NCERT Solutions Class 10 Science Chapter 9 Heredity and Evolution
NCERT Solutions Class 10 Science Chapter 9 Heredity and Evolution: National Council of Educational Research and Training Class 10 Science Chapter 9 Solutions – Heredity and Evolution. NCERT Solutions Class 10 Science Chapter 9 PDF Download.
NCERT Solutions Class 10 Science Chapter 9: Overview
Board |
NCERT |
Class |
10 |
Subject |
Science |
Chapter |
9 |
Chapter Name |
Heredity and Evolution |
Topic |
Exercise Solutions |
NCERT Solutions Class 10 Science Chapter 9 – Heredity and Evolution
A.) questions from boxes:
Page 143
1.) If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Ans. from the above statement, it is clear that the trait B has arisen earlier because in asexual reproduction, each daughter cell is an exact replica of its mother cell. Therefore, in such type of species, the traits are common in both the generations. As trait B exists more in percentage than A, and the species are asexually reproducing, we can confirm that the B trait has been arrived earlier.
2.) How does the creation of variations in a species promote survival?
Ans. Mutations in gene promotes variations. But not all variations are useful in the species. So, all the variations do not have chance of survival in nature. Those variations which are useful for the species only survive and the one which are not useful, are eliminated. Beneficial variation surely promotes survival of the species and vice- versa.
Page 147
1.) How do Mendel’s experiments show that traits may be dominant or recessive?
Ans. Mendel conducted his experiments on the Pisum Sativum or pea plant. To find out dominant and recessive traits in the plant, he selected and crossed homozygous tall (TT) pea plant with the homozygous dwarf (tt) pea plant and observed the next progeny. From this cross, it was observed that the F 1 generation is having all tall pea plants. So, he concluded that the genes which are responsible for tallness are dominant while the genes which are responsible for dwarfness are recessive. In this way, Mendel’s experiments show that traits may be dominant or recessive.
2.) How do Mendel’s experiments show that traits are inherited
independently?
Ans. to show that the traits are inherited independently, Mendel selected and crossed two pairs contrasting characters known as dihybrid cross and observed their results. The above cross showed that the segregation of traits in both the parents in gametes independently and their inheritance too.
3.) A man with blood group A marries a woman with blood group O and
their daughter has blood group O. Is this information enough to tell you
which of the traits – blood group A or O – is dominant? Why or why not?
Ans. to say anything about the nature of trait, we need to know about its genotype. From the given information, we cannot conclude anything about the nature of the trait as the information given above is insufficient and we need at least three generations to determine the dominant and recessive traits which is no given here.
4.) How is the sex of the child determined in human beings?
Ans. Human beings have 46 chromosomes in them out of which 44 are autosomes and 2 are sex chromosomes. Thus, each gamete receives 23 chromosome and one sex chromosome by the method of meiosis. Human female are homogamous producing 22+X gametes. But, human males are heterogametic producing 22+X or 22+Y types of gametes. Depending upon which type of male gamete fuses with female gamete, the sex of the child could be determined. If the resultant combination is 44+XX then a baby girl will be formed or if the genetic constitution of baby is 44+XY then it will be baby boy.
Page 150
1.) What are the different ways in which individuals with a particular trait may increase in a population?
Ans. the different ways in which individuals with a particular trait may increase in a population are- natural selection of a particular trait by nature and by the genetic drift.
2.) Why are traits acquired during the life-time of an individual not inherited?
Ans. individual acquire many traits in its life but they do not get inherited in the next progeny because the acquired traits does not interferes with the traits present in gametes. Only those traits which are present in the germ cells or reproductive cells do get inherited to the next progeny.
3.) Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Ans. the small number of surviving tiger can be co- related to the less amount of genes with further too the less chances of genetic variation. Hence, here are more chances of losing the genes due to extinction. Therefore, the tiny numbers of surviving tigers is a topic of worry from the point of view of genetics and genes.
Page 151
1.) What factors could lead to the rise of a new species?
Ans. There are some factors which give rise to the new species:
Natural selection, genetic drift, genetic recombination leads to variation and natural selection, etc.
2.) Will geographical isolation be a major factor in the speciation of a self- pollinating plant species? Why or why not?
Ans. Geographical isolation will not be a major factor in the speciation of a self- pollinating plant species because as plants are self- pollinating, flower of that plant will pollinate itself and there will be no role of mixing the genes from different parents. Also, there will be no separation of the plant in distance and hence, pollens can be easily carried out with the help of pollinators.
3.) Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Ans. Asexually reproducing animals involves only one parent to take place. Hence, there are no chances of genetic recombination to take place by mixing of genes from two different parents. Also, we cannot isolate a single organism geographically. Hence we can say that the geographical isolation will not be a major factor in the speciation of an organism that reproduces asexually.
Page 156
1.) Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Ans. we can determine how close are two species are in evolutionary terms by using the characters called as homologous structure. Homologous structure are similar in different species as they are inherited to the progeny from a common ancestor. More the closeness among the species, more are the no. of homologous structure present in between them.
2.) Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Ans. Wings of a butterfly and wings of a bat are not considered as homologous organs because both of them have different origin and they have different structure. Homologous organs have same origin and structure which is not followed in this case.
3.) What are fossils? What do they tell us about the process of evolution?
Ans. the remains of dead plants and animals which were living in the geological past are called as fossils. The organism in a fossil is dead now but it was living during the past time. Fossils are important to study the process of evolution because they tell us about the past flora and fauna which we cannot see today. We can connect a link of this fossils with the existing species to get the idea of evolution.
Page 158
1.) Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?
Ans. Human beings look different from each other in various terms but also they are said to be belonging to the same species because all humans have almost similar DNA sequences with little variation, they are originated from a common ancestor and they have ability to reproduce within the same species and they produce fertile organism. All this suggest that humans belongs to the same species.
2.) In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Ans.
We can observe the body designs of bacteria, spider, fish and chimpanzees. Nature has created variety body designs to suit that particular organism to live in a particular environment. Each and every organism does have capacity to live in a particular type of habitat which can provide it better chances of survival than other organisms. Therefore, we cannot compare body designs of organisms and say that a particular organism have better body designs than the rest.
Exercise Solution:
1.) A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw
Ans. (c) TtWW
Hint: Half of the progenies are short in height, that means the parent plant will also have a set of short genes and they are heterozygous tall; all of the progeny plants bore violet flowers, which means that violet colour of flower is dominant over the white colour.
2.) An example of homologous organs is
(a) our arm and a dog’s fore-leg.
(b) our teeth and an elephant’s tusks.
(c) potato and runners of grass.
(d) all of the above.
Ans. (d) all of the above
Hint: Homologous organs are the organs which have the same structure but they perform different functions. All the above mentioned examples are of homologous organs.
3.) In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.
Ans. (a) a Chinese school-boy.
Hint: we do not resemble with a chimpanzee, spider or a bacterium in evolutionary terms but we do resemble with a Chinese school boy hence correct option is a.
4.) A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Ans. According to given study it is found that those children who have light coloured Eyes are having parents with light coloured Eyes. So we can say that the trait of light coloured eyes is carried on from parents to children. But the given data is not enough to determine the nature of character. Hence we cannot predict about the dominant or recessive nature of light coloured Eyes.
Alternative Answer –
It is difficult to come to a conclusion whether it is dominant or recessive as these genotypes related to traits have not yet come under scientific scrutiny. A minimum of three generations of characterization is required to make a definitive determination as to whether these genotypes are dominant or recessive.
5.) How are the areas of study – evolution and classification – interlinked?
Ans. Mixing of genes occur in sexual reproduction but it does not occur in asexual reproduction. Due to the mixing of genes, sexual reproduction gives rise to more variation than the asexual mode of reproduction. Accumulation of the variations in an organism leads to evolution to a sub-species after a passage of time.
Alternative Answer –
The field of classification and evolution are interrelated. That is, classification is influenced by the evaluation of organisms. Based on characteristics of organisms, organisms are classified seperately. Because all organisms have evolved individually according to their adaptation, and the modern classification system is called phylogenetic classification,thus classification and evolution are closely related or interlinked.
6.) Explain the terms analogous and homologous organs with examples.
Ans. Analogous organs are the one which have different structure but performing similar function. For example, wings of birds and insects like mosquitoes, butterfly are different in looks, structure and origin but perform a same function i.e. flying.
Homologous organs are the organs which have the same structure but they perform different functions in nature. For example- forelimbs of humans and forelimb of lizard have same internal structure but they both perform different functions.
Alternative Answer –
Many of the organs have same basic structural design but they have different functions this type of organs are called homologous organs.
For example: Fore limb of man and wing of bird have same basic structural design but they have different functions.
Many of organs have similler functions but they have different basic structural design this type of organs are called as Analogous organs.
For example: The eyes of mammals and octopus have similler functions but they have different basic structural design.
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7.) Outline a project which aims to find the dominant coat colour in dogs.
Ans. We can find out the court colour of dogs with the help of a project. We have to do crossing of two homozygous parents. If a parent with homozygous black coat colour if Cross with a parent with homozygous brown coat colour parent then the puppy will be heterozygous with black coat colour. Therefore we can say that black coat colour is dominant in dogs. In this way by carrying out this project, we can find out dominant coat colour in dogs.
Alternative Answer –
We can find two types of gene in dog. One dominant gene and the other recessive gene in both homozygous and heterozygous conditions the dominant gene is expressed whereas in the homozygous condition only the recessive gene is produced. A dog’s coat colour is determined by genes. For example, one perent is homozygous brown (bb) and the other parent is homozygous black (bb). In a cross between two parents we do not know whether the black is dominant or the brown is dominant. Therefore, only after the generation of progeny can we know which trait is dominant in the progeny, the progeny is black, where black is dominant, if the progeny is brown, it can be said that brown is dominant. Thus, at least 11 genes have been identified to determine the coat colour.
8.) Explain the importance of fossils in deciding evolutionary relationships.
Ans. Fossils represents died organisms. This are important in deciding the evolutionary relationships as they serves as the source of knowledge to study past life. With the help of their study, we can compare today’s life with our ancestors and can make a link with them.
Alternative Answer –
Fossils can be obtained from embedded rocks. By examining it, we can learn as much as possible about the creatures of the past,how animals used to live hundreds of years ago and how the animals of the present time compare to those creatures,we can gain knowledge by comparing the shape of the animals of that time and the shape of the animals of present time. Thus fossils are helpful in knowing which animals have become extinct and which animals are endangered.
9.) What evidence do we have for the origin of life from inanimate matter?
Ans. Miller and Urey conducted an experiment to trace origin of living beings. For this, they take up apparatus like glass tubes, flask etc. Some gases were also taken up like methane, ammonia, hydrogen in a ratio in the presence of vapours of water. They give all this mixture an electric shock at a particular temperature. After few days, all this mixture was tested. The mixture was found to be consisting of mix of living substances like nucleotides, sugars, certain acids, etc. And all this set up confirmed that life was originated from non- living substances.
Alternative Answer –
Through the experiment of Miller and Urey, we can understand how living things evolved from non-living things in this creation. The two conduct an experiment. They artificially create an atmosphere comperable to the time of ancient Earth, i.e the atmosphere, that existed when life was absent when creation first took place. In this artificial atmosphere there were molecules like ammonia, hydrogen sulphide, methane apart from oxygen. And in this atmosphere the temperature was stabilized at 100°C and lightning was created by passing the mixture of sparks. Over time, the carbon from the methane gas was converted into simpler Compounds of carbon, such as amino acids. Thus amino acids in the form of proteins lead to the production of organisms.
10.) Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
Ans. Mixing of genes occur in sexual reproduction but it does not occur in asexual mode of reproduction. Due to the mixing of genes in sexual reproduction, it gives rise to more variation than the asexual mode of reproduction. Accumulation of this variations in an organism leads it on the way to evolution after a passage of time.
Alternative Answer –
Sexual reproduction involves the fusion of male and female gametes. We can expect a more viable change from sexual reproduction as compared to asexual reproduction. This is because the separation of the paternal and maternal chromosomes is random during gamete formation. Error in DNA replication can occur, although the event are rare. Difference in the same asexual reproduction are minimal because only one parent is involved in the asexual reproduction process. Even if a mistake is made while copying the DNA, there will be a small change. In asexual reproduction in this way, the breed is more likely to look like its parents. Thus it can be said that evolution occurs faster in sexual reproduction as compared to asexual reproduction.
11.) How is the equal genetic contribution of male and female parents ensured in the progeny?
Ans. Meiosis occurs in reproductive cells known as gametes. These gametes carry half number of total chromosomes present in an individual. Each parent provides half number of genetic contribution for their children which gets doubled later on. In this way, the equal genetic contribution is insured by both parents.
Alternative Answer –
Both play an equal role in giving male and female genetic chromosomes in the reproductive process. There are 23 pairs of chromosomes in the human body out of which 22 pairs are autosomes and the remaining one pair is sex chromosome. That one pair of sex chromosomes is X and Y in humans. Chromosome is in the form of 2X in the female body, while in the male body the chromosome is found in the form of X and Y. And females and males contribute equally when mating. Hence the contribution of both parents to the offspring is equal.
12.) Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Ans. Variations occurs during DNA replication. From variations are useful while some are not. Useful variation are beneficial for an organism, they provide advantage than previous one. But some variation are harmful also such as transfer cancer variation. Such a harmful variation can also be inherited from parents to the children and they also survive among the masses.
Alternative Answer –
Variation occurs when sexual reproduction takes place between organisms. Among such variations, only beneficial variation survive. Not all variation give organisms an equal opportunity to survive in an environment. Thus, to survive in the environment of organisms depends on their variation. For example, heat resistance bacteria find themselves at higher temperatures than their habitat to survive.
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