Examining Microorganisms: Bacteria and Protists – Taxonomy, Diversity, and Microscopy

Examining Microorganisms – Bacteria and Protists

Taxonomy: Classification of Life

Taxonomy is the scientific discipline concerned with naming, describing, and classifying organisms into groups based on shared characteristics. This hierarchical system helps biologists organize the diversity of life and understand evolutionary relationships.

• Taxonomic Ranks: The major ranks, from broadest to most specific, are: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

• Binomial Nomenclature: Each species is given a two-part scientific name (Genus species), e.g., Homo sapiens.

• Domains: The highest level of classification, including Bacteria, Archaea, and Eukarya.

• Purpose: Taxonomy allows scientists to communicate about organisms, study evolutionary relationships, and identify unknown species.

Example: Humans are classified as Domain Eukarya, Kingdom Animalia, Phylum Chordata, Class Mammalia, Order Primates, Family Hominidae, Genus Homo, Species sapiens.

Microscopy: Observing Microorganisms

Microscopes are essential tools for studying microorganisms, which are often too small to be seen with the naked eye. Compound light microscopes are commonly used in biology labs to observe bacteria and protists.

• Field of View (FOV): The visible area under the microscope, measured in micrometers (μm).

• Magnification: Determined by multiplying the power of the objective lens by the eyepiece lens.

• Preparation: Wet mounts are used to observe live specimens, allowing for the study of movement and behavior.

Formula:

$\text{FOV in μm (micrometers)} = \text{mm} \times 1000$

Microorganism Diversity

Domain Bacteria

Bacteria are prokaryotic organisms, meaning they lack a membrane-bound nucleus and organelles. They are among the oldest and most abundant forms of life on Earth.

• Prokaryotes: Cells without a nucleus; DNA is located in the nucleoid region.

• Shapes: Common shapes include cocci (spherical), bacilli (rod-shaped), and spirilla (spiral).

• Nutrition: Bacteria can be autotrophic (self-feeding via photosynthesis or chemosynthesis) or heterotrophic (feeding on organic material).

• Ecological Roles: Bacteria are essential for nutrient cycling, decomposition, and can be beneficial (e.g., gut flora) or pathogenic (disease-causing).

Examples: Cyanobacteria (photosynthetic bacteria), Streptococcus (pathogenic bacteria).

Domain Eukarya: Protists

Protists are eukaryotic organisms, meaning they have a true nucleus and membrane-bound organelles. They are a diverse group, including both unicellular and multicellular forms.

• Types: Includes algae (photosynthetic), protozoa (heterotrophic), and slime molds.

• Movement: Protists may move using cilia, flagella, or pseudopodia.

• Examples: Euglena (flagellated protist), Paramecium (ciliated protist), Amoeba proteus (uses pseudopodia).

Additional info: Protists are classified into supergroups such as Excavata, SAR, Archaeplastida, and Unikonta, based on molecular and morphological evidence.

Identification and Classification of Microorganisms

Dichotomous Key

A dichotomous key is a tool used to identify organisms based on a series of choices that lead the user to the correct name of a given item. It is especially useful in lab settings for classifying bacteria and protists.

• Process: Begin with a general characteristic (e.g., cell size), then follow the key to more specific traits (e.g., shape, movement, color).

• Application: Used to distinguish between different genera and species observed under the microscope.

Table: Classification of Bacteria and Protists

The following table summarizes the major groups and examples of bacteria and protists as presented in the notes:

Domain/Group	Phylum/Supergroup	Examples
Bacteria	Bacteria	Cyanobacteria (Oscillatoria, Spirulina)
Eukarya	Excavata	Euglena
Eukarya	SAR	Paramecium, Diatoms
Eukarya	Archaeplastida	Green algae (Chlamydomonas, Spirogyra, Volvox)
Eukarya	Unikonta	Amoeba proteus

Lab Activities: Observing and Comparing Microorganisms

Activity: Identifying Unknown Microorganisms

Students use prepared slides and dichotomous keys to identify unknown bacteria and protists. Observations include cell size, shape, color, and movement.

• Steps: Select an organism, observe under the microscope, record characteristics, use the key to identify.

• Movement Types: Flagella (whip-like), cilia (hair-like), pseudopodia (amoeboid movement).

Activity: Review and Make Comparisons

Students compare characteristics of green algae species to understand evolutionary trends toward multicellularity.

Species	Unicellular	Filamentous	Colonial	Chlorophyll	Aquatic
Chlamydomonas	Yes	No	No	Yes	Varies
Spirogyra	No	Yes	No	Yes	Varies
Volvox	No	No	Yes	Yes	Varies

Additional info: This comparison helps illustrate the evolutionary transition from unicellular to multicellular life forms in the green algae lineage.

Lab Techniques and Clean-up

Microscope Use and Maintenance

Proper use and care of the microscope are essential for accurate observations and maintaining equipment.

• Remove slides and return to proper tray.

• Rotate nosepiece to lowest power objective.

• Turn off light source.

• Clean lenses and microscope frame.

• Store microscope with ocular lenses facing away from you.

• Clean up lab bench area.

Summary

This guide covers the basics of taxonomy, the diversity of bacteria and protists, the use of microscopes in studying microorganisms, and practical lab activities for identification and comparison. Understanding these foundational concepts is essential for further study in biology, especially in areas related to cell structure, classification, and evolutionary biology.