Govt. Exams
Entrance 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.
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.
According to the histogen theory, the calyptrogen (root cap mother region) produces the root cap, while dermatogen produces epidermis, periblem produces cortex, and plerome produces stele.
The stele consists of pericycle, vascular tissues, and endodermis. The cortex lies outside the endodermis and is not part of the stele.
Petioles contain multiple vascular bundles arranged in characteristic patterns - often arc-shaped or scattered, providing strength and flexibility.
Radial arrangement is characteristic of monocot roots where xylem and phloem alternate on different radii. When they're on the same radii, it's called conjoint arrangement.
In roots, protoxylem is toward the center and metaxylem toward periphery, defining the endarch arrangement unique to roots among vascular organs.
Gymnosperm wood consists mainly of tracheids without true vessels, making it different from dicot wood which has both vessels and tracheids.
C4 plants have well-developed chloroplasts in bundle sheath cells for the Calvin cycle, while C3 plants have minimal chloroplasts in bundle sheaths.
