Historical Development, Anatomy, and Theory of the Cell and Microscope

Historical Development of the Microscope

  • The timeline below outlines the key events and individuals responsible for the development of modern microscopy, spanning from the late 16th century to contemporary advancements.

  • 1590: Hans Janssen and Zacharias Janssen

    • Hans Janssen and his son, Zacharias Janssen, discovered that placing multiple lenses in a tube allowed objects at the end of the tube to appear greatly enlarged. This is considered the precursor to the compound microscope.

  • 1609: Galileo Galilei

    • Galilei invented a compound microscope that utilized a combination of convex and concave lenses.

  • 1625: Giovanni Faber

    • Faber coined the term "microscope" to refer specifically to the compound microscope developed by Galileo Galilei.

  • 1665: Robert Hooke

    • An English physicist who published his observations in which he coined the term "cell."
    • He was the first individual to observe a plant cell using a single-lens microscope.

  • 1676: Antonie van Leeuwenhoek

    • The first person to observe living cells using a single-lens microscope of his own design.
    • His examinations included blood cells, yeast, and insects.

  • 1830: Joseph Lister

    • Lister discovered that using several weak lenses together at specific distances could reduce spherical aberrations.
    • This allowed for high magnification without significant blurring of the image.

  • 1874: Ernst Abbe

    • Introduced a mathematical formula that correlated resolving power to the wavelength of light.
    • This formula made it possible to calculate the theoretical maximum resolution of a microscope.

  • 1931: Ernst Ruska and Max Knoll

    • Designed and constructed the first transmission electron microscope (TEM).
    • Unlike light microscopes, the electron microscope depends on electrons rather than light, allowing for the visualization of objects as small as the diameter of an atom.

  • 1932: Frits Zernike

    • Invented phase contrast illumination, allowing for the imaging of transparent specimens without the need for staining.

  • 1942: Ernst Ruska

    • Invented the first scanning electron microscope (SEM), which transmits a beam of electrons across the surface of a specimen to create an image.

  • 1957: Marvin Minsky

    • Introduced the principle of confocal imaging, providing a higher resolution than that achievable with conventional light microscopy.

  • 1972: Godfrey Hounsfield and Allan Cormack

    • Developed the Computerized Axial Tomography (CAT) scanner, capable of generating cross-sectional views and three-dimensional (3D) images of internal organs and structures.

  • 1978: Thomas and Christoph Cremer

    • Developed the first practical confocal laser scanning microscope, which utilizes focused laser beams to scan a specimen.

  • 1981: Gerd Binnig and Heinrich Rohrer

    • Invented the scanning tunnelling microscope (STM), which can visualize individual atoms within materials.

  • 1986: Nobel Prize Recognition

    • Ernst Ruska was awarded the Nobel Prize for his contributions to the study of microscopy.
    • Gerd Binnig and Heinrich Rohrer also received Nobel Prizes for their work.

  • 1992: Douglas Prasher

    • Cloned the green fluorescent protein (GFP) for use in fluorescence microscopy.

  • 1993 - 1996: Stefan Hell

    • Pioneered the development of the first super-resolution microscopy.

  • 2008: Titan 80-300 Cubed

    • The first installation of this electron microscope in Canada revolutionized nanotechnology by pushing into more advanced frontiers.

  • 2010: University of California, Los Angeles (UCLA)

    • Researchers used a cryo-electron microscope to observe the individual atoms of a virus.

  • 2014: Nobel Prize in Chemistry

    • Awarded to Eric Betzig, Stefan Hell, and William Moerner for the invention of super-resolution microscopes that can see matter smaller than 0.2 nm0.2\,\text{nm}.

  • 2017: 3D Protein Structure

    • Researchers Jacques Dubochet, Joachim Frank, and Richard Henderson created a technique for generating the 3D structure of proteins at an atomic level using an electron microscope.

  • 2018: Titan Krios

    • A high-end transmission electron microscope developed by Thermo Fisher Scientific (an American company) was unveiled and inaugurated, facilitating the transition from 2D to 3D imaging with Cryo-EM (cryo-electron microscopy).

Anatomy and Functions of the Light Compound Microscope

  • General Overview

    • Classroom laboratories primarily use light compound microscopes to observe living or preserved specimens, including bacteria.
    • They can magnify specimens up to approximately 1,0001,000 times their original size.
    • Staining is often required to improve image contrast.

  • Measurement and Magnification Calculations

    • Total Magnification is determined by the following formula:     Total Magnification=Ocular lens×Objective lens\text{Total Magnification} = \text{Ocular lens} \times \text{Objective lens}
    • Example 1 (Low Power): 10x×10x=100x10x \times 10x = 100x
    • Example 2 (High Power): 10x×40x=400x10x \times 40x = 400x

  • Key Optical Concepts

    • Resolution: The ability of a microscope to show the details of an object. It is defined as the shortest distance between two points on a specimen that the observer or camera system can still distinguish.
    • Contrast: Refers to the darkness of the background relative to the specimen. Light specimens are generally easier to see against dark backgrounds.
    • Phase Contrast Microscope: A specific type of microscope used to view colorless or transparent specimens without staining.
I. Mechanical Parts
  • Body Tube: A hollow tube that allows light to pass from the objective lens to the eyepiece.
  • Revolving Nosepiece: Holds the objective lenses and can be rotated to select the desired magnification. The lenses must "click" into place.
  • Arm: Connects the base to the body tube and serves as the handle for carrying the instrument.
  • Stage: The platform where the slide or specimen is placed. It features a central opening to allow light to pass through from below.
  • Stage Clips: Used to secure the slide in position.
  • Base: The anchored part of the microscope that provides support for the entire structure and serves as the attachment point for illuminators.
  • Inclination Joint: Found in some models; a joint where the arm attaches to the pillar, allowing the microscope to be tilted for comfort.
  • Adjustment Knobs:
    • Coarse adjustment knob: Used for initial focusing.
    • Fine adjustment knob: Used for precision focusing.
II. Illuminating Parts
  • Mirror: Reflects light toward the specimen. One side is planar (flat) for artificial light, and the other is concave for natural light. It is supported by a mirror rack. Modern microscopes often replace this with a built-in bulb or light source.
  • Condenser: Located below the stage; it concentrates light from the source/mirror onto the specimen. Held by a rack.
  • Iris Diaphragm: Attached beneath the condenser; it regulates the intensity and amount of light reaching the specimen.
III. Magnifying Parts
  • Eyepiece (Ocular): The lens the observer looks through. Standard magnification is usually 10x10x, but ranges from 5x5x to 30x30x are available.
  • Objectives: The primary lenses for magnification. Modern microscopes usually house 3 to 5 objectives. Typical powers include 4x4x, 10x10x, 40x40x, and 100x100x.

Cell Theory: The Unifying Foundation of Cell Biology

  • 1820s Advances: Improved lens designs allowed for the visualization of detailed cell structures.
  • Robert Brown (Botanist): First observed a spherical structure in plant cells, naming it the "nucleus."
  • 1839: Theodore Schwann (Zoologist): Discovered that animal tissues are composed of cells.
  • 1839: Matthias Schleiden (Botanist): Concluded that all plant tissues are composed of cells.
  • Rudolf Virchow (Physician): Studied cell growth and development, concluding that all cells arise from preexisting cells.
The Tenets of Cell Theory
  • Original Tenets:
    1. Cells are the smallest unit of life. All living things are composed of one or more cells.
    2. Cells are the basic unit of organization of all organisms.
    3. Cells come only from preexisting cells.
  • Modern Additions:
    1. Cells carry and pass hereditary units (genetic material) to offspring during cell division.
    2. All cells are relatively the same in terms of chemical composition and metabolic activity.

Cell Shape and Internal Organization

Cell Shape
  • A cell's shape is determined by its specific function.
  • Nerve cells (Neurons): Long with cytoplasmic extensions (axons and dendrites) to transmit impulses from the central nervous system to the rest of the body.
  • Skin cells: Flat shape to provide an effective protective cover for the body.
  • Blood cells: Capable of changing shape, which aids in digesting and killing disease-causing germs.
Internal Organization
  • Structural characteristics are closely linked to function. Variations exist between species (e.g., plant vs. animal cells) and within a single organism.
  • Glandular Cells: Specialize in producing secretory materials (mucus, hormones). They contain a higher density of ribosomes and Golgi bodies.
  • Muscle Cells: Specialized for contraction. They contain a higher number of mitochondria to provide the necessary energy.

Questions & Discussion

Quiz 1.1

  1. Who is considered the "English Father of Microscopy"?

    • a. Robert Hooke
    • b. Hans Janssen
    • c. Robert Brown
    • d. Rudolf Virchow
    • Note: Based on transcript context regarding the English physicist who coined "cell," the answer is Robert Hooke.

  2. Which of the following is not a tenet of the cell theory?

    • a. All living things are made up of cells.
    • b. All living things are composed of atoms.
    • c. All cells come from preexisting cells.
    • d. Cells are the basic functional unit of life.
    • Note: Option B is not a tenet of Cell Theory.

  3. What part of the microscope focuses the light on the specimen being observed?

    • a. Mirror
    • b. Objective lens
    • c. Condenser
    • d. Ocular

  4. Who was the Dutch microscope maker who pioneered the study of protozoa?

    • a. Louis Pasteur
    • b. Robert Hooke
    • c. Galileo Galilei
    • d. Anton van Leeuwenhoek

  5. Which of the following is measured in cubic centimeters (cm3cm^3)?

    • a. Area
    • b. Volume
    • c. Weight
    • d. Height
Application and Analysis
  1. Why are the cells of giraffes not larger than those of a mouse?
  2. Leeuwenhoek’s microscope revealed microscopic organisms he called “animalcules,” yet he never concluded that the cells are the smallest unit of living organism. What could be the reason for this?
  3. It is said that the cell theory is a cornerstone in biology. Why do you think this is so?