Govt Exams
Secondary xylem in dicots shows growth rings (annual rings) due to variations in cell size and wall thickness between spring wood and autumn wood formed in different seasons.
Phloem fibers (bast fibers) provide mechanical support to vascular bundles and stems while permitting the translocation function of sieve tubes and companion cells.
Palisade mesophyll consists of tightly packed columnar cells with numerous chloroplasts oriented toward light, maximizing photosynthetic efficiency.
Stomatal pits create a humid chamber that reduces the vapor pressure gradient between intercellular spaces and external environment, thereby minimizing transpirational water loss.
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.