Development of cell theory

• Cell theory


  All living things are made up of one or more cells and the materials produced by these, cells are functional units of life, and all cells come from pre-existing cells
• Early microscopes


  • Invented by Hans and Zacharias Janssen, Dutch lens-makers, in about 1595
  • Used a two-lens system of an ocular lens and an objective lens
  • First compound microscope, meaning it used more than one lens to magnify objects
  • Had a magnifying power of approximately 20x
• Early microscopes


  • Robert Hooke's hand-made microscope in England in 1665 had a three-lens system
• Robert Hooke's observations


  • Examined thin slices of cork and saw many empty chambers which he called "cells"
  • Did not know these were the remnants of living cells, the simplest functional units of life
• Antoni van Leeuwenhoek's microscope


  • Used a simple single-lens microscope similar to a magnifying glass
  • Able to produce higher magnifications than compound microscopes of the day (up to 250x)
  • First to see the movement of different types of single cells that we now know as bacteria, sperm, and unicellular protozoa
• Van Leeuwenhoek made careful drawings of his discoveries and named them animalcules
• Spontaneous Generation


  The idea that life could emerge spontaneously from non-living matter
• Spontaneous generation was widely accepted from the time of the Romans through to the 19th century
• In 1668, Francesco Redi, an Italian physician and poet, questioned the belief that maggots appeared spontaneously from raw meat
• Redi's experiment


  1. Set out flasks containing raw meat, some sealed, some covered in gauze, some open to the air

  2. Maggots found only in the flasks open and accessible to flies to lay their eggs
• Despite the evidence, the idea of spontaneous generation continued to thrive
• Redi's experiment


  • Manipulated variable: meat/jar
  • Responding variable: microbacterial growth
  • Controlled variable: heat/broth/container
• In 1864, the French chemist Louis Pasteur disproved the theory of spontaneous generation
• Louis pasteur

  1. Heated the neck of the flask and bent it into an S-shape, allowing air to reach the boiled broth but trapping microorganisms and other particles in the S-bend

  2. Nothing grew in this broth, but if the flask was tipped or the neck broken, there would be microbial growth
• In 1859, the cell theory was further extended by Rudolf Virchow's statement that all cells arise only from pre-existing cells
• Cell Theory


  • 1. All living things are made up of one or more cells and the materials produced by these cells
  • 2. All life functions take place in cells, making them the smallest unit of life
  • 3. All cells are produced from pre-existing cells through the process of cell division
• The cell theory applies to all living things regardless of their size, shape, or the number of cells involved
• Biogenesis


  The development of living things from other living things through reproduction
• It was not until the 1830s with the improvements in lens technology and the increased number of observations made by scientists in several countries, that the importance of the cell as the functional unit of life was recognized
• Nucleus


  An important cell structure identified by Scottish microscopist Robert Brown in his study of orchids
• In 1838, a German professor of botany, M. J. Schleiden observed that all plants were composed of cells with nuclei and proposed that the nucleus was the structure responsible for the development of the remainder of the cell
• Schwann and Schleiden proposed that all plants and animals were composed of cells and that the cell was the basic unit of all organisms
• In 1859, the cell theory was further extended by Rudolf Virchow's statement that all cells arise only from pre-existing cells
• Manipulated variable


  The variable that is intentionally changed by the researcher
• Responding variable


  The variable that changes in response to the manipulated variable
• Controlled variable


  The variable that is kept constant throughout the experiment
• Pasteur provided strong evidence that spontaneous generation did not occur and that life arises through biogenesis
• Biogenesis


  The development of living things from other living things through reproduction
• The Development of the Cell Theory