Lecture 4 (Anatomy) - Pharmacognosy I - PDF

Pharmacognosy I Lecture 4 ‫اﶈﺎﴐة اﻟﺮاﺑﻌﺔ‬ Ahmed Elbermawi, PhD Lecturer of Pharmacognosy Type of stomata ? A B C D Describe ? Type of Vascular bundle ? A B  Anatomy...

Pharmacognosy I Lecture 4 ‫اﶈﺎﴐة اﻟﺮاﺑﻌﺔ‬ Ahmed Elbermawi, PhD Lecturer of Pharmacognosy Type of stomata ? A B C D Describe ? Type of Vascular bundle ? A B  Anatomy of primary plant organs Leaves  The plant main photosynthetic system. Stems  A support system for the plant body.  A transport system that carries nutrients.  A defense system that protects the plant against predators and diseases. Roots  Absorb water and dissolved nutrients.  Anchor plants in the ground.  Protect the plant from harmful soil bacteria and fungi. primary and secondary growth in plants. Primary growth increases the length of the plant, occurring at the tips of roots and shoots due to the activity of apical meristems, while secondary growth increases the thickness or girth of the plant due to the activity of lateral meristems (vascular cambium and cork cambium).  Anatomy of the root A root consists of a central vascular cylinder (stele) surrounded by ground tissue (cortex), and the epidermis (piliferous layer, epiblema). Why are root hairs important for plant survival? Answer: Root hairs increase the surface area for absorption, allowing the plant to take in more water and nutrients from the soil, which is essential for growth and development. The root cap protects the Apical meristem of the root during growth. 1- Piliferous layer: One layered, cells are thin with no cuticle or stomata, their outer walls have many root hairs. 2- Cortex: It consists of several layers of parenchyma cells, or some of them are sclerenchymatous as in monocot. After the piliferous layer is ruptured, the cells of the outermost layer or few layers of the cortex become suberized and replace the piliferous layer in the function of protection. This hypodermal layer called exodermis. What is the main function of the Casparian The innermost layer of the cortex strip in roots? develops into an endodermis, which is The Casparian strip regulates the flow of water characterized by the presence of the and dissolved minerals into the vascular tissue casparian strips. by forcing substances to pass through the Casparian strips are deposits of suberin plasma membrane of the endodermal cells. and lignin on the radial walls only (in dicots), or on radial and inner tangential Pericycle is the plant structure responsible for walls (in monocots). the initial formation of lateral roots. Vascular cylinder (Stele) It is surrounded by the pericycle. The pericycle consists of one layer of thin-walled parenchyma cells, rarely more than one layer. The vascular tissues are phloem and xylem on alternating radii. Xylem: is differentiated into proto- and meta- xylem Proto-xylem has narrow vessels and locates opposite to the pericycle, the meta-xylem vessels are wider and directed towards the center. Anatomy of the root Monocot root In dicot root the pith is usually vey narrow or absent Inmonocot roots the pith is always present and consists of parenchyma cells Dicot root Monocot root Comparison between Dicot root and monocot root Anatomy of the stem  1- Dicotyledons Stem 1- Epidermis single row of cells generally bears stomata and hairs and covered with cuticle. 2- Cortex (ground tissue): narrow, it may be differentiated into a- Hypodermis: collenchyma in nature devoid of contents. b- Ground parenchyma: o Outer region: usually contain chloroplasts (chlorenchyma). o Middle region: may show sclerenchyma or secretory structures (oil cells, glands or laticeferous ducts) or idioplasts of ca-ox crystals. c- Endodermis: The innermost layer of cortex of dicot stems contains starch grains and is called starch sheath. ♣ Cambium arranged in a single ring around central region called pith or medulla. ♣ M.R. are a number of parenchymatous strands between V.B. from pith to the cortex. ♣ Ground tissues: composed of cortex, pith, and medullary rays. through the activity of interfascicular cambium, they formed a continuous ring of V.B. with 1ry xylem directed toward the pith.  Pericyclic fibers Phloem Intrafascicular cambium Xylem vessels Dicot. stem vascular bundle