Friday, 29 November 2013

CBSE Class 10th Science | Chapter 9 : Heredity and Evolution | Solved Exercises

Solved Exercises | Chapter 9 : Heredity and Evolution | CBSE Class 10th Science

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 the genetic make-up of the tall parent can be depicted as
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw

Answer. (d) TtWw



Question 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.

Answer. (d) all of 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 trait is dominant or recessive? Why or why not?

Answer. As per the findings of study, children and parents both have the light-coloured eyes as the common trait, we can say light eye colour trait is dominant because only dominant traits from parents are inherited by the children in the first generation

Question 5. How are the areas of study – evolution and classification – interlinked?

Answer. . Every species or organisms has inbuilt tendency for genetic variation which plays an important role in the origin of new species and forms the the basis for evolution. Organisms appear to be same because of similarity in their inherited body designs.The more characteristics two species have in common, the more closely they are related. And they are likely to have a a common ancestor more recently. Classification of organisms necessarily involves, organizing them in different groups, based on the similarities and differences of characteristics. Classifying organisms helps us in recognizing the basic arrangement of a hierarchical structure among diverse species. It tells us about the resemblances and relationships between various organisms thus facilitating studies or research of wide variety associated with organisms effortlessly. In fact, classification of species is a reflection of their evolutionary relationship. Thus, we can say, the areas of study – evolution and classification – interlinked

Question 6. Explain the terms analogous and homologous organs with examples.

Answer.Analogous organs: The organs having the same functions but different in structure, origin and constituting parts are called analogous organs. For example, the wings of bats and the wings of birds are analogous organs as Their origins, designs , structure and components, are different, but they have a common use for flying
Homologous organs : The organs having the same structure, origin and constituting parts but different functions are called homologous organs. the forearms of a horse and the hands of human.

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

Answer. Select a homozygous black (BB) male dog and a homozygous white (bb) female dog. Allow them to mate and produce offspring (F1 generation). If all of the F1 offspring are black, we can conclude that black coat cover is dominant than white coat in the dog.



Question 8. Explain the importance of fossils in deciding evolutionary relationships.

Answer. Fossils are the remains or preserved traces of dead plants or animals, which died millions of years ago and some of them are already extinct. The remains or impressions of body part, sometime can be found between different layers of earth under its surface. The study of fossils have helped us to know about the evolution or 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 9. What evidence do we have for the origin of life from inanimate matter?

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

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?

Answer. Sexual reproduction gives rise to more viable variation than asexual reproduction. It is because there is an inbuilt tendency to variation during reproduction, both because of errors in DNA copying, and modes of sexual reproduction. The genes of the traits or characteristics are transmitted from one generation to the next generation and dominant characters are expressed. While in asexual reproduction, gene cannot be separated from the parent organism. The resulting variation in traits out of sexual reproduction not only help in survival of species but also support diversity in long run. Drift in genetic traits get accumulated spanning across generations, this gives rise to formation of new species


Question 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 pairs are known as autosomes and 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 chromosome.
During the course of reproduction, as fertilization process takes place, the male gamete (haploid) fuses with the female gamete(haploid) resulting in formation of the 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 parent contributes 22 autosomes and one X chromosome

Question 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 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 individual would have different kind of advantages. A bacteria that can withstand heat will survive better in a heat wave. Selection of variants by environmental factors forms the basis for revolutionary process.

Intext Questions| Page:143 | Chapter 9 : Heredity and Evolution | CBSE Class 10th Science

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 population, which trait is likely to have arisen earlier?

Answer. Trait B is likely to have arisen earlier. In asexual reproduction, cell divisions results in creation of similar cells with identical copies of DNA. There for, in such species, a trait may come into existence in some members due to sudden mutation induced by the environmental factors. This newly induced trait in some members of species is then inherited by future generations of such organism on replication over a period of time. This is but natural for trait B to exist earlier than trait A, as 60 % of population with trait B likely to have been replicating that trait for a longer period than 10 % of population with trait A

Question 2. How does the creation of variations in a species promote survival?

Answer. All the variations in the species do not have equal chances of survival in the environment. The survival of the variations depends upon the nature of variation. Different individuals have different chances. Selection of variants by environmental factors forms the basis for evolutionary processes.These variations may lead to increased survival advantages of the individuals due to positive adoption of traits or may merely contribute to the genetic drift

Intext Questions | Page : 147 | Chapter 9 : Heredity and Evolution | CBSE Class 10th Science

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

Answer. Mendel took pea plants with different characteristics – a tall plant and a short plant, produced progeny from them, and calculated the percentages of tall or short progeny. there were no halfway characteristics in this first generation, or F1 progeny – no ‘medium-height’ plants. All plants were tall. This meant that only one of the parental traits was seen, not some mixture of the two. He carried his experiment further by getting both the parental plants and these F1 tall plants to reproduce by self-pollination The progeny of the parental plants are, of course, all tall. However, the second-generation, or F2, progeny of the F1 tall plants are not all tall. Instead, one quarter of them are short. This indicates that both the tallness and shortness traits were inherited in the F1 plants, but only the tallness trait, which was dominant, was expressed while shortness, which was recessive trait, remained dormant in F1
Mendel’s first law of inheritance states that when a pair of contrasting factors is brought in a hybrid, one factor masks or inhibits the appearance of the other. The one which inhibits is the dominant one and which is inhibited is recessive

Question 2. How do Mendel’s experiments show that traits are inherited independently?

Answer. Mendel performed an experiments in which he took a tall plant with round seeds and a short plant with wrinkled-seeds. In F1, They were all tall and had round seeds. Tallness and round seeds were thus dominant traits. When, he used these F1 progeny to generate F2 progeny by self-pollination, he found that some F2 progeny were tall plants with round seeds, and some were short plants with wrinkled seeds. At the same time there tall plants, but had wrinkled seeds, while others were short, but had round seeds. Thus, Mendel’s experiments show that the tall/short trait and the round seed/wrinkled seed trait are independently inherited.

Question 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. The give information is not enough to tell us which of the traits – blood group A or O – is dominant. In blood heredity, blood Type A is always dominant and blood Type O is always recessive.
Here, father’s Blood group can be AA (homozygous) or AO (heterozygous) genotypically, where as that of mother can be OA or OO. For daughter to be born with blood group O, she must receive O type gene one each from father and mother. For this father must have heterozygous AO blood group and mother must have homozygous blood group OO.

Question 4. How is the sex of the child determined in human beings?

Answer. In human body, there are 23 pairs of chromosomes in the cell. Out of these, 22 pairs have a maternal and a paternal copy of genes, but do not take part in sex-determination in human being. The 23rd pair, which is not always a perfect pair, is called sex chromosomes. Women have a perfect pair of sex chromosomes XX. But men have a mismatched pair of chromosomes in the form XY. This cell is divided meiotically in both men and women to form gametes. All children will inherit an X chromosome from their mother regardless of whether they are boys or girls and an X or Y chromosomes from their father. Thus, the sex of the children will be determined by what they inherit from their father. A child who inherits an X chromosome from her father will be a girl, and one who inherits a Y chromosome from him will be a boy.

Intext Questions| Page : 150 | Chapter 9 : Heredity and Evolution | CBSE Class 10th Science

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

Answer. The different ways in which individuals with a particular trait may increase in a population, are :
(i) By natural selection - Organisms with a particular trait may be naturally selected because it provided a survival advantage. That particular trait may thus increase in the population. It may direct evolution of species population by adaptations to fit their environment better.
(ii) Genetic drift & inheritance - An accident in small populations may result in surviving of organisms with a particular variant only. This can increase the frequency of some genes in that population, even if they give no survival advantage. This is the notion of genetic drift, which provides diversity without any adaptations.

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

Answer.The germ cells of sexually reproducing populations are made in specialized reproductive tissue. Change in non-reproductive tissues, on account of acquired traits, cannot be passed on to the DNA of the germ cells. Therefore, experience gained or traits acquired during the life-time of an individual not inherited. For example, Offspring of an hockey player may not be a hockey player.

Question 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 surviving tigers is the cause of worry from the point of view of genetics because Genetics is the science of heredity and variations which support the evolutionary survival of a species. The size of its population, plays a dominant role for its evolutionary expansion. For a small population of tigers, diversity of traits will be adversely affected. Small population of tiger may indulge in inbreeding, which will further result in decrease in population due to untimely deaths caused by the genetic deformities. In the event of a disease or natural disaster possibility of survival against numbers will be greatly reduced. Not only this, Tiger forms an integral part of food chain in Eco-system. Its role as predator, in animal kingdom, helps in checking the population growth of animals in down food chain. The pretense of tiger, ensures an healthy and balanced Eco-system with all inherent diversity in other species. Small number of surviving tiger will affect the diversity negatively and will result in an ecological imbalance.

Intext Questions| Page : 151 |Chapter 9 : Heredity and Evolution | CBSE Class 10th Science

Question 1.  What factors could lead to the rise of a new species?

Answer. factors, what could lead to the rise of a new species are as follow :
(i) Natural selection.
(ii) Process of genetic drift
(iii) Genetic Mutation
(iv) Geographical isolation.
(v) Environmental factors on the isolated populations.
(vi) Reproductive isolation for a long time.
(vii) Quantum of genetic variant inherited from one generation to the next.

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

Answer. No. geographical isolation will not be a major factor in the speciation of a self-pollinating plant species because new gene variants will not be introduced in the population and there will be no evolution of a new species. On the other hand, in cross pollinated species, when geographical isolation is there, accumulation of variations in traits will take place.

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

Answer. No, in asexually reproducing organisms there is very little variation over generations. Asexual reproduction does not require two organisms to reproduce as variations in the DNA are not enough to raise a new species. Thus geographical isolation is not a major factor As asexual reproduction is carried out within the same organism, resulting organism in next generation will have identical copies of DNA, so there will be very less genetic variant to be a cause of the speciation of an organism. Geographical isolation can become a major contributory factor if is increases chances for a change to develop in gene flow (Genetic drift), leading to formation of a new species.

Intext Questions| Page : 156 |Chapter 9 : Heredity and Evolution | CBSE Class 10th Science

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

Answer. Different organisms with common ancestry in the past, are more likely to have similar characteristics due to inheritance. These similar characteristics are used to determine evolutionary relationships. Basic structure of Forelimbs in human and birds is one such example of a characteristic which shows closeness of two species in evolutionary terms. The forelimbs in both the species, have similar bones structure and similar origin, but, over period of time, spanning generations, they have been developed to perform different suitable functions as per the need. Such organs that have similar basic structure but perform different functions are called homologous organs. These are used to find out evolutionary relationships.

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

Answer.No, the wing of a butterfly and the wing of a bat can not be considered homologous organs because they both perform the same function of flying but their origin and structure is not similar. The bird's wing has well developed bone structure supported with flesh and feathers whereas insect's wing has evolved from hardening of membrane cover with a few associated muscles. Homologous organs have similar basic structure but perform different functions, where as analogous organs have different origin and structure but perform same functions.

Question 3. What are fossils? What do they tell us about the process of evolution?

Answer. The preserved remains or traces of dead plants and animals that lived in the geological past and were buried under the rocks millions of years ago are called fossils. Fossils tells us about the process of evolution. Fossils gives an idea about the structure of organisms and corresponding period of their existence in the past. Fossils found under different strata of earth across different geological locations, provide evidence of evolutionary relationship among existing and extinct species of organism. They give us clues about extinct species of organisms and reasons behind their disappearance from earth due to different conditions of climatic change in the past.

Intext Questions| Page : 158 |Chapter 9 : Heredity and Evolution | CBSE Class 10th Science

Question 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.The human beings are different from each other in terms of size, colour but are said to belong to the same species. This is because, despite of great diversity of human forms and features in different human races across the planet, the genetic footprints of all human beings can be traced back to same common ancestry of African roots. All humans are a single species and have originated from Homo sapiens, who were the earliest members of the human species in Africa. As there have been no well set geographical or reproductive isolation among different members of human species, this has lead to numerous genetic makeups of traits with slight variation.

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

Answer. In evolutionary terms, we can not say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design.The notion of Better body design among different species is not justifiable. Because evolutionary process takes into account the development of most efficient and suitable features in body designs of organisms for survival and adaptation favoring to a particular niche. For example, organisms with Complex and seemingly better body design, may not survive particular situation. Where as, organisms like bacteria with its primitive body design and simple microbial life form may survive in the most inhospitable and extreme environmental conditions that are extraordinarily hot, cold or acidic. Bacterial microbes can be found everywhere — deep under polar ice, in deserts, around volcanic eruption on earth surface or thermal vents under deep sea or over earth surface, or even in outer space.


Multiple Choice Questions  | Chapter 9 : Heredity and Evolution | CBSE Class 10th Science

Question 1. Which of these is an example of an acquired trait ?
(a). Dark skin
(b). Strong muscles
(c). Free ear lobe
(d). Brown hair

Answer : (b). Strong muscles

Question 2. which of these shows a pair of analogous organs
(a). Wings of bee and bats
(b). Wings of cockroach and bats
(c). wings of birds and bats
(d). All of the above

Answer : (d). All of the above

Question 3. Which of these plants were selected by Gregor John Mendel for his experiments ?
(a). Flax
(b). Mustard
(c). Garden Pea (Pisum sativum)
(d). Wheat

Answer : (c). Garden Pea (Pisum sativum)

Question 4. In human beings , out of 23 pairs of chromosomes, how many are perfect pair (autosomes) ?
(a). 16 pairs of chromosomes
(b). 18 pairs of chromosomes
(c). 20 pairs of chromosomes
(d). 22 pairs of chromosomes

Answer : (d). 22 pairs of chromosomes

Question 5. Who is called the father of Genetics ?
(a). Charles Darwin
(b). Gregos Johann Mendel
(c). Lamarck
(d). Watson

Answer : (b). Gregos Johann Mendel

Question 6. In human somatic cell, how many pairs of sex chromosomes do exist there ?
(a). 1 pair
(b). 2 pairs
(c). 3 pairs
(d). 4 pairs

Answer : (a). 1 pair

Question 7. During mono hybrid cross; what was the ratio of true tall plants to hybrid tall plants, in the F2 generation ?
(a). 1:1
(b). 3:1
(c). 1:4
(d). 1:3

Answer : (b). 3:1

Question 8. In somatic cell of human body, which numbered pair of chromosomes, is called sex chromosomes ?
(a). 3rd pair
(b). 13th pair
(c). 23rd pair
(d). 1st pair

Answer : (c). 23rd pair

Question 9. Which of these show correct phenotype ration in F2 generation during hybrid cross ?
(a). 3:2:2:1
(b). 8:4:4:1
(c). 9:3:3:1
(d). 4:3:3:1

Answer : (c). 9:3:3:1

Question 10. Which sex chromosomes type, do all children inherit from their mother ?
(a). X chromosome
(b). Y chromosome
(c). X or Y chromosome
(d). XX chromosomes

Answer : (a). x chromosome

Question 11. How many chromosomes are there in human somatic cell ?
(a). 12
(b). 23
(c). 32
(d). 46

Answer : (d). 46

Question 12. Which sex chromosomes type, can all children inherit from their father
(a). X chromosome
(b). Y chromosome
(c). xy chromosomes
(d). X or Y chromosome

Answer : X or Y chromosome

Question 13. Which is the key feature for the members of a particular species ?
(a). Similar appearance
(b). Ability to interbreed
(c). Almost identical genotype
(d). Similar size

Answer : (b). Ability to interbreed

Question 14. In human beings, the sex of the child depends on
(a). Maternal chromosome
(b). Paternal chromosome
(c). Both Maternal & Paternal chromosome
(d). None

Answer : (b). Paternal chromosome

Question 15. which of these shows a pair of homologous organs ?
(a). Wings of cockroach and birds
(b). Wing of birds and bats
(c). Wings of cockroach and bats
(d). Forelimbs of human and birds

Answer : (c). Forelimbs of human and birds

Question 16. For sex of a child, to be a girl, the right pairs of sex chromosomes will be
(a). XX
(b). XY
(c). YY
(d). None

Answer : (a). XX

Question 17. Which of the organisms given below, has very simple ‘eyes’ that are just eye-spots which detect light ?
(a). Hydra
(b). Planaria
(c). Tapeworm
(d). Earthworm

Answer : (b). Planaria

Question 18. For sex of a child, to be a boy, the right pairs of sex chromosomes will be
(a). XX
(b). XY
(c). YY
(d). None

Answer : (b). XY

Question 19. The ancestry of all human beings can be traced back to which continent ?
(a). Asia
(b). Europe
(c). Africa
(d). Australia

Answer : (c). Africa

Question 20. Evolution among different species should not be equated with
(a). Better Body design
(b). Size of body
(c). Complexity of organism
(d). All of above

Answer : (d). All of above


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