1. Only variations that confer an advantage to an individual organism will survive in a
population. Do you agree with this statement? Why or why not?
Ans. Variations that confer an advantage to an individual organism may or may not survive in the population depending upon the social behaviour of the organism. A variation in a social animal like ant may not survive in a population while a variation in an animal like a leopard may survive.
2. What are the different approaches to determine evolutionary history of man?
Ans. To construct evolutionary history of man, there are three approaches-
(1) Historical method- It gives direct evidence in the form of fossil records. The age of fossils can be determined by carbon dating methods.
(2) Comparative method- By comparing several existing forms, we can makes ideas about their common ancestors and reconstruct their about possible history.
(3) Analytic method- By observing present day human being vestigial organs and by studying the development pattern from embryo to adult.
3. What is fossilization? How are fossils formed?
Ans. The process of fossils formation is called fossilization. Fossils are formed when organisms die; their bodies get decomposed and lost. Sometimes the body or a part of it may be in such an environment that it does not let it decompose completely. The mud will eventually harden and retain the impression of the body parts of the organism. This mud with the impression will be called fossil of the organism.
4. What are homologous and analogous organ? Explain with the help of example.
Ans. Homologous organs are those which have similar basic structure and origin but may have different functions. For example- Hands of human beings and wings of birds. Analogous organs- Organs which have different basic structure and origin but have similar function are called analogous organs.
For example- (1) wing of bat and wing of bird.
(2) wing of birds and wing of insect.
5.Differentiate between convergent and divergent
Ans.Convergent Evolution
a.Adapted for similar function
b.Analogous organ
c.do not indicate evolutionary relationship
Divergent Evolution
a.Adapted for different function
b.homologous organ
c.Indicate evolutionary relationship
6. What are the different ways in which individuals with a particular trait may increase in a population?
Ans. The factors which are responsible for raising a new species are selection of environmental conditions for survival of a particular species. If a variation occurs in a population and that variation results in better survival of the organism in the prevailing natural conditions, then the trait would be selected naturally and more in the population.
7. What are the different theories about origin of life?
Ans. (a) Theory of special creation- According to this theory the almighty god created life.
(b) Theory of spontaneous generation- According to this theory, life originated from non- living materials by the process of a biogenesis wring mud, decomposing matter, sun, air and water, etc.
(c) Cosmozoic theory- It states that life came to Earth from some heavenly bodies in the form of spores or seeds.
(d) Biogenesis- This theory states that life originated from pre-existing life.
(e) Modern theory of origin of life- According to this, complex organic molecule was formed from simple inorganic molecules only in suitable condition.
8. What is the difference between chemical evolution and organic evolution?
Ans Chemical Evolution
a.it is the formation of the complex organic compoud from simple compound or element
b.It occured at the time of origin of life
c.Irreversible
d.Speed of evolution is fast
Organic evolution
a.It is the formation of complex form of life from simple form of life
b.It is still occuring
c.Reversible
d.Speed of evolution is slow
9. Give difference between homologous and analogous organs
Ans.Homologous Organs
a.Similar in origin and basic structure but may differ in function
b.Provide idea of common ancestry
c.For e.g hands of human beings and forelimbs of horse
Analogous Organs
a.Dissimilar in origin and basic structure but may have similar function
b.Do not provide the idea of common ancestry
c.for e.g wing of birds insects
10. State three laws of Mendel.
Ans. Mendel’s law-
(a) Law of dominance- when two dissimilar factors of a character are present in an organism only one expresses itself (dominant factor) while other remain unexpressed (recessive factor)
(b) Principle of segregation – two factors of a character are separated at the time of gamete formation and each gamete gets only one factor for that character.
(c) Principle of independent assortment- this principle states that inheritance of two or more pair of contrasting traits is such a way that one pair of contrasting traits is independent of the other pair of contrasting traits.
11. Describe how the sex of the offspring is determined in the zygote ins human beings?
Ans. The males can produce two types of gametes, either X-type or Y-type. The females produce only one type of gametes or ova, X-type. If X-type sperm fuses with the ovum, then the sex of the baby will be female. If Y-type sperm uses with the ovum, then the sex of the baby will be male. Sex of the baby is decided at the time. Sex of the baby is decided at the time of fertilization.
12. Give a suitable explanation for “geographical isolation of individual of a species lead to formation of a new species?
Ans. Reproduction barrier such as river (geographical isolation) between the sub population leading to:
(a) Genetic drift or random changes in the gene frequency by chance alone e.g. selection of red or blue beetles instead of green in presence of crows.
(b) Natural selection or selection of the fittest by nature itself eg. Selection of green beetles instead of red ones in the presence of crows.
13. State the evolutionary force which leads to origin of a new species.
Ans. Various elemental forces of evolution are-
(a) Mutation
(b) Recombination (Crossing over during meiosis, Random assortment of gene at the time of gamete formation).
(c) Natural selection or survival of the fittest.
(d) Genetic drift.
14. What is a fossil? How do fossils tell us about the process of evolution?
Ans. The dead remains of former living organisms are called fossils. The branch of biology which deals with the study of fossils is called paleontology. The study of fossils tells us that species arose from previously existing ones or that the evolution has occurred in nature and is still continuing.
15. Give difference between diploid and haploid.
Ans. Diploid
A.Two chromosomes set
b.Chromosomes present in pairs
c.Formed due to mitosis
d.Found in human beings and higher plants
Haploid
a.One chromosome set
b.Chromosomes present in singly
c.Formed due to meiosis
d.Found in lower plants
16. Who disproved Lamarckism and how?
Ans. The concept of inheritance of acquired character of Lamark was disproved by August Weismann. He cuts the tail of rat at the time of birth and continued this for 21 generation. But tailless rats were never born. This trait do not change the DNA of germ cells so cannot be inherited. Hence, the changes in non-reproductive tissue of an individual during its lifetime cannot be passed on to its progeny, and cannot direct evolution.
17. How does Archaeopteryx provide evidence for organic evolution?
Ans. Archeoptyrx has some features of reptiles, characters of dinosaurs as well as some features of birds like wings. This shows that birds are closely related to reptiles. Birds could evolve from reptiles.
18. What is divergent evolution? Explain with the help of an example.
Ans. The formation of dissimilar looking organisms from common ancestors is called divergent evolution. This is also known as adaptive radiation which represents evolution of new forms in several directions from the common ancestors type. The current example of such a process is the evolution of wild cabbage. For over more than 200 years, humans have cultivated wild cabbage as a food plant and generated different vegetables (like cabbage, broccoli, cauliflower, kohlrabi and kale etc) from it by different artificial selections. Thus all these structures of different vegetables are descended from the same ancestor i.e. wild cabbage.
20. Write similarities between Mendalian’s factors and gene.
Ans. Mendel proposed the inheritance of traits from parents to offsprings by hereditary units called factors. Mendel suggested that every character is controlled by a pair of factors. Sutton and Boveri (1902) found striking similarities between the behaviours of Mendelian factors and the chromosomes during meiosis and fertilization. Factor and chromosomes are present in paired condition in the parents, seprate during meiosis and again get paired after fertilization.
21. How does the creation of variations in a species promote survival?
Ans. Depending on the nature of variations different individuals would have difference kinds of advantage to adjust in particular habitat. Variation help the individual to have different traits that may develop the organisms more tolerable.
22. How do Mendel’s experiments show that traits may be dominant or recessive?
Ans. In Monohybrid cross of Mendel between tall and dwarf pea plant, all progeny in generation are tall and in generation, 75% of pea plants are tall but 25% are dwarf. This shows that traits are dominant or recessive.
23. How do Mendel’s experiments show that traitsare inherited independently?
Ans. When a pea plant having round green seeds is crossed with a pea plant having wrinkled yellow seeds in generation all the plants have round yellow seeds. But in generation two new traits that is round yellow and wrinkled green appear. This shows that traits are inherited independently.
24. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits-blood group A or O- is dominant? Why or why not?
Ans. No, the information is not enough because the blood group is determined by a pair of gene. One inherited from mother and other from father. In this case, the child inherited gene for O blood group from mother as well as father.
25. How is the sex of the child determined in human beings?
Ans. A child which inherits X chromosome from her father will be a girl and one who inherits Y chromosome from him will be a boy.
26. What factors could lead to the rise of a new species?
Ans. Following factors could lead to the rise of new species:
(a) Changes in gene frequency in small breeding isolated populations.
(b) Natural selection
(c) Changes in number of chromosome.
27. Will geographical isolation be a major factor in the speciation of self-pollinating plant species? Why or why not?
Ans. No, because geographical barrier do not allow breeding between such individuals of a population which reproduce sexually. Moreover asexually reproducing organism pass on the parental DNA to offspring which gives no chance of speciation.
28. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Ans. Yes, due to geographical isolation, the two populations are separated. The levels of gene flow between them will decrease. The isolated population will breed with local population resulting in entry of isolated population into new population.
29. What are fossils? What do they tell us about the process of evolution?
Ans. Preserved traces if living organisms are called fossils found closer to the surface of earth are more recent in origin than the fossils we find in deeper layers. Fossils also help us to find evolutionary relation between organisms.
30. 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?
Ans. No, since two copies of traits are inherited from parents, one from mother and the other form father. Unless we know the nature of these two variants of traits we can not tell which is dominant and which is recessive. Recessive traits appear when both the parents contribute recessive allele. From this statement we can only presume are that both parents are contributing recessive allele.
31. Explain the terms analogous and homologous organs with examples.
Ans. Analogous organs: Such organs which perform similar function but are different in structure and origin. Example- Wings of birds and wings of insects.
Homologous organs: Such organs which may have different functions but similar structure and origin. Example- fore arm of frog, lizard and bird.
32. What evidence do we have for the origin of life from inanimate matter?
Ans. The evidence was given by Stanley L. Miller and Harold C. Urey in 1953. They assembled an atmosphere similar to that thought to exist on early earth over water. This was maintained by them at a temperature just below 100 degree Celcious and sparks were passed through the mixture of gases to stimulus lightening. At the end of week, they found that 15% of the carbon had been converted to simple compounds of carbon including amino acids which make up protein molecules.
33. 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?
Ans. Variations arise either because of errors in DNA copying or as a result of sexual reproduction. Due to sexual reproduction genetic variability increases in the population from one generation to another. This happens due to the fact that sexually reproducing organism inherits half the genes from each parent. These variations are very important for the process of evolution.
34. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Ans. No, depending on the nature of variations different individuals have been different kinds of advantages. However, when a drastic change occurs in environment only those organisms in the population will survive which have an advantageous variation in that population to survive in changed environment.
35. How is the equal genetic contribution of male and female parents ensured in the progeny?
Ans. Equal contribution of male and female parents is ensured in progeny during sexual reproduction. Each trait of progeny is determined by a pair of alleles and gametes of male and female contain one allele. Each allele pairs during fertilisation combine together to determine traits. Thus, the traits of progeny are determined by equal genes from male and female.
36. Is it true that when a new species is emerged, the old species is eliminated and why?
Ans. No, it is not true that when a new species is emerged, the old species is eliminated. Because when there is a change in any species, the change is only in a part or a few members of the species population. If the newly generated species after genetic change is better in any way, it will get more opportunity to survive and if the genetic change is against the environment, it will die. Thus, unchanged members of other species may also remain and tend to live in changed environment.
37. Why are traits acquired during life-time of an individual not inherited?
Ans. Traits acquired during life-time of an individual not inherited because change in non- reproductive tissue or somatic cells cannot be passed on to the DNA of germ cells. Thus, the acquired trait will die with the death of the individual. It is therefore non-heritable and cannot be passed on to its progeny.
39. What are the causes of variations in clones?
Ans. i. inaccuracies during DNA copying
ii. Effect of environment termed acquired variation.
iii. Mutations are sudden stable changes which are discontinuous inheritable as produced due to changes in genetic make-up.
40. Only variation that confer and advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Ans. We agree with the statement. All the variation 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 variation. Different individuals have different kind of advantages. A bacteria that can withstand heat will survive better in heat wave.
42. Wild cabbage was converted into number of variants like cauliflower, broccoli and cabbage by man. What is this process known as ? Does it play an important role in organic evolution?
Ans. This process is known as artificial selection. It plays a important role in organic evolution because it is parallel to natural selection. It helps to produce new species having useful traits in less time.
43. How are variant genotypes produced?
Ans. Variant genotypes can be produced by:
1. Mutation in genes and chromosomes.
2. Recombination of genes.
3. Hybridization of genes.
44. Can geographical isolation lead to speciation? How?
Ans. Yes, geographical isolation can lead to speciation. Due to geographical isolation, the members of two sub groups may not be able to interbreed as a result of genetic drift. Natural selection also operates diffetently in these subgroups. This leads to speciation.
1. (i) Who provided the evidence of DNA as genetic material?
(ii) Why DNA is called polynucleotide?
(iii) List three important features of double helical model of DNA.
Ans. (i) Mendel.
(ii) DNA is made up many units of nucleotides.
(iii) Important features-
(a) Both the chains in helical runs anti-parallel.
(b) There two nitrogenous base Purine (A, G) and pyrimidine (T, C).
(c) A always bind with T and C always binds with G.
2. Give the basic features of the mechanism of inheritance.
Ans. Basic features of mechanism of inheritance-
(a) Each character is controlled by a pair of factors. The factors may be similar or dissimilar.
(b) When two dissimilar factors of a character are present in an organism, only one expresses itself while other remains unexpressed.
(c) Two factors of a character are separated at the time of gamete formation and get only one factor for that character.
(d) Inheritance of two or more pairs of contrasting traits in such a way that one pair of contrasting traits is independent of the other pairs of contrasting traits.
19. What is monohybrid and dihybrid cross? Give one example of each.
Ans. Monohybrid cross- It is the simplest cross in which inheritance of one character is studied. A cross is made between the pair of plants having one contrasting character such as tall or dwarf.
Dihybrid cross- A cross made between two plants having two pairs of contrasting character is called dihybrid cross. For ex. round and green seed crossed with yellow and wrinkled seed.
20. Why did Mendel choose pea plant for his experimentation
?
Ans. Mendel selected garden pea for his experiment for the following reasons- (a) The life span of this plant is very short so results can be obtained and studied faster.
(b) Garden pea has many characteristics which are in contrast to each other.
(c) Moreover this plant is small, easy to grow and reproduce large number of offsprings.
22. What are the different ways in which individuals with a particular trait may increase in a population? Ans. The different ways in which individual with a particular trait may increase are: (a) Natural selection- Certain variations give survival advantage to individuals in a population in a changed situation resulting in increase of their population. (b) Genetic drift- Accidents in small population even if they give no survival advantage also lead to increase to certain individual in population 23. How is the sex of a newborn determined in humans?
Ans. Somatic cell of human beings has 23 pairs of chromosomes. Out of them the 23 rd pair contains sex chromosomes. In a male, the somatic cell has X and Y chromosomes in 23 rd pair. In female, the somatic cell has XX chromosomes in 23 rd pair. So, a sperm can have either X or Y chromosome as the 23 rd chromosome. On the other hand, an egg has X chromosome as the 23 rd chromosome. When a sperm with X chromosome fertilizes the egg, the resulting zygote develops into a girl child. When a sperm with Y chromosome fertilizes the egg, the resulting zygote develops into a male child
24.How does the creation of variations in a species promote survival?
Ans. Depending on the nature of variations different individuals would have difference kinds of advantage to adjust in particular habitat. Variation help the individual to have different traits that may develop the organisms more tolerable.
25.How do Mendel’s experiments show that traits are inherited independently? Ans. W hen a pea plant having round green seeds is crossed with a pea plant having wrinkled yellow seeds in F1 generation all the plants have round yellow seeds. But in F 2 generation two new traits that is round yellow and wrinkled green appear. This shows that traits are inherited independently. 26.Why are fossils considered important in the study of evolution? Explain two ways by which age of fossils can be estimated. Ans.Fossils provide evidence in favor of evolution/ establish evolutionary relationships by providing missing links. Two ways 1 . Relative method – Fossils found closer to the surface are more recent than those in deeper layer. 2 . By detecting the ratios of different shapes of the same element in the fossils material
27.A change in DNA that is useful for one property to start with, can become useful later for a different function. Explain.
Ans.A change/feature/property of an organism that may have helped it to adapt to an environmental condition can also become useful for a completely different function in the future. For example: feathers in birds, a character developed and selected during natural selection because it provided insulation in cold weather have become useful in later stages for flight. Some dinosaurs had feathers, but they could not fly. Birds later adapted the feathers to flight
28.How do Mendel’s experiments show that traits may be dominant or recessive?
Ans.Mendel conducted a monohydric cross with pea plants, and he observed that one of the contrasting characters disappears in F 1 generator. This character reappears in F 2 generation (obtained by selfing F 1 ) in just 25% of the progeny. Mendel conclude that the character which expresses itself in F 1 is the dominant character while the other one when is not able to express through present in F 1 individuals is recessive. This recessive character is able to express only in its pure form i.e. in 25% of F 2 individuals.
29.A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Ans. A small population of a species faces a greater threat of extinction than a larger population. Following are some genetic explanation for this:
(a) Inbreeding: A small population promotes inbreeding. This results in least number of variations being incorporated in subsequent generations.
(b) Genetic drift: A small population is more exposed to sudden changes in the environment. The genetic drift because of sudden changes has the potential to wipe off the entire population.
(c) Inbreeding depression: It results in negative population growth which is further detrimental to the survival of the species.
Ans. Variations that confer an advantage to an individual organism may or may not survive in the population depending upon the social behaviour of the organism. A variation in a social animal like ant may not survive in a population while a variation in an animal like a leopard may survive.
2. What are the different approaches to determine evolutionary history of man?
Ans. To construct evolutionary history of man, there are three approaches-
(1) Historical method- It gives direct evidence in the form of fossil records. The age of fossils can be determined by carbon dating methods.
(2) Comparative method- By comparing several existing forms, we can makes ideas about their common ancestors and reconstruct their about possible history.
(3) Analytic method- By observing present day human being vestigial organs and by studying the development pattern from embryo to adult.
3. What is fossilization? How are fossils formed?
Ans. The process of fossils formation is called fossilization. Fossils are formed when organisms die; their bodies get decomposed and lost. Sometimes the body or a part of it may be in such an environment that it does not let it decompose completely. The mud will eventually harden and retain the impression of the body parts of the organism. This mud with the impression will be called fossil of the organism.
4. What are homologous and analogous organ? Explain with the help of example.
Ans. Homologous organs are those which have similar basic structure and origin but may have different functions. For example- Hands of human beings and wings of birds. Analogous organs- Organs which have different basic structure and origin but have similar function are called analogous organs.
For example- (1) wing of bat and wing of bird.
(2) wing of birds and wing of insect.
5.Differentiate between convergent and divergent
Ans.Convergent Evolution
a.Adapted for similar function
b.Analogous organ
c.do not indicate evolutionary relationship
Divergent Evolution
a.Adapted for different function
b.homologous organ
c.Indicate evolutionary relationship
6. What are the different ways in which individuals with a particular trait may increase in a population?
Ans. The factors which are responsible for raising a new species are selection of environmental conditions for survival of a particular species. If a variation occurs in a population and that variation results in better survival of the organism in the prevailing natural conditions, then the trait would be selected naturally and more in the population.
7. What are the different theories about origin of life?
Ans. (a) Theory of special creation- According to this theory the almighty god created life.
(b) Theory of spontaneous generation- According to this theory, life originated from non- living materials by the process of a biogenesis wring mud, decomposing matter, sun, air and water, etc.
(c) Cosmozoic theory- It states that life came to Earth from some heavenly bodies in the form of spores or seeds.
(d) Biogenesis- This theory states that life originated from pre-existing life.
(e) Modern theory of origin of life- According to this, complex organic molecule was formed from simple inorganic molecules only in suitable condition.
8. What is the difference between chemical evolution and organic evolution?
Ans Chemical Evolution
a.it is the formation of the complex organic compoud from simple compound or element
b.It occured at the time of origin of life
c.Irreversible
d.Speed of evolution is fast
Organic evolution
a.It is the formation of complex form of life from simple form of life
b.It is still occuring
c.Reversible
d.Speed of evolution is slow
9. Give difference between homologous and analogous organs
Ans.Homologous Organs
a.Similar in origin and basic structure but may differ in function
b.Provide idea of common ancestry
c.For e.g hands of human beings and forelimbs of horse
Analogous Organs
a.Dissimilar in origin and basic structure but may have similar function
b.Do not provide the idea of common ancestry
c.for e.g wing of birds insects
10. State three laws of Mendel.
Ans. Mendel’s law-
(a) Law of dominance- when two dissimilar factors of a character are present in an organism only one expresses itself (dominant factor) while other remain unexpressed (recessive factor)
(b) Principle of segregation – two factors of a character are separated at the time of gamete formation and each gamete gets only one factor for that character.
(c) Principle of independent assortment- this principle states that inheritance of two or more pair of contrasting traits is such a way that one pair of contrasting traits is independent of the other pair of contrasting traits.
11. Describe how the sex of the offspring is determined in the zygote ins human beings?
Ans. The males can produce two types of gametes, either X-type or Y-type. The females produce only one type of gametes or ova, X-type. If X-type sperm fuses with the ovum, then the sex of the baby will be female. If Y-type sperm uses with the ovum, then the sex of the baby will be male. Sex of the baby is decided at the time. Sex of the baby is decided at the time of fertilization.
12. Give a suitable explanation for “geographical isolation of individual of a species lead to formation of a new species?
Ans. Reproduction barrier such as river (geographical isolation) between the sub population leading to:
(a) Genetic drift or random changes in the gene frequency by chance alone e.g. selection of red or blue beetles instead of green in presence of crows.
(b) Natural selection or selection of the fittest by nature itself eg. Selection of green beetles instead of red ones in the presence of crows.
13. State the evolutionary force which leads to origin of a new species.
Ans. Various elemental forces of evolution are-
(a) Mutation
(b) Recombination (Crossing over during meiosis, Random assortment of gene at the time of gamete formation).
(c) Natural selection or survival of the fittest.
(d) Genetic drift.
14. What is a fossil? How do fossils tell us about the process of evolution?
Ans. The dead remains of former living organisms are called fossils. The branch of biology which deals with the study of fossils is called paleontology. The study of fossils tells us that species arose from previously existing ones or that the evolution has occurred in nature and is still continuing.
15. Give difference between diploid and haploid.
Ans. Diploid
A.Two chromosomes set
b.Chromosomes present in pairs
c.Formed due to mitosis
d.Found in human beings and higher plants
Haploid
a.One chromosome set
b.Chromosomes present in singly
c.Formed due to meiosis
d.Found in lower plants
16. Who disproved Lamarckism and how?
Ans. The concept of inheritance of acquired character of Lamark was disproved by August Weismann. He cuts the tail of rat at the time of birth and continued this for 21 generation. But tailless rats were never born. This trait do not change the DNA of germ cells so cannot be inherited. Hence, the changes in non-reproductive tissue of an individual during its lifetime cannot be passed on to its progeny, and cannot direct evolution.
17. How does Archaeopteryx provide evidence for organic evolution?
Ans. Archeoptyrx has some features of reptiles, characters of dinosaurs as well as some features of birds like wings. This shows that birds are closely related to reptiles. Birds could evolve from reptiles.
18. What is divergent evolution? Explain with the help of an example.
Ans. The formation of dissimilar looking organisms from common ancestors is called divergent evolution. This is also known as adaptive radiation which represents evolution of new forms in several directions from the common ancestors type. The current example of such a process is the evolution of wild cabbage. For over more than 200 years, humans have cultivated wild cabbage as a food plant and generated different vegetables (like cabbage, broccoli, cauliflower, kohlrabi and kale etc) from it by different artificial selections. Thus all these structures of different vegetables are descended from the same ancestor i.e. wild cabbage.
20. Write similarities between Mendalian’s factors and gene.
Ans. Mendel proposed the inheritance of traits from parents to offsprings by hereditary units called factors. Mendel suggested that every character is controlled by a pair of factors. Sutton and Boveri (1902) found striking similarities between the behaviours of Mendelian factors and the chromosomes during meiosis and fertilization. Factor and chromosomes are present in paired condition in the parents, seprate during meiosis and again get paired after fertilization.
21. How does the creation of variations in a species promote survival?
Ans. Depending on the nature of variations different individuals would have difference kinds of advantage to adjust in particular habitat. Variation help the individual to have different traits that may develop the organisms more tolerable.
22. How do Mendel’s experiments show that traits may be dominant or recessive?
Ans. In Monohybrid cross of Mendel between tall and dwarf pea plant, all progeny in generation are tall and in generation, 75% of pea plants are tall but 25% are dwarf. This shows that traits are dominant or recessive.
23. How do Mendel’s experiments show that traitsare inherited independently?
Ans. When a pea plant having round green seeds is crossed with a pea plant having wrinkled yellow seeds in generation all the plants have round yellow seeds. But in generation two new traits that is round yellow and wrinkled green appear. This shows that traits are inherited independently.
24. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits-blood group A or O- is dominant? Why or why not?
Ans. No, the information is not enough because the blood group is determined by a pair of gene. One inherited from mother and other from father. In this case, the child inherited gene for O blood group from mother as well as father.
25. How is the sex of the child determined in human beings?
Ans. A child which inherits X chromosome from her father will be a girl and one who inherits Y chromosome from him will be a boy.
26. What factors could lead to the rise of a new species?
Ans. Following factors could lead to the rise of new species:
(a) Changes in gene frequency in small breeding isolated populations.
(b) Natural selection
(c) Changes in number of chromosome.
27. Will geographical isolation be a major factor in the speciation of self-pollinating plant species? Why or why not?
Ans. No, because geographical barrier do not allow breeding between such individuals of a population which reproduce sexually. Moreover asexually reproducing organism pass on the parental DNA to offspring which gives no chance of speciation.
28. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Ans. Yes, due to geographical isolation, the two populations are separated. The levels of gene flow between them will decrease. The isolated population will breed with local population resulting in entry of isolated population into new population.
29. What are fossils? What do they tell us about the process of evolution?
Ans. Preserved traces if living organisms are called fossils found closer to the surface of earth are more recent in origin than the fossils we find in deeper layers. Fossils also help us to find evolutionary relation between organisms.
30. 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?
Ans. No, since two copies of traits are inherited from parents, one from mother and the other form father. Unless we know the nature of these two variants of traits we can not tell which is dominant and which is recessive. Recessive traits appear when both the parents contribute recessive allele. From this statement we can only presume are that both parents are contributing recessive allele.
31. Explain the terms analogous and homologous organs with examples.
Ans. Analogous organs: Such organs which perform similar function but are different in structure and origin. Example- Wings of birds and wings of insects.
Homologous organs: Such organs which may have different functions but similar structure and origin. Example- fore arm of frog, lizard and bird.
32. What evidence do we have for the origin of life from inanimate matter?
Ans. The evidence was given by Stanley L. Miller and Harold C. Urey in 1953. They assembled an atmosphere similar to that thought to exist on early earth over water. This was maintained by them at a temperature just below 100 degree Celcious and sparks were passed through the mixture of gases to stimulus lightening. At the end of week, they found that 15% of the carbon had been converted to simple compounds of carbon including amino acids which make up protein molecules.
33. 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?
Ans. Variations arise either because of errors in DNA copying or as a result of sexual reproduction. Due to sexual reproduction genetic variability increases in the population from one generation to another. This happens due to the fact that sexually reproducing organism inherits half the genes from each parent. These variations are very important for the process of evolution.
34. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Ans. No, depending on the nature of variations different individuals have been different kinds of advantages. However, when a drastic change occurs in environment only those organisms in the population will survive which have an advantageous variation in that population to survive in changed environment.
35. How is the equal genetic contribution of male and female parents ensured in the progeny?
Ans. Equal contribution of male and female parents is ensured in progeny during sexual reproduction. Each trait of progeny is determined by a pair of alleles and gametes of male and female contain one allele. Each allele pairs during fertilisation combine together to determine traits. Thus, the traits of progeny are determined by equal genes from male and female.
36. Is it true that when a new species is emerged, the old species is eliminated and why?
Ans. No, it is not true that when a new species is emerged, the old species is eliminated. Because when there is a change in any species, the change is only in a part or a few members of the species population. If the newly generated species after genetic change is better in any way, it will get more opportunity to survive and if the genetic change is against the environment, it will die. Thus, unchanged members of other species may also remain and tend to live in changed environment.
37. Why are traits acquired during life-time of an individual not inherited?
Ans. Traits acquired during life-time of an individual not inherited because change in non- reproductive tissue or somatic cells cannot be passed on to the DNA of germ cells. Thus, the acquired trait will die with the death of the individual. It is therefore non-heritable and cannot be passed on to its progeny.
39. What are the causes of variations in clones?
Ans. i. inaccuracies during DNA copying
ii. Effect of environment termed acquired variation.
iii. Mutations are sudden stable changes which are discontinuous inheritable as produced due to changes in genetic make-up.
40. Only variation that confer and advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Ans. We agree with the statement. All the variation 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 variation. Different individuals have different kind of advantages. A bacteria that can withstand heat will survive better in heat wave.
42. Wild cabbage was converted into number of variants like cauliflower, broccoli and cabbage by man. What is this process known as ? Does it play an important role in organic evolution?
Ans. This process is known as artificial selection. It plays a important role in organic evolution because it is parallel to natural selection. It helps to produce new species having useful traits in less time.
43. How are variant genotypes produced?
Ans. Variant genotypes can be produced by:
1. Mutation in genes and chromosomes.
2. Recombination of genes.
3. Hybridization of genes.
44. Can geographical isolation lead to speciation? How?
Ans. Yes, geographical isolation can lead to speciation. Due to geographical isolation, the members of two sub groups may not be able to interbreed as a result of genetic drift. Natural selection also operates diffetently in these subgroups. This leads to speciation.
1. (i) Who provided the evidence of DNA as genetic material?
(ii) Why DNA is called polynucleotide?
(iii) List three important features of double helical model of DNA.
Ans. (i) Mendel.
(ii) DNA is made up many units of nucleotides.
(iii) Important features-
(a) Both the chains in helical runs anti-parallel.
(b) There two nitrogenous base Purine (A, G) and pyrimidine (T, C).
(c) A always bind with T and C always binds with G.
2. Give the basic features of the mechanism of inheritance.
Ans. Basic features of mechanism of inheritance-
(a) Each character is controlled by a pair of factors. The factors may be similar or dissimilar.
(b) When two dissimilar factors of a character are present in an organism, only one expresses itself while other remains unexpressed.
(c) Two factors of a character are separated at the time of gamete formation and get only one factor for that character.
(d) Inheritance of two or more pairs of contrasting traits in such a way that one pair of contrasting traits is independent of the other pairs of contrasting traits.
19. What is monohybrid and dihybrid cross? Give one example of each.
Ans. Monohybrid cross- It is the simplest cross in which inheritance of one character is studied. A cross is made between the pair of plants having one contrasting character such as tall or dwarf.
Dihybrid cross- A cross made between two plants having two pairs of contrasting character is called dihybrid cross. For ex. round and green seed crossed with yellow and wrinkled seed.
20. Why did Mendel choose pea plant for his experimentation
?
Ans. Mendel selected garden pea for his experiment for the following reasons- (a) The life span of this plant is very short so results can be obtained and studied faster.
(b) Garden pea has many characteristics which are in contrast to each other.
(c) Moreover this plant is small, easy to grow and reproduce large number of offsprings.
22. What are the different ways in which individuals with a particular trait may increase in a population? Ans. The different ways in which individual with a particular trait may increase are: (a) Natural selection- Certain variations give survival advantage to individuals in a population in a changed situation resulting in increase of their population. (b) Genetic drift- Accidents in small population even if they give no survival advantage also lead to increase to certain individual in population 23. How is the sex of a newborn determined in humans?
Ans. Somatic cell of human beings has 23 pairs of chromosomes. Out of them the 23 rd pair contains sex chromosomes. In a male, the somatic cell has X and Y chromosomes in 23 rd pair. In female, the somatic cell has XX chromosomes in 23 rd pair. So, a sperm can have either X or Y chromosome as the 23 rd chromosome. On the other hand, an egg has X chromosome as the 23 rd chromosome. When a sperm with X chromosome fertilizes the egg, the resulting zygote develops into a girl child. When a sperm with Y chromosome fertilizes the egg, the resulting zygote develops into a male child
24.How does the creation of variations in a species promote survival?
Ans. Depending on the nature of variations different individuals would have difference kinds of advantage to adjust in particular habitat. Variation help the individual to have different traits that may develop the organisms more tolerable.
25.How do Mendel’s experiments show that traits are inherited independently? Ans. W hen a pea plant having round green seeds is crossed with a pea plant having wrinkled yellow seeds in F1 generation all the plants have round yellow seeds. But in F 2 generation two new traits that is round yellow and wrinkled green appear. This shows that traits are inherited independently. 26.Why are fossils considered important in the study of evolution? Explain two ways by which age of fossils can be estimated. Ans.Fossils provide evidence in favor of evolution/ establish evolutionary relationships by providing missing links. Two ways 1 . Relative method – Fossils found closer to the surface are more recent than those in deeper layer. 2 . By detecting the ratios of different shapes of the same element in the fossils material
27.A change in DNA that is useful for one property to start with, can become useful later for a different function. Explain.
Ans.A change/feature/property of an organism that may have helped it to adapt to an environmental condition can also become useful for a completely different function in the future. For example: feathers in birds, a character developed and selected during natural selection because it provided insulation in cold weather have become useful in later stages for flight. Some dinosaurs had feathers, but they could not fly. Birds later adapted the feathers to flight
28.How do Mendel’s experiments show that traits may be dominant or recessive?
Ans.Mendel conducted a monohydric cross with pea plants, and he observed that one of the contrasting characters disappears in F 1 generator. This character reappears in F 2 generation (obtained by selfing F 1 ) in just 25% of the progeny. Mendel conclude that the character which expresses itself in F 1 is the dominant character while the other one when is not able to express through present in F 1 individuals is recessive. This recessive character is able to express only in its pure form i.e. in 25% of F 2 individuals.
29.A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Ans. A small population of a species faces a greater threat of extinction than a larger population. Following are some genetic explanation for this:
(a) Inbreeding: A small population promotes inbreeding. This results in least number of variations being incorporated in subsequent generations.
(b) Genetic drift: A small population is more exposed to sudden changes in the environment. The genetic drift because of sudden changes has the potential to wipe off the entire population.
(c) Inbreeding depression: It results in negative population growth which is further detrimental to the survival of the species.
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