GetStudySolution

Getstudysolution is an online educational platform that allows students to access quality educational services and study materials at no cost.

NCERT Solutions for class 10 Science chapter 9 – Heredity and Evolution

Back Exercise

Question 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.

Question 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.

Question 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.

Question 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 for finding if an attribute is dominant or recessive. Hence, it is not possible to identify if the given trait is dominant or recessive.

Question 5.
How are the two areas of study, evolution and classification, interlinked ? (CBSE A.I. 2016)
Answer:
Organisms are classified into various groups on the basis of similarities and dissimilarities they share amongst each other. The more characteristics two species have in common, more closely they are related to each other. The closeness of two species indicates a common ancestor between them. Thus, classification of species is a reflection of their evolutionary relationship.

Question 6.
Explain the terms analogous and homologous organs with examples. (CBSE A.I. 2008 C)
Answer:
Analogous Organs: Analogous organs are those organs that have a different structural design as well as origin, however perform similar functions.
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.

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

Question 8.
Explain the importance of fossils in deciding evolutionary relationships.
Answer:
Fossil provide us evidence about
→ The organisms that lived long ago such as the time period during which they lived, their structure etc.
→ Evolutionary development of species i.e., line of their development.
→ Connecting links between two groups. For example, feathers present in some dinosaurs means that birds are very closely related to reptiles.
→ Which organisms evolved earlier and which later.
→ Development of complex body designs from the simple body designs.

Question 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.

Question 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:
Sexual reproduction causes more viable variations due to the following reasons:
→ Error in copying of DNA, which are not highly significant.
→ Random seggregation of paternal and maternal chromosome at the time of gamete formation.
→ Exchange of genetic material between homologous chromosomes during formation of gametes.
→ Accumulation of variations occured 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 copying pass on the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually repoducing organisms.

Question 11.
How is equal genetic contribution of male and female parents ensured in the progeny ?
Answer:
Equal genetic contribution of male and female parents is ensured in progeny through the inheritance of equal numbers of chromosomes from both parents. There are 23 pairs of chromosomes but not all is paired. The 22 pairs are called autosomes while the remaining 1 pair is called the sex chromosomes (represented as X and Y.) Females have two sets of X-chromosomes while males have 1 X-chromosome and 1 Y-chromosome. During the process of reproduction, fertilization takes place, where the male gamete fuses with the female gamete and it results in the formation of a diploid zygote. Furthermore, the zygote receives an equal contribution of genetic material from both parents. The male contributes 22 autosomes plus, 1 X or Y chromosomes. The female contributes 22 autosomes, plus 1 X-chromosome.

Question 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:
The statement holds true – only variations provide an advantage to individual organisms that will survive in a population. For example, variations that lead to the increase in heat-resistance in bacteria is very useful for survival if it finds itself in an environment where there is a sudden increase in ambient temperature. This will determine the difference between life and death for the bacteria

In-Text Questions

Question 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:
In asexually reproducing population, there is no reshuffling of traits. New traits do develop due to small inaccuracies produced during DNA copying. They will be in smaller proportion than the traits already present. Therefore, trait B which exists in 60% of population must have arisen earlier than the trait A which occurs in 10% of the population.

Question 2.
How does creation of variations in a species promote survival ?
Answer:
A number of different types of variations develop in a population. All of them do not have survival value. However, some of them are variations which can be beneficial under certain environmental conditions. For example, in a heat wave most of the bacteria will die but a few having variation to tolerate heat wave will survive and multiply. Genetic variations enable the species to better adapt to changes in its environment.

Question 3.
How do Mendel’s experiments show that traits may he dominant or recessive ?
(CCE 2012, CBSE Delhi 2016, 2017)
Answer:
Mendel showed that the traits can either be dominant or recessive through his experiments that focused on mono-hybrid cross. The experiment involved him crossing tall (TT) pea plants with dwarf (tt) pea plants. The resultant plants which formed after fertilization represented the F1 generation. All the F1 plants were tall. Mendel then proceeded to self-pollinate the F1 generation plants and the result was that 1/4th of the plants obtained in the F2 generation were dwarfs. From this experiment, Mendel concluded that the F1 tall plants were not true-breeding, instead they carried the traits for both tall and dwarf heights. A portion of the plants were tall due to the fact that the traits for tallness were dominant over the traits for dwarfness. This cements the notion that traits can either be dominant or recessive.

Question 4.
How do Mendel’s experiments show that traits are inherited independently ? (CCE 2012, CBSE A.I. 2016, Delhi 17)
Answer:
Independent inheritance of traits is proved by employing dihybrid crosses and obtaining dihybrid ratios. Mendel crossed pure breeding tall plants having round seeds (TTRR) with pure breeding short plants having wrinkled seeds (ttrr). The plants of F₁ generation were all tall and with rounded seeds (TtRr) indicating that the characteristics of tallness and round seededness were dominant. Self breeding of F₁ yielded plants in the ratio of 9 tall round seeded, 3 tall wrinkled seeded, 3 short round seeded and one short wrinkled seeded. Tall wrinkled seeded and short round seeded plants are new combinations which can develop only if the traits are inherited independently. If the two traits are considered individually, F₂ ratio would be same as for monohybrid crosses, i.e., 12 tall : 4 short, 12 round seeded : 4 wripkled seeded.

TR, Tr, rR, tr x TR, Tr, rR, tr Gametes 9 tall rounded : 3 tall wrinkled : 3 short rounded : 1 short wrinkled

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 ?
Answer:
No. The information is not enough to tell whether the trait of the blood group A (I^A) or blood group
0(I⁰) is dominant. Either can be possible. Each individual carries two alleles. A recessive trait appears only when the two alleles are similar.
Possibility I: Blood Group A is Dominant and O Recessive. The trait of blood group O can appear only when both the recessive alleles occur together as in mother and daughter (I⁰I⁰). A group father should carry both the alleles of A and O (I^AI⁰).
Possibility 2: Blood Group O is Dominant and A Recessive. In this case the father should carry the alleles of A(I^AI^A) while the mother can be homozygous or heterozygous (I⁰I⁰, I⁰I^A). The daughter will have one dominant alleles of 0(I⁰I^A).
As both the possibilities can occur, the given information is unable to tell whether allele for blood group A or O is dominant.

Question 6.
How is the sex of the child determined in human beings ? (CCE 2013)
Answer:
Humans hare 23 pairs of chromosomes. 22 pairs control our body features and are known as autosomes The 23rd pair is known as sex chromosomes in females, it is a perfect pair and both are X and X In males it is a mismatched pair as one is X and other is a shorter Y Males produce 2 types of gametes, Half have X chromosomes and the other half has Y chromosomes females produces similar gametes, i.e, all having only X chromosomes. When a sperm carrying X chromosomes fertilizes with the ova (X) a female child (XX) is born. When a sperm carrying Y chromosomes fertilizes with the ova (Y) a male child (XY) is born.

Question 7.
What are the different ways in which individuals with a particular trait may increase in a population ?
Answer:
There are three different ways in which individuals with a particular trait can increase in a population.

1. Survival Value (Natural Selection): The trait has survival value. It is picked up by natural selection. Through differential reproduction, it increases in population, e.g., green colour in beetles instead of red providing camouflage in bushes against being picked up by crows.
2. Genetic Drift: There is seasonal or accidental decline in population. The survivors have certain combination of traits which increase in number with the increase in population. The traits may not give any extra benefit to population.
3. Food: Individuals with particular trait may have extra abundance of food in their environment. They will naturally increase in number.

Question 8.
Why are traits acquired during the life time of an individual not inherited ?
(CCE 2011, 2012, 2013, CBSE A.I. 2017)
Answer:
Traits acquired during a life-time cannot be inherited for successive generations as the changes do not reflect in the DNA of the germ cells. For instance, a football player cannot pass on his skills to his offspring as they are limited to non-reproductive cells only.

Question 9.
Why are the small number 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 do 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 adopted to the existing environment and may extinct soon.

Question 10.
What factors could lead to the rise of a new species ? (CCE 2012, 2014, CBSE Foreign 2017)
Answer:

1. Absence of gene flow amongst sub-populations due to the presence of physical barriers, long distance, differences in habitats, environmental and climatic conditions.
2. Accumulation of different variations in the different sub-populations of the species.
3. Natural selection of particular traits in a particular environment.
4. Genetic Drift. Separation of a small population, changes in its allele frequency, new mutations and adaptations to new habitat.
5. Reproductive Isolation. Accumulation of different variations and genetic drift result in absence of interbreeding in the previous subpopulations of a species. This results in the formation of new species. e.g., Finches of Galapogos islands.

Question 11.
Will geographical isolation be a major factor in the speciation of a self pollinating plant species ? Why or why not ?
(CCE 2012)
Answer:
No, geographical isolation will not be a major factor in the speciation of self-pollinating plant species. Geographical isolation creates the separation of the population. It is because in self-pollinating species, new variants are not formed and they do not show any variation in the population. After self-pollination, homozygous line evolve. In contrast, after cross-pollination, heterozygous line evolve and it results in the variation of traits in the population.

Question 12.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Why or why not ?
(CCE 2012)
Answer:
Geographical isolation may not have any effect in case of self-pollinating or asexually reproducing plant species as they do not depend on other organisms for reproduction.

Question 13.
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
(CBSE Foreign 2017)
Answer:

1. Closeness of species is determined by presence or absence of fundamental characteristics and correlated characters. Two species of bacteria are closely related as they possess fundamental similarities of occurrence of nucleoid (instead of nucleus), absence of membrane covered cell organelles and presence of 70 S ribosomes. Human beings are close to monkeys because they possess similar eukaryotic multicellular body with vertebrate characters, mammalian traits and primate characters.
2. These days DNA matching is undertaken to find out the degree of closeness of the species.

Question 14.
Can the wing of a butterfly and the wing of a bat be considered homologous ? Why or why not ?
Answer:
No. Wings of butterfly and bat are fundamentally different in their origin and structure. In butterfly they are integumentary outgrowths having hollow tubes. In bat they are modified fore limbs which are covered by skin. Such organs which have a different origin and basic structure but are functionally similar are called analogous organs.

Question 15.
What are fossils ? What do they tell us about the process of evolution ? (CCE 2013, CBSE Foreign 2017)
Answer:
Fossils are the preserved remains of animals or plants or other organisms that died out millions of years ago. These fossils tell us about a lot of extinct animals and also give insights into how evolution might have occurred. Fossils can be used to understand how an organism would have lived and what it may have looked like. More importantly, we can correlate with fossils as well as extant organisms to understand their relationships. For instance, scientists were able to recover protein sequences from a dinosaur called the T-rex, which confirmed its avian lineage. This means birds are the extant relatives of (avian) dinosaurs. Moreover, the pattern of fossil distribution gives us an idea of the time in history when various species were formed or become extinct.

Question 16.
Why are human being who look so different from each other in terms of size, colour and looks said to belong to same species ? (CBSE A.I. 2009 C, CBSE Foreign 2017)
Answer:
Delimitation of a species is based on the presence of a common gene pool, free inbreeding and reproductive isolation. Differences in size, colour and looks are based on preponderance of specific alleles and their interactions with the environment. All human beings, despite presence of different races, belong to same species {Homo sapiens) because they share the same gene pool, can marry amongst themselves and produce fertile offspring.

Question 17.
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzee have a better body design ? Why or why not ?
Answer:
A better body design is the one which has more complexity, more elaboration and more controls which gives the organism a better competitive edge over others. There is no doubt that out of the four (bacteria, spiders, fish and chimpanzee), chimpanzee has a more elaborate body design or organisation. However, since body design is meant for competitive survival in their environment, all the four organisms or for that all living organisms, have a good body design that is suited to their environment.