This set of Class 12 Biology Multiple Choice Questions & Answers (MCQs) focuses on “Evolution – Origin of Life – 3” for MBBS Entrance Exam.
1. During the time of evolution, the possible energy sources were ______
b) Green plants
d) U.V rays and lightening
Explanation: 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.
2. The first living form named protocell originated in the primitive oceans.
Explanation: Nucleic acids and enzymatic proteins combine together to form protocell or eobionts. They were like viruses, that became active when they entered into other eobionts. They originated in primitive oceans.
3. During which period, origin of life took place?
Explanation: Precambrian is the period in which origin of life took place. Devonian is called the age of fishes, when fishes evolved. Cenozoic is called the age of mammals whereas Mesozoic is called the age of reptiles.
4. During which period, life didn’t exist?
b) Cambrian period
c) Paleozoic period
d) Azoic period
Explanation: Azoic period was the primitive era of no life. It was the period in which the earth was created. Whereas life existed during the other periods mentioned above.
5. During the origin of life, which of the following was absent in the atmosphere?
Explanation: Oxygen was absent because due to the presence of high temperature, active hydrogen atoms combined with all oxygen atoms present to form water. This left no free oxygen in the atmosphere.
6. “The organic compounds were the basis of life” were proved by?
d) Stanley Miller and Harold C. Urey
Explanation: These two scientists, in their experiment showed the formation of simple amino acids and organic acids. They concluded life came from organic compounds.
7. What is the time gap in between formation of Earth and origin of life?
a) 1 billion years
b) 0.5 billion years
c) 4 billion years
d) 4.5 billion years
Explanation: Earth was formed about 4.5 billion years ago whereas life originated about 4 billion years ago. So, the time gap is about 0.5 billion years.
8. The primitive atmosphere was reducing since ______
a) Hydrogen atoms are very few
b) Hydrogen atoms were active and many in number
c) Helium atoms were more
d) Oxygen atoms were more
Explanation: The active hydrogen atoms reacted with free oxygen atoms forming water. So, the primitive atmosphere was reducing without free oxygen unlike the present oxidizing atmosphere with free oxygen.
9. Which among the biologists, gave the most acceptable biochemical theory _____
Explanation: Oparin’s theory was called Naturalistic theory or Theory of chemical evolution. This theory states that life originated by the composition of chemicals, or life come from pre-existing nonliving organic.
10. Absence of oxygen in earth, made the atmosphere reducing. But it later became oxidizing in nature due to the emergence of ________
c) Eukaryotic algae
Explanation: 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.
11. Which scientist called water of primitive sea as pre biotic soup?
Explanation: Haldane had called water of primitive sea as pre biotic soup or hot dilute soup. It is because the primitive oceans were rich in mixture of organic compounds, and was the ground for emergence of life.
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