Learn: BOT 3015 - Anatomy: Roots and Leaves

Plant Morphology

The study of the physical form and external structure of plants.

Plant Anatomy

The study of the tissues and

cell structures of plant organs

Rhizosphere

Thin area around roots - where complex chemistry occurs for nutrient absorption

Zone of Division

Root apical meristem divides to create primary meristematic tissue; protected by root cap

Zone of Elongation

Newly divided cells grow longitudinally while cell wall remains flexible.

Zone of Maturation

Root hairs form and help absorb water and minerals. Branching starts here.

Quiescent Center

Area of the RAM that divides at an extremely slow rate.

Root Cap

A structure that covers the tip of a root, protecting the root from injury. Cells are constantly removed and replaced by apical meristem.

Epidermis

A single layer of cells at outer

boundary - arises from protoderm

Cortex

Several layers between epidermis and vascular cylinder.

Vascular Cylinder

Vascular tissue that differentiates from procambium - occupies center of the root.

Pericycle

Outer boundary of vascular cylinder - site for lateral root

development. Zone of root branching

Root Hairs - Epidermis

Sticky, Short lived, Constantly replaced. May or may not elongate from the external wall of the epidermis cells. These increase surface for water and mineral absorption

Endodermis - Cortex

Innermost layer of cortex. Single row of cells surrounding the vascular tissue. Helps control mineral accumulation

Casparian Strip

A waxy material embedded in the transversal and radial walls of endodermal cells. In some species, located in exodermis

Vascular Cylinder - Dicots

Xylem forms a central core organized in 2 or more radiating points.Phloem is placed in between radial

branches of xylem

Vascular Cylinder - Monocots

Central pith, surrounded by concentric rings of xylem and phloem

Xylem Tissue

Composed of tracheids and (sometimes) vessel

elements.

Phloem Tissue

Forms sieve tubes with companion cells

Protoxylem - Xylem

First xylem element to mature. Capable of transporting water while elongating - secondary walls form

annual ring

Metaxylem - Xylem

Mature after cell elongation is completed. Form thick secondary walls for water and mineral transport. Crush protoxylem cells as they grow

Phloem - Formation

Form in area between protoxylem

arms. First part of vascular system to

become functional

Lateral Root Primordia

Result of chemical growth regulators that cause the

pericycle to start dividing at specific sites

Vascular Cambium - Secondary Meristems

In long-lived dicot plants,part of pericycle cells combine with residual procambium (located between arcs of xylem and phloem) to produce this.

Secondary phloem - Secondary Meristems

Forms inner bark, pushing the remaining pericycle outwards. Cortex is crushed and flakes off, with the epidermis

Cork Cambium

Lateral meristematic tissue that produces the outer covering of stems. (forms from remaining pericycle)

Lateral Growth

Growth occurs in a similar fashion as in stems. Secondary forms towards inside of vascular cambium, forming wood-like tissue. Secondary phloem + periderm form the

bark. Bark encases origin point of lateral

roots.

Leaf Primordia

Fingerlike projections along the flanks of a shoot apical meristem, from which leaves arise. Contains a set of primary meristematic tissue (periderm, ground tissue, and

procambium). The pattern of production of this

defines the phyllotaxis of plant.

Mesophyll - Leaf

middle layer of cells, including chloroplast-containing cells. Divided in 2 parts: Palisade tissue & Spongy tissue

Veins - Leaf

Contain xylem and phloem that transverse the leaf blade.

Epidermis - Leaf

Single layer of cells in the upper and lower surfaces. Covers the entire surface of the blade and the petiole.

Epidermal Cells

Flattened; outer wall often covered by cuticle (a waxy layer) that prevents water loss.

Guard Cells

Surround pores known as stomata. These cells are on either side of stomata and control size of opening.

Subsidiary Cells

Support the guard cells

Trychomes

Hairs that can secrete substances - makes the leaf pubescent (hairy) instead of glabrous (shiny)

Stomata

Special pores that control exchange of gasses. There are usually many more of these pores in the lower epidermis than the upper epidermis

Stomata - Functions

Avoids having pores clogged by dust. Reduces infection from fungi. Allows to pack upper area with chloroplast-

containing cells. Species with up-right leaves are the

exception (e.g. corn)

Mesophyll - Palisade Cells

The cells that are closely packed and elongated in the upper part of the mesophyll. These cells contain chloroplast.

Mesophyll - Spongy Cells

The cells that are loosely packed and irregular in the lower part of the mesophyll. Main function is to

allow diffusion of gasses from stomata to the

palisade

Veins - Vascular Tissue

The veins consist of vascular bundles that form a network of xylem (on the upper part) and phloem (lower part).