Biology 2201: Unit one: Matter and energy for life

Historically, people (and scientist) believed in abiogenesis (also called spontaneous generation) because they made their conclusion from observation only they did not conduct experiments. Their observations included:
• In muddy soil, frogs emerged from nowhere, so they believed that frogs grew from meet.
• Meat hanging in a butcher shop grew flies.
• A dirty shirt in a barrel with some grain grew mice 21 days later.

Abiogenesis: is the theory that life can arise from non-living things.

In 1668, Francesco Redi conducted an experiment to test weather or flies arise from meat.

Francesco Redi covered the first jar with a cork, the second jar was left uncovered and the third jar was covered with gauze. The jar that was covered with a cork had so maggots. The jar that wasn’t covered had maggots appear in the jar, and the last jar that was covered with gauze had maggots on the gauze but not in the jar. Francesco Redi concluded that only flies can make more flies. This experiment disproved abiogenesis for larger organisms.

With the invention of the microscope, in the mid 1600's and the observations of microorganisms, people still believed in abiogenesis in microorganisms.

In 1745-1748, John Needham showed that microorganisms flourish in soups that have been exposed to the air. He stated that there was a ‘life force’ in organic matter including oxygen and air. He boiled the soup briefly and poured it into clean flasks with cork lids. Microorganisms still grew in the soup.
John Needham concluded that there is a ‘life force’ in the air which can cause spontaneous generation of microorganisms.

1765-1767 Lazzaro Spallanzani replicated Needham’s experiment with a few variations. Spallanzani boiled one flask of soup for one hour and sealed the flasks by melting the mouth (therefore the flask stayed sterile.) He boiled the second flask of soup briefly and sealed the flasks. (Microorganisms grew.) He boiled the third batch for one hour and sealed the flasks with corks. (Microorganisms grew.) Spallanzani concluded that soup was sterile when it was boiled for a hour, but briefly boiling th soup did not kill the bacteria. Microorganisms entered the soup from the air.

Heated debate between Spallanzani and Needham. The debate was so heated that the Paris Academy of Sciences offered a prize for whoever could conclusively end the debate.

Louis Pasteur in 1864 sought to answer these questions:
• Is there indeed a ‘life force’ present in air that can cause bacteria to develop by spontaneous generation?
• Is there a way to have air enter a container, and the ‘life force’ but not in the bacteria?

Pasteur already knew that bacteria existed in the air and that bacteria would settle out onto the walls of a long bent, glass tube as air was passed through it.

Pasteur created a flask with an S-shape neck which would allow air (but not bacteria) to flow into the soup. He boiled the soup inside the flasks. He boiled one flask in an open flask. Another batch of soup in a S-shape flask, another batch in flasks plugged with cotton. He concluded there is no ‘life force’, organisms do not arise from spontaneous generation in this way.

Aristotle was a Greek philosopher in the 4th century. He observed the nature and shared his observation and conclusions with the public. His ideas lasted in society’s beliefs for over 2000 years! One such belief was that living organisms could arise from nonliving matter.

The theory of abiogenesis persisted as true do to incorrect or misinterpreted observations and a lack of controlled experiments.

Biogenesis was finally accepted and abiogenesis was disproved, as a result of controlled experiments. This drastic change in knowledge is known as a paradigm shirt.

The debate between the theories of abiogenesis and biogenesis contributed to the creation of the cell theory. The invention