Maharashtra Board Class 12 Solutions for Biology Chapter 5 Origin and Evolution of Life

Single Choice Questions 

1. Who proposed that the first form of life could have come from pre-existing non-living organic molecules? 

1. Alfred Wallace

2. Oparin and Haldane

3. Charles Darwin 

4. Louis Pasteur

Ans: The correct option is (b) Oparin and Haldane. 

According to the theory of abiogenesis given by Oparin and Haldane, the pre-existing non-living organic molecules could have resulted in the formation of the first form of life. 

2. The sequence of origin of life may be 

1. Organic materials - inorganic materials - eobiont - colloidal aggregates - cell

2. Inorganic materials - organic materials - colloidal aggregates - Eobiont - cell

3. Organic materials - inorganic materials - colloidal aggregates - cell

4. Inorganic materials - organic materials - eobiont - colloidal aggregates - cell

Ans: The correct option is (b) Inorganic materials - organic materials - colloidal aggregates- Eobiont - cell.

It has been proven that organic materials can be formed from inorganic materials. In the beginning, there were inorganic materials on the earth that could have changed into organic materials by various chemical processes. When water is added to organic materials, they form colloidal aggregates. Later, these aggregates could have formed the Eobiont which later resulted in the formation of the cell. 

3. In the Hardy-Weinberg equation, the frequency of homozygous recessive individuals is represented by: 

1. p²

2. pq

3. q²

4. 2pq

Ans: The correct option is (c) q²

The Hardy Weinberg equation states the frequency of homozygous recessive, homozygous dominant, and heterozygous alleles in an individual. The p² represents the frequency of homozygous dominant alleles while q² represents the frequency of homozygous recessive alleles. The frequency of heterozygous alleles is represented by 2pq. 

4. Select the analogous organs-

1. Forelimbs of whale and bat

2. Flippers of dolphin and penguin

3. Thorns of bougainvillaea and Cucurbita

4. Vertebrates hearts and brains. 

Ans: The correct option is (b) Flippers of dolphins and penguins. 

Analogous organs are those organs that perform the same function but they are anatomically different. Flippers of dolphins and penguins help them to swim. But, the structure of Flippers in both organisms is different. 

5. Archaeopteryx is known as the missing link because it is a fossil and shares characteristics of both-

1. Fishes and amphibians 

2. Annelida and Arthropoda 

3. Birds and reptiles 

4. Chordates and non-chordates

Ans: The correct option is (c) Birds and reptiles. 

The Archaeopteryx has some characteristics of birds and some characteristics of reptiles. The presence of feathers, beaks, and wings are some features of birds that were present in Archaeopteryx. The presence of teeth in the jaw, absence of pneumatic bones, weak sternum, etc. are features of reptiles that were found in Archaeopteryx. 

6. Identify the wrong statement regarding evolution- 

1. Darwin's variations are small and directional 

2. Mutations are random and non-directional

3. Adaptive radiation leads to divergent evolution

4. Mutations are non-random and non-directional

Ans. The correct option is (d) Mutations are non-random and non-directional. 

Mutations are the random changes that occur in the sequence of nucleic acids during the process of cell division. They are non-directional as they don't follow the same pattern and are generally recessive. 

7. Gene frequency in a population remains constant due to 

1. Mutation 

2. Migration 

3. Random mating 

4. Non-random mating 

Ans. The correct option is (d) Non-random mating. 

Mutation, Migration, genetic drift, and random mating are some factors that affect the gene frequency in a population. In the absence of these factors, the frequency of genes in a non-random mating population remains constant. 

8. Which of the following characteristic is not shown by the ape-

1. Prognathous face 

2. Tail is present

3. Chin is absent 

4. Forelimbs are longer than hindlimbs

Ans: The correct option is (b) Tall is present. 

The apes are characterised by the presence of a Prognathous face and fur on their body. Some other characteristics that are found in apes are the presence of large Jaws, absence of tail, and Chin. Apes have longer Forelimbs than their hind limbs. 

9. …………………. can be considered as a connecting link between apes and men. 

1. Australopithecus 

2. Homo habilis 

3. Homo erectus 

4. Neanderthal man 

Ans: The correct option is (a) Australopithecus. 

Australopithecus is considered as a connecting link between man and ape as they had some features similar to man and apes. They were bipedal and had a short body just like humans. The presence of long arms, small brains, and chimpanzee-like faces are some ape-like features found in Australopithecus. 

10. The Cranial capacity of Neanderthal man was

1. 600cc

2. 940cc

3. 1400cc

4. 1600cc

Ans: The correct option is (c) 1400 cc. 

Neanderthal men had long noses and short bodies. They had Cranial capacity somewhat similar to modern humans i.e. 1400cc. Despite higher Cranial capacity, they were not capable of handling emotions. 

Very Short Answer Questions

1. Define the following terms: 

1. Gene pool

2. Gene frequency 

3. Organic evolution 

4. Population 

5. Speciation

Ans: The definition of the terms is given below: 

1. Gene Pool is the term used for the presence of all the genes that occur in all the populations of a species. If there is a large gene pool then it refers to the large genetic variations in the species. The presence of more variations in the species ensures the long survival of that species. Thus, a gene pool is very important in genetics and biotechnology for various study purposes. 

2. Gene Frequency of a specific gene is the ratio of the alleles of that gene present in a population to the total number of alleles present at the same locus of the chromosome in a population of a species. It generally remains constant but can change by some factors such as mutation, migration, natural selection, gene flow, etc. 

3. Organic Evolution is the change in the genetic composition of plants and animals in response to environmental changes with time. An example of organic evolution includes the flippers of dolphins and penguins. 

4. The Population of a species consists of the individuals that live in a particular geographical location at a time and can reproduce among themselves. They are not reproductively isolated. 

5. Speciation is the process that leads to the creation of new species from the pre-existing species by the process of evolution. Some factors can lead to speciation. These are- natural selection, recombination, geographical barrier due to natural calamities, etc. 

2. What is adaptive radiation? 

Ans: When many species are evolved or radiated from a single species that live in a geographical area then it is called adaptive radiation. All the radiated species evolved into different species but they have a common ancestor. 

3. If the variation occurs in a population by chance alone and not by natural selection and brings a change in frequencies of an allele. What is it called?

Ans: Whenever there is a random variation that occurs in a population of species, then it is called genetic drift. The environmental factors are not responsible for the occurrence of genetic drift. Genetic drift happens due to error in sampling but its effect is easily seen in species having a small population. 

4. State the Hardy-Weinberg equilibrium. 

Ans: The Hardy Weinberg equation states the frequency of homozygous recessive, homozygous dominant, and heterozygous alleles in an individual. The p² represents the frequency of homozygous dominant alleles while q² represents the frequency of homozygous recessive alleles. The frequency of heterozygous alleles is represented by 2pq. 

5. What are homologous organs? 

Ans: Homologous organs are the organs that are anatomically similar but perform different functions in different organisms. For example, the forelimbs of man and whale are anatomically similar but they are used for different functions in both organisms. 

6. What is a vestigial organ? 

Ans: The organs that don't perform any functions but are present in organisms are called vestigial organs. Previously, these organs might perform functions but they are useless today. In the human body, the tailbone and appendix are vestigial organs. 

7. What is the scientific name of modern man?

Ans: The scientific name of modern man is Homo sapiens. They are bipedal organisms with hairs on the body. The Cranial capacity of modern man is 1500cc which is similar to the Cranial capacity of Neanderthal man. But, modern men are considered the most intelligent species on earth due to their ability to think and control emotions which were absent in Neanderthal men. 

8. What is coacervate? 

Ans: According to the theory of chemical evolution, the coacervate is macromolecules containing colloidal particles or pre-cells that lead to the formation of first life i.e. living cells. 

9. Which period is known as the "age of Reptilia"? 

Ans: The Jurassic period of the Mesozoic era is known as "the age of Reptilia" as, during this geological period, the reptiles first appeared. The warm and wet climate during the Jurassic period favoured the growth of vegetation and the appearance of reptiles. 

10. Name the ancestor of a human which is described as a man with an ape brain. 

Ans: Australopithecus were the ancestors of humans and are described as a man with an ape brain because they had some features similar to man and apes. They were bipedal and had a short body just like humans. The presence of long arms, small brains, and chimpanzee-like faces are some ape-like features found in Australopithecus. 

Short Answer Questions 

1. Write a note on genetic drift. 

Ans: The genetic drift occurs whenever there is a change in the number of gene frequencies in the individuals of a population. There can be an increase in genetic variation or a decrease in genetic variation due to genetic drift. 

2. Enlist the different factors that are responsible for changing gene frequency. 

Ans: The factors that are responsible for changing gene frequency are- mutation, recombination, genetic drift, migration, etc. In the absence of these factors, the frequency of genes in a non-random mating population remains constant. 

3. Draw a graph to show that natural selection leads to disruptive change. 

Ans: The natural selection that leads to disruptive change is called disruptive natural selection. In disruptive natural selection, nature favours some traits. Hence, the individuals having intermediate traits get declined. 

Graph of Natural Selection

4. Write the significance of fossils.

Ans:  Significance of fossils are: 

• Fossils are very helpful to compare day organisms with the organisms that once existed on earth. 

• They are very important in studying the evolutionary process. 

• Fossils tell us the structure of organisms that once existed on earth and thus, we can know the ancestors of species.

• They are very helpful to find the missing links and connect similar species. 

5. Write the objections to the Mutation theory of Hugo de Vries. 

Ans: Objections to the Mutation theory of Hugo de Vries are: 

• Hugo de Vries observed many mutations that were large and actually due to chromosomal aberrations. As we know today, mutations are the result of changes in genes and they are small mutations. 

• A mutation is a very slow process and thus, could not be the only reason that leads to evolution. 

• He could not explain the discontinuity that we see today in different populations. 

6. What is disruptive selection? Give an example. 

Ans: The natural selection that leads to disruptive change is called disruptive natural selection. In disruptive natural selection, nature favors extreme traits and disfavors intermediate traits. Consequently, the individuals having intermediate traits get declined while the individuals having extreme traits get increased. For example- industrial melanism due to which the population of white moths declined while the population of black moths increased. 

Match the Following

Ans: The correct matches are: 

1. August Weismann - b. Germplasm Theory 

August Weizmann proposed the germ Plasm theory according to which the germplasm present in the germ cells is responsible for the transfer of genetic information from parents to offspring. Somatic cells Do not play any role in the transfer of genetic information. 

2. Hugo-de Vries - a. Mutation Theory 

According to the mutation theory of Hugo-de Vries, mutations are the cause of the formation of new species. The mutations can be beneficial or harmful for the organism. 

3. Charles Darwin - d. Theory of Natural Selection 

According to the theory of natural selection of Charles Darwin, the organisms that adapt themselves to the changing environmental conditions survive more and thus produce more offspring. 

4. Lamarck - c. Theory of Acquired Characters 

Lamarck proposed the theory of acquired characters according to which the physical modification that a person acquires during his lifetime can be transferred to his offspring. 

Long Answer Questions

1. Would you then consider the wings of butterfly and bat as homologous or analogous and why? 

Ans:  The wings of butterflies and bats are considered analogous organs. This is because

• Analogous organs are those organs that perform the same function but they are anatomically different. 

• The wings perform a similar function in both organisms i.e. flying but the structure of wings in both organisms is different. Hence, they are analogous organs. 

2. What is adaptive radiation? Explain with a suitable example. 

Ans: Adaptive radiation is explained below: 

• When many species are evolved or radiated from a single species that live in a geographical area then it is called adaptive radiation. 

• All the radiated species have evolved into different species but they have a common ancestor. The main reason for adaptive radiation is natural selection. 

• Darwin's finches on Galapagos island are the best example of adaptive radiation. There are different species of birds having different feeding habits but all of them evolved from seed-eating species. This was observed by Darwin by identifying their beaks. 

3. By taking industrial melanism as one example, explain the concept of natural selection. 

Ans: By taking industrial melanism as an example, natural selection is explained below: 

• Before industrialization, there were more white moths than black moths as they can camouflage with the colour of trees. 

• But, after industrialization, the number of black moths increased as compared to white moths. This is because, due to industrialization, the soot was deposited on the trees that favoured the easy camouflage of black moths as compared to white moths. 

• This resulted in more killing of white moths by predators and the population of black moths increased. 

• Thus, during industrialization, nature favoured the population of black moths over white moths. This is the concept of natural selection. 

4. Describe Urey and Miller's experiment.

Ans: Urey and Miller's experiment is described as follows: 

• The experiment of Urey and Miller was based on the concept of Oparin and Haldane on the origin of life. 

• Urey and Miller created the early Earth conditions in a flask in the laboratory. 

• They created the primitive earth's atmosphere in the flask having gases such as ammonia, hydrogen, water vapour, and methane that existed on the primitive earth. 

• The mixture of gases was provided with electric discharges for some days which later got condensed and accumulated in another chamber. 

• They observed the presence of complex organic molecules in the condensed liquid-containing chamber which supported the origin of life from pre-existing simple molecules. 

5. What is isolation? Describe the different types of reproductive isolations. 

Ans: Isolation is the separation of the population of a species or different species due to some barriers that can be natural or genetic. Whenever the isolation occurs due to geographical barriers then it is called geographical isolation and when the isolation occurs due to genetic barriers or reproductive barriers then it is called reproductive isolation. 

There are two types of reproductive isolation: 

(i) Prezygotic or Premating Reproductive Isolation

• Whenever there is no fertilization due to reproductive isolation, then it is called prezygotic reproductive isolation.

• The common reasons for pre-zygotic isolation are different habits of individuals in a population, individuals sexually mature at different times, different reproductive structures and different mating behavior. 

(ii) Post-zygotic or Post-mating Reproductive Isolation 

• When the isolation occurs after the formation of the zygote or post-fertilization, then it is called postzygotic reproductive isolation. 

• The common reasons for post-zygotic isolation are the mortality of zygotes and gametes. The sterility of hybrids is also a reason for this type of isolation. 

6. What is genetic variation? Explain the different factors responsible for genetic variations. 

Ans: Genetic variation is the less common variation or change that occurs in the gene of the population of a species. There are various factors responsible for genetic variations. These are 

• Mutation: Mutations are the random changes that occur in the sequence of nucleic acids during the process of cell division. They are non-directional as they don't follow the same pattern and are generally recessive. 

• Genetic Recombination: It is the recombination of genetic traits from two mating individuals due to the exchange of genetic material. The resultant genetic recombination may have traits not present in parent individuals. 

• Genetic Drift: Genetic drift occurs whenever there is a change in the number of gene frequencies in the individuals of a population. There can be an increase in genetic variation or a decrease in genetic variation due to genetic drift. 

• Migration or Gene Flow:  When the population migrates to a new geographical area, then gene flow occurs. 

7. Complete The Chart. 

Ans: The correct answer is 

• Cenozoic - Mammals 

The Cenozoic era is the latest era that is dominated by angiosperms and mammals. The present era is also a Cenozoic era. Hence, this era is also called the "age of mammals". 

• Mesozoic- Reptiles 

The Jurassic period of the Mesozoic era is known as "the age of Reptilia" as, during this geological period, the reptiles first appeared. The warm and wet climate during the Jurassic period favoured the growth of vegetation and the appearance of reptiles.

• Palaeozoic- Amphibians 

The Palaeozoic era was dominated by marine organisms such as Amphibians and fishes. The environmental conditions in this era were favourable for the survival of marine organisms. 

• Cambrian - Invertebrates

The Cambrian era is one of the six periods in which the Palaeozoic era is divided. The Cambrian era was dominated by lower Invertebrates. 

Importance of Class 12 Biology Chapter 5 Origin and Evolution of Life

We have studied the general features of living organisms in the previous classes. These features differentiate between living and non-living things. Imagining the display of such features by something that is made of non-living things intrigues our minds. This chapter deals with the protobiogenesis and evolution of life.

This chapter will explain the scientific theories behind the formation of life on earth. This is such a rare phenomenon that finding another trace of life is practically impossible. The theories of creation will be explained here with proper definitions.

Students will learn from the descriptions given by the experts in the Origin and Evolution of Life Solutions so that they can grab hold of the concepts. All these theories are based on the findings of different scientists in different eras.

Many theories arrived and have been disproved by scientists. These theories try to explain the incomprehensible path of the origin of life on the earth. Many believe that chemicals have self-assembled to form life. It means that we can be the result of intricate chemical evolution.

In order to make these chapters easier to understand, refer to the Maharashtra Board Class 12 Biology Solutions Chapter 5 Origin and Evolution of Life prepared by the subject experts. Find out how the experts have explained all the concepts and easy ways to answer the fundamental questions.

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