Biology Chapter on Spontaneous Generation

Endosymbiotic Theory

• Proposed by Lynn Margulis in 1970 with the book, The Origin of Eukaryotic Cells
• Suggests eukaryotic cells evolved from a symbiotic relationship between different prokaryotic organisms

Miller & Urey Experiments

• Attempted to demonstrate how organic compounds could have formed on early Earth
• Simulating lightning through a mixture of gases: methane, ammonia, hydrogen and water vapor
• Observed that after one week, 10% - 15% of the carbon was present as amino acids

Dichotomous Keys

• A tool used to identify organisms like trees, wildflowers, mammals, reptiles, rocks, and fish
• Keys consist of a series of choices leading to the correct name of an item
• "Dichotomous" means "divided into two parts," so each step presents two choices

Abiogenesis

• Developed by Aristotle (384-322 BC)
• The theory that life can originate from non-living matter
• Supported by the scientific community for nearly 2000 years
• Notably, Van Helmont provided “scientific evidence” in the 17th century by suggesting that mice arose from grains of rice in a piece of fabric

Francesco Redi’s Experiment (1668)

• Designed to test if rotting meat turns into flies
• Found that rotting meat does not produce flies, flies only come from other flies
• Disproved the theory of spontaneous generation

John Needham's Experiment (1748)

• Believed that spontaneous generation could occur
• Boiled chicken broth (thought to kill all life), then left it open to the air
• The broth became cloudy, leading Needham to believe organisms arose spontaneously from the broth
• Sent many scientists down the wrong path

Lazarro Spallanzani's Experiment (1776)

• Continued Needham's work
• Identified errors in Needham's experiment:
  • Broth wasn’t boiled long enough to eliminate all life
  • Flasks were not sealed tightly enough
• Boiled flasks longer and sealed them more securely, preventing microbial growth
• Critics argued against sealed flasks claiming air was needed for life

Louis Pasteur's Swan-Neck Flask Experiment (1864)

• Successfully disproved abiogenesis
• Believed bacteria was present in air with dust
• Designed a swan-neck flask to prove his theory:
  • Broth was boiled to kill microbes
  • Neck of flask was heated and shaped into an S-curve
  • This prevented dust particles with microbes from reaching the broth
  • Breaking the neck of the flask allowed air to reach the broth and growth occurred
  • Tilting the flask with the S-shaped neck allowed microbes to enter the broth and promote growth
• This experiment solidified the theory of biogenesis

Biogenesis

• The idea that living things can only arise from other living things
• Life only comes from life
• Bio - Life
• Gen - To be produced

Microscopes

• Anton Van Leeuwenhoek began making and using simple microscopes
• He often created a new microscope for each specimen
• Examined water and observed tiny organisms: fungi, algae single-celled protozoa (animalcules)
• These organisms were later termed microbes in the 19th century

Cells

• Robert Hooke observed a sliver of cork through a microscope lens and observed “pores” or "cells"
• He was the first to use the word "cell" when describing microscopic structures

Cell Theory

• Developed by Schleiden (botanist) and Schwann (zoologist)
• States that life consists of cells and they are the basic unit of life
• Further clarified by Virchow who established that cells come from pre-existing cells

Key Points of the Cell Theory

• All living things are made of cells
• Cells are the basic units of life
• All cells arise from pre-existing cells