NCERT Solutions for Class 10th Science
Chapter 9 – HEREDITY AND EVOLUTION
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.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 Trait B existing in 60% of the population is likely to have arisen earlier, because in case of asexually reproducing species there is a very minor variation in trait due to small inaccuracies in DNA copying. Hence trait existing in less % of population must have arisen recently.
Q.2 How does the creation of variations in a species promote survival?
Ans Variations in a species make them able to adapt to the changing environment and thus helps in their survival. Depending on the nature of variations, different individuals would have different kinds of advantages. For eg. bacteria that can withstand heat will survive better in a heat wave than non-variant bacteria having no capacity to tolerate heat. However not all variations are useful.
Q.3 How do Mendel’s experiments show that traits may be dominant or recessive?
Q.4 How do Mendel’s experiments show that traits are inherited independently?
Q.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?
Ans No, the information is not sufficient to tell which of the traits – blood group A or O – is dominant. This is because no data is given for all the progeny. Further, the gene responsible for blood group O of the daughter might be inherited from father or mother as man with blood group A can have AA (homozygous) or AO (heterozygous) as pairs. Hence the given information is not enough.
Q.6 How is the sex of the child determined in human beings?
Q.7 What are the different ways in which individuals with a particular trait may increase in a population?
Q.8 Why are traits acquired during the life-time of an individual not inherited?
Q.9 Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Q.10 What factors could lead to the rise of a new species?
Ans Factors that could lead to the rise of a new species:
1) Natural Selection – When the trait gives survival advantage.
2) Genetic Drift – Frequency of genes containing that trait become common in a population. It provides diversity without any adaptations but by chance factor alone.
3) Interbreeding – This results in flow of genes in a new population.
4) Geographical Isolation – It can occur may be due to some physical barrier etc.
Q.11 Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Q.12 Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Q.13 Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Q.14 Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Q.15 What are fossils? What do they tell us about the process of evolution?
Q.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?
Q.17 In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
EXERCISES
Q.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
Since half of the progeny were short, the genetic make-up of the tall parent has to be Tt. Further all progeny bore violet flowers, so the tall plant genetic make-up will be TtWW.
Q.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.
Homologous organs are organs which have similar origin and basic structure but they appear different and have been modified to perform different functions in various organisms.
Q.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
Q.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?
Q.5 How are the areas of study – evolution and classification – interlinked?
Q.6 Explain the terms analogous and homologous organs with examples.
Ans Analogous organs: Organs which are similar in appearance and function, but they do not have same origin and basic structure. For example, 1) wings of birds and bats 2) wings of bats and wings of insects.
Homologous organs: Organs which have similar origin and basic structure but they appear different and have been modified to perform different functions in various organisms. For example, 1) Hands of humans and forelimbs of horse have same basic structure but they appear differently. 2) Human’s teeth and an elephant’s tusks.
Q.7 Outline a project which aims to find the dominant coat colour in dogs.
Q.8 Explain the importance of fossils in deciding evolutionary relationships.
Q.9 What evidence do we have for the origin of life from inanimate matter?
Q.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?
Q.11 How is the equal genetic contribution of male and female parents ensured in the progeny?
Q.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 No. Variations occur due to the changes in frequency of certain genes (traits) in a population over generations. This is the essence of the idea of evolution. But all the variations that occur do not give survival advantage. Variations in a species that occur due to natural selection give them survival advantage. These variations make them able to adapt to the changing environment and thus helps in their survival. On the other hand variations that occur due to accidents in a small population do not give any survival advantage. This change in the frequency of some genes caused by chance factor alone is called Genetic drift, which provides diversity without any adaptations.