Spontaneous Generation Unit 3

What is Spontaneous Generation?

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

Aristotle

Aristotle ( 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

Examples of Spontaneous Generation

OBSERVATION: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times

CONCLUSION Spontaneous generation! – It was perfectly obvious to people back then that muddy soil gave rise to the frogs – In other words, they believed the frogs came from the mud

Observation #2 In many parts of Europe, medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice around.

Conclusion It was obvious to them that the mice came from the moldy grain…..

Example #3 Observation: In the cities centuries ago, there were no sewers, no garbage trucks, no electricity, and no refrigeration. Sewage flowed down the streets, and chamber pots and left over food were thrown out into the streets each morning. Many cities also had major rat problems and a disease called Bubonic plague.

Conclusion Obviously, all of the sewage and garbage turned into the rats.

Example #4 Observation: Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. Typically, carcasses were hung by their heels, and customers selected which chunk the butcher would carve off for them.

Conclusion Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies. The flies came from the meat, right?

Recipe for bees: Kill a young bull, and bury it in an upright position so that its horns protrude from the ground. After a month, a swarm of bees will fly out of the corpse. Spontaneous Generation!

Recipe for mice: Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear. There will be adult males and females present, and they will be capable o f mating and reproducing more mice.

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 meat 2. Sealed – no maggots on meat 3. 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

9DU

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