Multiple Choice Questions (MCQs): Evolution - NEET MCQ

At a certain point, probably during the great bombardment (of meteorites) some 4.4 Gy ago the Earth had no atmosphere at all - it was too hot and gravity wasn’t strong enough. We know this because our current atmosphere contains very little 36Ar (implying that 99% of the current argon is due to K40 decay). In the Sun, 36Ar is much more common (by a factor of say 10,000). The Earth cooled and icy comets continued to bring water, ammonia, carbon oxides, hydrogen cyanide, formaldehyde and other simple compounds. We can still detect these chemical in space. There was no oxygen gas.

Stanley Miller conducted a famous experiment in 1953 to provide experimental proof that hydrogen, methane, water, and ammonia can give rise to amino acids, the building blocks of proteins. The experiment was based on the hypothesis proposed by Russian scientist Alexander Oparin. Miller identified several amino acids, including glycine, alanine, and aspartic acid, in the mixture. The experiment demonstrated that simple organic molecules, such as amino acids, can be formed under conditions similar to those believed to exist on early Earth.

• Louis Pasteur in his swan neck flask experiment, found out that life originated from pre-existing life.
• He prepared sterilized syrup of sugar and later killed yeast by boiling them in flasks.

The primitive atmosphere of earth was reducing atmosphere with little or no oxygen but was rich in water vapour, carbon monoxide, carbon dioxide, nitrogen and hydrogen. Thus, oxygen was not present in primitive atmosphere. The high temperature, UV light and lightening provided energy for chemical reactions between hydrogen and free oxygen, nitrogen and carbon to form, ammonia, methane and cyanides. Owing to the high temperature of earth, water was present in form of superheated steam and ammonia, methane and cyanides were present in gaseous form. 

Therefore, the correct answer is option C.

• This theory states that life originates from nonliving things or decaying matter like mud, straw etc. spontaneously.
• It was theory which had no specific explanation. It was soon rejected.

• It was at 800°C in which the flask was maintained along with electric discharge.
• A moderately high temperature was required to keep the flask sterilized.
• Thus, creating amino acids as the product.

Miller took a mixture of water, methane, ammonia and hydrogen in a closed flask at 800°C.

• It was done in a closed flask and using electric discharge tubes, and later observed the formation of amino acids.

Origin of earth dates back around 4.6 billion years ago which makes options A and B incorrect as life originated only after the origin of earth. The period of 4.6 billion year ago to 3.8 billion years ago is termed as the Azoic era when the primitive earth conditions were too harsh to sustain any life form. During this period, the earth's temperature cooled down and the ocean and atmosphere were formed. The Archaeozoic era is marked by the appearance of first life form in the hot soup of the primitive ocean which dates back around 4 billion years ago. The first life forms were prokaryotic chemoheterotrophic anaerobic organisms.

Answer:
In his experiment, Stanley Miller synthesized the following:
- Virus: Not synthesized by Stanley Miller in his experiment.
- Protein: Not synthesized by Stanley Miller in his experiment.
- Amino acid: Stanley Miller successfully synthesized amino acids in his experiment. Amino acids are the building blocks of proteins and are essential for life.
- Cell: Stanley Miller did not synthesize cells in his experiment.
Therefore, the correct answer is option C: Amino acid. Stanley Miller's experiment demonstrated that the conditions present in the early Earth's atmosphere can lead to the formation of amino acids, which is an important step in the origin of life on Earth.

DNA is a polymer of nucleotide.Nucleotides are the elementary unit that forms DNA. It is made up of three components- nitrogenous base, a pentose sugar, and phosphate. It is formed through phosphorylation of nucleoside. Chain of nucleotides or the polymer of nucleotide is the DNA. It is acidic in nature.

Huge nucleoprotein were formed by uniting nucleic acids and protein molecules. The particles of nucleoprotein were described as free living genes. Hence, nucleoprotein gave the first sign of life . So, the correct option is a. 

• Water is most important for the origin of life because it acts as a universal solvent, enabling chemical reactions that are essential for life processes.
• It provides the medium for biochemical reactions, regulates temperature, and participates directly in chemical reactions.
• These unique properties make water indispensable for the formation and sustenance of life.

Miller's experiment, known as the Miller-Urey experiment, aimed to simulate the conditions of early Earth and test the theory of chemical evolution. In this experiment, a mixture of gases was subjected to electric sparks to simulate lightning. The electric sparks served as a source of energy that would have been present in the early Earth's atmosphere.
The combination of hydrogen, methane, ammonia, and water vapor, closely resembled the hypothesized composition of the early Earth's atmosphere. By subjecting this mixture to electric sparks, Miller was able to simulate the energy input from lightning strikes.
The electric sparks provided the necessary energy to drive chemical reactions among the gases, resulting in the formation of various organic compounds, including simple amino acids. This experiment provided evidence that the building blocks of life, such as amino acids, could have formed under the conditions believed to be present on early Earth.
Therefore, option B correctly represents the components used by Miller in the synthesis of simple amino acids in his experiment.

Louis Pasteur's 1859 experiment is widely seen as having settled the question. In summary, Pasteur boiled a meat broth in a flask that had a long neck that curved downward, like a goose. The idea was that the bend in the neck prevented falling particles from reaching the broth, while still allowing the free flow of air. The flask remained free of growth for an extended period. When the flask was turned so that particles could fall down the bends, the broth quickly became clouded . In detail, Pasteur exposed boiled broths to air in vessels that contained a filter to prevent all particles from passing through to the growth medium, and even in vessels with no filter at all, with air being admitted via a long tortuous tube that would not allow dust particles to pass. Nothing grew in the broths unless the flasks were broken open, showing that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth. This was one of the last and most important experiments disproving the theory of spontaneous generation. 

Therefore, the correct answer is option B.

• All the synthetic processes obtained energy from the Sun and lightening.
• Also, other alternate sources like volcanic eruptions and ionizing radiations like X-rays.
• These were the only available sources of energy during primitive time.

• The primitive atmosphere had no oxygen and reducing i.e. no free oxygen was available.
• It was converted into oxidizing nature by the emergence of cyanobacteria.
• They released oxygen into atmosphere by converting water into hydrogen and oxygen.

Theory of spontaneous generation believed that life originated spontaneously from the non-living decaying and rotting matter like straw and mud. This theory was disproved by Louis Pasteur. Louis Pasteur demonstrated that life comes from the pre-existing life.
Correct option is B. 

Reasons why life is not found on the moon:

• Absence of carbon: Carbon is an essential element for life as we know it. It is the building block of organic molecules, which are the basis of life on Earth. Without carbon, the formation of complex organic compounds necessary for life would not be possible.


• Absence of water: Water is also crucial for life. It is a universal solvent, and most biological processes require water to occur. Without water, the biochemical reactions necessary for life cannot take place.


• Absence of nitrogen: Nitrogen is an essential component of proteins and nucleic acids, which are fundamental to life. Without nitrogen, the synthesis of these crucial molecules would not be possible, making life unsustainable.

Considering these factors, it can be concluded that the absence of water on the moon is the primary reason why life is not found there. While the moon may have trace amounts of carbon and nitrogen, the lack of water makes it extremely challenging for life as we know it to exist.

Anaximander and Aristotle were main proponents of the theory of spontaneous generation which assumes origin of life from non living substances. It assumes the origin of frogs and toads from mud that of microorganisms from air and so on. Origin of life by God’s desire was refuted by scientific knowledge based upon fossil records and data from comparative anatomy, morphology and embryology.Thus, now life is not originating.

Source of oxygen to the atmosphere is photosynthetic organisms. Photosynthetic organisms, by performing photosynthesis, release oxygen into the atmosphere. So, oxygen in the atmosphere has been formed by Photosynthetic organisms. eg: Green plants, algae, cyanobacteria.

So, the correct option is ‘Photosynthesis of plants’.

The very first atmosphere of earth was composed mostly of hydrogen atoms and was lost to space because hydrogen is very light gas. The second atmosphere of earth was contributed by gases from earth’s rocky matrix and bombardment of meteorites, it was composed of hydrogen, nitrogen, carbon and water. Hydrogen was the most abundant gas. 

• Theory of special creation said that life has not changed a bit since its origin.
• Our solar system was formed from Big bang and not from a massive body.
• The remaining options are the connotations of theory of special creation.

Formation of Amino Acids by Electric Discharge
Amino acids are organic compounds that are the building blocks of proteins. They contain an amino group (-NH2) and a carboxyl group (-COOH) along with a side chain that differentiates each amino acid. The Miller-Urey experiment, conducted in 1953 by chemists Stanley Miller and Harold Urey, aimed to simulate the conditions of early Earth and investigate the possibility of the spontaneous formation of organic compounds, including amino acids.
The Miller-Urey Experiment:
1. The experiment involved creating an environment similar to the early Earth's atmosphere. Miller and Urey used a closed system consisting of a flask filled with a mixture of gases, including hydrogen (H2), ammonia (NH3), and water vapor (H2O), representing the reducing atmosphere thought to exist at that time.
2. This mixture was heated, and electric sparks were discharged through it to simulate lightning strikes, which were frequent during that period.
3. After a week of continuous operation, the mixture was analyzed, and it was found that several organic compounds, including amino acids, had formed.
Significance of the Experiment:
1. The Miller-Urey experiment provided evidence that the conditions on early Earth were conducive to the formation of organic compounds necessary for life.
2. The formation of amino acids in the experiment suggested that the building blocks of proteins could have been synthesized spontaneously on early Earth.
3. This experiment supported the hypothesis that life on Earth may have originated from simple organic molecules.
Answer:
According to the given information, Miller successfully demonstrated the formation of amino acids by electric discharge in a mixture of hydrogen, ammonia, and water vapor. Therefore, the correct answer is option C: Methane.
Note: The options provided in the question (Ether, Ethane, Methane, Carbon dioxide) are not directly related to the Miller-Urey experiment or the formation of amino acids.

• Charles Darwin had set voyage around the world in a ship named H.M.S Beagle.
• He traveled to different islands to research about evolution.
• He found out that the existing living organisms had many similarities with life forms that existed millions of years ago.

• Evolution is a stochastic process, which means that it is focusing on chance mutations.
• Based on determinism, evolution is not a direct process.
• It is also based on events that occurs in a chance.

Amino acid protiens etc are the precursor of life so we can say life starts with this.

Oxidising atmosphere is the region that life cannot originate from inorganic materials at present. Today's atmosphere is not conducive to the spontaneous synthesis of complex molecules because the oxygen attacks chemical bonds, extracting electrons. Hence, the correct option is b.

• Two mya, Australopithecines probably lived in East African grasslands.
• Fossils discovered in Java in 1891 revealed the next stage, i.e., Homo erectus about 1.5 mya.
• The Neanderthal man with a brain size of 1400cc lived in near east and central Asia between 1,00,000 - 40,000 years back.
• During ice age between 75,000 - 10,000 years ago modern Homo sapiens arose.

Bacteria is first inhabited in earth and so bacteria is heterotroph option C is correct.

Evolution for Darwin was gradual while deVries believed mutation caused speciation and hence called it saltation (single step large mutation).