Microscopy, Cell Structure, and Protist Diversity

Microscopy

Introduction to Microscopy

Microscopy is the study and use of microscopes to observe objects and structures that are too small to be seen with the naked eye. In biology, microscopes are essential tools for examining cells, tissues, and microorganisms.

• Microscopes magnify small objects, allowing detailed study of biological specimens.

• Two main types: Light microscopes (use visible light) and Electron microscopes (use electron beams).

• Common light microscopes: Compound and dissecting microscopes.

• Common electron microscopes: Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM).

Cells

Cell Theory and Types of Cells

Cells are the fundamental biological units of life. All living organisms are composed of one or more cells, which carry out all vital functions necessary for life.

• Cell Theory: All living things are made of cells; the cell is the basic unit of life; all cells arise from pre-existing cells. 2xx

• Two major types of cells:

  • Prokaryotic cells: Lack a nucleus and membrane-bound organelles. Example: Bacteria.

  • Eukaryotic cells: Have a nucleus and membrane-bound organelles. Examples: Plants, animals, fungi, protists.

Prokaryotic vs. Eukaryotic Cell Structure

Prokaryotic and eukaryotic cells differ in their internal organization and complexity.

Feature	Prokaryotic Cell	Eukaryotic Cell
Nucleus	Absent	Present
Membrane-bound organelles	Absent	Present
Examples	Bacteria, Archaea	Plants, Animals, Fungi, Protists
Size	Generally smaller (0.1–5 μm)	Generally larger (10–100 μm)

Example: Bacillus coagulans (prokaryote) and a typical animal cell (eukaryote) as shown in the provided diagrams.

Microscope Types and Usage

Compound Microscope

The compound microscope is a common laboratory instrument used to view small specimens at high magnification using multiple lenses.

• Key parts: Ocular (eyepiece), objectives (scanning, intermediate, high power), stage, condenser, lamp, coarse and fine focus knobs, arm, base.

• Magnification: Total magnification is calculated by multiplying the ocular lens magnification by the objective lens magnification.

Objective	Magnification	Total Magnification (with 10x ocular)
Scanning	4x	40x
Intermediate	10x	100x
High Power	40x	400x

Using the Compound Microscope

• Always start with the scanning lens (lowest power) to locate the specimen.

• Use coarse focus only with the scanning lens; use fine focus for higher magnifications.

• Never use coarse focus with intermediate or high power objectives to avoid damaging the slide or lens.

Field of View

The field of view is the visible area seen through the microscope eyepiece. As magnification increases, the field of view decreases.

• To measure the field of view, place a ruler on the stage and count the millimeters visible under the scanning lens.

• To calculate the field of view at higher magnifications, use the formula:

Formula:

$\text{Diameter of high power} = \frac{\text{Diameter of scanning}}{\text{Magnification of high power} / \text{Magnification of scanning}}$

Depth of Field

Depth of field refers to the thickness of the specimen that is in focus at one time. It decreases as magnification increases.

• To observe depth of field, use a slide with threads or layers and focus at different levels using different objectives.

• Note the order in which different layers come into focus as you adjust the fine focus knob.

Protists and Eukaryotic Diversity

Introduction to Protists

Protists are a diverse group of mostly unicellular eukaryotic organisms. They were once classified in their own kingdom but are now distributed among several eukaryotic supergroups based on genetic and structural characteristics.

• Protists can be autotrophic (photosynthetic), heterotrophic (phagocytotic), or mixotrophic (both).

• Examples include Euglena (mixotrophic), Paramecium (heterotrophic), and various algae (autotrophic).

Phylogenetic Classification of Eukaryotes

Modern classification divides eukaryotes into several supergroups based on evolutionary relationships. A clade is a group of organisms descended from a common ancestor.

• Four major supergroups:

  • Excavata

  • SAR (Stramenopiles, Alveolates, Rhizarians)

  • Unikonta

  • Archaeplastida

Examples of Protists by Supergroup

• Excavata: Trypanosoma levisi, Euglena

• SAR: Paramecium

• Unikonta: Amoeba proteus

• Archaeplastida: Red algae, green algae

Applications and Importance

• Protists play key roles in aquatic ecosystems as primary producers, decomposers, and pathogens.

• Some protists, such as Trypanosoma, cause diseases in humans and animals.

Additional Information

• For further study, refer to textbook exercises 13.1, 13.2, 13.3, and 13.4 as indicated in the notes.

• Post-lab questions on pages 360-361 (questions 1, 3, and 8) are recommended for review.