Back

Comparing Time Lines -

Make verticle 400 year time-line to compare the theory of biogenesis and cell theory.. On the left of the line, place a summary of the events in the development of the theory of biogenesis. To the right of the line place a summary of the events in the development of cell theory and cell biology.

Why was the importance of Hooke's and Leeuwenhoek's work not realized for 150 years?
Comparing the time-lines of the development of cell theory, and biogenesis and the relationship between these theories may help answer the above question. Note how improvements in microscopes corresponds to the development of the two theories. Note where the two theories intersect.

Biogenesis:
The theory of biogenesis developed as scientists investigated the origins of life. Before the theory of biogenesis was developed, scientists thought that life spontaneously generated from nonliving things. A few crucial experiments were pivotal in discrediting the idea of spontaneous generation.

In 1668 Francisco Redi put decaying meat in some jars, then covered half of them. When maggots appeared only on the uncovered meat, Redi concluded that they had hatched from fly eggs and had not come from the meat.

In 1745 John Needham heated broth sealed flasks. When the broth became cloudy with microrganisms, he mistakenly included that they developed spontaneously from the broth.

In 1768 Lazzaro Spallanzani boiled broth in sealed flasks for a longer time than Needham did. Only the ones he opened became cloudy with contamination.

In 1859 Louis Pasteur disapproved spontaneous generation by boiling broth in S-necked flasks that were open to be air. The broth became cloudy only when the flasks tilted and the broth was exposed to dust in the S-neck. Pasteur also studied the causes of many bacterial diseases and established germ theory.

In 1924 Alexander Oparin hypothesized that energy from the sun, lightning, and Earth's heat triggered chemical reactions early in Earth's history. The newly formed molecules washed into Earth's ancient oceans and became a part of what is often called the primordial soup. (The idea of spontaneous generation returns to the forefront of science.)

In 1953 Stanley Miller and Harold Urey produced amino acids in a laboratory using the conditions similar to Alexander Oparin's hypothesis. But, current theory is that the conditions of the early Earth were much different than this hypothesis.



Cell Theory and Discoveries in Cell Biology:
1590 – Two Dutch eye glass makers, Zaccharias Janssen and son Hans Janssen experimented with multiple lenses placed in a tube that made objects in front of the tube appeared greatly enlarged.

In 1665 Robert Hooke (English) publishes a book of microscope observations and establishes the microscope is a scientific tool. He made his observations with a compound microscope that could magnify things 20 to 30 times. In this book Hooke drew the cell walls of dead plant cells. (This book got Leeuwenhoek interested in studying cells.)

In 1674 Anton van Leeuwenhoek (Dutch)systematically studied and described living cells including single cell animals (protists). He made single lensed microscopes that could magnify things 200 to 400 times and discovered the world of microscopic organisms. He also described the bands observed in muscle and the nuclei in the blood cells of fish. How Leeuwenhoek made his lenses died with Him and lenses with an equal resolving power were not produces for over 100 years. The British Royal Society published many of the 500 letters Leeuwenhoek wrote them describing his observations.


In 1830 Joseph J. Lister greatly improved the lenses of compound microscopes. Lenses bend or refract different colors of light different amounts producing a blurred halo effect. Lister combined several weak lenses to reduce the halos of light caused by refraction. Due to this new lens scientist began using microscopes as powerful as Leeuwenhoek's that were much easier to use.

In 1838 Matthias Schleiden (German) made the generalization that all plants are made of cells after examining many plant parts which were made of cells. Schleiden didn't understand how new cells are formed. Schleiden and Schwann talked and reaffirmed each others ideas.

In 1839 Theodor Schwann (German) made the generalization that all animals are made of cells after examining many animal parts which are made up cell's. He further proposed that organisms are made of cells.

In 1855 Rudolf Virchow (German) infers that all new cells come from existing cells. He was a doctor and based this inference on his systematic study of diseases.

In 1857 Kolliker describes mitochondria in muscle.

In 1897 Camillo Golgi describes the Golgi apparatus in cells.

In 1953 James D. Watson and Francis Crick suggested what is now accepted as the first correct double-helix model of DNA structure. Their double-helix, molecular model of DNA was then based on a single X-ray diffraction image taken by Rosalind Franklin and Raymond Gosling in 1952, as well as the information that the DNA bases were paired— obtained from Erwin Chargaff in the previous years.