Solutions

NCERT Solutions for Class 10 Science Chapter 9 Heredity and Evolution

Question1.
How do Mendel experiments show that the traits may be dominant or recessive?

Answer:

Mendel Experiments: Monohybrid Inheritance (One Visible Con¬trasting Character): Mendel first took pea plants with different characteristics such as a pure bred tall plant and a dwarf plant and crossed them. He found that only tall pea plants were produced in the F1 progeny. Then he allowed the F1, tall plants to reproduce by self-pollination, and found that the F2 progeny of the F1 tall plants were not all tall. Both tall and dwarf plants were obtained in the ratio of 3 :1. This ratio is known as the monohybrid ratio.

This indicated that both tallness and shortness traits were inherited in F1 generation but only tallness trait was expressed which was dominant over the unexpressed trait, i.e. shortness.

Question2.
If a trait A exists in 10% of a population of an a sexually reproducing species and a trait B exisis in 60% of the same population, which trait is likely to have arisen earlier?

Answer:Trait B is likely to have arisen earlier than trait A. The new traits in a population occurs due to inaccuracies while DNA copying mechanism. Hence, the new traits would be present in a veiy small proportion compared to the old one which is already exists

Question3.
How does the creation of variations in a species promote survival?

Answer:Variations enable a species to adapt according to the changes and new needs and thus provide survival of species

Question4.
How do Mendel experiments show that traits are inherited independently?

Answer:

Dihybrid Inheritance (Two Visible Contrasting Characters): Mendel took pea plants having two different characteristics: of seeds such as round shape with yellow colour and wrinkled shape with green colour, and crossed them. He found that only round-yellow seeds were produced in the F1 progeny. Then he used F1 progeny to generate F2 progeny by self-pollination. He got four different combinations of seeds: round - yellow, round - green, wrinkled - yellow and wrinkled-green in the ratio of 9 : 3 : 3 : 1. This ratio is known as dihybrid ratio.

Question5.
A man with blood group A marries a woman with blood group 0 and their daughter has blood group 0. Is this information enough to tell you which of the trait - blood group A or 0 - is dominant? Why or why not?

Answer:No, this information is not enough to tell us which of the traits - blood group A or 0, is dominant. Because a pair of genes determines the blood group. In this case child has inherited 1° from mother as well as father. (Father having I°I° and mother having I°I°.)

Question6.
How is the sex of a child determined in human beings?

Answer:

Sex Chromosomes A male has XY sex chromosome and produces two types of sperms; 50% of them carrying X chromosomes and another 50% carrying the Y chromosomes. A female carries XX sex chromosomes and hence produces only X - carrying eggs. If X-carrying egg fuses with the X -carrying sperm, the child born will be a girl. If X - carrying egg fuses with the Y carrying sperm, the child born will be a boy.

Question7.
What are the different ways in which individuals with a particular trait may increase in a population?

Answer:

  • Natural selection
  • Genetic drift
  • Geographical isolation
Question8.
Why are traits acquired during the lifetime of an individual not inherited?

Answer:

Inherited Trait The transmission of certain genetically controlled traits from parents to their offspring or from one generation to the next, which bear all the basic features with a great deal of variation are called inherited traits.

Question9.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer:As the number of surviving tigers is small, the sets of genes will be limited. This results in limited variation in characters during sexual reproduction, thereby causing danger for their survival in changing conditions

Question10.
What factors could lead to the rise of a new species?

Answer:

  • Natural selection
  • Genetic drift
  • Geographical isolation
Question11.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?

Answer:In a self-pollinating plant species, geographical segregation cannot be a major factor in speciation. This is because in self-pollinating plants, pollination is occurring in the same plant.
So a natural barrier cannot cause hindrance

Question12.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

Answer:In case of an asexually reproducing organism, geographical isolation cannot be a major factor in speciation. This is because in asexual reproduction, only one parent is involved and natural barrier cannot pose a problem

Question13.
Give an example of characteristics being used to determine how close two species are in evolutionary terms?

Answer:Homologous characteristics are being used to determine how close two species are in evolutionary terms. For example, the forelimbs of human and bird have similar basic structure
though they are modified to perform different functions in them. The basic structure or anatomical similarity points to the existence of a common ancestor from these have evolved

Question14.
Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?

Answer:No, they are not to be considered as homologous organs because they perform the same function but they do not have same structures and origins. In fact, they are the examples of analogous organs

Question15.
What are fossils? What do they tell us about the process of evolution?

Answer:Fossils are the remains or traces of dead plants and animals that lived in the past They provide the proof of changes and the relationship between various groups of organisms. They show how one species gives rise to another species with certain modifications. They allow us to make estimates of how far back evolutionary relationships go

Question16.
Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?

Answer:

    Human beings who look so different from each other in terms of size, colour and looks said to belong to the same species because of the following reasons:
  • They have same number of chromosomes
  • They have a common ancestor
  • They interbreed to produce fertile offsprings
Question17.
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a better body design? Why or why not?

Answer:Chimpanzees have more complex body design than fish, followed by spiders and then bacteria. Yet, we cannot say that chimpanzees have a better body design, because evolution does not necessarily mean progress. Evolution simply means the generation of diversity and selection by nature. It is the adaptability of an organism to the environment that supports its survival, not its complexity. Bacteria which are the simplest life forms still survive today. They are found in varied habitats like hot springs, in ice sheets, etc. only because of their adaptability to the changing environment. Thus, in evolutionary terms, we cannot say that a particular organism has a better body design

Chapter End Questions

Question1.
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?
  • TTWW
  • TTww
  • TtWW
  • TtWw

Answer:

  • TtWW
Question2.
An example of homologous organs is?
  • our arm and a dog fore leg
  • our teeth and an elephant tusks
  • potato and runners of grass
  • all of the above

Answer:

  • all of the above
Question3.
In evolutionary terms, we have more in common with?
  • A Chinese school-boy
  • A chimpanzee
  • A spider
  • A bacterium

Answer:

  • A Chinese school-boy
Question4.
A study found that children with light-coloured eyes are likely to have parents with light- coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?

Answer:Yes, we can say that the light eye colour trait is dominant because children born from the parents having light-coloured eyes also had light-coloured eyes

Analogous Organs:
Question5.
Explain the terms analogous and homologous organs with examples?

Answer:

Analogous Organs:

Homologous organs :

Structures which perform similar functions in different organisms and have a common evolutionary origin are called homologous organs. Analogous organs : Organs by different organisms having similar functions but with different anatomy ( structure ) can analogous. Such organs are considered examples of convergence - where species not closely related independently evolve similar traits as a result of having to adapt to similar environments or ecological niches. Homologous //structures or organs -are those which have got similar origin in two different species, i,e structures evolved from common ancestors. The may have same function or they may not. Such organs are a product of divergent evolution that makes species evolve in other directions from an ancestral species.

Human and whale forelimb:

Humans have a very similar bone arrangement which consists of the humerus, radius, and ulna in their forlimbs to those found in whales because both inherited it from their common ancestor Though in whales, they have evolved to swim whereas humans require manipulation with these limbs

Question6.
Outline a project which aims to find the dominantcoat colour in dogs?

Answer:Let a dog with black colour homozygous trait (BB) mate with dog with white homozygous trait (bb). If the offspring of Ft generation are black, then the black trait is dominant. If the offspring of F1 generation are all white, then the white trait is dominant

Question7.
How are the areas of study - evolution and classification, interlinked?

Answer:Classification of organisms into groups is based on the similarities and differences between them. The more characteristics two species or organisms will have in common, the more closely they are related and the more recently they will have had a common ancestor. Classification shows that how closely organisms are related with respect to evolution. It is in fact a reflection of their evolutionary relationship

Question8.
Explain the importance of fossils in deciding evolutionary relationships?

Answer:Fossils are the remains or traces of dead plants and animals that lived in the past They provide the proof of changes and the relationship between various groups of organisms. They show how one species gives rise to another species with certain modifications. They allow us to make estimates of how far back evolutionary relationships go

Question9.
What evidence do we have for the origin of life from inanimate matter?

Answer:In 1953, Miller and Urey assembled an early earth atmosphere which consisted gases like NH3, CH4 and H2S, etc. except oxygen, over water. They maintained it at the temperature just below the 100°C and passed electric sparks in the mixture of gases to stimulate lightning. This was continued about one week. After that they found that 15% carbon from CH4 had been converted to simple organic compound like sugar and amino acids which constitute into protein molecules. This experiment gives the evidence for origin of life from inanimate matter

Question10.
Explain how sexual reproduction gives rise to more viable variations than asexual repro-duction. How does this affect the evolution of those organisms-that reproduce sexually?

Answer:In sexual reproduction, the DNA comes from two parents. Therefore, the variations are more obvious. When the next generation reproduces, it passes on the characteristics inherited from the parents as well as its own individual traits. This results in similarities and variations

Question11.
How is the equal genetic contribution of male and female parents ensured in the progeny?

Answer:Individually both male and female parents possess 23 pairs of chromosomes, i.e. they have a total of 46 chromosomes. During gametes formation, this diploid chromosome number gets halved. The female gamete has 22 + X chromosomes and the male gamete has 22 + X or 22 + Y chromosomes. When the female and the male gametes fuses, the diploid condition again get restored in the zygote

The zygote has 44 + XX or 44 + XY chromosomes.

In this way, the equal genetic contribution of male and female parents is ensured in the progeny.

Question12.
Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?

Answer:Yes, we agree with this statement because advantageous variations enable an organism to cope with changes in the environment. For example, there is a sudden drop in environ-mental temperature of an area where bacteria live. Under such condition only those bacteria that can tolerate low temperature will survive in a cold wave, while others do not. These survivors pass on their advantageous characters to their offspring resulting in the formation of new species

Important Question

Important Questions of How Do Organisms Reproduce Class 10 Science Chapter 8

Question 1.
Newly formed DNA copies may not be identical at times. Give one reason?
Year of Question :(2017)

Answer: When a cell reproduces, DNA replication occurs which results in formation of two similar copies of DNA. The process of copying the DNA leads to some variations each time. As a result, the DNA copies produced are similar to each other but sometimes may not identical

Question 2.
When a cell reproduces, what happens to its DNA?
Year of Question :(2012)

Answer: When a cell reproduces, DNA replication occurs which forms two similar copies of DNA

Question 3.
What is DNA?
Year of Question :(2013)

Answer: DNA (deoxyribonucleic acid) is a polymer made up of large number of nucleotide units. It carries genetic information from generation to generation

Question 4.
Name the life process of an organism that helps in the growth of its population?
Year of Question :(2012)

Answer: Reproduction is a life process that helps in multiplication of an organism and growth of its population

Question 5.
Reproduction is one of the most important characteristic of living beings. Give three reasons in support of the statement.?
Year of Question :(2017)

Answer: Reproduction is one of the most important characteristics of living beings because

  • it is essential for existence and continuity of a species
  • it helps to pass genetic information to next generation
  • it brings variations in next generation which is the basis for evolution
Question 6.
Define reproduction. How does it helps in providing stability to the population of species?
Year of Question :(2016)

Answer: The production of new organisms by the existing organisms of the same species is known as reproduction. It is linked to the stability of population of a species. DNA replication during reproduction ensures transfer of specific characters or body design features that is essential for an individual of a population to live and use that particular niche. Some variations present in a few individuals of population caused due to reproduction which also helps in their survival at changing niches

Question 7.
What is DNA copying? State its importance?
Year of Question :(2012)

Answer: DNA copying is the production of similar copies of DNA present in a cell using various chemical reactions. DNA copying is essential for reproduction through which the organisms pass on their body features to their offspring. Moreover, minor alternations during the process of DNA copying result in the production of variations. Such variations are useful for the survival of species over time

Question 8.
What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process? How does the amount of DNA remain constant through each new generation is a combination of DNA copies of two individuals? ?
Year of Question :(2014)

Answer: In the process of reproduction, if DNA copying is not perfectly accurate, variation occurs. These in turn may allow few individuals of a population to survive in an altered niche and becomes the basis of evolution and over time. Such variations are useful for the survival of species. The combination of DNA copies of two individuals, (male and female) occurs during sexual reproduction. Reduction division (meiosis) during gamete formation halves the chromosome number in both male and female gametes. Since these two gametes fuse during fertilisation, the original number of chromosomes (as in the parent) is restored in the offspring. By this way the amount of DNA remains constant in each new generation

Question 9.
Name the method by which Spirogyra reproduces under favourable conditions. Is this method sexual or asexual?
Year of Question :(2012)

Answer: The method by which Spirogyra reproduces under favorable conditions is fragmentation. This is an asexual mode of reproduction

Question 10.
How does Plasmodium reproduce. Is this method sexual or asexual?
Year of Question :(2017)

Answer: Plasmodium reproduces through multiple fission method. In this method, the parent organism splits to form many new organisms at the same time. This is an asexual method of reproduction

Question 11.
Name the part of Bryophyllum where the buds are produced for vegetative propagation?
Year of Question :(2012)

Answer: Bryophyllum propagates vegetatively by the buds produced at the margins of leaves

Question 12.
What happens when a Planaria gets cut into two pieces?
Year of Question :(2016)

Answer: When Planaria is cut into two pieces then each piece grows into a complete organism. This is known as regeneration

Question 13.
What happens when a mature Spirogyra filament attains considerable length?
Year of Question :(2016)

Answer: When a mature Spirogyra filament attains considerable length it simply breaks into two or more fragments and each fragment then grows into a new Spirogyra

Question 14. Name the method by which Hydra reproduces. Is this method sexual or asexual ?
Year of Question :(2016)

Answer: Hydra generally reproduces through budding. It is an asexual method of reproduction

Question 15.
Name two simple organisms having the ability of regeneration?
Year of Question :(2012)

Answer: Hydra and Planaria are two organisms that have the ability to regenerate

Question 16.
Name the causative agent of the disease "kala- azar" and its mode of asexual reproduction?
Year of Question :(2012)

Answer: Causative agent of the disease Kala-azar is Leishmania. It reproduces asexually by binary fission

Question 17.
Write two differences between binary fission and multiple fission in a tabular form?
Year of Question :(2015)

Answer: Differences between binary fission and multiple fission are as follows

Binary fission Multiple fission
  • (i) The parent organism, splits to form two new organisms, e.g., Amoeba, Paramecium
  • The parent organism splits to form many new organisms at the same time, e.g., Plasmodium.
  • The parent organism splits to form many new organisms at the same time, e.g., Plasmodium
  • The nucleus of the parent body divides repeatedly to produce many nuclei.
  • Question 18.
    List four modes of asexual reproduction other than fission in the living organisms?
    Year of Question :(2014)

    Answer: The four modes of asexual reproduction other than fission in living organisms are budding spore formation regeneration and Fragmentation

    Question 19.
    List four advantages of vegetative propagation?
    Year of Question :(2012)

    Answer: The following are the advantages of vegetative propagation The characters of the parent plants are preserved hence a good variety produced can be propagated by vegetative means. The plants, which do not produce viable seeds or produce very few seeds, can be reproduced by this method. For example, banana, potato, grapes, sugarcane, rose, orange, etc. It is an easier, quicker and cheaper method of propagation. It is easier to get rid of pathogen from any part of plant by vegetative propagation

    Question 20.
    List four modes of asexual reproduction?
    Year of Question :(2014)

    Answer: The four modes of asexual reproduction are : binary fission budding regeneration and vegetative propagation

    Question 21.
    Draw labelled diagrams to illustrate budding in Hydra?
    Year of Question :(2014)

    Answer: The given diagram illustrates budding in Hydra

    Question 22.
    How do Plasmodium and Leishmania reproduce? Write one difference in their mode of reproduction.?
    Year of Question :(2012)

    Answer: Plasmodium and Leishmania reproduce by the process of fission which is an asexual mode of reproduction. Plasmodium reproduces by multiple fission. About 1000 daughter cells are produced by the multiple fission of a Plasmodium. Leishmania reproduces by the process of binary fission. In Leishmania, the splitting of parent cell takes place in a definite plane (longitudinally) with respect to flagellum at its end to produce two daughter cells

    Question 23.
    Define multiple fission. Give its one exampl?
    Year of Question :(2014)

    Answer: Multiple fission is an asexual mode of reproduction in which the parent organism splits to form many new organisms at the same time. Multiple fission occurs in Plasmodium

    Question 24.
    List two advantages ofvegetative reproduction practised in case of an orange plant?
    Year of Question :(2012)

    Answer: The two advantages of vegetative propagation practised in case of an orange plant are

    • The new plants produced by vegetative propagation will be exactly like the parent plant. Therefore, any desirable features of the parent plant will be replicated in the new plants
    • The orange plants that have lost the capacity to produce seeds, can also be propagated
    Question 25.
    Name an organism which reproduces by spore formation. List three conditions favourable for spores to germinate and grow.?
    Year of Question :(2012)

    Answer: Rhizopus reproduce by the method of spore formation. The three conditions favourable for spores to germinate and grow are moisture, suitable temperature and food (nutrition)

    Question 26.
    List two advantages of practising vegetative propagation in plants. Select two plants raised by this method from the list given below : Banana, Gram, Pea, Rose, Tomato, Wheat?
    Year of Question :(2012)

    Answer: Two advantages of the vegetative propagation of plants are

    • Any desirable features of the parent plant can be replicated in the new plants
    • Flowers and fruits can be grown in a shorter time as compared to the plants grown from seeds. The two plants raised by this method are banana and rose
    Question 27.
    Write any two differences between binary fission and multiple fission in a tabular form as observed in cells of organisms?
    Year of Question :(2012)

    Answer:Differences between binary fission and multiple fission are as follows

    Binary fission Multiple fission
  • (i) The parent organism, splits to form two new organisms, e.g., Amoeba, Paramecium
  • The parent organism splits to form many new organisms at the same time, e.g., Plasmodium.
  • The parent organism splits to form many new organisms at the same time, e.g., Plasmodium
  • The nucleus of the parent body divides repeatedly to produce many nuclei.
  • Question 28.
    List any four reasons for vegetative propagation being practised in the growth of some type of plants?
    Year of Question :(2012)

    Answer: The following are the advantages of vegetative propagation The characters of the parent plants are preserved hence a good variety produced can be propagated by vegetative means. The plants, which do not produce viable seeds or produce very few seeds, can be reproduced by this method. For example, banana, potato, grapes, sugarcane, rose, orange, etc. It is an easier, quicker and cheaper method of propagation. It is easier to get rid of pathogen from any part of plant by vegetative propagation

    Question 29.
    What is vegetative propagation? Write two of its advantages?
    Year of Question :(2011)

    Answer: Vegetative propagation is a method of asexual reproduction in plants in which the parts other than seeds are used as propagules. Also refer to answer 26

    Question 30.
    Write one main difference between asexual and sexual mode of reproduction. Which species is likely to have comparatively better chances of survival - the one reproducing asexually or the one reproducing sexually?
    Year of Question :(2012)

    Answer: Difference between asexual and sexual mode of reproduction is as follows : Asexual reproduction: Gametes are not formed hence fertilisation does not take place. Sexual reproduction: Gametes are always formed and fertilisation takes place to form a zygote

    Important Questions and Answers from Chapter 9: Heredity and Evolution

    Question 1.
    What is Heredity?

    Answer:
    Heredity refers to the passing of "traits" (physical or behavioral characteristics) from parents to their offspring.
    It explains why children often resemble their parents but are not exactly the same.

    Question 2.
    What are Dominant and Recessive Traits?

    Answer:
    Dominant Traits:
    Traits that are expressed when two different versions (alleles) of a gene are present.
    Example: Tallness in pea plants is a dominant trait.
    Recessive Traits:
    Traits that are only expressed when both alleles are the same.
    Example: Shortness in pea plants is a recessive trait.

    Question 3.
    Who was Gregor Mendel, and what were his contributions to heredity?

    Answer:
    Gregor Mendel (1822-1884) is known as the "Father of Genetics."
    He conducted experiments on pea plants in a monastery garden to understand how traits are inherited.
    Key Contributions:
    Discovered the basic rules of heredity through his experiments.
    Introduced the concepts of dominant and recessive traits.
    Formulated the Laws of Inheritance, explaining how traits are passed down from parents to offspring.

    Question 4.
    Explain Mendel’s experiment with pea plants.

    Answer:
    First Experiment:
    Crossed a tall pea plant with a short pea plant.
    All the plants in the first generation (F1) were tall.
    Second Experiment:
    Allowed the F1 tall plants to self-pollinate.
    In the second generation (F2), some plants were tall, and some were short.
    The ratio of tall to short plants was 3:1.
    Conclusion:
    Tallness is a dominant trait, and shortness is a recessive trait.

    Question 5.
    What is Evolution?

    Answer:
    Evolution is the process by which living organisms gradually change over many generations to adapt to their environment.
    It explains how simple life forms evolved into more complex forms over time.

    Question 6.
    How is Sex Determined in Humans?

    Answer:
    Humans have two types of sex chromosomes: X and Y.
    Sex Chromosomes:
    Females have XX chromosomes.
    Males have XY chromosomes.
    How It Works:
    A child always inherits an X chromosome from the mother.
    If the father provides an X, the child will be a girl (XX).
    If the father provides a Y, the child will be a boy (XY).

    Question 7.
    What is Natural Selection?

    Answer:
    Natural Selection is the process by which certain traits become more common in a population because they provide a survival advantage.
    Coined by Charles Darwin in his theory of evolution.
    Example:
    In a population of beetles, green beetles may survive better in green bushes because predators like crows cannot see them easily, while red beetles are eaten more frequently.

    Question 8.
    What is Genetic Drift?

    Answer:
    Genetic Drift is a random change in the frequency of certain genes in a small population.
    It does not necessarily give a survival advantage but can still lead to changes in the population.
    Example:
    If a natural disaster kills many beetles, by chance, only the blue beetles may survive, causing them to become the dominant trait in future generations.

    Question 9.
    What are Fossils, and how do they provide evidence of evolution?

    Answer:
    Fossils are the preserved remains or traces of ancient organisms.
    They are usually found in layers of rock.
    Importance in Evolution:
    Fossils show the gradual changes in species over millions of years.
    By studying fossils, scientists can trace how life forms evolved and how species are related.

    Question 10.
    Explain the concept of Speciation.

    Answer:
    Speciation is the formation of new species from an existing species.
    How It Happens:
    A population of a species may become separated due to geographical isolation (e.g., a river).
    Over time, the two groups accumulate different genetic changes.
    Eventually, they may become so different that they can no longer reproduce with each other, forming new species.

    Question 11.
    What is the difference between Homologous and Analogous Organs?

    Answer:
    Homologous Organs:
    Organs that have the same basic structure but different functions.
    Example: Human arm and bird wing are homologous as they have the same structure but different uses.
    Analogous Organs:
    Organs that perform the same function but have different structures.
    Example: Bat wing and bird wing are analogous as they are used for flying but have different structures.

    Question 12.
    What are Acquired Traits? Why are they not inherited?

    Answer:
    Acquired Traits are characteristics that an individual develops during their lifetime due to environmental factors or actions (e.g., building muscles).
    Why Not Inherited:
    These traits do not change the DNA in reproductive cells and therefore cannot be passed to offspring.
    Only traits that are present in an organism’s genes are inherited.

    Question 13.
    How do Inherited Traits affect the survival of a species?

    Answer:
    Some inherited traits may provide a survival advantage.
    Examples:
    A green-colored beetle may survive better in a green environment as it is harder for predators to spot.
    This trait is likely to increase in the population over time due to natural selection.

    Question 14.
    How are Evolution and Classification Interlinked?

    Answer:
    Classification groups organisms based on their similarities.
    These similarities often indicate evolutionary relationships.
    The more characteristics two species share, the closer they are on the evolutionary tree.

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