Q.What are coacervates (protobionts), and what role are they believed to have played in the transition from simple organic molecules to the first living cells?
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Origin of Life and Chemical Evolution
The origin of life has been explained by several theories. Special creation and spontaneous generation (abiogenesis) were classical ideas; Louis Pasteur experimentally disproved abiogenesis, supporting biogenesis (life from pre-existing life). Panspermia/cosmozoic theory proposed that life reached Earth from space.
The widely accepted chemical (Oparin–Haldane) theory holds that life arose from non-living matter in the primitive ocean — the "hot dilute soup." The primitive atmosphere was reducing and lacked free oxygen (containing NH₃, CH₄, H₂, water vapour, CO₂). Energy from UV rays and lightning drove the formation of simple organic molecules, then complex polymers (amino acids, nucleic acids). These aggregated into coacervates (Oparin) or microspheres (Sydney Fox), giving rise to protocells/eobionts. A typical sequence of chemical evolution is: simple molecules → complex organic compounds → nucleic acids → protocell → eobionts. …
Coacervates (protobionts) are droplets of organic molecules with a loose boundary that concentrate molecules like a primitive membrane, seen as an intermediate stage before the first true living cell. …
Step 1. Once simple organic molecules had accumulated in the early ocean, the next step proposed is their spontaneous aggregation into small bounded droplets.
Step 2. These droplets, called coacervates or protobionts, are held together by a loosely organised boundary (largely proteins and lipids) resembling a primitive membrane.
Step 3. This boundary lets a protobiont selectively concentrate certain molecules from its surroundings, without yet being a fully functional living cell. …
Explain what a coacervate physically is (a bounded droplet of organic molecules) and its proposed ROLE a …
- Describing a coacervate as already a full living cell (it lacks self-replication/catalysis until the next proposed step). …
- CBSE 2025Set F1 markMCQQ.On which of the following planets is there a possibility of life?(a) Mars(b) Mercury(c) Venus(d) Jupiter
›Reveal solutionSolution
Of the given planets, Mars is regarded as having the best possibility of life.
Mars lies relatively near the Sun's habitable conditions and shows evidence of past water (dry river channels, polar ice), a thin atmosphere, and a surface that could once have supported microbial life, which is why it is the focus of the search for extraterrestrial life. Mercury is too hot and airless, Venus ha …
- CBSE 2025Set F1 markMCQQ.Which of the following gases was not present in the early period of the earth?(a) O2(b) CO2(c) H2(d) N2
›Reveal solutionSolution
Free oxygen (O2) was absent from the early Earth's atmosphere.
According to the Oparin-Haldane theory of chemical evolution, the primitive atmosphere was a reducing one containing gases such as water vapour, methane (CH4), ammonia (NH3), hydrogen (H2), carbon dioxide (CO2) and nitrogen, but no free molecular oxygen (O2). Free oxygen built u …
- CBSE 2024Set 57/3/11 markMCQQ.S.L. Miller in 1953, to support the theory of chemical evolution, created conditions in the closed flask that included : (A) CH3, O2, NH3, H2O vapour at 1800°C (B) CH4, H2, NH3, H2O vapour at 800°C (C) CH4, CO2, H2, H2O vapour at 1800°C (D) CH4, NH4, SO2, H2O vapour at 800°C
›Reveal solutionSolution
The Miller-Urey experiment simulated early Earth conditions using a mixture of methane (CH₄), hydrogen (H₂), ammonia (NH₃), and water vapour (H_2O) subjected to electrical sparks (simulating lightning) at a temperature around 800^circC. The correct option is (B).
The question tests your recall of one of the most famous experiments in the history of biology — the Miller-Urey experiment (1953). This experiment was designed to test the Oparin-Haldane theory of chemical evolution, which proposed that organic molecules could form from inorganic precursors under the reducing atmosphere of early Earth.
The key idea is that the early atmosphere was reducing (rich in hydrogen and lacking free oxygen), and energy sources like lightning or UV radiation could drive the formation of amino acids and other organic compounds. Miller and Urey built a closed apparatus that circulated gases through a spark discharge chamber, then condensed the products into a liquid trap.
Let’s examine each option carefully.
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Option (A): CH₃, O₂, NH₃, H_2O at 1800^circC
- CH₃ is not a stable gas — it’s a methyl radical, not a compound used in the experiment.
- More critically, oxygen (O₂) was absent in the Miller-Urey setup. Oxygen would have oxidised any organic products and prevented the reducing conditions needed for synthesis.
- The temperature 1800^circC is far too high — that would break down most molecules, not form them.
- ✗ Incorrect.
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Option (B): CH₄, H₂, NH₃, H_2O vapour at 800^circC
- This matches the actual gas mixture used by Miller and Urey: methane (CH₄), hydrogen (H₂), ammonia (NH₃), and water vapour (H_2O).
- The temperature of 800^circC is consistent with the hot region near the spark discharge (the flask was heated to produce steam, and the spark itself created local high temperatures).
- The spark discharge simulated lightning, providing energy for chemical reactions.
- ✓ Correct.
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Option (C): CH₄, CO₂, H₂, H_2O vapour at 1800^circC
- Carbon dioxide (CO₂) was not part of the original Miller-Urey mixture. CO₂ is an oxidised form of carbon; the experiment required a reducing atmosphere.
- Again, 1800^circC is too extreme.
- ✗ Incorrect. …
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- CBSE 2024Set ANNUAL1 markMCQQ.Origin of life was written by :(a) S.L. Miller(b) A.I. Oparin(c) De Vries(d) Charles Darwin.
›Reveal solutionSolution
The Russian biochemist Alexander Ivanovich Oparin proposed the theory of chemical evolution of life and authored the book 'The Origin of Life' (1924/1938).
Oparin proposed that life originated on primitive Earth through a gradual chemical evolution of simple inorganic molecules present in the early reducing atmosphere into complex organic molecules, and eventually into the first primitive self-replicating cells. His hypothesis, independently supported by J.B.S. Haldane, forms the basis of the widely accepted Oparin-Haldane theory of the origin of life, and …
- CBSE 2024Set ANNUAL1 markMCQQ.The Gas present in the early reducing atmosphere was :(a) O2(b) N2(c) Both(a) &(b)(d) None of these.
›Reveal solutionSolution
The early Earth's atmosphere was 'reducing' precisely because it lacked free molecular oxygen; its dominant gases were methane, ammonia, hydrogen and water vapour, not O2 or N2.
According to the Oparin-Haldane theory of chemical evolution, life originated in a primitive atmosphere very different from today's. This atmosphere is called a reducing atmosphere because it was rich in hydrogen-containing gases — chiefly methane (CH4), ammonia (NH3), hydrogen gas (H2), and water vapour (H2O) — and almost completely lacked free oxygen (O2). Free O2 only accumulated in Earth's atmosphere much later, after the evolution of photosynthetic cyanobacteria (the 'Great Oxidation Event'). Nitrogen gas (N2), while present in trace amounts from volcanic outgassing, was not the atmosphere's chemically defining feature in t …
- CBSE 2022Set ANNUAL1 markMCQQ.Which one was absent in the atmosphere at the time of the origin of life?(a) NH3(b) H2(c) CH4(d) O2
›Reveal solutionSolution
Earth's primitive atmosphere was reducing (no free oxygen); free O2 accumulated only later, after photosynthetic organisms evolved.
According to the chemical evolution theory (Oparin-Haldane hypothesis), the primitive Earth's atmosphere was a REDUCING atmosphere, containing gases like methane (CH4), ammonia (NH3), hydrogen (H2), and water vapour, but essentially no free molecular oxygen (O2). This reducing, oxygen-free environment was essential because it allowed simple organic molecules (amino acids, sugars, nucleotides) to form and accumulate from inorganic precursors under the influence of UV radiation, lightning, and he …
- CBSE 2021Set ANNUAL1 markQ.Fill in the blank: Oparin suggested the formation of clusters or specialised droplets called ___.
›Reveal solutionSolution
Oparin proposed that organic molecules aggregated into coacervates as a step toward the first living cells.
A. I. Oparin, in his theory of chemical evolution/origin of life, suggested that in the primitive ocean, simple organic molecules (formed from inorganic precursors under early-earth conditions) aggregated and organised themselves into small, membrane-bounded, colloidal clusters called coacervates. These proto-cell-like d …
- CBSE 2019Set HE1 markQ.Match the following: Column A item 'Origin of universe' with the correct term from Column B:(1) Big-Bang(2) D.N.A.(3) Tansley(4) Green revolution(5) Male-sterility.
›Reveal solutionSolution
'Origin of universe' matches with 'Big-Bang' — the widely accepted theory for how the universe began.
The Big Bang theory proposes that the universe originated from a single, extremely dense and hot point (singularity) that underwent a massive explosion roughly 20 billion years ago, after which the universe has been continuously expanding and cooling ever since. This explosive event led to the formation of galaxies, stars and eventually p …
- CBSE 2017Set ANNUAL1 markMCQQ.In the solar system, earth was supposed to have been formed about:(a) 200 Billion years back(b) 4.5 Million years back(c) 4.5 Billion years back(d) 400 Million years back
›Reveal solutionSolution
The Earth is estimated to have formed about 4.5 billion years ago, along with the rest of the solar system.
According to the widely accepted origin-of-the-universe/solar-system model taught alongside the theory of evolution, the universe originated about 20 billion years ago (Big Bang), while our solar system — including Earth — condensed out of a solar nebula roughly 4.5 billion years ago. Early Earth had no atmosphere in the modern sense; volcanic activity released water v …
- CBSE 2016Set ANNUAL1 markQ.Which theory talks about the huge explosion that leads to origin of universe?
›Reveal solutionSolution
The origin of the universe is explained by the Big Bang theory, which states that the universe originated from a single, immensely hot, dense point through a massive explosion roughly 15–20 billion years ago.
The theory that describes the huge explosion leading to the origin of the universe is the Big Bang theory. According to this theory, the universe began as an extremely small, hot and dense singularity, which underwent a colossal explosion (the 'Big Bang') roughly 15–20 billion years ago. This explosion caused rapid expansion, and matter (initially as hydrogen and helium …
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