A abampere (aA) The unit of electric current in the CGSeniu system, defined as that current that, if flowing through two parallel conductors of negligible cross section and infinite length, placed 1 cm apart in vacuo, would produce on each conductor a force of 1 dyne per centimeter of length. 1 abampere = 1 abcoulomb/s = r statampere (where c = speed of light in cm/s) = 10 ampere. aberration Imperfect image formation due to geometric imperfections in the optical elements of a system ablation 1 . The wasting of glacier ice by any process (calving, melting, evaporation, etc.). 2. The shedding of molten material from the outer sur- face of a meteorite or tektite during its flight through the atmosphere. absolute age The age of a natural substance, of a fossil or living organism, or of an artifact, obtained by means of an absolute dating method. See absolute dating method. absolute density Density in kg/m' or, more commonly, in g/cm\ both at STP. Cf. density, relative density abso
Heredity and evolution class 10 biology ncert MCQ & SAQ
Heredity and evolution class 10 biology ncert solution
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?
Trait B because in asexual reproduction traits which are present in the previous generation are carried over to next generation with minimal variations. Trait B has a higher percentage so it is likely to have arisen earlier.
2. How does the creation of variations in a species promote survival?
Variations occur due to sexual reproduction and also due to inaccurate copying of DNA. Depending on the nature of variations, different individuals would have different kinds of advantages. For example, bacteria variants which can withstand heat have better chances to survive in a heat wave than non-variant bacteria having no capacity to tolerate heat waves. Thus, variations in a population of a species help in survival of a species.
1. How do Mendel's experiments show that traits may be dominant or recessive?
The trait which appears in all the members of F1 generation and also in 75% numbers of F2 generation obtained by self-fertilization of F1 generation is the dominant character.
The trait which does not appear in F generation but after self-fertilization of F1 generation, reappears in 25% of F2 generation is known as recessive.
2. How do Mendel's experiments show that traits are inherited independently?
Mendel crossed true breeding tall plants having round seeds with pure breeding short plants having wrinkled seeds. The plants of the F1 generation were all tall with round seeds indicating that the traits of tallness and round seeds were dominant. Self-breeding of F1 yields plants with characters 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 when the 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?
No. This information is not sufficient to determine which of the traits - blood group A or O - is dominant. This is because we do not know about the blood group of all the progeny.
Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.
4. How is the sex of the child determined in human beings?
In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY.
The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.
Type of male gametes: 22+X OR 22+ Y.
However, since the females have XX sex chromosomes, their gametes can only have X sex chromosome.
Type of female gamete: 22+X
Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.
1. What are the different ways in which individuals with a particular trait may increase in a population?
Individuals with a particular trait may increase in a population as a result of the following:
→ Natural selection: When that trait offers some survival advantage.
→ Genetic drift: When some genes governing that trait become common in a population.
→ When that trait gets acquired during the individual's lifetime.
2. Why are traits acquired during the life-time of an individual not inherited?
This happens because an acquired trait involves change in non-reproductive tissues which cannot be passed on to germ cells or the progeny. Therefore, these traits cannot be inherited.
3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
The small number of members in a population of tigers do not allow large variations to occur which are essential to the survival of the species. A deadly disease or calamity may cause the death of all tigers. The small number of tigers also indicates that existing tiger variants are not well adapted to the existing environment and may become extinct soon.
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1. What factors could lead to the rise of a new species?
Natural selection, genetic drift and acquisition of traits during the lifetime of an individual can give rise to new species.
2. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Geographical isolation can prevent the transfer of pollen 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 speciation of an organism that reproduces asexually? Why or why not?
No, because geographical isolation does not affect much in asexually reproducing organisms. Asexually reproducing organisms pass on the parent DNA to offsprings that leaves no chance of speciation. However, geographical isolation works as a major factor in cross pollinated species. As it would result in pollinated species. As it would result in accumulation of variation in the two geographically separated populations.
1. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Feathers in some ancient reptiles like dinosaurs, as fossils indicate, evolved to provide insulation in cold weather. However, they cannot fly with these feathers; later on, birds adapted the feathers to flight. This means that birds are very closely related to reptiles, since dinosaurs were reptiles.
2. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
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 functions, they are analogous organs and not homologous.
3. What are fossils? What do they tell us about the process of evolution?
Fossils are the remains of organisms that once existed on earth.
They tell us about the development of the structures from simple structured to complex structured organisms. They tell us about the phases of evolutions through which they must have undergone in order to sustain themselves in the competitive environment.
1. Why are human beings who look so different from each other in terms of size, color and looks said to belong to the same species?
A species is a group of organisms that are capable of interbreeding to produce fertile offspring. Skin color, looks, and size are all a 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 the same species. Therefore, all human beings are a single species as humans of different color, size, and looks are capable of reproduction and can produce fertile offspring.
2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a 'better' body design? Why or why not?
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 environments.
Therefore, bacteria, spiders, fish, and chimpanzees are all different branches of evolution.
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
► (c) TtWW
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.
► (b) our teeth and an elephant's tusks.
3. In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.
► (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 color trait is dominant or recessive? Why or why not?
This information is not sufficient. To consider whether a trait is dominant or recessive, we need data of at least three generations. This data is about only two generations.
5. How are the areas of study - evolution and classification - interlinked?
Classification involves grouping organisms into a formal system based on similarities in internal and external structure or evolutionary history.
Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor.
For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation.
With subsequent generations, the variations make organisms more different than their ancestors.
This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.
6. Explain the terms analogous and homologous organs with examples.
Homologous organs are those organs which have the same basic structural design and origin but have different functions.
For Example: The forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar.
Analogous organs are those organs which have the different basic structural design and origin but have similar functions.
For Example: The wings of birds and insects.
7. Outline a project which aims to find the dominant coat color in dogs.
Dogs have a variety of genes that govern coat color. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat color in dogs.
A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown.
Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb)
In this case, all the offsprings will be heterozygous (Bb).
Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles.
If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offspring.
8. Explain the importance of fossils in deciding evolutionary relationships.
Fossils provide us with 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.
9. What evidence do we have for the origin of life from inanimate matter?
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 the experiment, they assembled an atmosphere containing molecules like ammonia, methane and hydrogen sulfide, but no oxygen, over water. This was similar to the atmosphere that was thought to exist on early earth . This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gasses 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 life in basic form. Thus, amply suggesting that life arose afresh on earth.
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?
Sexual reproduction causes more viable variations due to the following reasons:
→ Error in copying of DNA, which is not highly significant.
→ Random segregation of paternal and maternal chromosomes at the time of gamete formation.
→ Exchange of genetic material between homologous chromosomes during formation of gametes.
→ Accumulation of variations occurred 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 reproducing organisms.
11. How is the equal genetic contribution of male and female parents ensured in the progeny?
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 the fertilization process takes place, the male gamete (haploid) fuses with the female gamete(haploid) resulting in the 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 the female parent contributes 22 autosomes and one X chromosome.
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?
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 individuals would have different kinds 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 a revolutionary process.
Heredity and evolution class 10 biology ncert MCQ
Question : Surgically removing tails of mice over several generations do not yield mice without tails.This proves that
a) Both a and b are correct
b) Cutting tail does not cause genetic change. So it is not inherited.
c) Acquired characters during one's own life are not inherited.
d) Neither a nor b is correct
Answer : Both a and b are correct
Question : A random change in the frequency of alleles in any population over several generations due to errors in the gametes is called
a) Genetic Drift
b) Gene flow
c) Genetic error
d) Genetic crash
Answer : Genetic Drift
Question : How life might have originated on earth was experimentally shown by
a) Urey and Miller
b) Oparin and Haldane
c) Watson and Crick
d) None of the above
Answer : Urey and Miller
Question : The theory of Natural Selection was proposed by
a) Darwin
b) Lamarck
c) Mendel
d) Haldane
Answer : Darwin
Question : The number of autosomes in a human body cell is
a) 44
b) 46
c) 22
d) 23
Answer : 44
Question : The forelimbs of frogs, lizards, birds and man have some evolutionary relationship. These are
a) Homologous organs
b) Hand relationship
c) Missing links
d) Analogous organs
Answer : Homologous organs
Question : If in human a sperm (22+Y) fertilizes an egg (22+X), the sex of the foetus shall be
a) Male
b) Female
c) Either male or Female
d) None of the answers
Answer : Male
Question : A Yellow and Round seeded pea plant has the genotype YyRr. The gametes produced shall be
a) YR, yR, Yr, yr
b) Yy, Rr
c) YR, yr
d) Y, y, R, r
Answer : YR, yR, Yr, yr
Question : If T is for tallness and t for dwarfness, what shall be the genotype of a tall pea plant according to Mendelism?
a) Either TT or Tt
b) TT
c) Tt
d) tt
Answer : Either TT or Tt
Question : The F2 phenotypic ratio of a monohybrid cross studied by Mendel is
a) 3:1
b) 1:1
c) 2:1
d) 4:1
Answer : 3:1
Question : Mendel conducted his hybridisation experiment with :-
a) Chick pea
b) Pigeon pea
c) Garden pea
d) Wild pea
Answer : C
Question : Mendel studied seven contrasting characters for his breeding experiment with Pisum sativum, which of the following character did he not use :-
a) Pod color
b) Pod shape
c) Leaf shape
d) Plant height
Answer : C
Question : The main reason for Mendel's success in discovering the principles of inheritance was :-
a) He considered each character separately
b) He was lucky not to encounter the linkage problem
c) The plant was pure breeding
d) All the above
Answer : D
Question : Mendel was lucky in the choice of the material of his experiments, among the following, which contributed to his success ?
a) He observed distinct inherited traits
b) He qualitatively analyzed his date
c) He liked pea plants
d) He considered only one character at one time
Answer : D
Question : The year 1990 AD is highly significant for genetics due to :-
a) Principle of linkage
b) Chromosome theory of heredity
c) Rediscovery of Mendelism
d) Discovery of genes
Answer : C
Question : Genotype means :-
a) Genetic composition of the individual
b) Genetic composition of the germ cell
c) Genetic composition of plastids
d) Genetic composition of an organ
Answer : A
Question : The physical manifestation of an organism's genes is its :-
a) Environment b) Phenotype c) Genetic code d) Genotype
Answer : B
Question : An organism with two identical alleles of a gene in a cell is called :-
a) Homozygous b) Dominant c) Heterozygous) Hybrid
Answer : A
Question : When an individual is having both the alleles of contrasting characters it is said to be :-
a) Heterozygous b) Dioecious c) Monoecious d) Linked genes
Answer : A
Question : When an allele fails to express itself in F1 generation in the presence of other alleles, the former is said to be :-
a) Recessive b) Codominant c) Complementary d) Epistatic
Answer : A
Question : Alleles are :-
a) Homologous chromosome
b) Chromosomes that have crossed over
c) Alternate forms of gene
d) Linked genes
Answer : C
Question : Mendel's laws apply only when :-
a) F1 in monohybrid cross shows two types of individuals
b) The characters are linked
c) Parents are pure breeding
d) First pair of contrasting characters is dependent upon other pairs
Answer : C
Question : Which of Mendel's procedures differed from those of his predecessor and contributed most of his success ?
a) He observed many characteristics of each trait
b) He observed distinct inherited traits
c) He quantitatively analyzed his data
d) He kept breeding records
Answer : C
Question : If a plant is heterozygous for tallness, the F2 generation has both tall and dwarf plants. This proves the principle of :-
a) dominance b) segregation
c) independent assortment d) incomplete dominance
Answer : B
Question : Mendel crossed a pure white flowered recessive pea plant with a dominant pure red flowered plant. The first generation of hybrids from the cross should show :-
a) 50% white flowers and 50% red flowers
b) all red flowered plants
c) 75% red flowered and 25% red flowered plants
d) all white flowered plants
Answer : B
Question : If a couple has three daughters, what are the chances that the fourth child will be a son ?
a) 100% b) 75% c) 50% d) 0%
Answer : C
Question : If a heterozygous tall plant is crossed with a homozygous dwarf plant, the proportion of dwarf progeny will :-
a) 50% b) 75% c) 100% d) 25%
Answer : A
Question : The crossing of a homozygous tall plant with a dwarf would yield F2 plants in the ratio of :-
a) two tall and two dwarf
b) one homozygous tall, one homozygous dwarf and two heterozygous tall
c) all homozygous dwarf
d) all homozygous tall
Answer : B
Question : When a true breeding tall plant is crossed with a true breeding short plant and the F1 produced is self pollinated to produce F2 ratio of true breeding tall and true breeding short plant in F2 will be :-
a) 1 : 2 b) 1 : 1 c) 2 : 1 d) 1 : 3
Answer : B
Question : Blue eye color in humans is recessive to brown eye color. The expected children of a marriage between a blue-eyed woman and a brown-eyed male who had a blue-eyed mother are likely to be :-
a) all blue-eyed b) three blue-eyed and one brown-eyed
c) all brown-eyed d) one blue-eyed and one brown-eyed
Answer : D
Question : The genotype of a dominant parent is determined by crossing it with the recessive parent. This cross is called :-
a) back cross b) test cross c) long cross d) out cross
Answer : B
Question : The results of a test cross reveal that all the offspring resemble the parent being tested. This parent must be :-
a) heterozygous b) homozygous c) recessive d) haploid
Answer : B
1. Which of the following scientists gave the principles of inheritance?
(a) Mendel
(b) Griffin
(c) Johanssen
(d) Watson and Crick
► (a) Mendel
2. Which one of the following pairs are homologous organs?
(a) Forelimbs of a bird and wings of a bat.
(b) Wings of a bird and wings of a butterfly.
(c) Pectoral fins of a fish and forelimbs of a horse.
(d) Wings of a bat and wings of a cockroach.
► (a) Forelimbs of a bird and wings of a bat.
3. Select the group which shares maximum number of common characters-
(a) two genera of two families
(b) two species of a genus
(c) two genera of a family
(d) two individuals of a species
►(d) two individuals of a species
4. A cross between a tall pea-plant (TT) and a short pea-plant (tt) resulted in progenies that were all tall plants because
(a) tallness is the recessive trait.
(b) shortness is the dominant trait.
(c) The height of pea-plant is not governed by gene T or t.
(d) tallness is the dominant trait.
► (b) shortness is the dominant trait.
5. Process of selecting individuals with desired characters by man is called
(a) Hybridization
(b) Reproduction
(c) Artificial selection
(d) Natural selection
► (c) Artificial selection
6. What does the progeny of a tall plant with round seeds and a short plant with wrinkled seeds look like?
(a) All are tall with round seeds.
(b) All are short with round seeds.
(c) All are tall with wrinkled seeds.
(d) All are short with wrinkled seeds.
► (a) All are tall with round seeds.
7. Some dinosaurs had feathers although they could not fly but birds have feathers that
help them to fly. In the context of evolution this means that-
(a) reptiles have evolved from birds
(b) there is no evolutionary connection between reptiles and birds
(c) feathers are homologous structure in both the organisms
(d) Birds have evolved from reptiles.
► (d) Birds have evolved from reptiles.
8. A zygote which has an X-chromosome inherited from the father will develop into a
(a) girl
(b) boy
(c) either boy or girl
(d) X-chromosome does not influence the sex of a child.
► (a) girl
9. The process of evolution of a species whereby characteristics which help individual organisms to survive and reproduce are passed on to their offspring and those characteristics which do not help are not passed on is called
(a) Artificial selection
(b) Speciation
(c) Hybridization
(d) Natural selection
► (d) Natural selection
10. Which of the following decides the sex of the child?
(a) male gamete, i.e., sperm
(b) female gamete, i.e., ovum
(c) both sperm and ovum
(d) mother
► (a) male gamete, i.e., sperm
11. Which of the following is the ancestor of ‘Broccoli’?
(a) Cabbage
(b) Cauliflower
(c) Wild cabbage
(d) Kale
► (c) Wild cabbage
12. According to the evolutionary theory formation of a new species occurs generally
due to-
(a) Sudden creation by nature.
(b) accumulation of variations over several generations
(c) clones formed during asexual reproduction
(d) Movement of individuals from one habitat to another.
► (b) accumulation of variations over several generations
13. Which of the following is not correct-
(a) For every hormone there is a gene.
(b) For every protein there is a gene.
(c) For production of every enzyme there is a gene.
(d) For every molecule of fat there is a gene.
► (b) For every protein there is a gene.
14. If a round, green seeded pea-plant (RRyy) is crossed with a wrinkled yellow seeded pea- plant (rrYY), the seeds produced in F1 generation are
(a) round and green
(b) round and yellow
(c) wrinkled and green
(d) wrinkled and yellow
► (b) round and yellow
15. The concept of origin of species by natural selection was given by.
(a) lamarck
(b) weissman
(c) Darwin
(d) Linnaeus
► (c) Darwin
16. The genetic constitution of an organism is called.
(a) Genotype
(b) phenotype
(c) variation
(d) gene.
► (a) Genotype
17. A man with blood group A marries a woman having blood group O. What will be the blood group of the child?
(a) O only
(b) A only
(c) AB
(d) Equal chance of acquiring blood group A or blood group O.
► (d) Equal chance of acquiring blood group A or blood group O.
18. Identify the two organisms which are now extinct and are studied from their fossils.
(a) white tiger and sparrow
(b) dinosaur and fish (Knightia)
(c) ammonite and white tiger
(d) trilobite and white tiger
► (b) dinosaur and fish (Knightia)
19. Those organs which have the same basic structure but different functions are called
(a) Vestigial organs
(b) Analogous organs
(c) Homologous organs
(d) None of these
► (c) Homologous organs
20. Which of the following characters can be acquired but not inherited?
(a) Color of skin
(b) Size of body
(c) Color of eyes
(d) Texture of hair
► (b) Size of body
21. Differences between organisms in a species are described as variation. Which of the following would you describe as continuous variation?
(a) Hair color
(b) Eye color
(c) Weight
(d) Sex
► (c) Weight
22. Mendel proposed that every character is controlled by-
(a) one factor
(b) two factors
(c) one chromosome
(d) two chromosomes
► (b) Two factors.
23. Two pink colored flowers on crossing results in 1 red, 2 pink and 1 white flower progeny. The nature of the cross is-
(a) cross fertilization
(b) self pollination
(c) double fertilization
(d) no fertilization
► (a) cross fertilization
24. The remaps (or impressions) of dead animals or plants that lived in the remote past are known as
(a) extinct species
(b) fossils
(c) naturally selected species
(d) none of the above
► (b) fossils
25. A cross between two individuals results in a ratio of 9 : 3 : 3 :1 for four possible phenotypes of progeny. This is an example of a
(a) Monohybrid cross
(b) Dihybrid cross
(c) Test cross
(d) F1 generation
► (b) Dihybrid cross
26. The human species has genetic roots in
(a) Australia
(b) Africa
(c) America
(d) Indonesia
► (b) Africa
27. The more characteristics two species have in common :
(a) More closely they are related and more recently they had common ancestors.
(b) More distantly they are related and more recently they have common ancestors.
(c) More closely they are related and more distantly they have common ancestors.
(d) More distantly they are related and more distantly they have common ancestors.
► (a) More closely they are related and more recently they had common ancestors.
28. The number of pairs of sex chromosomes in the zygote of a human being is
(a) 2
(b) 3
(c) 1
(d) 4
► (c) 1
29. The process by which new species develop from the existing species is known as
(a) Evolution
(b) Natural selection
(c) Artificial selection
(d) Speciation
► (d) Speciation
30. The theory of chemical evolution of life was experimentally demonstrated by-
(a) Oparin
(b) Miller and Urey
(c) Mendel
(d) Darwin
► (b) Miller and Urey
31. Natural selection is called ‘survival of the fittest’. Which of the following statements best describes an organism?
(a) How strong it is compared to other individuals of the same species.
(b) How much food and resources it is able to gather for its offspring.
(c) The ability to adapt to the environment in the niche it occupies.
(d) The number of fertile offspring it has.
► (c) The ability to adapt to the environment in the niche it occupies.
32. What is the difference between genetic drift and change due to natural selection?
(a) Genetic drift does not require the presence of variation.
(b) Genetic drift never occurs in nature, natural selection does.
(c) Genetic drift does not involve competition between members of a species.
(d) There is no difference.
► (c) Genetic drift does not involve competition between members of a species.
33. The remaps (or impressions) of dead animals or plants that lived in the remote past are known as
(a) extinct species
(b) fossils
(c) naturally selected species
(d) none of the above
► (b) fossils
34. The fossil remains of Archaeopteryx is a connecting link between
(a) reptiles and mammals
(b) reptiles and bird
(c) fish and amphibian
(d) amphibian and reptile
► (b) reptiles and bird
35. Which concept was not included in Charles Darwin’s theory of Natural Selection?
(a) Struggle for existence
(b) Punctuated equilibrium
(c) Survival of the fittest
(d) Overproduction of offspring.
► (b) Punctuated equilibrium
36. Wild cabbage has evolved into new varieties like cabbage, broccoli and cauliflower by
(a) genetic drift
(b) natural selection
(c) reproductive isolation
(d) artificial selection
► (d) artificial selection
37. Wing of a bird and wing of an insect are
(a) Homologous organs
(b) analogous organs
(c) vestigial organ
(d) both (a) and (b)
► (a) Homologous organs
38. 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
► (c) TtWW
39. Human offspring’s sex is determined
(а) through father’s sex chromosomes.
(b) through mother’s sex chromosomes.
(c) by hormones.
(d) by enzymes.
► (а) through father’s sex chromosomes.
40. 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 grass runners.
(d) All of the above.
► (d) All of the above.
41. Assertion: Acquired traits cannot be passed on from one generation to the next generation.
Reason: Inaccuracy during DNA copying of acquired traits is minimum.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.
► (c) A is true but R is false.
42. Assertion: Variation is high in sexually reproducing organisms compared to asexually reproducing organisms.
Reason: Inaccuracies during DNA copying give rise to variation.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.
► (b) Both A and R are true but R is not the correct explanation of A.
43. Assertion: Speciation is the reproductive isolation amongst once interbreeding populations.
Reason: Genetic drift, Natural selection and Severe DNA change can cause speciation.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.
► (a) Both A and R are true and R is the correct explanation of A.
44. Assertion: Humans, frogs and birds have a common ancestor.
Reason: Limbs of human, bird and frog are homologous.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
(e) Both A and R are false.
► (a) Both A and R are true and R is the correct explanation of A.
Heredity and evolution class 10 biology ncert SAQ
Q.1. Define ‘artificial selection’. Comment on the reason why farmers selected the following vegetables to cultivate: [CBSE 2011, CBSE Sample Paper 2018-19]
(a) Cabbage
(b) Broccoli
(c) Cauliflower
(d) Kohlrabi through artificial selection
Ans. Human beings have artificially selected certain variants that arose in nature by chance. This led to the evolution of different species.
For example, wild cabbage was cultivated and its variants were selected due to different advantages, by artificial selection.
(а) Short distances between leaves - led to the formation of modern day cabbage.
(b) Arrested flower development - Broccoli.
(c) Sterile flowers - Cauliflower
(d) Swollen parts - Kohlrabi
(e) Large leaves - Kale
Q.2. Sometimes, accidently a dead body or its parts get buried under depositing sediments and are preserved. These are fossils. How can the estimation of the age of fossils be done? [CBSE 2013,2017-18 C, 2018-19]
Ans. It can be done in two ways:
(а) The fossils found in upper layers are recent and the ones that are deeper are older.
(b) By radio-active carbon dating.
Q.3. List in tabular form distinguishing features between acquired traits and inherited traits, with one example of each. [DoE, Delhi 2017, 2016, 2015; AI 2012]
Or
List two differences between acquired traits and inherited traits by giving an example of each. [Delhi 2019]
Ans.
Q.4. What are acquired traits? Why are these traits generally not inherited over generations? Explain. [CBSE 2017-18 C]
Ans. The traits that a person acquires during one’s lifetime and not by virtue of his/her genes, are known as acquired traits.
These traits are not present in our genes in reproductive cells. Hence they cannot be inherited.
Since these changes are in the non-reproductive cells and thus cannot be passed on to the germ-cells, hence are not inheritable by the future generations. An organism acquires them, for himself, in his lifetime, due to his environment/experiences.
Q.5. What is speciation? List four factors responsible for speciation. [CBSE 2017-18 C]
Ans. Speciation is the formation of new species from the pre-existing ones, due to accumulation of changes in such a way that two groups of individuals of one species can no longer interbreed. This results in the formation of two new, independent species.
Factors responsible for speciation are:
(i) Natural selection - Nature selects due to survival advantage.
(ii) Genetic drift - Due to accumulation of changes over generations in sub-population.
(iii) Geographical isolation - In different geographical locations, natural selection acts differently on different sub-population because of varying abiotic/biotic factors.
(iv) Mutation - DNA changes can be severe and hence the germ cells of two cannot fisip. ffiv off rise to new species.
Q.6. Briefly explain the role of natural selection and genetic drift in speciation by citing an example. [CBSE 2011,2017-18 C]
Or
With the help of an example, explain how new species are produced. [CBSE 2012]
Ans. Let us study the example of beetles. Let the original beetle population be red. If due to variation, a green beetle was produced it would have a survival advantage over red beetle. Thus green beetles would be naturally selected, and will grow in number.
If few of these green beetles move to some other area, adapt to the changed environment and after a few generations, would vary greatly from the original population of red beetles. These two populations may not be able to interbreed due to accumulation of variation.
Thus, due to Natural selection and Genetic Drift, a new species of beetles is formed.
Q.7. Distinguish between inherited traits and acquired traits giving one example of each. Give a reason why the traits acquired by an individual during the lifetime are not inherited. [Delhi 2017C]
Ans. Differences:
Since the acquired traits do not affect the DNA of the germ cells, they are not inherited.
Q.8. What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained. [Delhi 2011C]
Ans. Chromosomes are the structures that bear the DNA or genes; they can't the DNA or genes to the progeny cells.
1. There are special lineages of cells in the sexually- reproducing organisms.
2. These cells undergo a special type of cell division, called meiosis; consequently, the germ cells formed have only half the number of chromosomes as the parent cell.
3. When two such germ cells (with half the number of chromosomes) fuse, a zygote/new individual is formed with the same number of chromosomes as the parent organism.
Q.9. What are homologous organs? Give one example. Can the wings of a butterfly and the wings of a bat be regarded as homologous? Give reason in support of your answer. [AI 2017C]
Ans. 1. Homologous organs are those organs in different groups of organisms which are similar in theri basic structure, but are modified to perform different functions.
e.g. forelimbs of mammals, and those of reptiles and amphibians.
2. The wings of a butterfly and those of a bat cannot be considered as homo-logous, because they have a common function (flying), but their origin and basic structure are different.
3. They are analogous organs because they have a common function, though the basic structure is different.
Q.10. “Evolution and classification of organisms are interlinked.” Give reasons to justify this statement. [ AI 2017]
Ans. 1. We group organisms into groups based on the similarities in their characteristics.
2. Certain basic characteristics are shared by most or all organisms, like the cell is the basic unit of life in all organisms.
3. The characteristics at the next level of classification o would be shared by most organisms, but not by all organisms.
4. By taking the fundamental design differences, a hierarchy is developed that allows the making of classification groups.
5. We can work out the evolutionary relationships of the species by identifying the hierarchies of characteristics between them.
6. The more characteristics two species will have in common, the more closely related they are.
7. The more closely related the two species, they would have had a recent common ancestor.
8. Thus, classification of species is a reflection of their evolutionary relationship.
Q.11. Explain with the help of an example each, how the following provide evidence in favor of evolution: [Delhi 2017]
(а) Homologous organs
(b) Analogous organs
(c) Fossils
Ans. (а) Homologous organs are those organs in different groups of organisms, which are similar in their basic structure/anatomy but are different in their functions. Such a similarity indicates that they are inherited from a common ancestor and the two species are closely related. For example, forelimbs of vertebrates like humans, wings of binds.
(b) Analogous organs are those organs/structures in different groups of organisms, that are similar in their function, but are dissimilar in their basic structural plan design and origin. Such organs do not indicate common ancestry of the species. For example, wings of birds and those of bats.
(c) Fossils are the preserved traces of organisms that lived in the past. Fossils indicate the time periods when the different groups of organisms lived on the earth. For example, dinosaurs are reptilian: fossils, some of which show resemblance to birds in having feathers.
Q.12. If we cross-bred tall (dominant pea plants with pure-bried dwarf (recessive) pea plants, we will get plants of the F1 generation. If we now self-cross the pea plant of F1 generation, we obtain pea plants of F2 generation. [A12017C, 13,12]
(i) What do the plants of the F1 generation look like?
(ii) State the ratio of tall plants to dwarf plants in F2 generation.
(iii) State the type of plants not found in the F1 generation but appeared in the F2 generation. Write the reason for the same.
Ans. (i) The plants of the F1 generation will be tall like the dominant parent.
(ii) Tall plants 3 : Dwarf plants 1, i.e., 3 : 1.
(iii) Dwarf plants are not found in the F1 generation.
It is because, when two copies of a gene (alleles) exist together in the F1 plants, only the trait; tallness is expressed, i.e. it is dominant.
The other trait dwarfness remains hidden as it is a recessive trait.
Q.13. How did Mendel explain that it is possible that a trait is inherited but not expressed in an organism? [AI 2017]
Ans. 1. Mendel crossed a tall pea plant with a short pea plant.
2. All the plants produced in the F1 generation were tall.
3. When the F1 tall plants were self-pollinated, the F2 generation consisted of both tall and short plants.
4. It explains that the dominant trait expresses itself in the F1 plants, where the recessive trait (shortness) is hidden.
5. The appearance of short plants in the F2 indicates that the trait shortness has been inherited by the F1 plants, but not expressed.
Q.14. Give reasons for your answer:
Define speciation. Mention factors due to which this can happen. [CBSE 2013,2012,2016-17 C]
Ans. (a) Speciation - It is the process of formation of new species from an existing one. Factors that can lead to speciation are
(i) Natural selection.
(ii) Geographical isolation.
(iii) Migration - Genetic drift.
Q.15. List two differences in tabular form between dominant trait and recessive traits. What percentage/proportion of the plants in the F2 generation/progeny were round, in Mendel’s cross between round and wrinkled pea plants? [Foreign 2016]
Ans.
75% of the plants in the F2 generation were round in Mendel’s cross between round and wrinkled pea plants.
Q.16. How do Mendel’s experiments show that traits are Inherited independently? [Al 2016]
Ans. Mendel performed an experiment in which he took two different traits like tall and dwarf plants and round and wrinkled seeds. In the second (F2) generation, some plants were tall with round seeds and some were dwarf with wrinkled seeds. There would also be dwarf plants having round seeds. Thus, the tall/short traits and round/wrinkled seed traits are independently inherited.
Q.17. (a) If we cut the tail of a mouse, will tail occur in the next generation of that mouse? Give reason to support your answer.
(b) What are the features that Archaeopteryx had in common with the reptiles? [CBSE 2013,2016]
Ans. (a) Even after cutting the tail of a mouse, its progeny continues to have a tail. This is because ‘no tail’ is an acquired trait. The mouse continues to have information for the presence of the tail in its DNA and hence the progeny will have the tail.
(b) Archaeopteryx has reptilian features such as the presence of tail, vertebra, teeth etc.
Q.18. Name two homologous structures in vertebrates. Why are they named so? What is the significance of these structures in the study of evolution? [CBSE 2012,2016-17C]
Ans. (i) Homologous structures in vertebrates are wings in birds and forelimbs of lizards.
(ii) They are so named as they have the same structural design but different functions.
(iii) Such structures give us an idea about common ancestry.
Q.19. Give two uses of fossils. How does the study of fossils provide evidence in favor of organic evolution. [CBSE 2008,2012,2016-17 C]
Ans. Two uses of fossils are:
(а) To help study the evolution of plants and animals.
(b) To know past climatic conditions.
(c) To help calculate geological time etc. (Any two)
Evidence in favor of organic evolution:
(i) Fossils help to identify an evolutionary relationship between apparently different species.
(ii) The older fossils, present deeper, are simpler in body design, as compared to those present in upper layers which are more recent.
This clearly provides evidence in favor of organic evolution.
Q.20. What is DNA? [Delhi 2016]
Ans. Deoxyribonucleic Acid (DNA) is a molecule which carries the hereditary characters or traits in a coded form from one generation to the next in all the organisms.
Q.21. “We cannot pass onto our progeny the experiences and qualifications earned during our lifetime”. Justify the statement giving reason and examples. [Delhi 2015; Foreign 2012]
Ans. Experiences of life and qualifications we earn donot make any change in the genes of the individual. Changes made in the gene are only passed on from one generation to the next. These qualities are acquired by an individual in his life, and are called acquired traits which cannot be passed on to future progeny. For example, if a person reads a book on birds, the knowledge he earns by reading the book does not make any change in his genes. Hence, this knowledge will not get automatically transmitted to the next generation.
Q.22. A pea plant with a blue color flower denoted by BB is crossbred with a pea plant with white flower denoted by ww.
(a) What is the expected color of the flowers in their F1 progeny?
(b) What will be the percentage of plants bearing white flowers in the F2 generation, when the flowers of F1 plants were selfed?
(c) State the expected ratio of the genotype BB and Bw in the F2 progeny. [AI 2015]
Ans.
(a) All flowers in F1 progeny will be blue in color.
(b) When F1 progeny are selfed, 25% of the flowers in F2 progeny will be white.
(c) Expected ratio of the genotype BB and Bw will be 1:2.
Q.23. “It is possible that a trait is inherited but may not be expressed.” Give a suitable example to justify this statement. [Foreign 2015]
Ans. The statement “It is possible that a trait is inherited but may not be expressed” can be explained with the help of Mendel’s experiment on a pea plant with one visible contrasting character.
Mendel took a pure-breeding pea plant with one visible contrasting character viz, height of the plant (tall and short plant). The pure breed tall and short plant were crossed and it was found that all the plants in the F1 progeny were tall. Mendel then allowed the F1 progeny plants for self-pollination. It was found that all the F2 progeny plants are not tall, some are short. This indicates that both tallness and shortness traits were inherited separately in the F1 progeny but the shortness trait was not expressed in the F1 progeny.
Q.24. (i) We see eyes in Planaria, insects, octopus and vertebrates. Can eyes be grouped together in case of the above-mentioned animals to establish a common evolutionary origin? why?
(ii) State one evidence to prove that birds have evolved from reptiles. [Delhi 2015, 2013; Foreign 2015, 2012]
Ans. (i) Yes, eyes can be grouped together, which have evolved over generations from imperfect eyes in Planaria to perfect eyes in vertebrates.
(ii) Dinosaur is a type of reptile which has wings. Birds also have wings, so it can be opined that birds have evolved from reptiles.
Q.25. Explain the following: [AI 2015]
(a) Speciation
(b) Natural Selection
Ans. (a) Speciation: It is the evolution of reproductive isolation among once-interbreeding populations, i.e. the development of one or more species from an existing species.
(b) Natural Selection: It is the process, according to Darwin, which brings about the evolution of new species of animals and plants.
• It was noted that the size of any population tends to remain constant despite the fact that more offspring are produced than are needed to maintain.
• Darwin found that variations existed between individuals of the population and concluded that disease, competition and other forces acting on the population eliminated those individuals which are less well-adapted to their environment.
• The surviving population would pass the hereditary advantageous characteristics to their offspring.
Q.26. Define the following: [CBSE 2012, 2015]
(a) Natural selection
(b) Reproductive isolation.
Ans. (a) Natural selection - Nature selects the best traits in.a species, leading to survival of the fittest and evolution of species. This phenomenon is known as natural selection.
(b) Reproductive isolation - It refers to the mechanism which checks the organisms of two different groups from interbreeding.
Q.27. (a) Give the evidence that the birds have evolved from reptiles. [CBSE 2014, 2015]
(b) Insects, octopuses, planaria and vertebrates possess eyes. Can we group these animals together on the basis of the eyes that they possess? Justify your answer by giving a reason.
Ans. (a) Fossils are important evolutionary evidence to show what kind of organisms existed earlier.
Archeopteryx is a fossil dinosaur with wings. This proves that it has features of both reptiles as well as birds. Hence we can say that birds evolved from reptiles.
(b) These organisms cannot be grouped together as the structure of the eyes in each is very different. This means that they have a separate evolutionary origin.
Heredity and evolution class 10 biology ncert long question
Q.1. (a) What are homologous structures? Give an example.
(b) “The sex of a newborn child is matter of chance and none of the parents may be considered responsible for it”. Justify this statement with the help of a flow chart showing sex-determination in human beings. [Allahabad 2019]
Ans. (a) Homologous organs are those organs in different groups of organisms which are similar in theri basic structure, but are modified to perform different functions.
e.g. forelimbs of mammals, and those of reptiles and amphibians.
(b) Sex of a child depends on what happens during fertilization:
(i) The female gamete, ova, always contributes an X chromosome during fertilization.
(ii) The male gamete sperm contributes either X or Y chromosome during fertilization. Whether sperm will contribute the X chromosome or Y chromosome is a matter of chance and the man does not have any control over it.
(iii) If a sperm carrying an X chromosome fertilizes an egg which always carries a X chromosome, then the child will be a girl. But if a sperm carrying a Y chromosome fertilizes an egg which always carries an X chromosome, then the child will be a boy.
(iv) Thus, sex of a new born child is a matter of chance and none of the parents may be considered responsible for it.
Q.2. Define variation in a species. How does it increase the survival chance of a species? Why do environmentalists get worried due to the small population of a species? [CBSE 2013,2017-18 C]
Ans. Any deviation from the original trait in a species is a variation.
Sometimes these variations may give added advantage of being of nature so as to give better adaptability in changed conditions. Hence, it increases the chances of survival.
Smaller population of species would enforce inbreeding within the population which would result in fewer variations. This would also result in inbreeding depression and expression of recessive traits, thereby making it prone to diseases or extinction.
Hence, environmentalists are worried about small population size.
Q.3. (a) What is variation? How is variation created in a population? How does the creation of variation in a species promote survival?
(b) Explain how, offspring and parents of organisms reproducing sexually have the same number chromosomes. [CBSE 2018 C]
Ans. (a) Variation refers to the differences in the characteristics among the individuals of a species.
1. Variation is created in a population by
(i) Errors in DNA copying
(ii) Recombination during reproduction
2. In case of a drastic change in the environment of the niche of the population, at least some variants would have chances of survival.
(b) 1. There are special lineages of cells in specialized organs i n multicellular organisms.
2. Such cells undergo a special type of cell division, called meiosis, and the germ cells (gametes) formed have only half the amount of chromosomes as the parent cell.
3. When two such germ cells (with half the number of chromosomes) fuse, a zygote/ new individual is formed with the reestablishment of the number of chromosomes as in the parent organism.
Q.4. What is meant by a trait of a species ? Distinguish between acquired and inherited traits giving an example of each. [CBSE 2013,2016,2017]
Ans. The typical characteristics present in all individuals of a species are said to be traits of that species.
Q.5. What are the various evidences in favor of evolution? [CBSE 2015,2017]
Ans. Evidence in favor of evolution are:
(i) Homologous organs: Such organs which perform different functions but have similar structure and origin are called homologous organs. For example, the forelimbs of birds, forelimbs of man and frog perform different functions, but have similar basic structures. Presence of such organs indicates that all these vertebrates had common ancestors.
Fig. 9.8 Skeleton of forelimbs of (a) Frog (b) Bird and (c) Human, showing homologous features.
Fig. 9.9 Wing of a bird and an insect showing analogous features.
(ii) Analogous organs: Such organs which perform similar functions but are structurally different are called analogous organs. For example, wings of a bird and wing of an insect. Presence of such organs shows that these organisms have different origins.
(iii) Evidence from embryology: Early embryos of different vertebrates show striking similarities such as the presence of the tail. This indicates common origin and ancestry of different vertebrates.
Fig. 9.10 Comparison of early development stages: (a) Fish (b) Bird and (c) Human.
Fig. 9.11 Vermiform Appendix of human beings as vestigial organs.
(iv) Vestigial organs : These are the organs which appear functionless in one organism and functional in some others. For example, the Vermiform appendix of the large intestine is nonfunctional in human beings but functional in herbivorous, ruminant animals. Presence of such organs also shows common ancestry.
(v) Evidence from fossils : Archaeopteryx is a fossil that resembles reptiles but has some bird-like features. This shows that birds have evolved from reptiles.
Fig. 9.12 Various kinds of fossils. Note the different appearances and degrees of detail and preservation. The dinosaur skull fossil shown was found only a few years ago in the Narmada valley.
Q.6. “A trait may be inherited, but may not be expressed.” Justify this statement with the help of suitable examples. [CBSE 2016-17 C]
Ans. A trait may be inherited, but if it is recessive, it will not be expressed unless it is homozygous, e.g.,
Hence, genotype Tt with a recessive gene is expressed as a phenotype of Tall. This shows that only the dominant gene is expressed as the trait (T) while ‘t’ is not expressed.
Q.7. What are Chromosomes ? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained. [CBSE 2016-17 C]
Ans. Chromosomes are long DNA strands, present in the nucleus, carrying genes which code for a trait. Hence, they are the hereditary material.
In an organism, each cell has two copies of a chromosome, one each from a male and female parent. In sexually reproducing organisms, where fusion of gametes (germ-cells) takes place, one chromosome from each pair is taken up in formation of a germ-cell (these may be either maternal or paternal in origin) by a special cell division called meiosis. When two germ cells fuse, they restore the original number of chromosomes in the progeny.
Q.8. If we cross-bred tall (dominant) pea plants with pure-bred dwarf (recessive) pea plants, we will get plants of the F1 generation. If we now self-cross the pea plant of F1 generation, we obtain pea plants of F2 generation. [CBSE 2016-17 C]
(i) What do the plants of the F1 generation look like?
(ii) State the ratio of tall plants to dwarf plants in F2 generation.
(iii) State the type of plants not found in the F1 generation but appeared in the F2 generation. Write the reason for the same.
Ans. On crossing tall (dominant) i.e., TT with dwarf (recessive) tt, we get F1,
Hence, all plants of F1 will appear tall.
(ii) On self crossing F1
F2 ratio : 3 tall; 1 dwarf
(iii) tt i.e., Dwarf plants are not found in F1. In FI generation, all plants are tall. This is because the gene £t’ even though present in F1 along with 'T’ is unable to express itself and hence all plants appear tall. It expresses itself in a pure (homozygous) condition when any dominant gene is not present. This makes ‘t’ a recessive trait.
Q.9. Define evolution. How does it occur? Explain how fossils provide evidence in support of evolution. [CBSE 2016-17 C]
Ans. The inbuilt tendency of variation, either due to errors in DNA copying or due to sexual reproduction, both result in some changes in the existing population of an organism. This continuous change ultimately leads to Evolution.
It occurs due to changes in DNA which keep accumulating over generations, ultimately giving rise to new species - Natural selection, genetic drift, mutation etc.
Fossils provide evidence for evolution as they are preserved traces of once living organisms. The fossils are formed when on death of an organism, the body doesn’t decompose, instead it gets trapped in the environment where it gets preserved. For example, an organism getting trapped in volcanic lava will not decompose. On cooling the lava will harden and retain the impression of the body parts of those organisms, as fossil.
Q.10. (a) Can the wing of a butterfly and the wing of a bat be regarded as homologous? Why?
(b) What is speciation? State any two factors which could lead to speciation.
(c) Name the vegetables made from wild cabbage by artificial selection when farmers:
(i) opted for swollen stems
(ii) opted for sterile flowers
(iii) opted for arrested flowers
(iv) opted for large leaves. [AI 2017C]
Ans. (a) No, the wing of a butterfly and the wing of a bat cannot be considered homologous organs because they have a common function of flying but their origin and basic structural designs are not common. So, they are analogous organs.
(b) - Speciation refers to the phenomenon in which new species are formed from the existing species.
- The factors leading to speciation are: (i) genetic drift and (ii) natural selection
(c)(i) Kohlrabi
(ii) Cauliflower
(iii) Broccoli
(iv) Kale
Q.11. How do Mendel’s experiments show that the [Delhi 2017(C); DoE, AI 2015]
(a) traits may be dominant or recessive,
(b) traits are inherited independently?
Ans. Mendel’s Experiments on Inheritance of Traits. Mendel used a number of visible contrasting characters of garden peas like round/wrinkled seeds, tall/short plants, white/violet flowers, etc.
Independent inheritance of two separate traits, shape and color of seeds
(i) Traits may be dominant or recessive:
- Mendel used a number of visible contrasting pairs of characters in garden pea.
- He made crosses between pea plants with different characters; there were no halfway or intermediate characters.
- Only one of the parental traits appeared in the F1 generation; it is called the dominant trait and the trait which remains hidden, is called the recessive trait.
- When the F1 plants were self-pollinated, the F2 progeny consists of plants with the dominant trait and recessive trait in the ratio of 3 : 1; it proves that traits may be dominant or recessive.
(ii) Traits are inherited independently:
- When a cross is made between a tall plant with round seeds, (when inheritance of two traits is considered), with a short plant with wrinkled seeds, the F1 progeny plants were all tall with round plants.
- When the F1 plants are self-pollinated, the F2 progeny consists of some tall plants with round seeds and some short plants with wrinkled seeds; these two are the parental types of combinations of traits.
- There were also some new combinations like tall plants with wrinkled seeds and short plants with round seeds.
- Thus it is clear that the tall and short traits and round and wrinkled seed traits are inherited independently of each other.
Q.12. What is speciation? List four factors that could lead to speciation. Which of these cannot be a major factor in the speciation of a self-pollinating plant species? Explain. [Delhi 2016; Foreign 2015]
Ans. Speciation: Speciation is the evolution of reproductive isolation among once-interbreeding populations. Factors which can lead to speciation are:
(i) Genetic drift: Over generation, genetic drift may lead to the accumulation of different changes which lead to speciation.
(ii) Natural selection: Natural selection may work differently in different locations which may give rise to speciation.
(iii) Severe DNA change: Variations during DNA copying often leads to speciation.
(iv) A variation may occur which does not allow sexual act between two groups.
Out of these variations, severe DNA change is not a major factor in the speciation of a self- pollinating plant species, because:
(i) Variation is the differences in the characters among the individuals of species. In self- pollinating species, pollen grains fall on the stigma of the same flower or another flower of the same plant. Since self pollination is taking place in the same plant, changes among the flowers of the same plant is negligible and hence variation in self-pollinating plant don't have any major effect in speciation of a self- pollinating plant.
(ii) Due to severe DNA change, individuals may vary from each other. In case of self-pollinating plants, pollination takes place within the same plant and hence severe DNA change among individual plants doriot have any major impact.
Q.13. (a) What is meant by natural selection? Explain.
(b) Why are thorns of the Bougainvillea plant and the tendrils of the Passiflora plant considered homologous. [CBSE 2013,2016]
Ans. (a) Natural selection - It is selection of certain traits in nature in an individual in a population of a particular species.
This leads to survival advantage and hence variation leading ultimately to speciation.
(b) Thom of Bougainvillea and tendril of Passiflora both are modified stems, i.e., both have similar structure, but different functions.
Thorn of Bougainvillea protects plants from being grazed while tendrils of Passiflora help the plants to climb up a support.
Hence, they are homologous organs.
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