Maharashtra Board | Origin and Evolution of life questions & Answers | Class 12


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Q. 1 Multiple choice questions.
1. Who proposed that the first form of life could have come from per- existing non-living organic molecules? 
a. Alfred Wallace
b. oparin and Haldane
c. Charles Darwin
d. Louis Pasteur

2. The sequence of origin of life may be-
a. Organic materials- inorganic
materials – Eobiont- colloidal
aggregates- cell.
b. Inorganic materials – organic
materials – colloidal aggregates –
Eobiont- cell.
c. Organic materials- inorganic
materials – colloidal aggregates -
cell
d. Inorganic materials- organic
materials – Eobiont- colloidal
aggregates - cell
Answer :   -------------

3. In Hardy - Weinberg equation , the 
frequency of homozygous recessive 
individual is represented by :-
a. P2
b. pq
c. q2
d. 2pq

4. Select the analogous organs-
a. Forelimbs of whale and bat
b. Flippers of dolphins and penguin
c. Thorn and tendrils of bougainvillea
and cucurbita.
d. Vertebrates hearts or brains.

5. Archaeopteryx is known as missing 
link because it is a fossil and share 
characters of both-
a. Fishes and amphibians
b. Annelida and arthropoda.
c. Birds and reptiles
d. Chordates and nonchordates.

6. Identify the wrong statement regarding 
evolution.
a. Darwin’s variations are small and
directional.
b. Mutations are random and non-
directional.
c. Adaptive radiations leads to
divergent evolution.
d. Mutations are non- radamon and 
directional.

7. Gene frequency in a population remain constant due to –
a. Mutation
b. Migration
c. Random mating
d. Non- random mating

8. Which of the following characteristic is not shown by the ape?
a. Prognathous face
b. tail is present
c. Chin is absent
d. forelimbs are longer than hind limbs

9. .................. can be considered as 
conncting link between between ape 
and man.
a. Austalopithecus
b. Homo hablis
c. Homo erectus
d. Neanderthal man.

10. The Cranial capacity of Nanderthal 
man was
a. 600 cc
b. 940 cc
b. 1400 cc 
d. 1600 cc


Q. 2 Very short answer question.

1. Define the following terms-
a. Gene pool : The total genetic information encoded in sum total of genes in a Mendelian population is called gene pool.

b. gene frequency : Gene frequency definition is - the ratio of the number of a specified allele in a population to the total of all alleles at its genetic locus.

c. Organic evolution :  Organic evolution can be defined as slow, gradual, continuous and irreversible changes through which the present day complex forms of the life developed (or evolved) from their simple pre-existing forms.

d. Mendelian Population : The populations occur in small groups of ‘interbreeding populations’. Such small interbreeding group of a population is referred as ‘Mendelian population’.

e. Speciation : The process of formation of a new species from the per-existing species is called speciation.


2. What is adaptive radiation?
Answer : Adaptive Radiation :
The process of evolution which results in transformation of original species to many different varieties, is called, adaptive radiation.
Darwin’s Finches is one of the best example of adaptive radiation. During his visit to Galpagos Islands. Charls Darwin also noticed a variety of small birds. These birds are called Darwin’s finches.


3. If the variation occur in population by chance alone and not by natural selection and bring change in frequencies of an allele. What is it called?
Answer : Genetic Drift


4. State the Hardy – Weinberg eqnilibrium.
Answer : The law states that ‘at equilibrium point both the gene (allele) frequency and geneotypic frequency remain constant from generation to generation’.


5. What is homologous organs?
Answer : Homologous organs are those organs, which are structurally similar but perform different functions. For example : Forelimbs of vertebrates such as lizzard, bird, bat, horse, whale and man.


6. What is vestigeal organ?
Answer : Vestigeal organs are imperfectly developed and non-functional, degenerate structures which were functional in some related and other animals or in ancestors.


7. What is the scientific name of modern
man?
Answer : Homo sapiens


8. What is coacervate?
Answer : Coacervates are organic-rich droplets formed via liquid-liquid phase separation, mainly resulting from association of oppositely charged molecules or from hydrophobic proteins.


9. Which period is known as “age of
Reptilia”?
Answer : During the Mesozoic, or "Middle Life" The period, which spans from about 252 million years ago to about 66 million years ago, was also known as the age of reptiles or the age of dinosaurs.


10. Name the ancestor of human which is described as man with ape brain.
Answer : Homo erectus was first discovered on the island of Java in Indonesia, in 1891. The discoverer, Eugene Dubois originally called it Pithecanthropus erectus based on its morphology that he considered to be intermediate between that of humans and apes. Homo erectus lived from about 1.8 million to 70,000 years ago.


Q. 3 Short answer question..


1. Write a note on Genetic drift.
Answer : Any alternation in allete frequency in the natural population by chance, is called genetic drift. Concept of genetic drift was first given Sewall wright, hence, called as Sewall wright effect. For example, elimination of a particular allele from a population due to events like accidental death prior to mating of an organism. Genetic drifts are random or directionless.

The effect of genetic drift is more significant in small population than in large population. Due to genetic drift, some alleles of a population are lost or reduced by chance and some others may be increased. Some time, a few individuals become isolated from the large population and they produce new population in new geographical area. The allele frequency of new population become different. The original drifted population (i.e. colonizing ancestor/ pioneer) becomes ‘founders’ and the effect is called founder effect.


2. Enlist the different factors that are
responsible for changing gene frequency.
Answer :  Gene frequencies tend to remain constant from generation to generation when disturbing factors are not present. Factors that disturb the natural equilibrium of gene frequencies include mutation, migration (or gene flow), random genetic drift, and natural selection.


3. Give the significance of fossils.
Answer :
i. Fossils can give us insight into how pre- historic plants and animals obtained food, reproduced and even how they behaved.

ii. It provide evidence for how or why the fossil organism died.

iii. Fossils allow researchers to match layers of rock in different locations by age based on how similar the fossils in each rock layer are.

iv. It helps in understanding when the layers of rocks were formed even when large distances separate them.

v. The type of fossil in a particular location tells us what kind of environment existed when the fossil was formed.

vi. Using information pieced together from fossil evidence, scientists can reconstruct body types of animals that no longer exist and put together to describe the evolutionary relationships between organisms.


5. Write the objections to Mutation theory of Hugo de vries.
Answer :
Objections to Mutation Theory :
i. The large and discontinuous variation observed by Hugo de Vries were actually due to chromosomal aberrations were as gene mutations usually bring about minor changes.
ii. Rate of mutation is very slow as compared to the requirement of evolution.
iii. Chromosomal aberrations have little significance in evolution as they are quite unstable.

iv. Natural mutations are not common
as Hugo de Vries thought them to occur.

v. Most of the mutations are negative or retro­gressive.

vi. Mutations are generally recessive while traits taking part in evolution are usually dominant.

vii. Mutation theory cannot satisfactorily explain the development of mimicry, mutual dependence of flowers and pollinating insects.

viii. This theory does not explain the role of nature

Q. 4 Match the following


Column- I                        Column – II
1. August Weismann.    a. Mutation theory
2. Hugo de vries             b. Germplasm
3. Charl Darwin              c. Theory of                                                                aq. characters
4. Lamark                        d. Theory of natural                                                 selection

Answer :  1:b, 2:a, 3:d, 4:c

Q. 5 Long answer questions.


1. Would you consider wings of butterfly and bat as homologous or analogous and why?
Answer : No, the wing of a butterfly and the wing of a bat can not be considered homologous organs because they both perform the same function of flying but their origin and structure is not similar. The bird’s wing has well developed bone structure supported with flesh and feathers whereas insect’s wing has evolved from hardening of membrane cover with a few associated muscles. Homologous organs have similar basic structure but perform different functions, where as analogous organs have different origin and structure but perform same functions.


2. What is adaptive radiation? Explain with suitable example.
Answer : The process of evolution which results in transformation of original species to many different varieties, is called, adaptive radiation.

Darwin’s Finches is one of the best example of adaptive radiation. During his visit to Galpagos Islands. Charls Darwin also noticed a variety of small birds. These birds are called Darwin’s finches. Darwin concluded that the American main land species of bird was the original one from which they migrated to the different islands of Galpagos. They adapted to the different environmental conditions of these islands. From original seed eating features many other forms with altered beaks evolved into insectivorous features.

Another example of adaptive radiation is Australian Marsupials. In Australia, there are many marsupial mammals who evolved from common ancestor.


3. By talking industrial melanism as one example. Explain the concept of natural selection.
Answer : Industrial melanism is an example of thenatural selection of a particular form of an organism in an environment which has changed due to the ill effects of pollution created by industrial activities. The peppered moth Biston Betularia is a moth found  in Manchester, England. It exists in two forms, one a light patchy white and the other a sooty black. Under normal conditions, the majority of the white moths survive because the trees they rest on have white bark.

The black moths have negligible numbers. Due to the Industrial Revolution in Manchester, the number of industrial establishments increased manifold, and the soot released from their chimneys started coating the tree trunks nearby, turning them black. The black variety now started getting camouflaged better on these blackened trunks, and their numbers rose and stabilized. The number of the white variety dwindled due to predation as they started getting easily spotted on the black trunks and get easily picked up by predators.


4. Describe the Urey and Millers experiment.
Answer :
Fig : Urey and Miller’s Experiment


Urey and Miller’s Experiment :
Stanley L.Miller and his teacher Harold C.
96 Urey provided the first experimental evidence in support of chemical evolution theory of Oparin. They designed a glass-apparatus called spark-discharge apparatus.

The apparatus  was first sterilized and evacuated. Methane, ammonia and hydrogen gases were pumped in the proportion of 1:2:2 into the glass chamber. A tube carrying water vapour was also connected to the chamber. Lightning effect was mimicked by electric discharge carbon arc spark in the chamber. Process of evaporation and precipitation was also simulated by the use of heating mantle and condenser respectively.

The mixture of CH4, NH3, H2 was exposed continuously to electric discharge for several days causing the gases to interact, after which these were condensed. The liquid collected in the U-tube turned brown. Chemical analysis of this liquid reported the presence of simple organic compounds. (urea, amino acids, lactic acid, etc). This experiment strongly supports that the simple molecules present in the earth’s early atmosphere combined to form the organic building blocks of life.


5. What is Isolation? Describe the different types of reproductive Isolatons.
Answer : Isolation : Isolation is the separation of the population of a particular species into smaller units which prevents interbreeding between them. Some barrier which prevents gene flow or exchange of genes between isolated populations, is called isolating mechanism.
Number of isolating mechanisms are operated in nature and therefore divergence and speciation may occur. The isolating mechanisms are of two types namely, geographical isolation and reproductive isolation.

Reproductive Isolation :
Reproductive isolations occurs due to change in genetic material, gene pool and structure of genital organs. It prevents interbreeding between population.
Types of Isolating Mechanisms :
A. Pre-mating or pre-zygotic isolating mechanism : This mechanism prevent fertilization and zygote formation.

i. Habitat isolation or (Ecological isolation) : Members of a population living in the same geographic region but occupy separate habitats so that potential mates do not meet.

ii. Seasonal or temporal isolation : Members of a population living in the same geographic region but are sexually mature at different years or different times of the year.

iii. Ethological isolation : Due to specific mating behaviour the members of population do not mate.
iv. Mechanical Isolation : Members of two population have difference in the structure of reproductive organs.

B. Post-mating or Post-zygotic barriers :
i. Gamete mortality - Gametes have a limited life span. Due to one or the other reasons, if union of the two gametes does not occur in the given time, it results in the gamete mortality.

ii. Zygote mortality - Here, egg is fertilized but zygote dies due to one or the other reasons.

iii. Hybrid sterility - Hybrids develop to maturity but become sterile due to failure of proper gametogenesis (meiosis). e.g. Mule is an intergeneric hybrid which is sterile.


6. What is Genetic variations? Explain the different factors responsible for genetic variations.
AnswerGenetic variations : The change in gene and gene frequencies, is known as genetic variation. Genetic variations are caused by following factors :

i. Gene Mutation : Sudden permanent heritable change is called mutation. Mutation can occur in the gene, in the chromosome and in chromosome number.

ii. Genetic recombination : In sexually reproducing organisms, during gamete formation, exchange of genetic material occurs between non-sister chromatids of homologous chromosomes. This is called crossing over.

iii. Gene flow : Gene flow is movement of genes into or out of a population. Gene movement may be in the form of migration of organism, or gametes (dispersal of pollens) or segments of DNA (transformation). Gene flow also alters gene frequency causing evolutionary changes.

iv. Genetic drift : Any random fluctuation (alteration) in allele frequency, occurring in the natural population by pure chance, is called genetic drift. For example, when the size of a population is severely reduced due to natural disasters like earthquakes, floods, fires, etc.

v. Chromosomal aberrations : The structural, morphological change in chromosome due to rearrangement, is called chromosomal aberrations. It changes the genes arrangement (order or sequence) that results in the variation. Chromosomal aberrations occur due to -

a. Deletion : Loss of genes from chromosome.

b. Duplication : Genes are repeated or doubled in number on chromosome.

c. Inversion : A particular segment of chromosome is broken and gets reattached to the same chromosome in an inverted position due to 1800 twist. There is no loss or gain of gene complement of the chromosome.

d. Translocation : Transfer (transposition) of a part of chromosome or a set of genes to a non-homologous chromosome is called translocation. It is effected naturally by the transposons present in the cell.