1. (a)What is the homology between fore limb of frog, lizard and wing of a bird? What does it indicate? 

(b)State one function each of forelimbs of 

(i) Human being, 

(ii) birds


(a)All of these are similar in fundamental structure but perform different functions. It indicates that more similarity in the fundamental structure, more close is the relationship among the species. 

(b)Function of forelimbs are: 

(i) Fore limbs of human beings – Eating and writing 

(ii) Forelimbs of birds – flying

Q  2. (a) Why traits such as intelligence and knowledge cannot be passed on to the next generation? (b) How can we say that birds are closely related to reptiles and have evolved from them?


(a) Traits such as intelligence and knowledge are not inheritable traits and they do not change the DNA of the germ cells and therefore cannot be passed on to the progeny. (b) Birds are closely related to reptiles and have evolved from them.This can be said because traits such as feathers were first seen in reptiles like dinosaurs, which performed the function of providing insulation to them in cold weather although they could not fly using the feathers but birds adapted the feathers for flight. This means that birds are very closely related to reptiles, as dinosaurs were reptiles.

Q  3. Mention some of the tools for tracing evolutionary relationships among species.


The tools that can be used to trace evolutionary relationships among species are: i. Excavation ii. Time-dating iii. Determining DNA sequences iv. Studying fossils

Q  4. List two ways by which we can estimate the age of fossils.


Two ways by which we can estimate the age of fossils: i. Relative method in which the fossils found in upper layers of earth are of recent origin than the ones found in deeper layers. ii. Carbon dating is the method in which the age of fossils is found by comparing the carbon-14 radioactivity left in fossils with the carbon-14 radioactivity present in the living objects today.

Q  5. The genotype of green stemmed tomato plants is denoted as GG and that of purple stemmed tomato plants as gg. Whenthese twoare crossed 

(i) What colour of stem would you expect in their F1 progeny? 

(ii) What is the percentage of purple stemmed plants in F2 progeny if F1 plants are self pollinated? 

(iii) In what ratio would you find the genotype of GG and Gg in the F2 progeny?


(a) F1 -Progeny – green (b) Purplestemmedplant -25% (c) Ratio of GG and Gg is 1:2:1

Q  6. (a) If a purple flowered pea plant (PP) is crossed with a white flowered pea plant (pp), will we have white flowered pea plant in F1 generation? Why or why not? (b)What do you mean by dominant and recessive trait?


a) No. This is because all the F1 progeny plants show the genetic make up ‘Pp’, which results in purple flowers, as ‘P’ purple coloured flower trait is dominant over the white trait. b) Dominant trait is a genetic trait that is expressed even if there exists only one copy of that gene in the individual. Recessive trait is a genetic trait that is expressed only when two copies of the gene are present.

Q  7. What is a monohybrid cross?


Monohybrid cross is a kind of breeding experiment that considers only one character or trait at a time.

Q  8. Who was the first person to devise the principles of inheritance?


Principles of inheritance was proposed by Gregor Johann Mendel.

Q  9. In Mendel’s experiments what is the meaning of term dominance?


In monohybrid cross where only a single trait is studied at a time, only one of the contrasting characters appears in F1 progeny. The character that expresses itself is known as dominant character and phenomenon is called ‘dominance”.

Q  10. What are fossils? What do they tell about the process of evolution?


Fossils are the impressions or remains of ancient life found preserved in sedimentary rocks, snow or oil. Information given by fossils: 

(i) Fossils reveal that the life form which existed earlier do not exist today. This suggests that the living forms are ever changing. 

(ii) Fossils indicate the time when these organisms existed on earth. 

(iii) Fossils indicate about the extent of evolution that has taken place when they are compared with their present forms.

Q  11. What do you mean by the term variation?


Variation refers to the number of changes that appear among the same members of species and their offspring as a result of genetic recombination.

Q  12. How has the method of artificial selection by humans helped in the evolution of

different vegetables? Explain in brief with the help of an example.


Humans have cultivated wild cabbage and generated different vegetables. Example: i. Some farmers wanted to have very short distances between leaves of  wild cabbage and produced the common variety of ‘cabbage’. ii. When farmers opted for the arrested flower development of wild cabbage plant, it led to the production of broccoli. iii. Some farmers went in for sterile flower of wild cabbage and developed another variety of cabbage called cauliflower. iv. When farmers opted for the swollen part of wild cabbage, it led to the production of Kohlrabi v. Finally, the farmers wanted to grow large leaves of wild cabbage and ended up producing a leafy vegetable called Kale.

Q  13. (a) Give the pair of contrasting traits of the following characters in pea plant and mention which is the dominant and recessive trait. i) Yellow seed ii) round seed (b)What is inheritance?


(a) i) Yellow: dominant    Green: recessive  ii) Round: dominant     Wrinkled: recessive  (b)Inheritance is the transmission of genetically controlled characteristics (or traits) from one generation to the next generation. 

Q  14. What will happen when a pea plant with violet flowers is cross bred with pea plant having white flowers?


Consider a pea plant with violet flower (VV) and a pea plant with white flower (vv) Gametes formed: Plant having violet flowers:    V      V                              Plant having white flowers:    v      v The F1 generation thus produced:     v v V Vv Vv V Vv Vv   All plants of F1 generation will have violet flowers as factor for the violet colour is the dominant trait and white colour is the recessive trait.

Q  15. Describe the mechanism that determines the sex of a child.


In humans, the females have XX sex chromosome while the males have XY chromosome. When the X chromosome of female unites with X chromosome of male, a girl will be born and when X chromosome of females unites with Y chromosome of male, a boy will be born. Thus, the Y chromosome of male (father) determines the sex of child.

Q  16. Distinguish between analogous organs and homologous organs. Identify the analogous and homologous organs amongst the following: Wings of an insect, wings of a bat, forelimbs of frog, forelimbs of human


Analogous Organs Homologous Organs Organs having dissimilar origin and structural plan but perform similar functions are called analogous organs.   Organs having similar origin and structural plan but perform different functions are called homologous organs. Analogous organs – Wings of an insect and wings of a bat. Homologous organs – Forelimbs of frog and forelimbs of human.

Q  17. Mrs. Kumar is pregnant for the last three months and she goes for regular check-up to her doctor. During her last visit, the doctor asked Mrs. Kumar to get an ultrasound done. Both Mr. and Mrs. Kumar went to a radiologist and got the ultrasound done. Once the ultrasound is over, Mr. Kumar asked the doctor whether the baby in the womb is a boy or a girl. 

(a) What should the doctor reply to the couple? 

(b) Is it ethical to determine the sex of a child? 

(c) What should government do to discourage sex determination?


(a) The doctor should not tell the sex of the foetus. (b) No, it is not ethical to determine the sex of a child. (c) The government should ban the process of sex determination and should punish or fine whosoever does so.

Q  18. Birds are very closely related to reptiles. Justify your answer with a suitable example.


Feather provided insulation to dinosaurs in cold weather. Later in the evolutionary process, feathers were used for flight in birds. Because dinosaurs were reptiles, it means that birds are closely related to reptiles.

Q  19. (a) How Archaeopteryx serves as a connecting link between birds and reptiles? (b) What do you mean by the term evolution?


(a) Archaeopteryx looks like a bird but it has many other features which are found in reptiles. It has feathered wings like those of birds but teeth and tail like those of reptiles. Archaeopteryx is, therefore, a connecting link between the reptiles and birds and hence suggests that the birds have evolved from the reptiles. 

(b) Evolution may be defined as the formation of wide varieties of organisms which have been evolved from pre-existing organisms through their gradual changes (variations) since the beginning of life.   

Q  20. (a) State Mendel’s first law of inheritance. (b) How the age of fossils is obtained by carbon dating?


(a) According to Mendel’s first law of inheritance the characteristics (or traits) of an organism are determined by internal ‘factors’ which occur in pairs. Only factor of each pair of such factors can be present in a single gamete.  

(b) All the living objects contain some carbon-14 atoms which are radioactive. When a living object dies and forms fossil, its carbon-14 radioactivity goes on decreasing gradually.  In the carbon dating method, the age of fossils is found by comparing the carbon-14 radioactivity left in fossils with the carbon-14 radioactivity present in living objects today. 

Q  21. Explain the theory of natural selection given by Darwin.


Darwin proposed the theory of natural selection to understand the process of evolution. According to this theory, nature itself selects various traits or characteristics that will suit the members of a species. And thus the individuals who have those traits will be able to survive and reproduce to maintain the continuity of their species while others who are not able to survive perish over time.

Q  22. Why it is more appropriate to compare the process of evolution with branches of a tree rather than with a ladder?


The process of evolution shows similarity when it is compared to the branches of a tree in place of a ladder. It is because of the fact that due to the requirements of changing environment, organisms show some changes or modifications in their existing structures which later on gets inherited in the new generation also. As these changes occur in already existing structures the process of evolution said to progress from simple to complex level rather than from a previous step to the new one as in case of a ladder.

Q  23. Guinea pig having black colour when crossed with guinea pig having same colour produced 100 offsprings out of which 75 were black and 25 were white. Now find out. (a) What is the possible genotype of the guinea pig? (b) Which trait is dominant and which trait is recessive? (c) What is this cross called as, and what is the ratio of F2 progeny obtained from these cross?


(i) Possible genotype of the guinea pig : Bb X Bb 

(ii) Black is dominant and white is recessive. 

(iii) Monohybrid cross. Phenotypic ratio=3:1

Q  24. Describe any three ways in which individuals with a particular trait may increase in a population.


Different ways in which individuals with a particular trait may increase in population are:variation,natural selection and genetic drift. i. Variation:Variations are defined as the occurrence of differences among the individuals. No two individuals are exactly alike. Variations arising during the process of reproduction can be inherited and leads to increased survival of individuals. ii.Natural selection: It results in adaptations in population to fit their environment better. Thus, natural selection directs evolution in the population of a particular species. iii. Genetic drift: The change in the frequency of certain genes in a population over generations is called genetic drift. 

Q  25. Mention the contribution of Lamarck in understanding the concept of evolution.


Lamarck proposed a theory that defined the process of evolution and how it occurs. Major postulates of his theory are: i. ‘Use and disuse of organs’ on long term basis leads to changes in the body structure of individuals. These changes are inheritable and later on bring about evolution. ii. The number of changes that appear as a result of evolution are all acquired by individuals during their life time as per the reQ  uirement of changing environment.

Q  26. (i)What does the forelimb of bird and forelimb of human being indicates? 

(ii)Explain the term analogous organs with examples.


(a) The forelimb of bird and forelimb of human being are homologous organs.  (b) Analogous organs- Those organs which have different basic structure but have similar appearance and perform similar functions are called analogous organs. Example- Wings of an insect and a bird have different structures but perform similar functions.

Q  27. What will happen if due to some accident, changes occur in the gene frequency of members of sub population of a species? Also, identify the name of this phenomenon.


This phenomenon is known as ‘Genetic drift’. It is said to occur when the genetic make up of organisms change a bit accidentally. As these changes occur without any kind of adaptation they have no survival advantage.

Q  28. What is speciation? Describe in brief the factors that control the process of speciation.


Speciation: The formation of a new and distinct species in the course of evolution is called speciation. Factors controlling process of speciation: 

(i) Genetic Drift: It is a mechanism of evolution and refers to random fluctuations in the frequencies of alleles from generation to generation due to chance events. 

(ii) Mutation: It occurs when a gene is damaged or changed in such a way as to alter the genetic message carried by that gene. 

(iii) Natural selection: It is the process whereby organisms better adapted to their environment tend to survive and produce more offsprings. 

(iv) Migration: It is the periodic seasonal movement of organisms from one geographic region to another, typically coinciding with available food supplies or breeding seasons.

Q  29. What are the evidences that can be used to study organic evolution?


The evidences that are used to study organic evolution in nature are basically grouped in three categories: i. Morphological and anatomical evidences: These evidences include the study of homologous, analogous and vestigial organs to trace evolutionary relationships. ii. Embryological evidences: These evidences include the study of development of embryo from an egg to an adult in different organisms (animal groups). iii. Palaeontological evidences: These evidences deal with the study of fossil records to know about how far this evolutionary relationship goes.

Q  30. Study the given data and answer the questions that follow: 1 2 3 Parental plant cross fertilized and seeds collected F1 Generation offspring F2 Generation offspring after self pollination of F1 hybrid Male parent- Round Yellow seeds Female Parent- Wrinkled Green seeds All seeds- round Yellow 314- round yellow 110-Round Green 102-Wrinkled yellow 32-wrinkled Green (a) What is the term given to this type of cross? (b) What does the data in column 2 indicate? State how did you arrive at this conclusion.


(a) Dihybrid Cross. (b) Round shape and yellow colour in the pea plants are the dominant traits. In F1 generation, the off springs are hybrid ones i.e. RrYy. When both dominant and recessive traits are present together then only dominant traits are expressed.

Q  31. (a) What is speciation? 

(b) Explain whether the traits like eye colour or height is genetically inherited or not. 

(c)Do power to lift weight and reading French also belong to same category? Justify your answer.


(a) The process in which new species are formed from the preexisting species is known as speciation.

(b) Yes, traits like eye colour or height is genetically inherited because they can be passed on from one generation to the next. (Inherited characters) 

(c)No, power to lift and reading French does not belong to same category as it cannot be passed on from one generation to the next (as they are acquired characters)

Q  32. A black mouse mates with a brown mouse, and all the off springs are black. 

(a) Why are no brown off springs produced? 

(b) If two of the black off springs mate with each other what kind of offspring would you expect and in what proportions? Give reason for your answer.


(a) Because black colour genes are dominant over brown colour genes. 

(b) Three black mice and one brown mouse will be obtained in F2 generation. It is a monohybrid cross.

Q  33. Briefly explain Darwin’s theory of evolution.


(i) Within any population, there is natural variation. Some individuals have more favourable variations than others. 

(ii) Even though all the species produce a large number of offsprings, populations remain fairly constant naturally. 

(iii) This is due to the struggle between members of the same species and different species for food, space and mate. 

(iv) The struggle for survival within populations eliminates the unfit individuals. The fit individuals possessing favourable variations which survive and reproduce. This is called natural selection. 

(v) The individuals having favourable variations pass on these variations to their progeny from generation to generation. 

(vi) These variations when accumulated over a long period of time, leads to the origin of a new species.

Q  34. Explain the term analogous organs with the help of an example.


Analogous organs have different origin and different basic structure but are present in organisms to perform the same functions. For example: wings of a bird and wings of a bat have the same function i.e. help them to fly but structurally they are different. Wings of a bird are present in the form of feathery covering while in case of bat wings are the skin folds between elongated fibers.

Q  35. What do you mean by the term evolution?


Evolution is a gradual and continuing process of change that occur over a period of time, due to slight variations in genetic compositions as well as changes in environment, leading to formation of new species.

Q  36. What is the importance of DNA copying in reproduction? Why is variation beneficial to the species but not necessary for the individual? Explain.


DNA copying is essential part of reproduction because it ensures that same blue print of the body design is maintained. Variation for the species is beneficial for adaptation and better survival. It may result in the formation of new species; however in an individual variation may not always be beneficial and may lead to disease or disorders, hence variation is beneficial for the species but not for an individual. 

Q  37. “A brother and sister are more related to each other as compared to the case when any one of them is related with his/her cousin”. Through this statement what will we get to know about their ancestors?


A brother and sister are more closely related to each other which mean that they have common ancestors more recently as compared to the case when any one of them (brother or sister) is related to the cousin. A brother and sister have their “parents” in common while a brother or sister and cousin have “grandparents” in common.

Q  38. (a) Mendel selected garden Pea plant for his experiments. List two reasons. (b) State the meaning of recessive and dominant genes.


(a) Mendel selected garden Pea plant for his experiment because 

(i) It is normally self – pollinated but can be easily cross – pollinated. 

(ii) It has traits with distinctly contrasting forms and also it has a short life span. 

(b) (i) Recessive genes – Those genes which are notable to express themselves in the presence of their allele are called recessive genes. 

(ii) Dominant genes – Those genes which are able to express themselves in the presence of their allele are called dominant genes.

Q  39. Describe briefly the origin of earliest members of human species and how they were spread in different parts.


It was found that the earliest members of human species i.e. Homo sapiens were found in Africa. From there some members stayed in Africa while others migrated and spread out in various parts like Central Asia, Eurasia, South Asia, Australia etc. These species travelled both backwards and forwards from a common place where they initially originated and then evolved and settled as either a new separate group or sometimes re-mixed with the original group.

Q  40. Describe the law of independent assortment with the help of an example.


The law of independent assortment states that during dihybrid cross when two characters are studied simultaneously then factors for a particular trait (character) are inherited in the new progeny irrespective of each other. For example: When a pea plant with round and yellow seed (RRYY) is cross bred with plant having wrinkled and green seeds (rryy).     ry ry RY RrYy RrYy RY RrYy RrYy    The new progeny (F1 generation) has all plants with round and yellow seeds. When these are self pollinated ratio of 9:3:3:1 is obtained which depicts their independent inheritance.   RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy