KSEEB Class 10 Science Important Questions Chapter 9 Heredity and Evolution

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Karnataka SSLC Class 10 Science Important Questions Chapter 9 Heredity and Evolution

Question 1.
What are inherited traits?
Answer:
The traits (characteristics) that are transferred from the parents to their offspring through genes are called inherited traits.

Question 2.
What is heredity?
Answer:
The transmission of characteristics (traits) from the parents to their offspring through genes is known as heredity.

Question 3.
What is genetics?

OR

Define genetics.
Answer:
The branch of biology that deals with the systematic study of heredity, variation and factors responsible for these is known as genetics.

Question 4.
Who is considered as the father of modern genetics?
Answer:
Gregor Johann Mendel is considered as the father of modem genetics.

Question 5.
Name the plant on which Gregor Mendel did his experiments on genetics.
Answer:
Mendel performed his experiments on heredity and genetics on garden pea plants.

Question 6.
What is the contribution of Gregor Mendel to our understanding of inheritance of characteristics?
Answer:
Mendel did his experiments on garden pea (Pisum sativum) and discovered the scientific principles which govern patterns of inheritance, i.e., the principle of inheritance. He explained that contrasting characters are controlled by units which he called factors. Today these factors are called genes.

Question 7.
Why did Mendel choose pea plants for his experiments on inheritance?
Answer:
Mendel chose pea plants for his experiments for the following reasons

1. Pea plants could be grown easily either in an open field or in pots.
2. They have short growth period and short lifecycle.
3. They bear self-pollinating flowers, which could be cross-pollinated artificially.
4. They produce large number of seeds.
5. They show a fairly large number of contrasting heritable characters.
6. They produce fertile hybrids on cross-pollination.

Question 8.
What is variation? Why are hereditary variations important?
Answer:
The differences in the characters among the offspring compared to that of their parents is called variation. Variation is necessary for organic evolution.

Question 9.
Give an example for the variation found in human population.
Answer:
If we Observe the ear lobes of a set of people, some have free ear lobes while a few have attached ear lobes. This is an example of variation in human population.

Question 10.
Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
Answer:
Sexual reproduction involves two parents and hence produces relatively large number of variations. The two parents already have variations accumulated from the previous generations and hence their progeny would be novel as they inherit traits from both parents. In asexual reproduction, however, the organisms have fewer variations due to errors in DNA copying.

Variations in organisms are the key for evolution. Since sexually reproducing organisms have more variations, the process of evolution gains speed. Asexual reproduction takes longer time for the evolution of newer species.

Question 11.
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, the variations that give advantage to an individual organism will increase its survival in the population. This is because the favourable variations enable the organism to survive even in unfavourable conditions and hence increase the chances of its survival.

Such organisms reproduce and increase their number in the population. Those with unfavourable variations diminish in number and eventually perish. Thus more offspring and population with genetic variations will survive.

Question 12.
If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier? Give reason.
Answer:
Asexually reproducing species reproduce by cell division creating two identical organisms (same DNA). In asexual reproduction, the chances of variation due to inaccuracies in DNA copying are quite small.

If a trait is found in only some members of a species then it originally occurred due to a random mutation. This random mutation then is passed down to future generations every time the organism with the trait replicates itself.

Thus, if 60% of a population contains this trait, it means that its members have been replicating themselves for a longer period of time than those in the population where the trait is seen in only 10% of the population. Hence it is more likely that trait B has emerged earlier than trait A.

Question 13.
How does the creation of variations in a species promote survival?
Answer:
Variations occur in species due to errors in DNA copying. Some of these variations may be favourable to the organism while others may not be. Depending on the nature of the variations, different individuals of a species get different kinds of advantages and enable them to adjust and adapt to changes in the environment.

Organisms with favourable variations survive even under changed conditions and reproduce and continue their species. This is how variations help species to adapt and hence promote their survival.

Question 14.
When a pesticide is sprayed on a population of insects, all insects do not get killed and a few of them survive. Give reason.
Answer:
When a pesticide is sprayed on a field, most of the insects are killed because they are sensitive to the pesticide. A few of the insects survive because they have variations, which have made them resistant to the pesticide. Hence the pesticide has no effect on these insects.

Question 15.
What is pollination? What is its importance? Mention its types.
Answer:
The transfer of pollen from the anther of a flower to the stigma of the same flower or of another flower is called pollination. Pollination is an essential prerequisite for fertilization.
There are two types of pollination namely

• self-pollination
• cross-pollination.

Question 16.
Differentiate between self-pollination and cross-pollination.
Answer:
Self-pollination:

1. The transfer of pollen grains from the anther to the stigma of the same flower or another flower of the same plant is called self¬pollination.
2. Self-pollinating flowers usually are small and less attractive without coloured petals, nectar, scent or long stamens and pistils.
3. It results in uniform progeny. It allows plant to be less resistant as a whole to diseases. However, if does not need to expend energy to attract pollinators.
4. Self-pollinating flowers usually have fewer pollen grains.

Cross-pollination:

1. The transfer of pollen grains from the anther of a flower to the stigma of a flower of a different plant of the same species is called cross-pollination.
2. Cross-pollination is seen in plants with brightly coloured petals, nectar and scent, long stamens and pistils.
3. It allows for diversity in the species. However, it relies on pollinators that travel from plant to plant.
4. Cross-pollinating flowers have large number of pollen grains.

Question 17.
Make a list offour observable traits in pea plants with their contrasting forms of characters.
Answer:

1. The length of the stem has two contrasting forms namely ‘tall’ and ‘dwarf.
2. The colour of the pod has two contrasting forms namely ‘yellow’ and ‘green’.
3. Colour of the seed coat has two contrasting forms namely ‘grey’ and ‘white’.
4. Position of the flower has two contrasting forms namely ‘axial’ or ‘terminal’.

Question 18.
Which were the seven pairs of contrasting traits in pea used by Mendel for his experiments on heredity?
Answer:

• Character:
• Stem height
• Flower colour
• Flower position
• Pod shape
• Pod colour
• Seed shape
• Seed colour

Contrasting traits:

• Tall/dwarf
• Red/white
• Axial/terminal
• Full/constricted
• Green/yellow
• Round/wrinkled
• Yellow/green

Question 19.
Define the following terms: Character, Trait, Gene, Hybrid, Phenotype, Genotype, Homozygous, Heterozygous, Dominant, Recessive, Monohybrid cross, and Dihybrid cross.
Answer:

1. Character: Any inheritable feature of an organism is called character.
2. Trait: Any detectable contrasting variant of a character is called a trait.
3. Gene: A gene is a unit of heredity that determines particular traits.
4. Hybrid: A plant or an animal produced by parents that have contrasting characteristics of a trait is called a hybrid.
5. Phenotype: Observable characteristics of an organism, which are genetically controlled, are called phenotype.
6. Genotype: The genetic constitution of an organism is called its genotype.
7. Allele: An alternative form of the same gene found at the same place on a chromosome is called allele.
8. Homozygous: Two alleles of a gene are said to be homozygous if they are similar and hence two copies of the same allele exist. (Eg. RR or rr.)
9. Heterozygous: Two alleles of a gene are said to be heterozygous if they are different. (Eg. Rr.) Dominant: A gene in a pair is said to be dominant if it masks or hides the expression of the other.
10. Recessive: A gene in a pair is said to be recessive if it expresses itself only when there are two of them. Recessive genes do not express in the presence of a dominant allele.
11. Monohybrid cross: Mendelian cross in which only one pair of contrasting characteristics is taken into consideration at a time is called monohybrid cross.
12. Dihybrid cross: Mendelian cross in which two pairs of contrasting characteristics are taken into consideration at a time is called dihybrid cross.

Question 20.
Describe Mendel’s monohybrid cross experiments.
Answer:
Mendel took pure varieties of pea plants with contrasting characteristics. For instance, he took pure tall varieties and pure dwarf varieties and cross-pollinated them. He collected the seeds of these plants and sowed them in the next season. All the seeds bore tall varieties of plants. He called these hybrids ‘the first filial generation’ (F₁ generation).

In the next season, Mendel sowed seeds obtained in the F₁generation and self-pollinated them. He collected the seeds of these plants and sowed them in the next season. He found that these seeds produced tall and dwarf varieties in the ratio 3:1. He called these plants ‘the second filial generation’ or F₂ generation.

Question 21.
How many factors will be there for each trait in sexually reproducing organisms? What are they?
Answer:
In any sexually reproducing organism, there will be two factors for each trait. One is the dominant factor and the other is the recessive factor.

Question 22.
What is monohybrid cross? What is its ratio? Show with the help of a checker board.
Answer:
Mendelian crosses, in which only one pair of contrasting characteristics is taken into consideration at a time, is called monohybrid cross. Monohybrid ratio obtained when only one pair of contrasting characteristics is taken at a time is 3:1.

Phenotypic ratio: 3 tall: 1 dwarf
Genotypic ratio: 1 pure tall: 2 impure tall: 1 pure dwarf.

Question 23.
State the principle of dominance with an illustration.
Answer:
For any given trait, there are two forms of factors. One of these factors is dominant and the other is recessive. This idea is known as the principle of dominance. Consider a situation where tall pea plants are cross-pollinated with dwarf pea plants. When seeds obtained from them are sown again, we get all tall plants.

Here, tallness is a dominant factor and dwarfness is a recessive factor. When the plants grown from these seeds are self-pollinated and the next generation (F₂ generation) seeds are obtained and sown again, dwarfness appears in some plants. This shows that the factor for dwarfness was masked in the F₁ generation by the factor of tallness. We consider the factor for dwarfhess as the recessive trait.

Question 24.
Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and which is recessive

1. Yellow seed
2. Round seed.

Answer:

1. Seed colour: Yellow (Dominant); Green (Recessive).
2. Seed shape: Round (Dominant); Wrinkled (Recessive).

Question 25.
How do Mendel’s experiments show that traits may be dominant or recessive?
Answer:
In his experiment on pea plants, Mendel cross-pollinated plants with contrasting pair (say tall and dwarf) of characteristics and obtained the seeds of F₁ generation. All the plants grown from the F₁ generation seeds showed only one trait of the pair (tall) and the other trait (dwarfhess) was missing in all the plants.

He self-pollinated these plants and collected the seeds ef this generation and grew plants of the F₂ generation. A trait that appeared in all the members of the F₁ generation (tallness) appeared only in 75% of members of F₂ generation and the other 25% were dwarf. This means a trait that did not appear in the Fj₁generation had reappeared in 25% plants of F2 generation.

This indicated that the trait that appeared in F₁ generation in all plants was the dominant trait. A trait that did not appear in F₁ but reappeared in F₂ generation was the recessive trait. This established that traits may be dominant or recessive.

Question 26.
Genes related to one character have two contrasting traits. But only one among them is considered as dominant. Why?
Answer:
Of the two contrasting traits of an inherited character, the one that expresses itself in the next generation and determines the phenotype of the individual is called the dominant trait. This trait determines the character of the individual despite the presence of a contrasting allele for the same character.

Question 27.
In Mendel’s experiments on pea plants, were the tall plants in the Ft generation exactly the same as the tall plants of the parent generation? Explain.
Answer:
In Mendel’s experiment, the tall pea plants in the F, generation were not the same as the tall plants of the parent generation. The parent generation had pure tall varieties with homozygous alleles. Their genotype can be represented by TT.

This means the seeds obtained by self-pollination of these plants would yield only tall plants. In the Fi generation, the tall plants were heterozygous with their genotype being Tt. The seeds obtained by self-pollination of these plants’would yield some tall plants and a few dwarf plants.

Question 28.
The findings of Mendel’s experiment with pea plants with pure purple and pure white flowers are shown in the diagram given below. State the dominant trait and the recessive trait in this.
Answer:

In this experiment, the trait for purple colour flowers is dominant. The trait for white flowers is recessive.

Question 29.
Outline a project that aims to find the dominant coat colour in doss.
Answer:
Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series that influence coat colour in dog. In order to find the dominant coat colour, we may choose one pair of contrasting traits. A dog inherits one gene for its coat colour from each of its parents. The dominant gene gets expressed.

For example, let us consider the factors that make a dog genetically black or brown. Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb). By cross breeding these pure varieties we get the following genotypes:

In this case, all the offsprings will be heterozygous black (Bb). B is the dominant factor while b is the recessive factor. If such heterozygous dogs are crossed again, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offsprings.

This shows that the factor for black is dominant while the factor for brown is recessive.

Question 30.
How do Mendel’s experiments show that traits are inherited independently?
Answer:
Mendel crossed pure breeds of tall plants having round seeds with pure breeds of short plants having wrinkled seeds. The plants of Fj generation were all tall with round seeds indicating that the traits of tallness and roundness of seeds were dominant.

Self-breeding of Ft yielded plants with characters of 9 tall round seeded, 3 tall wrinkled seeded, 3 short round seeded and 1 short wrinkled seeded. Tall wrinkled seeded and short round seeded plants are new combinations which could develop only when the traits are inherited independently.

Question 31.
How does inheritance work with asexually reproducing organisms? How is it different from the , inheritance in sexually reproducing organisms?
Answer:
The asexually reproducing organisms receive the complete set of chromosomes from a single parent but in sexually reproducing organisms, one set is received from each parent through gametes. These gametes then fuse and restore the chromosome number similar to that of parents.

Question 31.
How does inheritance work with asexually reproducing organisms? How is it different from the inheritance in sexually reproducing organisms?
Answer:
The asexually reproducing organisms receive the complete set of chromosomes from a single parent but in sexually reproducing organisms, one set is received from each parent through gametes. These gametes then fuse and restore the chromosome number similar to that of parents.

Question 32.
A study found that children with tight-coloured eyes are likely to have parents with lieht- coloured eves. On this basis, can we say whether the lisht eve colour trait is dominant or recessive? Why or why not?
Answer:
On the basis of the information provided, it is difficult to say if light colour of eye is a dominant trait or a recessive trait. However if the eye colours of both the parents were known along with the knowledge of whether the genes contributing for it are dominant or recessive type, then the nature of the trait could have been predicted.

Question 33.
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?
Answer:
The information provided here is not enough to decide whether the trait for blood group A is dominant or the trait for blood group O is dominant. Either is possible as the individual carries two alleles for a trait. Recessive trait appears only when the two alleles are similar (homozygous). In the present case, there can be two possibilities

Possibility 1: When blood group A is dominant trait but blood group O is recessive trait: When father’s blood group A is dominant trait, it can have two genotypes: IAIA and IAI°. And when mother’s blood group O is recessive trait it can have only one genotype: I°I° (because it should have two recessive alleles). Now, if one recessive allele 1° comes from father and one recessive allele 1° comes from mother, then the daughter can also have the genotype I°I° which can give her blood group O.

Possibility 2: When blood group A is recessive trait but blood group O is dominant trait: When father’s blood group A is recessive trait, it can have only one genotype: IAIA (because it should have two recessive alleles). And when mother’s blood group O is dominant trait, then it can have two genotypes: I°I° and I°IA. Now, if one dominant allele 1° comes from the mother and one recessive allele IA comes from the father, the daughter will have the genotype I°IA which will again give her blood group O.

Question 34.
What is dihybrid cross? What is the dihybrid ratio obtained in the F2 generation by Mendel in his experiments on inheritance of characteristics?
Answer:
Show this with the help of a checker board. Mendelian crosses in which two pairs of contrasting characteristics are taken into consideration at a time are called dihybrid cross. The dihybrid ratio obtained by Mendel in the F₂ generation was 9:3:3:1.

This means that for every nine tall plants with red flowers, there were three tall plants with white flowers and three dwarf plants with red flowers. There was one dwarf plant with white flowers for every nine tall plants with red flowers.

• Dihybrid ratio of the phenotype is 9:3:3:1
• Tall plants with red flowers: 9
• Tall plants with white flowers: 3
• Dwarf plants with red flowers: 3
• Dwarf plants with white flowers: 1.

Question 35.
What are chromosomes?
Answer:
A thread-like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes is called chromosome. Chromosomes bear genes, which are composed of DNA. Genes are responsible for the transmission of hereditary characteristics from one generation to another.

Question 36.
What is DNA?
Answer:
DNA stands for Deoxyribonucleic Acid. It is a macromolecule found in chromosomes of living beings and carries the genetic information of the organism.

Question 37.
Define gene.
Answer:
A segment of DNA that forms the hereditary unit is called a gene.

Question 38.
How is the sex of the child determined in human beings?

OR

Explain the process of sex determination in human beings.
Answer:
The sex of a child in humans is determined by the kind of male gamete (sperm) that fertilizes the female gamete (ovum). If a sperm carrying X chromosome fertilizes the ovum, the child will be a girl. If a sperm carrying Y chromosome fertilizes the ovum, the child will be a boy.

question 39.
Write the differences between the sex chromosomes of man and the sex chromosomes of woman.
Answer:
A woman has a pair of identical sex chromosomes namely XX. A man has a normal sized chromosome called X and a shorter chromosome called Y. Thus the sex linked chromosome in a man are XY.

Question 40.
Sex of a child is determined by the father. How?
Answer:
A mother can give only X chromosome to her progeny. The father can give either X or Y chromosome. A child who gets X chromosome from the father will be a girl and a child who gets Y chromosome from the father will be a boy. Thus the sex of a child is determined by the father.

Question 41.
How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer:
In human beings, equal genetic contribution of male and female parents is ensured in the progeny through inheritance of equal number of chromosomes from both parents. There are 23 pairs of chromosomes. All human chromosomes are not paired. Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosome represented as X and Y.

Females have a perfect pair of two X sex chromosomes and males have a mismatched pair of one X and one Y sex chromosome. During the course of reproduction, as fertilisation takes place, the male gamete (haploid) fuses with the female gamete (haploid) resulting in formation of the diploid zygote.

The zygote in the progeny receives an equal contribution of genetic material from the parents. Out of 23 pairs of chromosomes in progeny, male parent contributes 22 autosomes and one X or Y chromosome and female parent contributes 22 autosomes and one X chromosome.

Question 42.
What are acquired traits? Give an example.
Answer:
A trait of an organism, which is not inherited from parents but develops in response to the environment, is called an acquired trait. For example, a person may learn the skills of skating during her lifetime. This trait is not passed on to the person from her parents through genes. Thus, acquired traits are not inherited.

Question 43.
What are inherited traits? Give an example.
Answer:
Those traits that come to an individual from parents through gene transfer and hence can be passed on to the next generation through genes are called inherited traits. For example, colour of eyes, hair texture, etc., are inherited traits.

Question 44.
Why are traits acquired during the lifetime of an individual not inherited?
Answer:
Traits acquired during the lifetime of an individual just enable an individual to adapt itself to the surrounding and do not change the genetic make up of the organism. An acquired trait involves change in non-reproductive tissues, which cannot be passed on to germ cells or the progeny. Therefore, these traits cannot be inherited.

Question 45.
Rana’s father is a wrestler and has a robust body. His son is thin and has a relatively weak body structure.

1. Is it true that a wrestler’s son should also have heavy muscles?
2. What type of character is it – acquired or inherited?
3. If you are Rana’s friend, how will you convince him that his son is normal?

Answer:
1. It is not necessary that a wrestler’s son should also have heavy muscles.

2. Having heavy muscles in the body is an acquired trait. They are not inherited through genes. Heavy muscles can be acquired by regular exercising and good diet.

3. We can convince Rana by telling him that traits like heavy muscles are not inherited but are acquired in one’s lifetime. His son can start exercising on a regular basis and take nutritious food and develop muscles just like his father. If he is not as strong as his father, there is also a possibility that he has inherited more traits from his mother.

Question 46.
What is DNA copying? What is its importance?
Answer:
The process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules is called DNA copying. DNA copying gains tremendous importance during cell division. DNA copying during cell division ensures the restoration of the same genetic information in the next generation of cells.

Question 47.
What are the different wavs in which individuals with a particular trait may increase in a population?
Answer:
Traits arise due to variations, which occur due to sexual reproduction of inaccuracies during DNA copying or environmental factors. Individuals with a particular trait may increase in a population due to the following factors:

1. Natural selection: Those variations, which give survival advantage to an organism, are selected in nature and such traits increase in the population.
2. Genetic drift: It occurs due to change in gene frequency due to accumulation of particular type of genes.
3. Geographical isolation: It leads to change in gene frequency leading to expression of one type of trait in a eographically isolated population.
4. Migration: It leads to flow of a particular type of gene in a specified population.

Question 48.
Why are the small number of surviving tigers a cause of worry from the point of view of genetics?
Answer:
The small number of tiger population does not allow large number of variations to occur. Wider range of variations are however essential for the survival of the species. A deadly disease or calamity may cause death of all of the few remaining tigers. The small number of tigers also indicates that existing tiger variants are not well adapted to the existing environment and hence may be facing threat of extinction.

Question 49.
What is speciation ? How does it happen? Explain.
Answer:
The evolutionary process that leads to the formation of new but distinct species from the main population of an existing species is known as speciation. The new species that are formed have a distinct genetic composition that is different from the main population and therefore interbreeding between the members of the main population and those of the new population is not possible.

Speciation occurs when a population exhibits a continuous change due to changes in the environment. These unit changes get accumulated over a period of time in a section of the population which slowly alter the individual’s genetic structure and functions to give rise to a new species.

Question 50.
With the help of the following pattern briefly explain the reason for

• DNA stability,
• Variation phenomenon found in successive generations of species.

Answer:
A close observation of the given diagram reveals that the DNA molecule has a double helical structure with two strands twisted in a twisted ladder shape. All molecules of DNA have the same twisted ladder structure, which is highly stable. The double helix structure of DNA gives the DNA molecule its physical and chemical properties as well as stability. The stability of DNA structure helps the strands to hold together.

Sexual reproduction involves two parents and hence produces relatively large number of variations due to DNA crossing over. A few variations will also occur due to errors in DNA copying. The two parents pass on the accumulated variations to their progeny.

Hence their progeny would be unequal as they inherit traits from both parents. In asexual reproduction, however, the organisms have only fewer variations due to errors in DNA copying. Variations in organisms are the key for evolution.

Question 51.
What is genetic drift? Explain with an example.
Answer:
A random change (happens strictly by chance) in the gene pool of a small population is called genetic drift. Consider the example of an exploding volcano that destroys almost all of the most common trees on a small island. Over time, the types of trees that were not affected by the volcano continue to flourish, while the population of the tree that was once common in the area would dwindle.

Question 52.
What factors could lead to the rise of a new species?
Answer:
The factors that could lead to the rise of a new species are
1. By natural selection:
Organisms with a particular trait may be naturally selected because it provided a survival advantage. That particular trait may thus increase in the population. It may direct evolution of species population by adaptations to fit their environment better.

2. Genetic drift and inheritance:
An accident in small populations may result in surviving of organisms with a particular variant only. This can increase the frequency of some genes in that population, even if they give no survival advantage. This is the notion of genetic drift, which provides diversity without any adaptations.

Question 53.
Read the following information and answer the given questions:

• Thousands of years ago only one species of squirrels was there and were evolved from a common ancestor.
• At present there are two species of squirrels; though they have similarities among them, they cannot perform reproduction between them.

1. Analyze the factor responsible for this change.
2. How can this kind of changes be considered as beneficial for a species?

Answer:
1. In this case, two species of squirrels have emerged from a single common ancestral species. This has happened through a process called speciation. Speciation is an evolutionary process that has led to the formation of new but distinct species of squirrels from the main population of the pre-existing species of squirrels.

The new species of squirrels has a distinct genetic composition that is different from that of the main population. Therefore interbreeding between the members of the main population of squirrels and those of the new population is not possible. Speciation occurs due to the variations that exist among the members of the species.

These variations might have occurred due to natural selection, geographical isolation or genetic drift. Any one or a combination of these factors might have contributed to the evolution of a new species of squirrels over several generations. Speciation occurs because the individual members of a species (squirrels in this case) show lot of variation.

Some of these variations are favourable to the organisms. These favourable variations are transmitted to the progeny. These unit changes (variations) get accumulated over a period of time in a section of the population, which slowly alter the individual’s genetic structure and give rise to a new species of squirrels.

2. There is competition amongst the members of a given species for resources leading to struggle for existence. In this struggle, only the most adaptable will survive and reproduce. This produces young one’s that are better adapted for the next phase of struggle for existence.

These variations get accumulated over several generations leading to the emergence of new species that are distinct from the original species. This is called descent with modification. Thus the variations favour the survival of species and the emergence of better-adapted new species.

Question 54.
What is geographical isolation? How does it occur?
Answer:
The separation of two populations of the same species by a physical barrier, such as a mountain or body of water, is known as geographical isolation. Geographical isolation of a species occurs as a result of physical changes in the natural environment.

Any physical barrier such as a mountain or a water body that separates two populations of the same species results in geographical isolation and may lead to speciation.

Question 55.
Will geographical isolation be a major factor in the speciation of a self-oollinatine plant species? Why or why not?
Answer:
Geographical isolation can prevent cross-pollination with flowers of different plants. Since the plants are capable of self-pollination, the pollens are transferred from the anther of one flower to the stigma of the same flower or of another flower of the same plant and its distance from other plants hardly affects its reproduction.

Moreover, self-pollinated plants rarely show variations in characters. Therefore, geographical isolation cannot prevent speciation in the given case.

Question 56.
Will eeoeraphical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer:
No, geographical isolation cannot be a major factor in the speciation of an organism that reproduces asexually. This is because, asexually reproducing organisms pass on the parent DNA almost entirely to the offspring. This leaves no chance for speciation. However, geographical isolation works as a major factor in sexual reproduction involving cross-pollination.

Question 57.
Give an example of characteristics beine used to determine how close two species are in evolutionary terms.
Answer:
Presence of some common characteristics in two different species indicates a close relationship among them. For example, fossil studies indicate the presence of feathers in some ancient reptiles like dinosaurs.

However these animals used feather only to get some protection from cold and could not use them to fly. Birds evolved further and adapted the feathers for flight. This means that birds are very closely related to reptiles. In fact, birds are known to have evolved from reptiles.

Question 58.
What is organic evolution?
Answer:
The slow emergence of well adapted newer forms of organisms from pre-existing simpler organisms through modifications that occurred over millions of years is known as organic evolution.

Question 59.
What evidence do we have for the orisin of life from inanimate matter?
Answer:
The experiment conducted by Miller and Urey provides evidence for the origin of life from inanimate matter. These scientists took molecules of compounds that existed on early earth such as methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water (H₂O) in a specially designed glass jar.

They provided energy for the interaction of these molecules in the form of an electric arc to simulate lightning storms. At the end of one week, they observed that as much as 10-15% of the carbon was now in the form of organic compounds. Two percent of the carbon had formed some of the amino acids which are used to make proteins.

This experiment showed that organic compounds such as amino acids, which are essential to cellular life, could be made easily under conditions that scientists believed to be present on early earth. This also gave support to the idea that life evolved from inanimate matter.

Question 60.
What is the theory proposed by Charles Darwin to explain organic evolution?
Answer:
The theory developed by Charles Darwin is called ‘theory of natural selection’. It is also known as Darwinism.

Question 61.
What are the main ideas of Darwin’s theory of evolution by natural selection?
Answer:
The following are the key points of Darwin’s theory of evolution

• Existence of variation: There is variation in characteristics in every population.
• Overproduction: All organisms tend to produce more offspring than can survive.
• Struggle for existence: Organisms compete for limited resources.
• Survival of the fittest: Only those individuals, which have most favourable variations, will survive and reproduce. Darwin called this ‘natural selection’.
• Inheritance: Organisms with favourable adaptive characteristics will pass on their traits to their offspring.
  Origin of species: The accumulated changes over a long period of time lead to the emergence of new species.

Question 62.
What is natural selection? What is its consequence?
Answer:
The process by which nature selects individuals with the most favourable traits to survive and reproduce is known as natural selection.
As a consequence of natural selection, individuals in a given species with most favourable adaptations will survive.

Those with less favourable adaptations perish. As a result, individuals with favourable characteristics become more common in successive generations of a population and those with unfavourable characteristics become less common.

Question 63.
According to Darwin’s theory, how do new species originate?
Answer:
Darwin proposed in his theory that new species originate by natural selection. In the struggle for existence, only the fittest will survive and reproduce. This produces young ones which are better adapted for the next phase of struggle for existence. Darwin called it descent with modification. As the environment is ever changing, it demands new variations in the organisms.

Gradually new characters are accumulated in the offspring across generations. These accumulated changes over a long period of time will produce offspring, which vary in a major way from their original ancestors and hence will form new species.

Question 64.
What is artificial selection? Give an example.
Answer:
The process in which human beings artificially produce new plants or animals with improved characteristics through selective breeding is known as artificial selection.

The wild cabbage plant is a good example for artificial selection. Humans have, over more than two thousand years, cultivated wild cabbage as a food plant. They have generated different vegetables from it by artificial selection.

Question 65.
Mention some of the evidences that support evolution of life.
Answer:
The evidences that support evolution of life include the following

• Fossil evidences
• Presence of homologous organs
• Presence of analogous organs.

Question 66.
How are the areas of study – evolution and classification – interlinked?
Answer:
The classification of organisms is a reflection of their evolutionary relationships. Classification is based on similarities and differences amongst organisms the more characteristics two organisms have in common, the more closely they are related and the more recently thpy will have had a common ancestor in the evolutionary chain the more different characteristics two organisms have, the more remotely they are related and they will have had a common ancestor in the more remote past.

Question 67.
What are fossils? Where are fossils usually found?
Answer:
The naturally preserved remains or impressions of a prehistoric plant or animal that had lived in the geological past are called fossils. Fossils are usually found between layers of rocks in petrified (rocky) form.

Question 68.
Which are the three basic types of fossils?
Answer:
Fossils are commonly found in the following forms

• Fossils in the form of actual remains,
• Petrified fossils, and
• Moulds and casts.

Question 69.
Name the fossil bird that had characteristics of both reptiles and birds.
Answer:
The fossil bird that had characteristics of both reptiles and birds was archaeopteryx.

Question 70.
What do fossils tell us about evolution of life on earth?

OR

What are fossils? What do they tell us about the process of evolution?
Answer:
Fossils are the dead and decayed remains of organisms that lived millions of years ago. Fossils indicate that the present day organisms have evolved from previously existing ones. Thus fossils help us to reconstruct the evolutionary history of an organism.

The distribution pattern of fossils shows that the ancient fossils present in the bottom rocks are simpler, while the most recent fossils found in the upper strata are more highly evolved. It means, fossils form and become more and more complex as we proceed from earliest to recent rocks.

They give us an idea of time in history when different species were formed or became extinct. Fossils also help to trace the evolutionary history of some organisms.

Question 71.
Explain the importance of fossils in decidtne evolutionary relationships.
Answer:
Fossils are the remains of organisms formed over millions of years ago. Evolutionary relationship tells us how closely two organisms are related in the evolutionary tree. The fossils are an easy way of understanding the ancient species and also it helps us to find the missing link in the evolutionary tree.

By knowing more about the organism that lived so many centuries ago, we can understand the changes in the body designs and functions that led to the creation of species in due course of evolution and also evolution itself.

We get to understand the prehistoric period and the geographical changes that might have given rise to the organisms by analysing the structure of the organisms in fossils. Fossils are the key to understand the similarity between organisms and create a hierarchy that would help to classify the organisms and learn them easily without having learnt about all the organisms that ever survived.

A study of fossils helps us to know about the evolution of species. Fossils tell us how new species are developed from the old. Therefore, fossils have an importance in deciding evolutionary relationships.

Question 72.
Explain the terms analoeous and homologous organs with examples.
Answer:
Homologous organs:
The organs in different groups of organisms, which have the same basic structural design and origin but perform different functions, are called homologous organs.

For example, the forelimbs of a frog, a bird and a man have the same basic design of bones, but they perform different functions (frogs use them to jump, birds use them to fly and man use them to grasp).

Analogous qrgans:
The organs in different groups of organisms, which have different basic structural design and origin but have similar functions, are called analogous organs.

For example, the wings of birds and insects have different structural design but perform the same function, that is, assisting in flight. Therefore, they are analogous organs.

Question 73.
Write the differences between homologous organs and analogous organs.
Answer:

Homologous organs	Analogous organs
1. Organs of different organisms have common origin.	Organs of different organisms have different origins.                                                 •
2. They have similar structures but perform different functions.	They have different structures but perform similar functions.
3. Ex: Forelimbs of frog and forelimbs of bird.	Ex: Wings of bird and wings of bat.

Question 74.
Can the wine of a butterfly and the wine of a bat be considered homologous organs? Why or why not?
Answer:
Homologous organs are those that have the same basic structural design but perform different functions. Analogous organs are those organs that have different basic structural design but perform similar functions.

The structure of the wings of a butterfly and that of a bat are different but perform the same function. They help in flying. Therefore the wings of a butterfly and that of a bat are analogous organs and not homologous organs.

Question 75.
Is it necessary that organisms with homologous organs always have a common ancestor?
Answer:
Yes, organisms with homologous organs will have a common ancestor. This is because these organs have similar basic structure and similar embryonic origin. However, the organs are modified to perform different functions in different organisms.

Question 76.
Justify the following statements with one illustration each:

1. Though organs of different organisms have more similarities in the shapes of organs, they need not be evolved from a common ancestor.
2. Though variations are more between organisms, they might have evolved from a common ancestor.

Answer:
1. We see instances of different organisms having organs that are similar in shape but not evolved from a common ancestor. These are known as analogous organs. For example, birds, insects and bats have wings, and they all perform the same function, but they did not evolve from a common ancestor. Their wings work on different principles.

2. We see instances of more variations between the organisms but they have evolved from a common ancestor. These are called homologous organs. For example, the forelimbs of a frog, a bird and a man have the same basic design but perform different functions. Frogs use them to jump, birds use them to fly and humans use them to grasp.

Question 77.
Why are human beines who look so different from each other in terms of size, colour and looks said to belong to the same species?
Answer:
All human beings, even though they look different from each other in terms of size, colour and looks, belong to the same species because they have similar DNA sequences and have descended from the same ancestors. Further, human beings are capable of reproducing among themselves. These variations that we find in humans have arisen due to environmental factors, mutation or mixing of characters during reproduction.

Question 78.
In evolutionary terms, can we say which among bacteria, spider, fish and chimpanzee have a *better’ body design? Why or why not?
Answer:
Evolution is the generation of diversity due to environmental selection. Evolution has led to the emergence of more and more body designs over time. Among bacteria, spider, fish and chimpanzee, we can say that the chimpanzees have a better body design because their body design is highly complex with specialized body tissues and organs.

Chimpanzees are better adapted than others to survive in the present day environment. Therefore, we can say that from among the given set of organisms, chimpanzees are. better evolved and have a ‘better’ body design.

Question 79.
Is it true that human beings have evolved from chimpanzees? Justify your answer.
answer:
It is not true that human beings have evolved from chimpanzees. However, both human beings and chimpanzees have descended from a common ancestor. It is quite unlikely that the common ancestor is neither humans nor chimpanzees.

Also, the first step of separation from that ancestor is unlikely to have resulted in modem chimpanzees and human beings. Instead, the two resultant species have probably evolved in their own separate ways to give rise to the current forms.

Question 80.
Cat’s paw, human hand and horse’s legs – are these organs homologous or analogous? Give reason.
Answer:
Cat’s paw, human hand and horse’s legs are all homologous organs because they are of same origin (modified forearm) but perform different functions.

Question 81.
Is it fair to say that the body structure of the organisms that have emerged recently is more efficient than that of those that evolved earlier? Explain.
Answer:
It is not true that the body structure of recently evolved organisms is more efficient than that of those which evolved earlier. Many of the organisms that evolved earlier and have simpler body design are still well adapted to their conditions and are surviving in the environment.

Many of the simpler organisms are best adapted to survive in most inhospitable conditions. Therefore, there is no justification to argue that recently evolved organisms are better than those that evolved earlier. In other words, human beings are not spread across the world in stages.

Question 82.
What are the techniques commonly used to study human evolution?
Answer:
The tools such as excavating, time dating, studying fossils and determining DNA sequences are commonly used to study human evolution. These are the same techniques that are used to trace evolutionary relationships.

Question 83.
What is the scientific name of human beings? Where did they originate first?
Answer:
The scientific name of humans is Homo sapiens. The earliest members of Homo sapiens have been traced to Africa. Our genetic footprints can be traced back to our African roots.

Question 84.
How and why did human race spread from Africa to other parts of the world?
Answer:
The earliest members of the human species can be traced back to our African roots. A couple of hundred thousand years ago, some of the early humans left Africa while others stayed on. While the residents spread across Africa, the migrants slowly spread across the planet. Their movement however was not linear.

They 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. Thus, study of the evolution of human beings indicates that all of us belong to a single species that evolved in Africa and

Fill In The Blanks

1. The plant used by Mendel to study the inheritance of characteristics was pea plant
2. The heredity material in all eukaryotes is DNA
3. The scientist who is called the father of modem genetics is Gregor Mendel
4. The scientist who gave the most acceptable theory about the origin of life was J.B.S. Haldane
5. The units of inheritance are called genes
6. Darwin’s theory of organic evolution is known as natural selection
7. The monohybrid ratio in Mendel’s experiment was 3:1
8. The gene with two identical alleles is said to be homozygous

Multiple Choice Questions

Question 1.
A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short This suggests that the genetic make-up of the tall parent can be depicted as
(A) TTWW
(B) TTww
(C) TtWW
(D) TtWw
Answer:
(C) TtWW

Question 2.
An example of homologous organs is
(A) our arm and a dog’s foreleg.
(B) our teeth and an elephant’s tusks.
(C) potato and runners of grass.
(D) all of the above.
Answer:
(D) all of the above.

Question 3.
The critical determinant of the sex of a male child is the
(A) X-chromosome in the zygote.
(B) Y-chromosome in the zygote.
(C) Cytoplasm of germ cell.
(D) Environmental factor.
Answer:
(B) Y-chromosome in the zygote.

Question 4.
Exchange of genetic material takes place only in
(A) vegetative reproduction
(B) asexual reproduction
(C) sexual reproduction
(D) budding
Answer:
(C) sexual reproduction

Question 5.
A cross between a tall plant (TT) and a short pea plant (tt) resulted in progeny that were all tall plants because
(A) tallness is the dominant trait
(B) shortness is the dominant trait
(C) tallness is the recessive trait
(D) height of pea plant is not governed by gene ‘T’ or ‘t’
Answer:
(A) tallness is the dominant trait

Question 6.
Father of Human genetics is
(A) Gregor Mendel
(B) Charles Darwin
(C) Sir Archibald Garrod
(D) J. B. S. Haldane
Answer:
(A) Gregor Mendel

Question 7.
The tendency of offspring to differ from parents is called
(A) heredity
(B) inheritance
(C) resemblance
(D) variation
Answer:
(D) variation

Question 8.
The character, which predominates and is clearly seen in F₁ generation, is said to be
(A) acquired
(B) dominant
(C) recessive
(D) inherited
Answer:
(B) dominant

Question 9.
In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F₂ is
(A) 1: 3
(B) 1 : 1
(C) 2:1
(D) 3: 1
Answer:
(D) 3: 1

Question 10.
If a round, green seeded pea plant (RR yy) is crossed with wrinkled, yellow seeded pea plant, (rr YY) the seeds produced in F₁ generation are
(A) wrinkled and yellow
(B) round and green
(C) round and yellow
(D) wrinkled and green
Answer:
(C) round and yellow

Question 11.
How life might have originated on earth was experimentally shown by
(A) Gregor Mendel
(B) Oparin and Haldane
(C) Urey and Miller
(D) Watson and Crick
Answer:
(C) Urey and Miller

Question 12.
A gamete contains
(A) all alleles of an organism
(B) two alleles
(C) three alleles
(D) only one allele of a gene
Answer:
(D) only one allele of a gene

Question 13.
The two versions of a trait (character), which are brought in by the male and female gametes, are situated on
(A) copies of the same chromosome
(B) two different chromosomes
(C) sex chromosomes
(D) any chromosome
Answer:
(A) copies of the same chromosome

Question 14.
Surgically removing tails of mice over several generations does not yield mice without tails. This proves that
(A) cutting the tail does not cause genetic change. So it is not inherited.
(B) characters acquired during one’s lifetime are not inherited.
(C) neither A nor B is correct
(D) both A and B are correct
Answer:
(D) both A and B are correct

Question 15.
The variation in the relative frequency of different genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce is called
(A) Gene flow
(B) Genetic drift
(C) Genetic error
(D) Genetic inheritance
Answer:
(B) Genetic drift

Question 16.
Select the correct statement from among the following
(A) The eyes of octopus and vertebrates are homologous organs.
(B) The limbs of amphibians and mammals are analogous organs.
(C) The wings of birds and limbs of lizards are analogous organs.
(D) The wings of birds and wings of bats are homologous organs.
Answer:
(D) The wings of birds and wings of bats are homologous organs.

Question 17.
According to evolutionary theory, formation of a new species is generally due to
(A) sudden creation by nature
(B) accumulation of variations over several generations
(C) clones formed during asexual reproduction
(D) movement of individuals from one habitat to another
Answer:
(B) accumulation of variations over several generations

Question 18.
In evolutionary terms, we have more in common with
(A) a Chinese schoolboy
(B) chimpanzee
(C) spider
(D) bacterium.
Answer:
(A) a Chinese schoolboy

Question 19.
Identify the correct pair of analogous organs among the following
(A) The forelimb of man and the forelimb of a frog
(B) The wing of a butterfly and the wing of a bat
(C) The wing of a bird and the wing of a bat
(D) The forelimb of a lizard and the forelimb of a frog.
Answer:
(C) The wing of a bird and the wing of a bat

Match The Following

Column A	Column B
1. Heredity	(a) Development of new organism by modifications in pre-existing ones
3.  Genetics	(b) Transmission of characters from parent to offspring
4.  Variation	(c) Alleles representing the same trait
4.  Evolution	(d) A fossil bird
5. Archaeopteryx	(e) Branch of science that deals with heredity and variation
	(f) Differences among the individuals of same species

Answer:
1 – b, 2 – e_; 3 – f, 4 – a, 5 – d.