Secondary growth: This growth contributes to the thickening of the plant, primarily in stems and roots, and is typically observed in gymnosperms and dicots (woody plants).
