Biology XI Content
BIOGENESIS (life from life)
According to this view, life can origin only from its pre-existing form, not from non-living components. That means to originate new life, there should be pre-existing life.
The Three experiment in biogenesis are :-
- Redi`s Experiment
- Spallanzani`s Experiment
- Pasteur`s Experiment
1. Redi`s Experiment:
- Conducted by Fancesco Redi (1626-1698), an Italian Doctor.
- This was conducted to demonstrate that maggots could not be created from flesh or meat but the smell of meat attracted flies to come and lay egg on flesh.
- He took 3 jars, A, B & C placing lumps of boiled meat in them
- Jar A- Covered by parchment paper; Jar B- by fine muslin dolt; Jar C- uncovered.
- Few days later, meat decayed in all 3 jars but maggots appeared only in uncovered jars.
Thus, it proves theory of Biogenesis.
2. Spallanzani`s Experiment:
- Conducted by Lazzaro Spallanzoni (Italian Scholar)
- To oppose abiogenesis
- Hay infusions were put in 8 test tubes, four of them (air tight) while remaining were uncovered (air free)
- Few days later, he found thick growth of micro-organism in air-tight tubes while not in air-free test tube.
- Conclusion: Air contaminated with microorganisms entered the air free test tubes where their growth occurred.
- Theory of biogenesis was proved.
3. Pasteur`s Experiment:
- Conducted by Louis Pasteur, a French microbiologist.
- An experiment in support of Biogenesis.
- He prepared hay infusion in a swan0necked flask.
- The infusion was boiled to kill the microbes and to make it sterile.
- The experiment was left for observation for a few days.
- His observation showed that the flask remained free of life for several months (about 18 months).
- Later, he broke the neck of flask, making the hay infusion come in contact to air.
- The microbes appeared in the hay infusions.
- He conducted that life originates from pre-existing life only.
“Miller & Urey`s Experiment”
- An experiment support by biochemical origin of life
- Conducted by Stanley Miller and Urey
- Created the probable condition of primitive atmosphere in the earth.
- Use CH4, N2, H2, H2O etc.
Abiogenesis (life from non-living):-
This theory explains that life originates from non-living body. For E.g. toads and frogs evolved from mud, etc.
Other concepts or view of origin of life:-
- Special Creation Theory (tautology):
It states that the lives i.e. plants and animals on the earth are special creations of the supernatural power. The Christian mythology and the Hindu mythology say this earth and life were created by God.
– Spanish priests Fateher Saurez person to put forward this theory.
- Cosmozoic theory:
“Life has come to earth from some other planets or space through a piece of rock or metal (meteorite) in this form of primitive life such as spores, called Panspermia”.
– Given by Ritcher in 1864 AD
– was discarded in absence of evidences.
Other different views on abiogenesis are given, which is not mentioned in syllabus.
For the diagrams of different experiments (mentioned above in biogenesis), refer to the books or notes by teacher!
One long question is asked from one of the theories of evolution or origin of life, so prepare well for it!
Various 1 mark and 3 marks type questions are possible!