Detailed Notes Chapter6-Anatomy Of Flowering Plants

Introduction

1. Introduction to Plant Anatomy:

   • Definition: Plant anatomy involves studying the internal structure of plants.
   • Focus: It examines how cells, tissues, and organs are organized within plants.

2. Basic Unit: Cells:

   • Cells are the fundamental unit of plants, akin to cells in animals.
   • Function: They perform various tasks essential for plant survival.

3. Organization into Tissues:

   • Definition: Cells are grouped into tissues, which are collections of cells with similar functions.
   • Types of tissues: Dermal, ground, and vascular tissues are examples.
   • Function: Tissues carry out specific functions crucial for plant growth and development.

4. Organization into Organs:

   • Definition: Tissues further organize into organs, each with distinct functions.
   • Examples: Roots, stems, leaves, and flowers are major plant organs.
   • Function: Organs perform specialized tasks necessary for plant life.

5. Differences in Internal Structure of Organs:

   • Despite similarities, each organ has unique internal structures.
   • Example: Roots have different internal structures compared to leaves due to their differing functions.

6. Differences Between Monocots and Dicots:

   • Angiosperms are categorized into monocots and dicots based on seed leaf count.
   • Anatomical differences: Monocots and dicots exhibit variations in vascular bundle arrangement, leaf venation, and root structure.

7. Adaptations to Diverse Environments:

   • Plants show adaptations in their internal structures to thrive in diverse habitats.
   • Examples: Desert plants have specialized root structures for water conservation, while aquatic plants have modified leaves for efficient gas exchange.

6.1 THE TISSUE SYSTEM

1. Epidermal Tissue System:

   • Structure: This tissue system consists of a single layer of cells called the epidermis, which covers the entire outer surface of the plant.
   • Location: It is located on the outermost layer of the plant body, serving as a protective barrier against physical damage, pathogens, and water loss.
   • Function: The epidermal tissue system regulates gas exchange, controls water absorption and loss, and secretes substances such as waxes and cuticles to reduce water loss.

2. Ground or Fundamental Tissue System:

   • Structure: The ground tissue system is composed of various types of cells, including parenchyma, collenchyma, and sclerenchyma cells.
   • Location: It occupies the space between the epidermis and the vascular tissue system, making up the bulk of the plant’s body.
   • Function: Ground tissue provides structural support, stores nutrients, and performs photosynthesis in the case of parenchyma cells. Collenchyma and sclerenchyma cells provide mechanical support to the plant.

3. Vascular or Conducting Tissue System:

   • Structure: The vascular tissue system consists of two types of tissues: xylem and phloem.
   • Location: It is located deep within the plant body, usually arranged in discrete strands or vascular bundles.
   • Function: Xylem transports water and minerals from the roots to the rest of the plant, while phloem transports organic nutrients (e.g., sugars) produced during photosynthesis to various parts of the plant.

6.1.1 Epidermal Tissue System

1. Composition:

   • The epidermal tissue system consists of:
     • Epidermal cells
     • Stomata
     • Epidermal appendages such as trichomes and hairs.

2. Structure:

   • Epidermis forms the outermost covering of the entire plant body.
   • Composed of elongated, compactly arranged cells forming a continuous layer.
   • Usually single-layered.
   • Epidermal cells are parenchymatous with a small amount of cytoplasm and a large vacuole.
   • The outer surface of the epidermis is often covered with a waxy cuticle layer, which prevents water loss. However, cuticle is absent in roots.

3. Stomata:

   • Structures present in the epidermis of leaves.
   • Regulate transpiration and gaseous exchange.
   • Each stoma consists of two bean-shaped guard cells enclosing a stomatal pore.
   • In grasses, guard cells are dumb-bell shaped with thin outer walls and thickened inner walls.
   • Guard cells possess chloroplasts and regulate stomatal opening and closing.
   • Subsidiary cells, specialized in shape and size, are found in the vicinity of guard cells. Together with guard cells and stomatal pore, they form the stomatal apparatus.

4. Epidermal Hairs:

   • Root hairs are unicellular elongations of epidermal cells, aiding in water and mineral absorption from the soil.
   • On stems, epidermal hairs are called trichomes.
   • Trichomes may be multicellular, branched or unbranched, soft or stiff, and even secretory.
   • Trichomes help prevent water loss due to transpiration.

6.1.2 The Ground Tissue System

1. Composition:

   • The ground tissue system includes all tissues except for the epidermis (outermost covering) and vascular bundles (composed of xylem and phloem).
   • It comprises simple tissues, namely parenchyma, collenchyma, and sclerenchyma.

2. Types of Cells:

   • Parenchyma: These cells are typically found in the cortex, pericycle, pith, medullary rays, and primary stems and roots.
   • Collenchyma: These cells provide flexible structural support, usually found in regions requiring flexibility, such as young stems and petioles.
   • Sclerenchyma: These cells provide rigid support and protection, found in regions requiring mechanical strength, such as mature stems, veins of leaves, and seed coats.

3. Function:

   • Parenchyma cells have diverse functions and are involved in photosynthesis, storage of nutrients, and secretion.
   • Collenchyma cells provide flexible support to growing parts of the plant.
   • Sclerenchyma cells provide mechanical strength and support to mature plant parts.

4. Ground Tissue in Leaves:

   • In leaves, the ground tissue system consists of thin-walled cells containing chloroplasts.
   • This tissue is called mesophyll and is responsible for photosynthesis.
   • Mesophyll cells are located between the upper and lower epidermis layers of the leaf.

6.1.3 The Vascular Tissue System

1. Composition:

   • The vascular system consists of complex tissues: xylem and phloem.
   • Xylem and phloem together form vascular bundles, which are found throughout the plant body.

2. Dicotyledonous Stems:

   • In dicotyledonous stems, vascular bundles contain cambium tissue between phloem and xylem.
   • Cambium allows for the formation of secondary xylem and phloem, making these bundles “open.”
   • Open vascular bundles possess the ability to undergo secondary growth.

3. Monocotyledonous Stems:

   • In monocotyledonous plants, vascular bundles lack cambium tissue.
   • Without cambium, these bundles cannot produce secondary tissues and are termed “closed.”

4. Arrangement of Xylem and Phloem:

   • Radial Arrangement: In some plants, such as roots, xylem and phloem within vascular bundles are arranged alternately along different radii.
   • Conjoint Arrangement: Xylem and phloem are jointly situated along the same radius of vascular bundles. This arrangement is common in stems and leaves.
   • In conjoint vascular bundles, phloem is usually located only on the outer side of xylem.