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Question
Read the following statements and select the correct option.
Statement 1: The non-cellular aggregates of giant macromolecules were able to evolve into cells with membranous envelopes and some of these cells had the ability to release oxygen.
Statement 2: The oxygen liberating reaction in the primitive cells could have been similar to the light reaction in photosynthesis involving photolysis of water.
Read the following statements and select the correct option.
Statement 1: The non-cellular aggregates of giant macromolecules were able to evolve into cells with membranous envelopes and some of these cells had the ability to release oxygen.
Statement 2: The oxygen liberating reaction in the primitive cells could have been similar to the light reaction in photosynthesis involving photolysis of water.
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Solution
The correct option is A Both the statements 1 and 2 are correct
First cellular forms of life appeared on Earth around 2000 million years ago.
Formation of non-cellular aggregates happened much before that in the primordial Earth. The atmosphere of the early or primordial Earth was a reducing atmosphere.
According to Oparin and Haldane, simple organic compounds polymerised to form large (macro) molecules in these conditions. The reactions that might have happened in the reducing atmosphere are as follows:
Simple sugars → Polysaccharides
Fatty acids + Glycerol → Lipids
Amino acids → proteins
Pyrimidines and Purines + Sugar + Phosphate → Nucleotides
Various nucleotides polymerized and formed nucleic acid molecules. Then, nucleic acids and proteins aggregated to form nucleoproteins, the main components of all living cells. The first cell is presumed to have formed by the enclosure of (self-replicating) RNA in a membrane composed of phospholipids as depicted in the image below:
As the cells originated in a sea of organic molecules, they were able to obtain food and energy directly from their surrounding environments.
In the initial anaerobic conditions of the Earth, the first energy-generating reactions presumably would be the breakdown of organic molecules in the absence of oxygen.
Later the first forms of the autotrophic bacteria evolved in the primordial Earth, probably because they utilised H₂S as a source of hydrogen to fix CO₂ into organic molecules (chemoautotrophic). It is still used as a pathway of fixation of carbon dioxide by some chemoautotrophic bacteria.
Using H₂O as a donor of electrons and hydrogens in photosynthesis, instead of H₂S for the fixation of CO₂ into organic molecules (glucose) evolved later. The use of H₂O in photosynthetic reactions produced free oxygen as a by-product. This mechanism is thought to have been responsible for making O₂ abundant in the Earth's atmosphere. This was an important event as it changed the Earth's atmosphere from reducing to oxidising. The release of O₂ as a by-product in the photosynthesis changed the environment in which cells evolved and it led to the development of oxidative metabolism (a mechanism using O₂ to produce energy efficiently). Hence, statement 1 is correct.
The oxygen liberating reaction observed in the primitive cells could have been similar to the light reaction in photosynthesis involving photolysis of water. This is observed in all the green plants that exist today.
Therefore, statement 2 is also correct.
First cellular forms of life appeared on Earth around 2000 million years ago.
Formation of non-cellular aggregates happened much before that in the primordial Earth. The atmosphere of the early or primordial Earth was a reducing atmosphere.
According to Oparin and Haldane, simple organic compounds polymerised to form large (macro) molecules in these conditions. The reactions that might have happened in the reducing atmosphere are as follows:
Simple sugars → Polysaccharides
Fatty acids + Glycerol → Lipids
Amino acids → proteins
Pyrimidines and Purines + Sugar + Phosphate → Nucleotides
Various nucleotides polymerized and formed nucleic acid molecules. Then, nucleic acids and proteins aggregated to form nucleoproteins, the main components of all living cells. The first cell is presumed to have formed by the enclosure of (self-replicating) RNA in a membrane composed of phospholipids as depicted in the image below:
As the cells originated in a sea of organic molecules, they were able to obtain food and energy directly from their surrounding environments.In the initial anaerobic conditions of the Earth, the first energy-generating reactions presumably would be the breakdown of organic molecules in the absence of oxygen.
Later the first forms of the autotrophic bacteria evolved in the primordial Earth, probably because they utilised H₂S as a source of hydrogen to fix CO₂ into organic molecules (chemoautotrophic). It is still used as a pathway of fixation of carbon dioxide by some chemoautotrophic bacteria.
Using H₂O as a donor of electrons and hydrogens in photosynthesis, instead of H₂S for the fixation of CO₂ into organic molecules (glucose) evolved later. The use of H₂O in photosynthetic reactions produced free oxygen as a by-product. This mechanism is thought to have been responsible for making O₂ abundant in the Earth's atmosphere. This was an important event as it changed the Earth's atmosphere from reducing to oxidising. The release of O₂ as a by-product in the photosynthesis changed the environment in which cells evolved and it led to the development of oxidative metabolism (a mechanism using O₂ to produce energy efficiently). Hence, statement 1 is correct.
The oxygen liberating reaction observed in the primitive cells could have been similar to the light reaction in photosynthesis involving photolysis of water. This is observed in all the green plants that exist today.
Therefore, statement 2 is also correct.
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