Ans. Children do not resemble their parents completely. They possess characters obtained from both the parents. These changes in the phenotypic and genotypic characters are known asvariations. Thus a given population of a species has indefinite variants.
Ans. A gene is a small portion of the DNA, with codes for a particular polypeptide or a protein. In other words, it is the functional unit of the DNA. It is also responsible for the transmission of hereditary characters from the parents to the offspring.
Ans. A chromosome consists of two Chromatids joined together at the centromere. The chromaid consists of the DNA material wound over small protein molecules called histones.
Q 5 – Write one word for the formation of new species due to gradual change over long period oftime.
Ans. Homologous organs are those organs, which have similar origin and basic plans ofdevelopment, but may or may not differ in their functions. The forelimbs of a human, a birdand a horse are homologous organs.
Ans. The process of evolution of species where the characteristics of the organisms whichenable them to survive and reproduce are passed on to their progeny iscalled natural selection.
Q 11 – Identify the analogous and homologous organs amongst the following – wings of aninsect, wings of a bat, forelimbs of lizard, and forelimbs of bird.
Ans. The male sex gametes have X and Y chromosomes, whereas the female sex gametes have two X chromosomes. When a sperm containing a Y chromosome fuses with the ovum containing X chromosome, the zygote develops into a male. When a sperm containing the X chromosome fuses with an ovum containing X chromosome, the zygote develops into a female. Thus the sex of an individual is determined by the sex chromosomes X and Y, which is present in the male chromosomes.
Q 14 – How can we say that change in genes can be brought about by change in DNA?
Ans. Segment of DNA on a chromosome which carries information for the appearance of a particular character is called a gene. It helps in the inheritance of the character from one generation to another. So, we can say that changes in gene can be brought about by change in DNA.
Q 15 – In pea plant, round seed is dominant over wrinkled. If a cross is carried between these two plants, give answer to the following questions. (a) Mention the genes for the traits of parents. (b) State the trait of F1 hybrids. (c) Write the ratio of F2 progeny obtained from this cross. What is the name of the cross?
Ans. (a) RR/rr (b) The F1 hybrid will be Round (Rr). (c) Phenotypic ratio = 3 : 1; Genotypic ratio = 1 : 2 : 1; The cross will be called as Monohybrid cross.
Q 16 – What do you understand by reproductive isolation?
Ans. If the members of the two species are unable to reproduce themselves due to physical, behavioural, ecological, and temporal or development reasons, then the process is called as reproductive isolation.
Q 17 – Explain with the help of a suitable example where the colour change gives no survival advantage to a species?
Ans. In the illustration shown the colour of the red coloured beetles living in the green coloured bushes changes to blue colour, but still, it offers no advantage in the green colour bushes because the predators can easily spot the beetles. An elephant stumps on the bushes and kills most of the red beetles. The blue beetles survive merely by chance and not due to their body colour.
Q 18 – Distinguish between acquired and inherited traits with example of each.
Ans. Reptiles like Dinosaurs had feathers to maintain their body temperature. The birds have adapted the feathers for flight. So, it can be said that the birds have evolved from the reptiles. Archaeopteryx is a fossil which forms a link between the birds and the reptiles.
Ans. Darwin’s theory of evolution is also known as the Theory of Natural Selection or Darwinism. Darwin explained that despite having enormous potential of fertility, the population size of any kind of organism remains within a limit. It is due to the struggle between members of the same species and different species for food, space and mate. This struggle eliminates the unfit individuals. In other words, the fit organisms possess some variations, which are favorable and can leave the progeny to continue the variations. This is called Natural Selection.
Q 21 – Define Genetics. What is the contribution of Mendel in the field of genetics?
Ans. The branch of biology that deals with the study of heredity and variations is known as Genetics. Gregor Johann Mendel was the first person to carry out experiments regarding the heredity of certain characters from one generation to another in a scientific manner. He worked mainly on the garden pea plant. His observations regarding the occurrence of contrasting characters in various generations of garden pea led him to interpret that these are controlled by units which he called, factors. These factors are today known as genes. He is also known as the Father of Genetics.
Q 22 – Can you justify the statement that “Human males are responsible for determining the sex of the baby and not females”?
Ans. The sex in human beings or the sex of the individual is largely genetically determined. A male cell has two types of sex chromosomes i.e., X – chromosome and Y – chromosome because of which male produces two types of sperms with genotype A + X and A + Y. Female cells have two X – chromosomes so the genotype of eggs produced by her is A + X. During fertilisation the chances are:
Q 23 – How do embryological studies provide evidence for evolution?
Ans. The embryology of different vertebrates provide very strong evidence favoring organic evolution. The early embryos of different vertebrates show striking similarities. This indicates common origin and ancestry of different vertebrates. Thus embryological studies provide direct evidence for evolution.
If a sperm carrying Y – chromosome fertilises the egg, then the child born will be a male i.e., AA + XY.
If a sperm carrying X – chromosome fertilises the egg then the child born will be a female i.e., AA + XX
Thus we can infer that the sperm of the male determines the sex of the child.
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Q 24 – Red beetles live in a bush with green beetles. Eventually, the number of green beetles increases as compared to red beetles”.
(a) Give a reason for the increased number of green beetles. (b) State two advantages of variations
Ans. The theory of evolution by natural selection, first formulated in Darwin’s book “On the Origin of Species” in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioural traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring.
The four steps in the process can be summarised as:
Large numbers: The parent produces more offspring than that can survive.
Competition: There is a limited amount of resources, so competition occurs among the offsprings and also with the other members of the population.
Survival of the fittest: Only the members who have favourable variations survive the competition.
Natural selection: The surviving members reproduce and pass on the variations to their progeny.
Q 26 – Define the term ‘Evolution’. “Evolution cannot be equated with progress”. Justify.
Ans. The process by which the new types of organisms are formed from the pre-existing organisms through variations and modifications is called evolution.
Natural selection and genetic drift cause evolution but that does not mean thatOne species is eliminated to form the new one, orThe new species is better than the older one. So, evolution should not be equated with progress as multiple branches are possible at each and every stage of evolution.
Example: Human beings have not evolved from chimpanzees. Both have evolved in their own separate ways from a common ancestor a long time ago.
Q 27 – Our teeth and elephant’s tusks are homologous organs”. Justify this statement. What do the analogous organs indicate?
Ans. Our teeth and elephant’s tusks are homologous organs because they have the same basic structure and origin but perform different functions. Analogous organs are those organs which perform the same function but have different structure.
Q 28 – How and why did human race spread from Africa to other parts of the world?
Ans. Earliest members of human species (Homo sapiens) came from Africa. Some of our ancestors stayed back in Africa while others moved and spread across to West Asia, Central Asia, Eurasia, South Asia, and East Asia.
They moved from the islands of Indonesia and the Philippines to Australia, and some crossed the Bering land bridge to reach America. They did not go in a single line but went forwards and backwards, with groups sometimes separating from each other, sometimes coming back to mix with each other, even moving in and out of Africa.
Q 29 – Give reasons why acquired characters are not inherited.
Ans. No change in the DNA of germ cells is produced by the acquired characters, so they cannot be inherited. Only those characters are inherited which have a gene for them.
Q 30 – Demonstrate with an example that traits may be dominant or recessive. Write down Mendel’s law related to it.
Ans. The cross shown below demonstrates that the traits may be dominant or recessive.
The law related to it is the Mendel’s first law of inheritance i.e., Law of dominance, which states that:
Characters are controlled by discrete units called factors.
Factors occur in pairs.
In a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive).
Q 31 – In a monohybrid cross between tall pea plants denoted by TT and short pea plants denoted by tt, Preeti obtained only tall plants denoted by Tt in the F1 generation. However, in F2 generation she obtained both tall and short pea plants. Using the above information, explain the law of dominance.
Ans. The process of formation of new species from the existing species is called speciation. The factors which lead to the formation of new species are:
(i) Reproductive Isolation: (a) Allopatric speciation: Caused by the various types of barriers like mountain ranges, rivers, seas, etc. It leads to reproductive isolation between members of the species and this is also called geographicalisolation.
(b) Sympatric speciation: It occurs when populations of a species that share the same habitat become reproductively isolated from each other.
(ii) Genetic Drift: It is caused by change in the frequency of a particular genes by accident or by chance alone.
(iii) Natural Selection: The process by which a group of organisms adopts to fit their environment in a better way.
(iv) Migration: When movement of a section of population to another place and population occurs.
(v) Mutation: Sudden changes in the sequence of DNA.
Q 33 – In a cross between plants with purple flowers and plants with white flowers, the FI had all white flowers. When F1 generation was self bred, the F2 generation gave rise to 100 individuals, 75 of which had white flowers. Make a cross and answer. (а) What are the genotypes of F2 individual? (b) What is the ratio of purple flowered plants in F2 generation?
Ans. Yes, geographical isolation gradually leads to genetic drift. It leads to productive isolation between members of the species as it imposes limitations to sexual reproduction of the separated population.
Slowly new variations arise as the separated individuals reproduce among themselves. Accumulation of the variations which arise through a few generations may ultimately lead to the formation of a new species.
Q 35 – Bacteria have a similar body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria. provide a suitable explanation.
Ans. It depends on the perspective which we consider while assessing whether humans are more evolved than the bacteria because, if appearance of complexity is concurrent with evolution, then human beings are certainly more evolved than bacteria.
But if we take the toataliy of life characteristics into account, then it is hard to lable either organisms are evolved.
Q 36 – Give the basic features of the mechanism of inheritance.
Ans. The basic features of the mechanism of inheritance are:
Characters are controlled by genes.
Genes are present on the chromosomes.
Each gene controls one character.
There may be two or more forms of the same gene.
One form of the gene may be dominant over the other.
Two forms of the gene whether similar or dissimilar are present in an individual.
The two forms of the gene separate at the time of gamete formation.
The two forms of the gene are brought together in the zygote.
Q 37 – In a cross between plants with purple flowers and plants with white flowers, the F1 had all purple flowers. When F1 generation was self bred, the F2 generation gave rise to 100 individuals, 75 of which had purple flowers. Make a cross and answer. (a) What are the genotypes of F2 individual? (b) What is the ratio of purple flowered plants in F2 generation?
Ans. Learning a trick at the circus is not an inherited trait. It is an acquired trait which cannot be transferred into the progeny. So, his offsprings will not know the trick by birth.
Q 39 – Do genetic combination of mother’s play a significant role in determining the sex of a new born?
Ans. No, because mothers have a pair of X-chromosomes. All children will inherit an “X’ chromosome from their mother regardless of whether they are boys or girls.
Q 40 – Mention three important features of fossils which help in the study of evolution.
Ans. The type of sex chromosome contributed by the male gamete determines the sex of an infant. Since the ratio of male gametes containing X chromosome and those containing Y chromosome is 50 : 50, the statistical probability of male or a female infant is also 50 : 50.
Q 42 – A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Ans. Extensive inbreeding is imposed by fewer individuals in a species. This limits the appearance of variations and the species is put at a disadvantage if there are changes in the environment. Such individuals fail to cope up with the environmental changes and may become extinct.
Q 43 – A man who has four sons and one daughter believes that he produces more of sperms with Y as a chromosome. With suitable reasons, justify whether he is right or wrong in thinking this way.
Ans. A man produces 50% sperms with Y chromosome and 50% with X chromosome whereas a female produces 100% ovum with X chromosome. So, it’s just a matter of chance which sperm fertilises the ovum. If sperm with Y chromosome fertilises the ovum the progeny will be son and if sperm with X chromosome fertilises the egg, then the progeny will be daughter. So, the man is not right in his thinking that he is producing more sperms having Y chromosome.
Q 44 – Akshat and his wife have attached earlobe (recessive trait) and are professional dancers. They told their colleagues that their offspring would also have attached earlobe and will be a good dancer. Is their notion right? Support your answer with suitable reasons.
Ans. Attached earlobe or free earlobe is an inherited trait. Also, both parents have attached earlobe which is a recessive trait, so the progeny produced will have attached earlobe. But, the ability to dance or being a good dancer is an acquired trait which an individual acquires during its lifetime. So, there is no certainty that the offspring produced will be a good dancer or not. Therefore, the notion they perceive is not right.
Q 45 – “An individual cannot pass on to its progeny the experiences of its lifetime.” Justify the statement with the help of an example and also give reason for the same.
Ans. Experience achieved during the lifetime of an individual does not make any change in the gene of the individual. .
For example: if a person reads a book on birds, the knowledge he earns by reading the book does not make any change in the gene, hence, this knowledge will not get automatically transmitted to his next generation. Such a trait is called acquired trait
Q 46 – Rohit’s father is a wrestler and has a robust body. He was also awarded as Mr. India when he was young. Rohit is the only child. As Rohit grew older, everyone expected him to have the same body built as his father. But he is thin. His friends tease him and he feels depressed by it. (а) Is it true that a wrestler’s son should also have heavy muscles? (b) What type of character is it: acquired or inherited? (c) What are the values shown by Rohit’s friends?
Ans. (a) No, it is not true that a wrestler’s son should also have heavy muscles. (b) It is an acquired character. (c) Rohit’s friend are careless and ignorant. They lack scientific attitude in relation to the above situation.
Q 47 – Explain the mechanism of sex determination in humans. Or With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of sex of a child?
Ans. Homologous organs are those organs which have the same basic structural design and developmental origin but have different unctions and appearance
Example: The forelimb of a frog, a lizard, a bird and a man seem to be built from the same basic design of bones, but they perform different functions.
No, the wing of a butterfly and the wing of a bat cannot be considered homologous organs because they have a common function for flying but their origin and structure are not common. So, they are analogous organs.
Q 49 – Distinguish between homologous organs and analogous organs. In which category; would you place wings of a bird and wings of a bat? Justify your answer giving a suitable reason.
Developed as a result of the adaptation to a different environment
Developed as a result of the adaptation to a similar environment
An arm of a human, the leg of a dog or a flipper of a whale are all homologous structures
From wings in birds, bats and insects to fins in penguins and fishes are all analogous structures
Wings of a bird and wings of a bat are analogous organs as they have different basic structural design but have similar appearance and perform similar functions.
Q 50 – A blue colour flower plant denoted by BB is cross breed with that of white colour flower plant denoted by bb. (a) State the colour of flower you would expect in their F1 generation plants. (b) What must be the percentage of white flower plants in F2 generation if flowers of F1 plants are self-pollinated? (c) State the expected ratio of the genotypes BB and Bb in the F2 progeny.
