AIPMT-NEET Biology Aspirants, read out the next AIPMT-NEET Biology Study material/ Notes on Origin of Life. In this we will learn about experiments on theory of Spontaneous generation and Biogenesis, important for AIPMT-NEET Biology. Free online notes for AIPMT-NEET.
Origin of life is always a topic of discussion from past. Different scientists supported different opinion on this. Two major hypothesis about origin of life are: Spontaneous generation and Biogenesis.
- Aristotle (384–322 b.c.) proposed Spontaneous generation which states that living things arise from non-living material. This concept was widely accepted until the seventeenth century. Examples supporting spontaneous generation are: maggots develop from decaying meat; mice develop from wheat stored in dark, damp places etc.
- Concept of Biogenesis states that living things develop only from other living things and not from non-living matter.
Redi’s experiment: Francesco Redi (Italian physician) in 1668 performed a experiment to challenge the concept of spontaneous generation that maggots arise from decaying meat.
- He took two identical set of jars, both contained decaying/rotting meat and were exposed to atmosphere.
- One set of jar was covered by gauze while the other set was left uncovered/open jars (control).
- Redi observed that flies settled on the meat in the open jars, but in the covered jars gauze blocked their access to the meat. Maggots appeared on the meat of uncovered jar, but not on the meat in the covered ones.
- Redi concluded that the maggots appeared on the meat in the uncovered jars from the eggs of the flies (i.e. from living thing) which they laid on the meat, thus supporting biogenesis, and not from spontaneous generation in the meat.
John Needham experiment: In 1748, John Needham (English priest) again supported concept of Spontaneous generation in his experiment.
- He placed a solution of boiled mutton broth in containers, which he sealed with corks. He gave reason that boiling would kill any organism in the broth and that the corks would prevent any living thing from entering.
- Experimental apparatus was left for few days, to see the result. If the broth was found to contain living things, it must be the result of spontaneous generation and if no life was found concept of biogenesis is right.
- After several days, the broth became cloudy with a large population of microorganisms, so he concluded that life in the broth was the result of spontaneous generation.
Spallanzani’s experiment: In 1767, Lazzaro Spallanzani (Italian scientist and Catholic priest) , challenged John Needham’s findings stating that Needham’s experimental design may have allowed something to enter the broth accidently.
- Spallanzani took two jars. He boiled meat and vegetable broth, placed this mixture in jars and sealed the opening of one jar by melting the glass over a flame to prevent anything from entering the flask, and leaved other jar open (control) to allow air to enter the flask.
- Then he placed the jars in boiling water to kill any living things that might enter the broth accidently.
- After two days, he observed that open jar had a large population of microorganisms, but there were no microorganisms or no growth in the sealed jar.
- He concluded that spontaneous generation did not occur and something had entered the unsealed jar from the air that caused the growth in the broth.
Pasteur’s experiment: In 1861, Louis Pasteur (French chemist) again supported Biogenesis by his experiment and finally disapproved spontaneous generation by convincing almost complete scientific authority.
- He performed his experiment to disapprove the clause raised by scientists that Spallanzani removed the vital element “oxygen” (factor essential for spontaneous generation) by boiling the broth.
NOTE: In 1774, Joseph Priestly discovered Oxygen.
- He took 2 jars and placed fermentable solution of sugar and yeast in flasks, that had a long swan neck. The long swan neck of flask would allow only air to enter a flask and prevent any tiny living things from entering it.
- Flasks were then boiled for a long time.
- Swan-neck of one flask was cut-off (control) and other flask was left open as it is with intact neck.
- After 2 days, fermentable solution of swan-neck cutoff flask was seen supporting a population of microorganisms as broken neck allowed microorganisms from the air to fall into the flask
- In intact flask, no organisms developed in the mixture although the swan neck design of flask allowed oxygen (vital element) to enter. In this flask organisms did not enter the part of the flask with the sugar mixture as they settled on the bottom of the curved portion of the neck and could not reach the sugar-water mixture.