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NCERT Solutions for Heredity and Evolution of Class10 Science





Question 1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exist in 60% of the same population, which trait is likely to have arisen earlier?
Solution 
Trait A is likely to have arisen earlier because traits reduce from one generation to the next generation.
Question 2.How does the creation of variations in species ensure survival?
Solution
All the variations in the species do not have equal chances of surviving in the environment. The survival the variations depends on the nature of variations. Different individuals have different chances. Selection of variants the environmental factors forms the bases for evolutions process.
Question 3.How do Mendel’s experiments show that traits may be dominant or recessive?
Solution
Mendel took pea plants having different characteristics, like a tall plant and a short plant. He produced progeny from them and calcukated the percentages of tall or short progeny. There was no halfway characteristics in the first generation. All plants were tall. his meant that only one of the parental traits was seen, not the other. here, the trait of tallness is dominant while shortness is the recessive characteristic.
Question 4.How do Mendel’s experiments show that traits are inherited independently?
Solution
Mendel performed an experiment in which he took two different traits, like tall and short plant, and round and wrinkled seeds. In 2nd (F2) generation, some plants were tall with round seeds and some were short with wrinkled seeds. There would also be short plants having round seeds. Thus, the tall/ short traits and round/ wrinkled seed traits are independently inherited.
Question 5.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?
Solution
Yes, this information is enough to tell that trait A is dominant. It is because only dominant traits are expressed from one generation to next generation.
Question 6.How is the sex of a child determined in human beings?
Solution
There are 23 pairs of chromosomes in the cell of human body. Out of these, 22 pairs do not take part in ex – determination in human beings. The 23rd pair in gonadal cell called sex chromosome which is not always a perfect pair. Women have a perfect pair having XX- chromosomes. But men have a pair having XY – chromosomes. This cell is divided meiotically in both men and women to form gametes. All children will inherit an X – chromosome from mother and an X – or Y- chromosomes from their father. Thus, the sex of children is determined by the chromosomes they inheriting from their father. A child inheriting X – chromosome from father will be a girl and one inheriting Y – chromosome from him will be a boy.

Question 7.What are the different ways in which individuals with a particular trait may increase in population?
Solution
There are following ways in which individuals with a particular trait may increase in a population:
(i) By natural selection
(ii) By inheritance

Question 8.Why are traits acquired during the lifetime of an individual not inherited?
Solution
The germ cells of sexually reproducing populations are made in specialized reproductive tissue. The acquired traits cannot change the DNA of the germ cells. Therefore, the acquired traits cannot be inherited over generations during the lifetime of an individual.
9.Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Solution Genetics is the science of heredity and variations. It explains how the traits are inherited from generation to generation. The small numbers of surviving tigers is the cause of worry from the point of view of genetics because the diversity and the traits are reduced gradually. This fact wants explanation and genetics should answer it.

Question 10.What factors could lead to the rise of a new species?
Solution Following factors could lead to the rise of a new species:
(i) Natural selection.
(ii) Processes of genetic drift.
(iii) Mutation (sudden change in genetic makeup)
(iv) Environmental factors.
(v) Local factors.
(vi) The differences or variations from one generation to the next.

Question 11.Will geographical isolation be a major factor in the speciation of a self – pollinating plant species? Why or why not?
Solution
No, geographical isolation will not be a major factor in the speciation of a self – pollinating plant species. It is due to the fact that new genes do not enter in the population, so new species is not produced or formed.

Question 12.Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Solution
yes, geographical isolation is a major factor in the speciation of an organism. It is due to the fact that migrant organism will reproduce with the local population. This will result in the genes of migrant organism entering a new population. This kind of gene flow is bound to happen between populations that are partly but not completely separated.
Question 13.Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Solution
Forelimbs of human and birds show the closeness between these species. The basic structure of the limbs is similar, though it has been modified to perform different functions.
Question 14.Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Solution
the wings of the butterfly and the wing of a bat cannot be considered homologous because they have a common use for flying but their origins and structure are not common. Rather, they are analogous organs.
Question 15.What are fossils? What do they tell us about the process of evolution?
Solution
The remains of dead plants and animals which were buried under the rocks millions of years ago are called fossils. Fossils tell us about the process of evolution. The fossils of different organisms have some features similar to ine species, while some features are similar to the other species. In this way, they show the link between two species. They tell us that one species evolves from the other species.
Question 16.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?
Solution
the human beings are different from each other in terms of size, colour and looks but they are said to belong to the same species. It is due to their fundamental characteristics. The fundamental characteristics of one species are closer among these organisms than the other organisms of other species. All human have same fundamental characteristics. So they belong to the same species.
Question 17.In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a better body design? Why or why not?
Solution
Chimpanzees have a better body design because they have a well – developed body system, well – developed brain, and the thumb opposite to the finger to catch very small and minute things.
Question 18.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 traits is dominant or recessive? Why or why not?
Solution
We can say that light eye colour trait is dominant because only dominant traits are transferred from the parents to the children in the first generation.
Question 19.How are the areas of study – evolution and classification – interlinked?
Solution
Evolution and classification are interlinked with each other. Classification is the most important term to explain evolution. Classification is based on the similarities and differences between two species or among two organisms. More closer the characteristics are, the more closer is the evolution and more chances are to remain in the same group of classification/. We can appreciate that classification of species is in fact a reflection of their evolutionary relationship.
 
Question 20.Explain the terms analogous and homologous organs with example
Solution
Analogous organs The organs having the same functions but different in structure, origin and components are called analogous organs.
For example, the wings of a bat and the wings of an insect are analogous organs.
Homologous organs The organs having the same structure, origin and components but different functions are called homologous organs.
For example: the forearms of a horse and the hands of a human.

Question 21.Explain the importance of fossils in deciding evolutionary relationship.
Solution
Fossils are the remains of dead plants or animals which died millions of years ago. The study of fossils helps us to know about the evolution r the link between two species. Fossils tells us how new species are developed from the old. So fossils have an importance in deciding evolutionary relationship
Question 22.What evidence do we have for the origin of life from inanimate matter?
Solution
An experiment conducted by Stanley L. Miller and Harold C. Urey in 1953 proved that origin of life takes place from inanimate matter. They assembled the atmosphere containing NH3, CH4 and H2S but no O2 over water. This was maintained at a temperature just below 100*C and end of a week, 15% carbon from methane had been converted to simple compounds of carbon like amino acid which make up protein molecules. So life arose afresh on earth.
Question 23.Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce asexually?
Solution
Sexual reproduction gives rise to more viable variations than asexual. It is because the genes of the traits are transmitted from one generation to the next generation and dominant characters are expressed. While in asexual reproduction, gene cannot be separated from the parental organisms. So no more variations occur.
This cause of variation affects the evolution of those organisms that reproduce sexually. By this process, more and more variations are produced in the next generations. In this way, the genetic drift will accumulate, which causes the formation of new species.
 
Question 24.How is the equal genetic contribution of male and female parents ensured in the progeny?
Solution
There are 23 pairs of chromosomes. Most human chromosomes have material and a paternal copy. We have 22 such pairs. These pairs contain half chromosomes from mother and half from father. One pair is called sex chromosomes. At the tme of sex determination, the egg cell fuses with the sperm cell with the sperm cell which is haploid to form zygote. Zygote is diploid which contains 23 chromosomes from mother and 23 from father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.
Question 25.Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why not?
Solution
We agree with this statement that only variations that confer an advantage will survive in a population.
The entire variations do 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 kinds of advantages. Bacteria that can withstand heat will survive better in a heat wave. Selection of variants by environment factors forms the basis for evolutionary processes.
Question 26.What are traits?
Solution
The characters in individuals are called traits.
Question 27.Name the biological term used to show similarities among individuals.
Solution
Heredity.
 
Question 28.Who is known as the father of genetics?
Solution
Gergor Johann Mendel is known as the father of genetics.
Question 29.What are variations?
Solution
Variations are the occurrence of differences among individuals. For example, even two real brothers are not exactly similar to each other or even two leaves of the same plant may have some differences in size, shape etc.
Question 30.What is a sex chromosomes?
Solution
A sex chromosome is one which helps in sex- determination.
In males, the sex chromosomes are XY, and the gametes (sperm) they produce are of two types: X – bearing and Y – bearing.
In females, the sex chromosomes are XX, and the gametes (eggs) they produce are of only one type X – bearing.
Question 31.Define genetics. What is the contribution of Mendel in this branch of biology?
Solution Genetics is the study of transmission of body characteristics (both similarities and differences) from parents to offsprings, and the laws relating to such transmission.
In other words, genetics is the “science of heredity and variation”.
Mendel’s contribution: Mendel observed the occurrence of contrasting characters in various generation of garden pea (Pisum sativum). Based on his observations Mendel interpreted that these contrasting characters, (e. g. tall and dwarf plants, wrinkled and smooth seeds) are controlled by “factors”. He considered each and every character as a unit, which is controlled by a “factor”. What Mendel called “factor” – the carries of hereditary information – are now known as genes.
Question 32. 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
Solution (c) TtWW
Question 33. 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.
Solution (b) our teeth and an elephant's tusks.
Question 34. In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.
Solution (a) a Chinese school-boy.

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