Which growth process is driven by apical meristems?

• A. Primary growth
• B. Secondary growth
• C. Tertiary growth
• D. Quaternary growth

Answer: (A)

Apical meristems drive primary growth, the lengthening of roots and shoots. Located at the tips of growing organs, these meristems constantly divide to add new cells that elongate as they mature, pushing the tip farther from the plant body. This growth forms the plant’s primary tissues: epidermis from the protoderm, ground tissue from the ground meristem, and vascular tissue (xylem and phloem) from the procambium. Because it adds cells at the tips, primary growth increases height and depth rather than girth. Secondary growth, which thickens stems and roots, comes from lateral meristems and is responsible for wood and bark formation. Tertiary and quaternary growth are not the standard terms used to describe plant growth in this context.