Entrance Exams
Govt. Exams
Succulent plants like cacti have specialized thin-walled parenchymatous tissues that store water. The waxy cuticle reduces water loss, not parenchyma.
Dicot roots typically show tetrarch arrangement (4 xylem groups), while monocot roots show polyarch arrangement. Triarch is less common in roots.
The middle lamella is composed mainly of pectin and calcium pectate, which acts as a cement holding adjacent cells together.
Xylem transports water and minerals (inorganic nutrients) from roots to all parts of the plant in an upward direction.
The endodermis contains Casparian strips—bands of suberin and lignin that prevent lateral movement of water and minerals, forcing them through the cell.
Monocot stems have scattered vascular bundles distributed throughout the ground tissue, whereas dicot stems have bundles arranged in a ring.
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.