1.ABIOGENESIS
This theory is also known as theory of spontaneous generation.
" The living beings can spontaneously develop from the non- living is termed as Abiogenesis."
Man had believed since ancient times that living organisms (both plants and animals) arise from clay, earth and other non-living matter not from pre- existing parents of their own kind. This was based on such observations as growth of fungus on pieces of bread and the appearance of maggots on dead bodies of animals. Aristotle believed that fishes, frogs and aquatic insects spontaneously developed from mud.
2.BIOGENESIS
"The view that living beings can develop only from other living being is called Biogenesis."
The idea of production of living from the non- living was experimentally analyzed. The pioneer in such experiments was an Italian scientist named Francisco Redi. Through several experiments he showed that all living organisms arise from their parents and negated the idea of Abiogenesis.
REDI'S EXPERIMENT
STEP 1 Redi knew that flies often appeared on and around rotting meat. So, he placed rotting meat in three jars.
STEP 2
In the first jar, Redi left the jar open to
the air
STEP 3
On the 2nd jar, Redi placed a cover on the jar. The flies could not smell the meat, nor could they land in the meat.
STEP 4
On the 3rd jar, Redi placed a gauze or netting over the jar. The flies could smell the meat, but could not land on the meat.
RESULTS
In the first jar, the flies could lay their eggs on the rotting meat; maggots would appear and later grow into flies.
In the second jar, the flies could not smell the meat, or land on it, so they would lay their eggs somewhere else.
In the third jar, the flies could smell the meat, so they would lay their eggs on the netting thinking there was a food source for the maggots.
Events in spontaneous generation
1668 Francisco Redi attacks spontaneous generation and disproves it.
1745 John Needham adds chick broth to a flask and boils it, lets it cool and waits. Microbes grow and he proposes it as an example of spontaneous generation.
1768 Lazzaro Spallanzani repeats Needham's experiment, but removes all the air from the flask. No growth occurs.
1859 Louis Pasteur's swan-neck flasks show that spontaneous generation does not occur.
1870 Thomas H. Huxley gives his "Biogenesis and Abiogenesis" lecture. The speech offered powerful support for Pasteur's claim to have experimentally disproved spontaneous generation.
1877 John Tyndall publishes his method for fractional sterilization, showing the existence of heat-resistant bacterial spores.
In the first jar, the flies could lay their eggs on the rotting meat; maggots would appear and later grow into flies.
In the second jar, the flies could not smell the meat, or land on it, so they would lay their eggs somewhere else.
In the third jar, the flies could smell the meat, so they would lay their eggs on the netting thinking there was a food source for the maggots.
Events in spontaneous generation
Year Event
1668 Francisco Redi attacks spontaneous generation and disproves it.
1745 John Needham adds chick broth to a flask and boils it, lets it cool and waits. Microbes grow and he proposes it as an example of spontaneous generation.
1768 Lazzaro Spallanzani repeats Needham's experiment, but removes all the air from the flask. No growth occurs.
1859 Louis Pasteur's swan-neck flasks show that spontaneous generation does not occur.
1870 Thomas H. Huxley gives his "Biogenesis and Abiogenesis" lecture. The speech offered powerful support for Pasteur's claim to have experimentally disproved spontaneous generation.
1877 John Tyndall publishes his method for fractional sterilization, showing the existence of heat-resistant bacterial spores.
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