Entrance Exams
Govt. Exams
As the root grows and matures, protophloem sieve tubes collapse and are obliterated, replaced functionally by metaphloem which lies closer to the periphery.
Bulliform cells are large, colorless epidermal cells that absorb water and swell, causing the leaf to unfold; they lose water and collapse during drought, causing leaf rolling to reduce transpiration.
Gymnosperms lack vessel elements and rely on tracheids with bordered pits for water conduction, which is less efficient than angiosperm vessel elements.
Dicots develop secondary tissues (secondary xylem and phloem) through vascular cambium activity, creating dense wood that provides greater mechanical strength than herbaceous monocots.
Monocot stems have numerous scattered collateral vascular bundles distributed throughout the ground tissue, unlike the organized ring in dicots.
Root hairs develop from the root hair zone of epidermis, not from pericycle. The pericycle produces lateral roots, vascular cambium, and in some species, cork cambium.
Aerenchyma consists of large air-filled intercellular spaces that facilitate gas exchange and provide buoyancy in aquatic plants.
Calcium oxalate crystals store excess calcium ions and help maintain osmotic balance in plant cells.
Companion cells are living cells derived from the same mother cell as sieve tubes; they provide metabolic support and regulate loading/unloading of photosynthates.
Radial arrangement of xylem and phloem in alternate pattern is typical of dicot roots, where xylem arms point toward the periphery and phloem patches lie between them.