NCERT Solutions Class 10 Science
The NCERT Solutions in English Language for Class 10 Science Chapter – 9 (Heredity and Evolution) have been provided here to help the students solve the questions from this exercise.
Chapter – 9 (Heredity and Evolution)
Questions
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 species, which trait is likely to have arisen earlier ?
Answer – Trait B is more probable to arise early as this trait has already been existing and replicating in a larger percentage of the population as compared to trait A.
2. How does creation of variations in a species promote survival ?
Answer – Genetic variations enable the species to better adapt to changes in its environment. Moreover, it is an important force in evolution as it allows the frequency of alleles to increase or decrease through natural selection. These variations will determine the difference between extinction or continuation of the species.
Questions
1. How do Mendel’s experiments show that traits may he dominant or recessive ?
Answer – In Monohybrid cross of Mendel between tall and dwarf pea plant, all progeny in F1 generation are tall and in F2 generation, 75% of pea plants are tall but 25% are dwarf. This shows that traits are dominant or recessive.
2. How do Mendel’s experiments show that traits are inherited independently ?
Answer – When a pea plant having round green seeds is crossed with a pea plant having wrinkled yellow seeds in F1 generation all the plants have round yellow seeds. But in F2 generation two new traits that is round yellow and wrinkled green appear. This shows that traits are inherited independently.
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, the information is not enough because the blood group is determined by a pair of gene. One inherited from mother and other from father. In this case, the child inherited gene for O blood group from mother as well as father.
4. How is the sex of the child determined in human beings ?
Answer – A child which inherits X chromosome from her father will be a girl and one who inherits Y chromosome from him will be a boy.
Questions
1. What are the different ways in which individuals with a particular trait may increase in a population ?
Answer – Individuals with a particular trait may increase in a population as a result of the following:
(i) Natural selection: When that trait offers some survival advantage.
(ii) Genetic drift: When some genes governing that trait become common in a population.
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 (somatic cells) which cannot be passed on to germ cells or the progeny. Therefore, these traits cannot be inherited.
3. Why are the small number of surviving tigers a cause of worry from the point of view of genetics ?
Answer – Small numbers of tigers means that fewer variations in terms of genes are available. This means that when these tigers reproduce, there are less chances of producing progeny with some useful variations. Hence, it is a cause of worry from the point of view of genetics.
Questions
1. What factors could lead to the rise of a new species ?
Answer – Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.
2. Will geographical isolation be a major factor in the spéciation of a self pollinating plant species ? Why or why not ?
Answer – Geographical isolation can prevent the transfer of pollens among different plants. However, since the plants are self-pollinating, which means that the pollens are transferred 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 this case.
3. Will geographical isolation be a major factor in the spéciation of an organism that reproduces asexually ? Why or why not ?
Answer – Geographical isolation prevents gene flow between populations of a species whereas asexual reproduction generally involves only one individual. In an asexually reproducing organism, variations can occur only when the copying of DNA is not accurate. Therefore, geographical isolation cannot prevent the formation of new species in an asexually reproducing organism.
Questions
1. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer – The presence of feathers in dinosaurs and birds indicates that they are evolutionarily related. Dinosaurs had feathers not for flying but instead these feathers provided insulation to these warm-blooded animals. However, the feathers in birds are used for flight. This proves that reptiles and birds are closely related and that the evolution of wings started in reptiles.
2. Can the wing of a butterfly and the wing of a bat be considered homologous ? Why or why not ?
Answer – The wing 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.
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 represent the ancestors of plants and animals that are alive today. They provide evidences of evolution by revealing the characteristics of the past organism and the changes that have occurred in these organisms to give rise to the present organisms.
Questions
1. Why are human being who look so different from each other in terms of size, colour and looks said to belong to same species ?
Answer – A species is a group of organisms that are capable of interbreeding to produce a fertile offspring. Skin colour, looks, and size are all variety of features present in human beings. These features are genetic but also environmentally controlled. Various human races are formed based on these features. All human races have more than enough similarities to be classified as same species. Therefore, all human beings are a single species as humans of different colour, size, and looks are capable of reproduction and can produce a fertile offspring.
2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzee have a better body design ? Why or why not ?
Answer – Evolution cannot always be equated with progress or better body designs. Evolution simply creates more complex body designs. However, this does not mean that the simple body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms found on earth. They can survive hot springs, deep sea, and even freezing environment.
Therefore, bacteria, spiders, fish, and chimpanzees are all different branches of evolution.
Exercises
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 genetic make up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw.
Answer – (c) TtWW.
2. An example of homologous organ is
(a) Our arm and a dog’s fore leg
(b) Our teeth and elephant tusks
(c) Potato and runners of grass
(d) All the above.
Answer – (d) All the above.
3. In evolutionary terms we have more in common with
(a) A Chinese school boy
(b) A chimpanzee
(c) A spider
(d) A bacterium.
Answer – (a) A Chinese school boy.
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 is dominant or recessive ? Why or why not ?
Answer – Knowledge of at least 3 generations is required to find if an attribute is dominant or recessive. Hence, it is not possible to identify if the given trait is dominant or recessive.
5. How are the two areas of study, evolution and classification, interlinked ?
Answer – Classification is based on similarities and differences amongst organisms. The more characteristics two species have in common, the more closely related they are. They must have evolved from a common ancestor. Similarly more differences mean different adaptations and divergence from common ancestor in the remote past.
6. Explain the terms analogous and homologous organs with examples.
Answer –
Analogous Organs – They are organs which have similar appearance and function but are quite different in their origin, development and anatomy.
Examples: Wings of Butterfly (integumentary outgrowths) and bird (modified fore-limbs).
Homologous Organs – They are organs which have similar origin, similar development and similar internal structure but have different forms and functions.
Examples: Fore-limbs of Horse, human hand, flipper of whale, wing of bird or bat.
7. Outline a project which aims to find the dominant coat colour in dogs.
Answer – Dogs have a certain set of genes that govern coat colour. There are a minimum of eleven known sequence series (A, B, C, D, E, F, G, M, P, S, T) that influence the colour of a dog. A dog inherits one copy from each of its parents. As an example, within the B series, a dog is genetically black or brown. Assume that one parent is homozygous black (BB), whereas the other parent is homozygous brown (bb).
| bb | BB | ||
| B | B | ||
| b | Bb | Bb | |
| b | Bb | Bb | |
In this case, all the offspring are going to be heterozygous (Bb).
Since black (B) is dominant, all the offspring are going to be black. However, they are going to have each B and b alleles. If such heterozygous pups are crossed, they are going to produce 25 homozygous blacks (BB), 15 heterozygous black (Bb), and 25 homozygous brown (bb) offspring.
| B | b | |
| B | BB | Bb |
| b | Bb | Bb |
8. Explain the importance of fossils in deciding evolutionary relationships.
Answer – Fossils give evidence about:
(a) The organism and their paleobiology
(b) Even the behaviour of an organism can be deduced to some extent (for example, palaeontologists) have unearthed a site with more than 10,000 skeletons of a dinosaur called Hadrosaurus. This implies that the dinosaur lived in herds.
(c) Fossils also provide insight into the evolutionary history of animals and plants (for instance, palaeontologists have discovered that whales had evolved from goat-sized land-dwelling animals called Pakicetus).
9. What evidence do we have for the origin of life from inanimate matter ?
Answer – Miller and Urey (1953) assembled an apparatus which had a spark chamber (for producing lightning), a flask for boiling and a condenser. They introduced a mixture of methane, ammonia, hydrogen and water into the apparatus. The gaseous mixture was exposed to electric discharges, boiling (800°C) and condensation with the temperature kept just below 100°C. The experiment was continued for a few days. At the end of one week, 15% of carbon (from methane) had been converted into simple organic compounds of amino acids, organic acids, sugars and nitrogen bases. It clearly proved that organic compounds or building blocks of life developed from inanimate matter in the remote past when the hot earth was cooling.
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 reproducing organism?
Answer – Variations arise either because of errors in DNA copying or as a result of sexual reproduction. Due to sexual reproduction genetic variability increases in the population from one generation to another. This happens due to the fact that sexually reproducing organism inherits half the genes from each parent. These variations are very important for the process of evolution.
11. How is equal genetic contribution of male and female parents ensured in the progeny ?
Answer – Equal contribution of male and female parents is ensured in progeny during sexual reproduction. Each trait of progeny is determined by a pair of alleles and gametes of male and female contain one allele. Each allele pairs during fertilisation combine together to determine traits. Thus, the traits of progeny are determined by equal genes from male and female.
12. Only variations that confer an advantage to an individual will survive in a population. Do you agree with this statement ? Why or why not ?
Answer – No. Alongwith advantageous variations, a number of indifferent variations remain in the populations. Only the disadvantageous variations which are either lethal or extremely harmful are eliminated. All other variations persist in the population. Many of them function as preadaptations.
