Question

 After about how many years of formation of earth, life appeared on this planet? [NEET (Oct.) 2020]

(a) 500 billion years

(b) 50 million years

(c) 500 million years

(d) 50 billion years

Answer/Explanation

Ans. (c)

During the course of evolution, earth probably formed about $4.5$ billion years ago. After its formation, life appeared about 500 million years ago in oceans. The first living forms were believed to be heterotrophs and used to derive nutrition from external sources.

Question

From his experiments, SL Miller produced amino acids by mixing the following in a closed flask. [NEET (Sep.) 2020]

(a) $\mathrm{CH}_3, \mathrm{H}_2, \mathrm{NH}_4$ and water vapour at $800^{\circ} \mathrm{C}$

(b) $\mathrm{CH}_4, \mathrm{H}_2, \mathrm{NH}_3$ and water vapour at $600^{\circ} \mathrm{C}$

(c) $\mathrm{CH}_3, \mathrm{H}_2, \mathrm{NH}_3$ and water vapour at $600^{\circ} \mathrm{C}$

(d) $\mathrm{CH}_4, \mathrm{H}_2, \mathrm{NH}_3$ and water vapour at $800^{\circ} \mathrm{C}$

Answer/Explanation

Ans. (d)
The carrect option is (d) because in 1953, SL Miller, created electric discharge in a closed flask containing $\mathrm{CH}_4, \mathrm{H}_2, \mathrm{NH}_3$ and water vapours at $800^{\circ} \mathrm{C}$.

Question

Variations caused by mutation, as proposed by Hugo de Vries are [NEET (National) 2019]

(a) random and directionless

(b) small and directional

(c)small and directionless

(d) random and directional

Answer/Explanation

Ans. (a)
Hugo de Vries proposed that the variations caused by mutation are random and directionless. These are the sudden, heritable changes in the genetic material and these variations constitute the raw material for evolution. He also proposed that mutations play a key role in speciation and used the term saltation for single step large mutations.

Question

 According to Hugo de Vries, the mechanism of evolution is [NEET 2018]

(a) phenotypic variations

(b) saltation

(c) multiple step mutations

(d) minor mutations

Answer/Explanation

Ans. (b)

According to Hugo de Vries, the mechanism of evolution is saltation. Hugo de Vries (1901)proposed mutation theory of evolution and stated that evolution is a jerky process in which new species are evolved due to discontinous sudden variations or saltation. These are the single step large mutations occurring in population.

Question

 Following are the two statements regarding the origin of life [NEET 2016, Phase 1]

1. The earliest organisms that appeared on the earth were non-green and presumably anaerobes.

II. The first autotrophic organisms were the chemoautotrophs that never released oxygen. Of the above statements which one of the following options is correct?

(a) II is correct but $\mathrm{l}$ is false

(b) Both I and II are correct

(c) Both I and Il are false

(d) I is correct but Il is false

Answer/Explanation

Ans. (b)
The earliest organisms that appeared on earth were anaerobic chemoautotrophs.
Chemoautotrophs were the first autotrophic arganisms. They were unable to perform photolysis of water and never released oxygen, e.g. sulphur bacteria.

Question

 Which of the following is the correct sequence of events in the origin of life? [NEET 2016, Phase II]
I. Formation of protobionts.
II. Synthesis of organic monomers.
III. Synthesis of organic polymers.
IV. Formation of DNA-based genetic systems.
(a) I, II, III, IV

(b) I, III, II, IV

(c) $\mathrm{II}, \mathrm{III}, \mathrm{I}, \mathrm{IV}$

(d) II, III, IV,I

Answer/Explanation

Ans. (c)

Question

Which one of the following is incorrect about the characteristics of protobionts (coacervates and microspheres) as envisaged in the abiogenic origin of life? [CBSE AIPMT 2008]
(a) They were able to reproduce

(b) They could separate combinations of molecules from the surroundings

(c) They were partially isolated from the surroundings

(d) They could maintain an internal environment.

Answer/Explanation

Ans. (d)
Homeostasis is keeping the internal environment of the body constant. It is necessary for normal life processes.
Microspheres are molecular aggregates of proteinoids. Oparin and Sydney Fox held that large organic molecules synthesised abiotically on primitive earth formed large colloidal aggregates due to the intermolecular attraction.
These colloidal particles were called coacervates. Oparin called giant nucleoproteinoid molecules as protobionts. These reproduce elther by budding or binary fission but do not exhibit homeostasis.

Question

 Which one of the following pair of items correctly belongs to the category of organs mentioned against it? [CBSE AIPMT 2008]

(a) Thorn of $\quad$ Analogous Bougainvillea and organs tendrils of Cucurbito

(b) Nictitating – Vestigial membrane and blind organs spot in human eye

(c) Nephridia of – Excretory earthworm and organs Malpighian tubules of cockroach

(d) Wings of honeybee – Homologou and wings of crow sorgans

Answer/Explanation

Ans. (c)
In annelids like Nereis, earthworm, leech, etc., the tubular coiled structures called nephridia are excretory organs. In phylum-Arthropoda, insects centipedes, millipedes and arachnides possess Malpighian tubules as their principal excretory organ. Analogous organs have almost similar appearance and perform the same function but develop in totally different groups and are totally different in their basic structure and developmental origin, e.g. wings of butterfly, birds, bats.
The homologous organs have common origin, perform different type of functions and have different appearance, e.g. thorns of Bougainvilleo and tendrils of Cucurbita.
Vestigial organs are useless remnants, which might have been large and functional in the ancestors, e.g. nictitating membrane, vermiform appendix, etc.

Question

 The concept of chemical evolution is based on  [CBSE AIPMT 2007]

(a) crystalisation of chemicals

(b) interaction of water, air and clay under intense heat

(c) effect of solar radiation on chemicals

(d) possible origin of life by combination of chemicals under suitable environmental conditions

Answer/Explanation

Ans. (d)

The concept of chemical evolution is based on possible origin of life by combination of chemicals under suitable environmental conditions.

Question

 Evolutionary history of an organism is known as [CBSE AIPMT 2006]

(a) ancestry

(b) palaeontology

(c) ontogeny

(d) phylogeny

Answer/Explanation

Ans. (d)
Phylogeny (Gr. Phylon – tribe or race; geneja $=$ origin) is the origin and diversification of any taxon or the evolutionary history of its origin and diversification. It is usually represented as a diagrammatic phylogenetic tree (that traces putative evolutionary relationships), i.e., dendrogram. Palaentology is the study of fossils. Ontogeny is the whole course of an individual’s development and life history.

Question

 Which one of the following amino acid was not found to be synthesised in Miller’s experiment? [CBSE AIPMT 2006]

(a) Aspartic acid

(b) Glutamic acid

(c) Alanine

(d) Glycine

Answer/Explanation

Ans. (b)
Miller and Urey were the two scientists who recreated the conditions of primitive earth in laboratory and abiotically synthesised amino acids and bases. They synthesised glycine, aspartic acid and alanine in abundant quantities while, glutamic acid could not be synthesised in their experiment.

Question

 Which one of the following experiments suggests that simplest living organisms could not have originated spontaneously from non-living matter?
[CBSE AIPMT 2005]
(a) Larvae could appear in decaying organic matter

(b) Microbes did not appear in stored meat

(c) Microbes appeared from unsterilised organic matter

(d) Meat was not spoiled, when heated and kept sealed in a vessel

Answer/Explanation

Ans. (d)
Pasteur performed experiments in which he took sterilised (by boiling) yeast and sugar solution in a long naked flask, then he bent the neck of the flask like a neck of swan. After one month he observed that no life appeared in flask solution because the curved flask neck acts as a filter. He later on broke down the neck and observed the solution. He found that many microorganisms were originated in solution.

Question

 According to Oparin, which one of the following was not present in the primitive atmosphere of the earth? [CBSE AIPMT 2004]

(a) Methane

(b) Oxygen

(c) Hydrogen

(d) Water vapour

Answer/Explanation

Ans. (b)
According to Oparin the atmosphere of primitive earth was reducing because $\mathrm{H}$ atoms were most numerous end most reactive. Large quantities of $\mathrm{H}_2, \mathrm{~N}_2$. water vapour, $\mathrm{CO}_2, \mathrm{CH}_4$ and $\mathrm{NH}_3$ were present, but free oxygen was not present in significant amount.

Question

 Identify the correct sequence in which the following substances have appeared during the course of evolution of life on earth [CBSE AIPMT 1996]

(a) glucose, amino acids, nucleic acids, proteins

(b) ammonia, amino acids, proteins, nucleic acids

(c) water, amino acids, nucleic acids, enzymes

(d) amino acids, ammonia, phosphates, nucleic acids

Answer/Explanation

Ans. (b)

Primitive atmosphere was reducing type (without free oxygen). Hydrogen atoms combined with oxygen forming water and with nitrogen, forming ammonia. Water and ammonia were probably the first compound molecules on primitive earth. The primitive atmosphere contained gases like $\mathrm{CO}_2, \mathrm{CO}, \mathrm{N}, \mathrm{H}_2$, etc. and methane $\left(\mathrm{CH}_4\right)$ was the first organic compound formed in primitive atmosphere.
In the primitive atmosphere, electric discharge, ATP and solar energy provided the source of energy for polymerization reactions of organic synthesis which lead to the synthesis of amino acids, that joined to form polypeptides and proteins. Simple sugar units combined to form polysaccharides; fatty acids and glycerol to form fats; sugars, nitrogenous bases and phosphates combined into nucleotides which polymerised into nucleic acids in the ancient oceans.

Question

 The first organisms were [CBSE AIPMT 1992]
(a) chemoautotrophs

(b) chemoheterotrophs

(c) autotrophs

(d) eukaryotes

Answer/Explanation

Ans. (b)
The first cells were almost certainly heterotrophs, obtaining energy and nutrients from organic molecules in their environment. The prokar-yotes evolved before the eukaryotes, the earliest prokaryotes must have been chemoheterotrophs.

Question

 Which was absent in the atmosphere at the time of origin of life? [CBSE AIPMT 1991]
 (a) $ \mathrm{NH}_3 $

(b) $ \mathrm{H}_2 $

(c) $\mathrm{O}_2$

(d) $\mathrm{CH}_4$

Answer/Explanation

Ans. (c)
The atmosphere of earth at the time of origin of life was without free oxygen atoms. The primitive atmosphere chiefly consisted of methane, ammonia, water vapour, hydrogen gas, nitrogen gas, and some carbon monoxide.
Hydrogen atoms were most numerous and most reactive in primitive atmosphere. They combined with all available oxygen atoms and formed water.

Question

 ‘Origin of species’ was written by [CBSE AIPMT 1989]

(a) Oparin

(b) Weismann

(c) Lamarck

(d) Darwin

Answer/Explanation

Ans. (d)
Darwin and Wallace published a joint paper titled ‘Origin of species’ in 1858. Later in 1859, Darwin published his detailed theory in his book titled ‘Origin of species by means of Natural selection’.
According to Darwin, variations are progressive factors for evolution.

Question

 Evolution is [CBSE AIPMT 1989]

(a) progressive development of a race

(b) history and development of race along with variations

(c) history of race

(d) development of race

Answer/Explanation

Ans. (b)
Evolution is defined as history and development of race with variations. The term ‘evolution’ in Biology means gradual changes. It is an excellent working hypothesis to approach the problems of diversity of organisms.

Question

 First life on earth was [CBSE AIPMT 2001]

(a) cyanobacteria

(b) chemoheterotrophs

(c) autotrophs

(d) photoautotrophs

Answer/Explanation

Ans. (b)
First living beings were formed in the environment of sea having abundant organic molecules. They absorbed the organic materials for the sake of nutrition and hence, were chemoheterotrophs.

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