anatomy of flowering plants

Anatomy of Flowering Plants

Introduction

• The study of the internal structure of plants is called anatomy.

• Organisms exhibit both structural similarities and variations in external morphology (both plants and animals).

• Higher plants consist of cells organized into tissues, which form organs.

• Monocots and dicots within angiosperms demonstrate anatomical differences.

• Internal structures can adapt to diverse environments.

The Tissue System

• Plant tissues vary based on location and structure.

• Three types of tissue systems:

  • Epidermal Tissue System

  • Ground Tissue System (fundamental tissue system)

  • Vascular Tissue System (conducting tissue system)

6.1.1 Epidermal Tissue System

• Forms the outermost covering (of the whole plant body) consisting of:

  • Epidermal cells

  • Stomata

  • Epidermal appendages (trichomes and hairs)

• The epidermis is usually a single layer of parenchymatous cells with a cuticle.

  • The cuticle prevents water loss.

• Root Hairs: Unicellular, help absorb water and minerals from the soil.

• Trichomes: Multicellular, may be branched or unbranched; help prevent transpiration.

6.1.2 The Ground Tissue System

• Comprised of all tissues excluding the epidermis and vascular bundles.

• Contains simple tissues such as:

  • Parenchyma: Found in the cortex, pith, medullary rays.

  • Collenchyma: Provides support and flexibility.

  • Sclerenchyma: Offers structural support.

• In leaves, the ground tissue is called mesophyll, containing chloroplasts for photosynthesis.

6.1.3 The Vascular Tissue System

• Contains complex tissues, namely phloem and xylem.

• Vascular bundles form the transport system of water, nutrients, and photosynthates.

• Types of Vascular Bundles:

  • Open: Present in dicots (contains cambium allowing secondary growth).

  • Closed: Present in monocots (lacks cambium, no secondary growth).

  • Arrangement types:

    • Radial Arrangement: Alternate xylem and phloem (common in roots).

    • Conjoint Arrangement: Xylem and phloem on the same radius (common in stems and leaves).

Anatomy of Dicotyledonous and Monocotyledonous Plants

6.2.1 Dicotyledonous Root

• Transverse section features:

  • Outermost layer: Epiblema (contains root hairs).

  • Cortex: Composed of parenchyma cells with intercellular spaces.

  • Endodermis: Single layer of barrel-shaped cells with casparian strips (inner most layer of cortex) that regulate the flow of water and nutrients into the vascular system.

  • Pericycle: A layer of cells located just inside the endodermis, responsible for the formation of lateral roots and contributing to the secondary growth of the plant.

  • Vascular tissue: Comprised of xylem and phloem, which are essential for the transport of water, nutrients, and food throughout the plant.

  • It contains a pericycle that initiates lateral roots and vascular cambium during secondary growth.

  • conjuctive tissues : These tissues serve as a connection between different types of tissues, facilitating communication and transport within the plant.

  • Ground tissue: This tissue type provides structural support, storage, and is involved in photosynthesis, consisting of parenchyma, collenchyma, and sclerenchyma cells.

  • pith : The central part of the stem, composed mainly of parenchyma cells, which store nutrients and contribute to the plant's overall growth.

6.2.2 Monocotyledonous Root

• Anatomy similar to dicot root but has:

  • More than six xylem bundles (polyarch).

  • A well-developed pith.

  • No secondary growth.

6.2.3 Dicotyledonous Stem

• Features:

  • Epidermis: Thin protective layer (may have trichomes and stomata).

  • Cortex: Contains collenchymatous hypodermis providing mechanical strength.

  • Endodermis: Starch-rich tissue.

  • Vascular bundles arranged in a ring, each conjoint and open.

6.2.4 Monocotyledonous Stem

• Anatomy includes:

  • Sclerenchymatous hypodermis and scattered vascular bundles.

  • Conjoint, closed vascular bundles with sclerenchymatous sheath.

6.2.5 Dorsiventral (Dicotyledonous) Leaf

• Structure includes:

  • Epidermis on both surfaces with a cuticle.

  • Mesophyll containing:

    • Palisade parenchyma: Elongated cells for photosynthesis.

    • Spongy parenchyma: Loosely arranged with air spaces.

  • Vascular System: Vascular bundles in veins and midrib, surrounded by bundle sheath cells.

6.2.6 Isobilateral (Monocotyledonous) Leaf

• Similar to dorsiventral leaf but features:

  • Stomata on both surfaces.

  • Undifferentiated mesophyll (no palisade/spongy distinction).

  • Presence of bulliform cells that regulate leaf curling to minimize water loss.

Summary

• Plants are composed of different tissue types: meristematic and permanent.

• Main functions include food assimilation, storage, transportation, and support.

• Distinct variations exist between monocotyledonous and dicotyledonous plants, particularly in tissue organization and vascular bundles.

Exercises

1. Draw anatomical differences between monocot and dicot roots/stems.

2. Observe and identify the young stem structure under a microscope.

3. Identify plant material based on vascular bundle features.

4. Explain the stomatal apparatus structure with a diagram.

5. Name the three basic tissue systems and their corresponding tissues.

6. Discuss the significance of plant anatomy studies.

7. Describe dorsiventral leaf structure with labeled diagrams.