General Biology Practical II

General Biology Practical II is a hands-on course designed for 100-level students to reinforce theoretical knowledge gained in General Biology through laboratory experiments and activities. The course covers practical aspects of topics such as the structure of plant and animal tissues, classification of organisms, and basic ecological techniques. Students learn essential laboratory skills, including the proper use of microscopes, preparation of slides, observation of specimens, and accurate recording and interpretation of experimental results. 

Lecture Note: Examination of Various Groups of Lower Invertebrates Under Microscopes

Course: BIO 108
Topic: Examination of Various Groups of Lower Invertebrates Under Microscopes

Introduction

Lower invertebrates are a diverse group of simple animals that lack a backbone. They play significant roles in ecological balance and biological research. These organisms are often microscopic or small enough to be observed effectively under a light microscope. In this lecture we will discuss the examination of various groups of lower invertebrates, their distinguishing features, and the importance of microscopic study.

Classification of Lower Invertebrates

Lower invertebrates can be classified into various phyla based on their structural and functional characteristics. The primary groups we will focus on include:

  1. Phylum Protozoa – Single-celled organisms
  2. Phylum Porifera – Sponges
  3. Phylum Cnidaria – Jellyfish, hydra, and corals
  4. Phylum Platyhelminthes – Flatworms
  5. Phylum Nematoda – Roundworms
  6. Phylum Rotifera – Rotifers

Microscopic Examination of Different Groups

1. Protozoa (Single-celled Protists)

  • Examples: Amoeba, Paramecium, Euglena
  • Key Features:
    • Unicellular, motile organisms
    • Locomotion using cilia (Paramecium), flagella (Euglena), or pseudopodia (Amoeba)
    • Can be free-living or parasitic
  • Microscopy Techniques:
    • Use a drop of pond water on a glass slide and cover it with a coverslip.
    • Observe movement and feeding behavior under 10x and 40x magnification.

2. Porifera (Sponges)

  • Examples: Leucosolenia, Sycon
  • Key Features:
    • Simplest multicellular animals
    • Body is porous with a canal system for water flow
    • No distinct tissues or organs
  • Microscopy Techniques:
    • Observe sponge spicules under a microscope using prepared slides.
    • Look for skeletal structures that provide support to the organism.

3. Cnidaria (Jellyfish, Hydra, Corals)

  • Examples: Hydra, Obelia
  • Key Features:
    • Radial symmetry
    • Tentacles with stinging cells (nematocysts) used for capturing prey
    • Two basic body forms: polyp (Hydra) and medusa (jellyfish)
  • Microscopy Techniques:
    • Use a dissecting microscope to observe a live Hydra in a petri dish.
    • Watch for tentacle movements and feeding behavior.

4. Platyhelminthes (Flatworms)

  • Examples: Planaria, Fasciola (liver fluke)
  • Key Features:
    • Dorsoventrally(back/belly) flattened body
    • Bilateral symmetry
    • Some are free-living (Planaria), while others are parasitic (Fasciola)
  • Microscopy Techniques:
    • Observe a prepared slide of Planaria to study its internal structure.
    • For parasitic species, stained sections reveal complex reproductive structures.

5. Nematoda (Roundworms)

  • Examples: Ascaris, Trichinella
  • Key Features:
    • Cylindrical, unsegmented body
    • Pseudocoelomate (fluid-filled body cavity)
    • Free-living or parasitic (Ascaris in human intestines)
  • Microscopy Techniques:
    • View a prepared slide of Ascaris cross-section to see digestive and reproductive systems.
    • Observe live nematodes in a drop of water under low power magnification.

 

6. Rotifera (Rotifers)

  • Examples: Philodina
  • Key Features:
    • Tiny, multicellular organisms with a wheel-like ciliated crown
    • Freshwater dwellers, contributing to nutrient recycling
    • Exhibit parthenogenesis (reproduction without fertilization)
  • Microscopy Techniques:
    • Observe rotifers in pond water under a microscope.
    • Focus on their rotating cilia used for locomotion and feeding.

Importance of Microscopic Study of Lower Invertebrates

  • Understanding Evolution: These organisms provide insights into the evolution of multicellular organisms and early animal life.
  • Ecological Significance: Many lower invertebrates play crucial roles in ecosystems, such as decomposers, primary consumers, or parasites.
  • Medical Relevance: Some, like parasitic worms, are responsible for human and animal diseases.
  • Research and Biotechnology: Protozoa and other invertebrates are used in biological and medical research.

 

 

Comparison of Lower Invertebrate Groups

Phylum

Body Symmetry

Body Cavity

Digestive System

Locomotion

Examples

Porifera

Asymmetrical

None

Filter-feeding(Aquatic orgs)

Sessile(can’t move)

Sycon, Spongilla

Cnidaria

Radial

None

Incomplete

Tentacles, Medusa

Hydra, Jellyfish

Platyhelminthes

Bilateral

None

Incomplete

Cilia, Muscular movements

Planaria, Tapeworm

Nematoda

Bilateral

Pseudocoelomate

Complete

Thrashing motion(violent uncontrolled movement)

Ascaris, Hookworm

Rotifera(wheel in latin)

Bilateral

Pseudocoelomate

Complete

Ciliated corona

Philodina, Brachionus