Cell Structure and Microscopy in Microbiology

Cell Structure and Microscopy

Magnification and Resolution

Understanding cell structure in microbiology requires the use of microscopes, which rely on two key concepts: magnification and resolution.

• Magnification: The process of making an object appear larger than its actual size. Essential for observing microorganisms that are too small to be seen with the naked eye.

• Resolution (resolving power): The minimum distance at which two distinct objects can be distinguished as separate. Higher resolution allows for clearer and more detailed images of cell structures.

Example: Electron microscopes have much higher resolution than light microscopes, allowing visualization of subcellular structures.

Types of Microscopes

Different types of microscopes are used in microbiology to study cells and their components.

• Light Compound Microscope: Uses visible light and glass lenses to magnify specimens. Suitable for viewing living cells and basic cell structures.

• Transmission Electron Microscope (TEM): Uses electron beams to pass through thin sections of specimens, providing detailed images of internal cell structures.

• Scanning Electron Microscope (SEM): Scans the surface of specimens with electron beams, producing three-dimensional images of cell surfaces.

Example: TEM is used to study the ultrastructure of bacteria, while SEM is ideal for examining the surface morphology of microbial cells.

Characteristics of Living Things

Defining Life

To be considered living, an organism must exhibit several key characteristics:

• Order: Organized structure and function.

• Evolutionary adaptation: Ability to change over generations in response to environmental pressures.

• Response to the environment: Reacting to stimuli.

• Regulation: Maintaining internal stability (homeostasis).

• Energy processing: Obtaining and using energy for growth and maintenance.

• Growth and development: Increasing in size and complexity.

• Reproduction: Producing new individuals.

Example: Bacteria reproduce by binary fission and respond to chemical gradients (chemotaxis).

Additional info: Viruses do not fulfill all these criteria independently and are often considered non-living.

Prokaryotic Cells vs. Eukaryotic Cells

Key Differences

Cells are classified as either prokaryotic or eukaryotic based on their structural features.

Feature	Prokaryotic Cells	Eukaryotic Cells
Size	Smaller	Larger
DNA Location	Not enclosed in a membrane; no histones	Enclosed in a nucleus; packed with histones
Organelles	Absent (except ribosomes and some specialized structures)	Numerous organelles present
Cell Wall	Peptidoglycan (PG) cell wall	May be present; made of materials other than PG
Cell Division	Binary fission	Cytokinesis & mitosis/meiosis

Example: Escherichia coli is a prokaryote; human cells are eukaryotic.

Prokaryotes: Cell Shape and Arrangement

Common Shapes

Prokaryotic cells exhibit a variety of shapes, which are important for identification and classification.

• Coccus (cocci): Spherical or round cells.

• Bacillus (bacilli): Rod-shaped cells.

• Coccobacillus: Short, plump rod-shaped cells.

• Curved rods:

  • Vibrio: Single curved rod.

  • Spirillum: Short, rigid helical rod.

  • Spirochete: Long, flexible helical rod.

Example: Staphylococcus aureus (coccus), Bacillus subtilis (bacillus), Vibrio cholerae (vibrio).

Additional info: Cell shape can influence motility, pathogenicity, and environmental adaptation.