Entrance Exams
Govt. Exams
Sieve tube elements are enucleate at maturity, losing their nucleus to facilitate the flow of photosynthates. Companion cells remain nucleate and control sieve tube metabolism.
Wood is formed by secondary xylem, and annual rings result from seasonal variation in secondary xylem formation.
Monocot roots display radial vascular bundles where xylem and phloem alternate in a radial pattern from the center.
Companion cells are parenchymatous cells attached to sieve tube elements, providing metabolic support for phloem transport.
Vascular cambium is derived from residual procambium (between primary xylem and phloem) and adjacent ground meristem cells.
Xerophytes have sunken stomata (reducing direct exposure) and thick, waxy cuticles to minimize transpiration.
Aerenchyma tissue with large intercellular air spaces provides buoyancy to aquatic plants.
Periderm, consisting of cork, cork cambium, and phelloderm, replaces the epidermis in older stems.
Annual rings result from the difference in growth rate between spring wood (lighter) and autumn wood (darker) formed by secondary xylem.
Secondary growth, mediated by vascular cambium, produces secondary xylem (wood) and secondary phloem (inner bark).