Spontaneous Generation

Unit 3

What is Spontaneous Generation?

Who was the first person to come up with the idea of Spontaneous

Generation?

Aristotle

Aristotle (384-322 BC)• First person to propose the

theory of spontaneous generation

• Spontaneous generation – the idea that living things can arise from nonliving matter

• Spontaneous generation is also known as abiogenesis

• The idea of spontaneous generation lasted for almost 2000 years!

• For centuries, people based their beliefs on their interpretations of what they saw going on in the world around them without testing their ideas

• They didn’t use the scientific method to arrive at answers to their questions

• Their conclusions were based on untested observations

Disproving Spontaneous Generation

Francesco Redi (1668)

• In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide mouth jars containing meat

Redi’s Findings• Redi used open & closed flasks

which contained meat.• Hypothesis: If you leave meat

sitting out uncovered, then flies will lay their eggs on the meat.

• He observed the flasks to see in which one(s) maggots would develop.

Evidence against spontaneous generation:

1. Unsealed – maggots on meat2. Sealed – no maggots on meat3. Gauze – few maggots on gauze, none on meat

Redi’s Findings• He found that if a flask was closed with a lid so

adult flies could not get in, no maggots developed on the rotting meat within.

• In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared.

Did Redi Disprove Spontaneous Generation?

• The results of Redi’s experiment disproved the idea of spontaneous generation for larger organisms (such as flies, mice, bees, etc.)

• But people still thought microscopic organisms like algae or bacteria could arise through spontaneous generation.

Anton van Leeuwenhoek• Leeuwenhoek began making

and looking through simple microscopes

• He often made a new microscope for each specimen

• He examined water and visualized tiny animals, fungi, algae, and single celled protozoa called animalcules

• By end of 19th century, these organisms were called microbes

John Needham• Showed that microorganisms flourished in

various soups that had been exposed to the air– Claimed that there was a life force present in the

molecules of all inorganic matter, including air and the oxygen in it, that could cause spontaneous generation to occur

Did Needham Prove Spontaneous Generation was True?

• Needham’s experiments seemed to support the idea of spontaneous generation

• People didn’t realize bacteria were already present in Needham’s soups

• Needham didn’t boil long enough to kill the microbes

Lazzaro Spallanzani (1765)• Boiled soups for almost an hour and sealed

containers by melting the slender necks closed.– The soups remained clear.– Later, he broke the seals & the soups became cloudy

with microbes.

After Spallanzani’s Experiment..

• Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed life force

• Therefore, spontaneous generation remained the theory of the time

The Theory Finally Changes..

How do Microbes Arise?

• By 1860, the debate had become so heated that the Paris Academy of Sciences offered a prize for any experiments that would help resolve this conflict

• The prize was claimed in 1864 by Louis Pasteur, as he published the results of an experiment he did to disproved spontaneous generation in microscopic organisms

Pasteur’s Problem• Hypothesis: Microbes

come from cells of organisms on dust particles in the air; not the air itself.

• Pasteur put broth into several special S-shaped flasks. Each flask was boiled and placed at various locations

Pasteur’s Experiment – Step 1

• S-shaped Flask - Filled with broth

• The special shaped was intended to trap any dust particles containing bacteria

Pasteur’s Experiment – Step 2

Boiled broth in the flasks which killed the microbes

Pasteur’s Experiment – Step 3

• Flask left at various locations• Did not turn cloudy• Microbes not found• Notice the dust that collected in the neck of

the flask

Pasteur’s Experimental Results

The Theory of Biogenesis • Pasteur’s S-shaped flask kept microbes out but let

air in.• Proved microbes only come from other microbes

(life from life) - biogenesis

Cell Theory Websites

• http://www.smithlifescience.com/celltheory.htm

• http://www.timetoast.com/timelines/cell-theory-timeline--3

What are the three parts of the cell theory…

1.)2.)3.)

What are the three parts of the cell theory…

1.) All living things are composed of cells

2.) Cells are the basic unit of structure and function

3.) New cells are produced from existing cells

Schleiden, Schwann & Virchow:

• http://en.wikipedia.org/wiki/Theodor_Schwann

• http://migration.wordpress.com/2007/03/02/basics-cell-theory/

• http://science.jrank.org/pages/6408/Spontaneous-Generation.html

• http://en.wikipedia.org/wiki/Rudolf_Virchow