Genbio

Genbio

General Biology — Cell Theory, Microscopy & Cell Structure

Opening & Closing Prayers

Augustinian context frames the lesson with unity, peace, wisdom, grace, mercy, and love.

Invocations: Our Lady of Grace; Saint Augustine; affirmation that God is present where people gather “in His Name.”

Microscopy Basics

A microscope is an instrument that allows visualization of objects too small for the naked eye.

Microscopy = the science of investigating small objects/structures with microscopes.

“Microscopic” = invisible unless aided by a microscope.

Major Types of Microscopes

Optical/Light microscopes (compound, fluorescence, etc.).

Electron microscopes

Transmission Electron Microscope (TEM) ‑ invented 1931 by Max Knoll & Ernst Ruska; modern TEM image shown.

Scanning Electron Microscope (SEM).

Magnify up to

500,000

×

500,000×.

Scanning-Probe Microscopes (SPM)

STM (Scanning-Tunneling Microscope, 1981, Gerd Binnig & Heinrich Rohrer) gives 3-D images.

SNOM, APM, etc.

Fluorescence microscope coupled with a digital camera—high-contrast imaging of tagged molecules.

Anatomy of a Compound Light Microscope

Eyepiece/ocular lens

Revolving nosepiece holding objectives (scanner, LPO, HPO, OIO)

Objective lenses (scanner

4

×

4×, low

10

×

10×, high

40

×

40×, oil immersion

100

×

100×)

Stage & stage clips

Coarse-adjustment knob (initial focusing)

Fine-adjustment knob (resolution refinement)

Mirror / built-in illuminator

Diaphragm or iris diaphragm (light regulation)

Arm & base (support)

Practice Tasks Mentioned

Labeling exercise (#15) for microscope parts.

Table completion for total magnification:

Total

=

Objective

×

10

x (ocular)

Total=Objective×10x (ocular).

Quiz items ask for part names vs. functions (e.g., “connects eyepiece to objectives” = body tube).

Historical Development of Cell Discovery & Microscopy

1597 Hans & Zacharias Janssen: simple tube microscope; saw “single cell animal.”

1663 Robert Hooke: thin cork slice; coined term “cell.”

1675 Antonie van Leeuwenhoek: single-lens scope (≈

300

×

300×); first to observe nuclei, bacteria, spermatozoa.

1830 Robert Brown: clarified nucleus in diverse organisms.

1838 Matthias Schleiden: all plants are made of cells.

1839 Theodor Schwann: all animals consist of cells; cell is basic unit of life.

1855 Rudolf Virchow: “Omnis cellula e cellula”—cells arise from pre-existing cells.

1880-1890 Robert Koch: staining techniques for bacteria.

1939 Ernest Everett Just: structure/function correlations in cells.

1967 Lynn Margulis: Endosymbiont hypothesis.

Cell Theory (formalized ~1850’s)

All living organisms comprise one or more cells.

The cell is the smallest functional unit of life.

Cells arise only from pre-existing cells.

Endosymbiotic Theory

Proposed by Lynn Margulis (1967).

Step 1 (internal infolding) produced endomembrane system & nucleus.

Step 2 engulfment of aerobic bacterium → mitochondrion.

Step 3 engulfment of photosynthetic cyanobacterium → chloroplast.

Evidence: double membranes, own circular DNA, ribosomes similar to bacteria, phylogenetic analyses.

Prokaryotic Cells

Small, simple, high surface-area/volume ratio; no membrane-bound organelles.

DNA resides in nucleoid (circular), no true nucleus.

Cell envelope: capsule (sticky protection), cell wall (shape; peptidoglycan in Bacteria, pseudo-peptidoglycan in Archaea), plasma membrane (permeability).

Internal: cytoplasm, ribosomes (70S), plasmids.

Appendages: pili (adhesion), flagellum (motility).

Reproduction: binary fission.

Examples & notes:

Bacteria shapes: cocci (single, diplo-, strepto-), bacilli, spirillum, spirochete, vibrio.

Lactobacillus acidophilus (anaerobe in dairy; therapeutic).

Streptococcus pneumoniae (pneumonia, meningitis; other invasive diseases).

Staphylococcus aureus (skin colonizer → staph infections).

Cyanobacteria (blue-green algae) – only photosynthetic prokaryotes that produce