# NCERT Solutions For Class 10 Science Chapter 9 Heredity and Evolution

## NCERT Solutions For class 9 science chapter 10 Heredity and Evolution

### NCERT Books Solutions For Class 10 Science Chapter 9 Heredity and Evolution

Class 10 is the first stepping stone for a student in the competitive world. With the introduction of the CBSE Board Exam for class 10 a few years back, this has become an important gateway for a student as based on the results of class 10th a student selects his future stream of Science, Commerce, or Arts.

Takshila Learning provides you with detailed and well explained NCERT Solutions for Class 10 of each chapter of each subject for NCERT Class 10. These NCERT Solutions help you to easily understand every concept so that you can score high in your CBSE Class 10 Board Exams.

Below you can find the NCERT solution for Class 10th Science. You can get a Solution for the all-important question of “Heredity and Evolution”

Ques 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?

Answer: Trait B because in asexual reproduction traits which are present in the previous generation are carried over to the next generation with minimum variation. Trait B have a higher percentage, so it is likely to have arisen earlier.

Ques 2: How does the creation of variations in a species promote survival?

Answer: Variations or could you do sexual reproduction and also due to in accurate copying of DNA. Depending on the nature of variations, different individuals would have different kind of advantages. For example, bacteria variants which can with stand heat have better chances to survive in a heat wave, non-variant bacteria have no capacity to tolerate heat wave. Thus, variations in a population of species help in survival of species.

Intext question (set 2)

Page no.147

Ques 1: How do Mendel’s experiments show that traits may be dominant or recessive?

Answer: The trait which appears in all the members of F1 generation and also in 75% numbers of F2 generation obtained by self-fertilisation of F1 generation is dominant character.

The trait which does not appear in F generation but after self-fertilisation of F1 generation, reappears in 25% of F2 generation is known as recessive.

Ques 2: How do Mendel’s experiments show that traits are inherited independently?

Answer: Mendel crossed pure breeding tall plants having round seeds with pure breeding short plants having wrinkled seeds. The plans of F1 generation where all tall with round seeds indicating that the traits of tallness and round seeds were dominant. Self breeding of F1 yielded plans with character of 9 tall round seeded and one short wrinkled seeded. All wrinkled seeded and short round seeded plants are new combinations which can develop only when that treats are inherited independently.

Ques 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?

Answer: No. This information is not sufficient to determine which of the traits -blood group A or O- is dominant. This is because we do not know about the blood group of all progeny.

Blood group A can be genotypically AA or AO. Hence the information is incomplete to draw any search conclusion.

Ques 4: How is the sex of the child determined in human beings?

Answer: In human being the females have two X chromosomes in the males have one X and one Y chromosome. Full therefore, the females are XX and the male are XY.

The Gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.

Type of mail gametes: 22+ X or 22+ Y

However, since the female have XX chromosomes, their gametes can only have X sex chromosome.

Type of female gamete: 22+ X

Thus, the mother provides only X chromosomes. The sex of the body is that remind by the type of male gamete (X or Y) did fuses with the X chromosomes of the female.

Intext questions (set 3)

Page no.150

Ques 1: What are the different ways in which individuals with a particular trait may increase in a population?

Answer: Individuals with a particular treat me increase in population as a result of the following:

• Genetic drift: when some genes governing that trade become common in a population.
• When the trip gets acquired during the individual’s lifetime.

Ques 2: Why are traits acquired during the life-time of an individual not inherited?

Answer: This happens because an acquired trait involves change in non-reproductive tissues which cannot be passed on to Germ cells or the progeny. Therefore, these traits cannot be inherited.

Ques 3: Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer: The small number of members in a population of tigers does not allow large number of variation to occur which are essential to survival of the species. A deadly disease or calamity may cause death of all the Tigers. The small number of Tiger also indicates that existing tiger variants are not well adapted to the existing environment and may extinct soon.

Intext questions (set 4)

Page no.151

Ques 1: What factors could lead to the rise of a new species?

Answer: Natural selection, genetic drift and acquisition of trade during the lifetime of an individual can give rise to new species.

Ques 2: Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?

Answer: Geographical isolation can prevent the transfer of pollen among different plants. However, since the plans are self-pollinating, which means that the pool and is a transfer from the anther of one Flower to the stigma of the same flower or of another flower of the same plant, geographical isolation cannot prevent speciation in that case.

Ques 3: Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

Answer: No, because geography kill isolation does not affect much in asexually reproducing organisms. Asexually reproducing organisms pass on the parent DNA to offspring that leaves no chance of speciation. However, geography kill isolation works as a major factor in cross pollinated species. As it would result in pollinated species. As it would result in accumulation of variation in the two geographically separated population.

Intext questions (set 5)

Page no.156

Ques 1: Give an example of characteristics being used to determine how close two species are in evolutionary terms.

Answer: Feathers in some ancient reptiles like dinosaurs, as fossils indicate, involved providing insulation in cold weather.  However, they cannot fly with these feathers, later on birds adapted the feathers to flight. This means that birds are very closely related to reptiles, since dinosaurs were reptiles.

Ques 2: Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Answer: The wings of a butterfly and the wing of a bat are similar in function.  They help the butterfly and the bat in flying. Since they perform similar function, they are analogous organs and not homologous.

Ques 3: What are fossils? What do they tell us about the process of evolution?

Answer: Fossils are the remains of organisms that once existed on earth. They tell us about the development of the structures from simple structured to complex structured organisms. They tell us about the fees is of evolution through which they must have undergone in order to sustain themselves in the competitive environment.

Intext questions (set 6)

Page no.143

Ques 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?

Answer: A species is a group of organisms that are capable of interbreeding to produce of a tile of spring. Skin colour, looks, and size are all variety of features present. In human beings. These features are Genetic but also environmentally controled. Various, human races are formed based on these features. All human races have more than enough similarity to be classified as same species. Therefore, all human beings are a single species as humans of different colour, size, looks are capable of reproducing and can produce a fertile offspring.

Ques 2: In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?

Answer: Evolution cannot always be equated with progress or better body designs. Evolution simply create more complex body designs. However, this does not mean that the simple body designs are inefficient. In fact, bacteria have a simple body design are still the most Cosmopolitan organisms found on earth. They can survive hot Springs, dead Sea and even freezing environment.

Therefore, bacteria, spiders, fish and chimpanzees are all different branches of evolution.

Exercise Questions:

Page no.158

Ques 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 –

1. TTWW
2. TTww
3. TtWW
4. TtWw

Ques 2: An example of homologous organs is

1. Our arm and a dog’s fore-leg.
2. Our teeth and an elephant’s tusks.
3. Potato and runners of grass.
4. All of the above.

Answer: (b) our teeth and an elephant’s tusks.

Ques 3: In evolutionary terms, we have more in common with

1. A Chinese school-boy.
2. A chimpanzee.
3. A spider.
4. A bacterium.

Ques 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?

Answer: This information is not sufficient. For considering a trait as dominant or recessive , we need data of at least three generation. This data is about only two generations.

Ques 5: How are the areas of study – evolution and classification – interlinked?

Answer: Classification in walls grouping of organism into formal system based on similarities in internal and external structure or evolutionary history.

Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have more recent ancestors. For example, in a family, a brother ancestor is closely related, and they have a recent common ancestor that is, the parents. Brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor that is the grandparents in the second generation whereas the parents were from the fourth generation.

With subsequent generations, the variations me organisms more different than their ancestors.

This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.

Ques 6: Explain the terms analogous and homologous organs with examples.

Homologous Organs are those organs which have the same basic structural design and origin but have different functions.

For example: the four limbs of humans in the wings of bird look like different externally but there is skeletal structure is similar.

Analogous organs are those organs which have the different basic structural design and origin but have similar functions.

For example: the wings of birds and insects.

Ques 7: Outline a project which aims to find the dominant coat colour in dogs.

Answer: Dogs have a variety of genes that govern coat colour. There are at least 11 identified genes (A, B, C, D, E, F, G, M, P, S, T) That influence coat colour in a dog.

A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the beast series, a dog can be genetically black or brown.

Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown(bb).

In this case, all the, off-springs will be Heterozygous (BB). Since black is dominant(B), all the, off-springs will be black. However, they will have both B and b alleles.

If such heterozygous pubs are crossed, they will produce 25% how much I got black (BB), 50% heterozygous black (Bb)and 25% homozygous brown(bb) off-springs.

Ques 8: Explain the importance of fossils in deciding evolutionary relationships.

The organisms that lived long ago such as the time period during which they live, the structure etc.

An evolutionary development of species i.e., line of their development.

Connecting link between two groups. For example, feathers present in some dinosaurs means that both are very closely related to reptiles.

Which organism it was earlier in which later.

Development of complex body designs from the simple body design.

Ques 9: What evidence do we have for the origin of life from inanimate matter?

Answer: The evidence for the origin of life from in animate the matter was provided through an experiment, conducted in 1953, by Stanley L Miller and Harold C. Urey. In experiment, they assembled in at most fair containing molecule is like ammonia, methane and hydrogen sulphide, but no oxygen, over water. This was similar to atmosphere that thought to exist on only early earth. This was maintained at a temperature just below 100 degree Celsius and sparks were passed through the mixture of gases to stimulate lightning. At the end of the week, 15% of the carbon from Methane, had been converted to simple compounds of carbon including amino acids which make up protein molecules in support the life in basic form. This, amply suggesting that life arose afresh on earth.

Ques 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?

Answer: Sexual reproduction cause more viable variations due to the following reasons:

• Error in coping of DNA, which are not highly significant.
• Exchange of genetic material between homologous chromosomes during formation of gametes.
• Random segregation of paternal and maternal chromosome at the time of gamete formation.
• Accumulation of variations awkward due to sexual reproduction over generation after generation and selection by nature created wide diversity.

In case of asexual reproduction, only the very small changes due to inaccuracies in DNA a copying pass on the progeny. Does, off-springs of asexual reproduction or more or less genetically similar to their parents. So, it can be conducted that evolution in sexually reproducing organisms proceed at a faster pace than in asexually reproducing organisms.

Ques 11: How is the equal genetic contribution of male and female parents ensured in the progeny?

Answer: In human beings, equal genetic contribution of male and female parents is ensured in the progeny through inheritance of equal number of chromosomes from both parents. There are 23 pairs of chromosomes all human chromosomes are not paired. Out of these 23 pairs, the first 22 pair is known as autosomes in the remaining one pair is known as sex chromosomes represented as X and Y. Females have a perfect pair of two X sex chromosomes and males have a mismatched pair of one X and one Y sex chromosomes.

During the course of reproduction, as fertilisation process takes place, the male gamete (haploid) fuses with the female gamete (haploid) resulting in formation of diploid zygote. The zygote in the progeny receive an equal contribution of genetic material from the parents. Out of 23 pairs of chromosomes in progeny, male parent contributes 22 autosomes and one X or Y, chromosome and female parents contribute 22 autosomes and one X chromosome.

Ques 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?

Answer: We agree with the statement that only variations that confer an advantage to an individual organism will survive in a population. All the variation does not have an equal chance of surviving in the environment in which they find themselves. The chances of surviving depend on the nature of variations. Different individuals would have different kind of advantages. Bacteria that can withstand heat will survive better in a heatwave. Selection of variance by environmental factors from the basis of revolutionary process.

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### NCERT Solutions For Class 10 Science

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