Origin of life
Origin - the point or place where something begins, arises, or is derived.
Evolution - the process by which different kinds of living organism are believed to have developed from earlier forms during the history of the earth.
Theories for the origin of life:
The numerous theories are of hypothetical type and do not have evidences or concrete proof. Most of these imaginary theories are strongly supported by one group but criticized by the others. Some of the theories having strong support are listed here:
1. Theories of special creation, vital force theory.
2. Cosmogenic theory
3. Theory of abiogenesis (spontaneous generation)
4. Theory of biogenesis
5. Theory of Abiogenesis, Modern theory, Oparin-Heldane theory or the theory of bio-chemical origin.
Theories of special creation or vital-force theory:
These theories are purposed by ritual religious people stating that some supernatural forces like gods are responsible for the creation of the livings across the globe. These theories are not yet proved and they do not give any strong proof for the theories. Different religion have different ideology and they do not match at all.
The theory is not widely accepted by the modern people, but religious and elderly people strongly support ideas. It was first purposed by father Saurez, but different religious people contradict the ideas.
Theory of cosmogeny:
This theory states that the life on the earth could have come from space or the other planets. This theory is purposed by Ritcher and supported by Arrhenius. This theory states that the spores called Panspermia could have come from Mars after the collision with comet. The conclusion is that NASA is trying to prove the theory but no scientific verification yet.
Theory of abiogenesis or spontaneous generation;
This theory states that all the livings developed from non- livings or inanimate sources instantly. According to this theory, frogs, snakes, toads were created from mud. Parasites, beetles, flies on the other hand developed from sweat and manures. Micro-organism developed from spontaneously from air and water. The maggots developed from flesh. Young mice developed from grains kept in sacks and clothes kept in dark for long. Aphids and other insects developed moisture, heat and plant juice.
The theory, however, has no specific evidences, hence not widely accepted by many. It was purposed by Greek philosophers Aristotle, Empedocles, Thales, Plato, etc.
Theory of Biogenesis:
This theory states that life was originate not from non-livings but from living organism present in the atmosphere in the pre- existing form. When these micro-organism get suitable condition or medium, they grow and multiply. This theory disapproves abiogenesis (spontaneous generation). Many experimental verifications were made by different researchers to support this theory of biogenesis.
Redi’s Experiment
Italian physician, Francisco Redi (1668)demonstrate that the flies were not created from non-living meat , but, created by micro-organism present in the atmosphere. To verify the idea, he used three jars ; one jar having boiled meat in a sealed , the second having boiled meat but covered with gauze and the last having boiled meat but it was left uncovered. The experiment was left for few weeks.
Observation: After few weeks, he observed the jars and find that only the jar which was left uncovered (open jar) had maggot flies and it’s larvae.
Conclusion: They concluded that maggots were not originated from the inanimate or nonliving meat, but from the preexisting form already present in the atmosphere. This supports biogeny and disapproves abiogeny.
Spallanzani Experiment
He also conducted experiment an experiment to support biogenesis and disapprove the theory of abiogenesis.
He took two containers to boil the broth (hay infusion) for some hours and one was left open while the next was sealed. Both the containers were left for some days.
Observation; After few days, he observed the thick growth of micro-organisms in the opened jar but the one which was sealed didn’t have micro- organisms.
Conclusion; From the experiment concluded that micro-organism developed were not originated from the inanimate or nonliving hay infusion or broth, but from the pre-existing form already present in the atmosphere. This supports biogeny and disapproves abiogeny.
Pasture’s Experiment;
French Biologist, Pasture (1864) also conducted a similar experiment to support biogenesis and disapprove the theory of abiogenesis.
he took a swan necked flask which was sterilized after boiling for long after pouring hay infusion or broth which left for 18 months.
Observation; Even after 18 months, there was no change indicating micro-organisms didn’t develop over the time. He then broke the neck ( after 18 months) then he observed the thick growth of micro-organisms in the cracked swan-necked bottle after few days of cracking.
Conclusion; From the experiment concluded that micro-organism developed were not originated from the inanimate or nonliving hay infusion or broth, but from the pre-existing form already present in the atmosphere. This supports biogeny and disapproves abiogeny.
Theory of bio-chemical origin, Oparin- Haldane theory, Modern theory or Abiogenesis;
This theory is called modern theory of origin because it has some experimental verification but those verifications are not complete. It was first purposed by Russian scientist, Alexander Ivanovich Oparin in 1938 along with British researcher John Haldane. Among the theories, this theory is widely accepted by the elite people.
The theory is expressed in three steps;
1. Chemogeny or chemical evolution
2. Biogeny or evolution in living
3. Cognogeny or evolution of preception,expression and communication
1.Chemogeny or chemical evolution;
The chemical reactions converting the simple inorganic atoms and molecules into a series of organic biomolecules is called chemogeny. It can be expressed in steps;
1. Formation of water, ammonia, methane and cyanamide;
The primitive atmosphere had carbon, hydrogen, nitrogen, oxygen (oxygen was not found in free state but was available in compound state hence the atmosphere of the time is called reducing atmosphere). All these elements existed due high temperature but reacted among themselves when the earth cooled down forming water, methane, ammonia, cyanamide, etc.
C + 2H2 CH4
H2+ 2O2 H2O
H2+3N2 2NH3
Formation of hydrocarbons: When the temperature of the earth declined to around 1000 degree Celsius, various highly reactive free radicals like -CH, CH2 condensed into various saturated and unsaturated hydrocarbons.
CH+ CH C2H2( Acetylene).
CH2 +CH2 C2H4 (Ethylene).
CH2 +CH2 CH4 + C
Formation of oxy and hydro-oxy derivatives of hydrocarbons;
As the atmosphere cooled downed, the hydrocarbons further reacted with the steam, aldehydes and ketones were formed mainly due to unusual bonding property of Carbon.
C2H2 + H2O CH3CHO ( Acetaldehyde).
Formation of Carbohydrates, Amino-acids and Fatty-acids;
Oxidation, reduction, polymerization and condensation reactions of the molecules thus formed lead to the formation of macro-molecules like simple sugars, amino-acids and fatty-acids.
CH4+ H2O C6H12O6 or sugars
CH4+H2O+NH3 Amino-acids
Formation of Purines, Pyrimidines and Nucleotides;
The molecules thus formed reacted again forming purines, pyrimidines and nucleotides.
The sources of energy available were the heat from the radiation sun of the as the earth didn’t have Ozone layer at that time , volcanoes and high temperature of the Earth and thunder in the sky. Due to all these properties, the hot primitive seas were rich in minerals and primary organic nutrients. This hot water containing those chemicals was described as hot-dilute or pre-biotic or primordial soup by Haldane.
This is the formation of complex and self-replicating biological molecules which can be described as;
Formation of Nucleic acids;
The large molecules like Pentose sugar, phosphate group, and nucleotides reacted together forming nucleic acid like RNA and DNA making it possible for the formation of life.
The formation plays very significant role for the formation of self-replicating macromolecules capable of controlling and transferring heredity characters. These molecules are considered to have first sign of the life.
Formation of Coacervates;
These are the small immiscible liquid droplets consideredto be transitional form between living and non-living containing macromolecules
with opposite charges or hydrophobic proteins. These were simple to complex and often had nucleic acid at the center with micro and macro molecules surrounding the acid. They can absorb the molecules and expand leading to self-replication forming exactly similar molecules the continuous replication changed the primitive oceans into thick soup like body (Thick-soup).
Formation of primary organism or protobionts; The coacervates started absorbing other organic nutrients from the oceanic soup, enlarge and multiply resulting the formation of the most primitive organisms called eobionts. These anaerobic heterotrophs can be best compared to the Virus of these days.
Formation of Prokaryotes; The protobionts developed into the most primitive self-dividing cells without distinct nucleus called Monera represented by bacteria and cyanobacteria.
Formation of Eukaryotes; These are the unicellular organisms having distinct or developed nucleus. They developed from prokaryotes when they developed DNA inside distinct nuclear membrane and different cell organelles having double envelop or membrane like; mitochondria, Golgi-bodies, endoplasmic reticulum, etc.
Cognogeny; The protobiants developed and diversified into various metazoans and the process continued among the metazoans leading to the formation of different organisms. Due to the shortage of food , most of the organisms diversified their feeding habits changing themselves into parasitic, saprozoic, chemosynthetic, autotrophic etc. Some of them developed chloroplasts and started a process called photosynthesis
Origin of autotrophs; Due to rapid increase in the number of heterotrophs, there was scarcity of nutrients in the primitive oceans because of which, the creatures of the time were forced to change their nutrition mode.
Chemoautotrophs: in the course of time, some prokaryotes acquired enzyme that support for the synthesis of simple sugars. This lead the formation of organic compounds from inorganic molecules and it was the beginning of autotropism. The energy required for the process was obtain from the anaerobic breakdown of the chemical molecules as there was no free oxygen in the primitive atmosphere. Moreover, they didn’t have chlorophyll but only some unknown inorganic catalyst hence they are called chemo-autotrophs and the process called chemo-autotropism. Deep-sea Sulphur Bacteria represent the organisms of this kind which can be expressed
6CO2+12H2S energy of bactriochlorophyll C6H12O6 + 6H2O +12S
Some of the chemoautotrophs started absorbing solar radiation making the process faster than before for the formation of carbohydrates at faster pace like in some Sulphur bacteria
6CO2+12H2S energy of bactriochlorophyll C6H12O6 + 6H2O +12S
+ Solar energy
Some of the Sulphur bacteria developed true Chlorophyll due to continuous change in the molecules in the course of time making the process of photosynthesis utilizing water instead of Hydrogen-sulphide with the formation of free Oxygen in the atmosphere.
6CO2+6H2O Light+chlorophyll C6H12O6 + 6O2
Evolution of Oxygen;
The primitive atmosphere didn’t have free Oxygen ( Reducing Atmosphere ). Due to the development of blue -green algae, free Oxygen evolved and the atmosphere became Oxidizing but it had vary small quantity of the gas. Due to continuous growth of the cyano-bacteria or blue-green algae across the primitive seas and oceans, the concentration increased rapidly. Furthermore, the oxygen formed Ozone layer in the stratosphere due to UV radiation making the earth a suitable place to live.
Miller -Urey Experiment
Horold C Urey, an astronomy professor supported his student, Stanley L Miller, a biochemist to carry out an experiment in 1953 to verify Oparin-Heldane theory of biochemical origin.
They arranged glass apparatus like shown in the figures containing two chambers, one for the gases of the primitive atmosphere and another containing distilled water. Using the vacuum-pump, they inserted Methane, Ammonia, and Hydrogen gasses(2:1:2 ratio ) in the empty container. They also boiled the water in the container using Bunsen burner a source of energy. Furthermore, electric sparks from the electrodes in the gas chamber also provides the energy and the condenser is used to cool down the cycle. All these arrangements were done to replicate the primitive atmosphere.
After one week of the experiment, they obtained various products
like; glycine, alanine, asparatic, aldehydes, simple sugars, ribose sugars, etc.
It is concluded that those simple inorganic molecules changed into organic compounds supporting the theory of bio-chemical origin as purposed by Miller-Uray.
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