GSEB Solutions Class 10 Science Chapter 9 Heredity and Evolution

Gujarat Board GSEB Textbook Solutions Class 10 Science Chapter 9 Heredity and Evolution Textbook Questions and Answers, Additional Important Questions, Notes Pdf.

Gujarat Board Textbook Solutions Class 10 Science Chapter 9 Heredity and Evolution

Gujarat Board Class 10 Science Heredity and Evolution InText Questions and Answers

Question 1.
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?
Answer:
Trait B is likely to have arisen earlier as it occurs in more number.

Question 2.
How does the creation of variations in a species promote survival?
Answer:
Variations increases the adaptability of an organism to its changing environmental conditions. ,

Question 3.
How do Mendel’s experiments show that traits may be dominant or recessive?
Answer:
Mendel took pea plants of two different characters i.e., tall plants and short plants. The first generation of Fj progeny formed were all tall. This shows that traits may be either dominant or recessive, there is no way in between traits obtained.

Question 4.
How do Mendel’s experiments show that traits are inherited independently?
Answer:
When Mendel crossed pure breed tall pea plants with pure breed short pea plants, he found that only tall plants were produced in F₁ generation. Mendel, further crossed the tall pea plants obtained in F₁ generation with dwarf plants and obtained the ratio of Tall: Short plant as 3 : 1 in F₂ generation. This experiment proved that traits are inherited independently so other intermediate traits or new traits were formed.

Question 5.
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 given information is not enough to tell us which of the traits-blood group A or O – is dominant. In blood heredity, hood type A is always dominant and blood type O is always recessive. Here, father’s Blood group can be I^AI^A (homozygous) or I^Ai (heterozygous) genotypically, whereas that of mother is ii. For daughter to be bom with blood group O, she must receive i type gene one each from father and mother. For this father must have heterozygous I^Ai blood group and mother must have homozygous blood group ii.

Question 6.
How is the sex of the child determined in human beings?
Answer:
In case of human beings, females have a pair of XX chromosomes (sex) and males have a pair of XY sex chromosome. When the crossing of male and female gametes takes place then the sex of the child is determined as follows:

This shows that the ratio of male Sex of the child is same i.e., (1 : 1), 50% possibility of each is seen here.

Question 7.
What are the different ways in which individuals with a particular trait may increase in a population?
Answer:
The ways in which individual with a particular trait may be increased in a population are:

1. If it can survive in the adverse condition i.e., naturally selected.
2. It can also be increased by the inheritance.

Question 8.
Why are traits acquired during the life-time of an individual not inherited?
Answer:
The traits can be inherited from one generation to the other only if there is a variation/change in DNA. The traits acquired during the life-time of an individual may not bring change in the genes of DNA.

Question 9.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer:
The small number of tigers are causing a worry for the genetics because if they become extinct then the genes of this species will be lost forever. There will be no scope of I again getting this species back to life without their genes.

Question 10.
What factors could lead to the rise of a new species?
Answer:
The factors which can lead to the rise of a new species are gene flow, genetic drift, reproductive isolation and natural selection.

Question 11.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species. Why or why not?
Answer:
No, geographical isolation cannot be a major factor in the speciation of self-pollinating plant species. It is because such plants do not depend on other plants for its further reproduction to be carried out.

Question 12.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer:
No, because the asexually reproducing organisms does not depend on other organisms for their reproduction.

Question 13.
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer:
Two organisms with similar characteristics have genes with similar DNA codes. Whereas the organisms with different characteristics will have different genes, different DNA structures.

Question 14.
Can the wing of a butterfly and the wing of a bat be considered homologous organ? Why or why not?
Answer:
The wing of butterfly and the wing of a bat cannot be considered homologous organs because both have different structures but same function. They have different basic structural design and developmental origin. They are analogous organs.

Question 15.
What are fossils? What do they tell us about the process of evolution?
Answer:
Preserved traces of living or dead organisms on solid hard surface is called fossil. Fossils help us to know the evolution. If a fossil is found closer to the surface of earth, then it is more recent in origin than the fossils we find in deeper layers. Fossils, like Archaeopteryx, help us to find evolutionary relation between organisms.

Question 16.
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:
Because irrespective differences in characters they have capacity of interbreeding. Interbreeding is an important criteria to categorize them as one species.

Question 17.
In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a better body design? Why or why not?
Answer:
Evolution shows that body design changed from simple to complex. Hence, bacteria has the simplest body design and chimpanzee has the most complex and better body design.

In-Text Activities Solved

Activity 9.1
Answer:
To study the earlobes of students in the class.

Observation : It is observed that the lowest part of the ear, called the earlobe, is r closely attached to the side of the head in some of us, and not in others. Hence, free and attached earlobes are two variants found in human populations.

Activity 9.2
Answer:
For Mendel’s experiment.

T – is dominant hence
∴ TT – Tall
Tt – Tall
tt – Short

Gujarat Board Class 10 Science Heredity and Evolution Textbook Questions and Answers

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 fore-leg.
(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.
In evolutionary terms, we have more in common with –
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.
Answer:
(a) a Chinese school-boy

Question 4.
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:
No, we cannot say that the traits is recessive or dominant unless we know the nature of the two variants of a trait.

Question 5.
How are the areas of study – evolution and classification – interlinked?
Answer:
For classification of organisms, we generally group the organisms of same characteristics together and those with different characteristics are grouped or classified separately. A set of characteristics tells about the level of evolution of an organism.

Question 6.
Explain the terms analogous and homologous organs with examples.
Answer:

1. Analogous organs – Organs with different structure and same function example: wings of bird, insects.
2. Homologous organs – Organs which have same structure but different functions are called homologous organ example: forearm of lizard, bird and human.

Question 7.
Outline a project which aims to find the dominant coat colour in dogs.
Answer:
Dominant → WW (white colour) Recessive → ww (black colour)

Question 8.
Explain the importance of fossils in deciding evolutionary relationships.
Answer:
Fossils help us to know the following:

1. Fossils help to trace the racial history of organisms.
2. They help to measure the geological time.
3. Older fossils lie’ at the depth and young fossils are at the upper surface of the earth.
4. Complex organisms are present at top and simple organisms are present at the bottom.
5. Fossil like – Archaeopteryx-show the link between two different types of species.

Question 9.
What evidence do we have for the origin of life from inanimate matter?
Answer:
Miller and Urey in 1953 assembled an atmosphere similar to that thought to exist at 1 early period (Gases like ammonia, methane, hydrogen sulphide) over earth. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lighting.

At the end of a week 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules. Presence of protein cell membrane correlates with above experiment. This shows that life originated from inanimate matter.

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:
Variations are seen more in sexual reproduction than asexual reproduction because variations occur due to change in DNA coding and due to sexual reproduction in which two genes from two different sexes i.e., male and female genes crossing over takes place and hence cause the variation.

Question 11.
How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer:
By studying the crossing over of genes of male sex and female sex is as follows:

Question 12.
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:
No, depending on the nature of variations different individuals have different kinds of advantages. However, when a drastic change occurs in environment only those organism in the population will survive which have an advantageous variation in that population to survive in changed environment.

Gujarat Board Class 10 Science Heredity and Evolution Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
Define heredity.
Answer:
Heredity deals with the inheritance of characters from one generation to the next.

Question 2.
Define variations.
Answer:
Variations are differences that occur between the organisms of the same species in spite of the same basic feature.

Question 3.
How does the creation of variations in a species promote survival?
Answer:
Variations increases the adaptability of an organism to its changing environmental conditions.

Question 4.
What is a trait?
Answer:
A characteristics feature is called a trait.

Question 5.
Name two human traits that show variations.
Answer:
Colours of eyes and shape of external ears.

Question 6.
What is adaptation?
Answer:
An adaptation is characteristics feature which helps an organism to survive in its habitat in a better way.

Question 7.
Which of the two sperm or egg-decides the sex of the child?
Answer:
The sperm decides the sex of the child.

Question 8.
The forelimbs of frog, reptiles, birds and arms of man show the same basic design. What kind of organs are these?
Answer:
Homologous organs.

Question 9.
What is microevolutions?
Answer:
Microevolutions is the evolution that takes place on a relatively small scale at the population level and can change the common characteristics of particular species.

Question 10.
What is speciation?
Answer:
Speciation is the process of formation of a new species from the already existing species by accumulation of variations, natural selection, gene flow, genetic drift, etc.

Question 11.
What is a gene?
Answer:
Gene is the unit of inheritance. It is a part of the chromosome which controls the appearance of a set of hereditary characteristics.

Question 12.
Who is known as the “father of Genetics”?
Answer:
G.J. Mendel is called the “father of Genetics”.

Question 13.
What is evolution?
Answer:
Evolution is the sequence of gradual changes which take place in living organisms over millions of years to give rise to new species.

Question 14.
What type of reproduction gives rise to more number of successful variations?
Answer:
Sexual reproduction.

Question 15.
What are fossils?
Answer:
Fossils are preserved traces or remains of living organisms of geological past.

Question 16.
What are the uses of fossils?
Answer:

• Fossils helps to trace the racial history of organisms.
• They help to analyse the past climatic conditions.
• They help to measure the geological time.

Question 17.
Name the scientist who put forth the theory of natural selection.
Answer:
Charles Darwin.

Question 18.
What is artificial selection?
Answer:
It is the process of modification of a species by selective breeding. Animals and plants with desirable characters are selected and propagated. Artificial selection by farmers has resulted in the formation of cauliflowers, cabbage, broccoli and kohlrabi from the wild cabbage.

Short Answer Type Questions

Question 1.
How can we trace evolutionary relationships?
Answer:
Evolutionary relationships can be traced by studying fossils, by studying homologous and analogous organs, by comparing the embryos of different animals and by comparing the DNA’s of different species.

Question 2.
What is phylogeny and molecular phylogeny?
Answer:
Phylogeny is the evolutionary history of an organism. Molecular phylogeny traces the evolutionary relationships by comparing the differences in the DNA of different organisms.

Question 3.
What is environmental selection?
Answer:
It is the selection within a population resulting from the influence exerted by the environment. It leads to a change in the composition of genes within a population.

Question 4.
What term did Mendel use for genes? Where are the genes located?
Answer:
Mendel used the term ‘factors’ for genes. Genes are portions of DNA which code for a single protein.

Question 5.
How many pairs of chromosomes do human beings have, specify the types of chromosomes also?
Answer:
Human beings have 23 pairs of chromosomes the first 22 pairs are called autosomes are similar in males and females. The 23rd pair is called the sex chromosome. In males it is XY and in females it is XX.

Question 6.
What are homologous organs? Explain with an example.
Answer:
Homologous organs are those organs in different plants or animals which have the same basic structural design and origin but may have different functions.
Example : hand of human and fore-limb of frog.

Question 7.
What are analogous organs? Explain with an example.
Answer:
Analogous organs have the same function but have different structural design and origin.
For example, wings of birds and insects have the same function but have different structural design and origin.

Question 8.
What is the significance of studying homologous and analogous organs?
Answer:
Organisms that have homologous organs show relatedness and a common ancestory.

Question 9.
Which of the following combinations of sex chromosomes produces a male or a female child-XX or XY?
Answer:
XX combination produces a female child while the XY combination produces a male child.

Question 10.
Which of the following are homologous and analogous organs?
(a) Wings of birds and insects.
(b) Flippers of whale and fins of fish
(c) Flippers of whale and wings of bat.
(d) Our teeth and elephants tusks.
(e) Potato and runners of grass.
Answer:
(a) – Analogous organs
(b) – Analogous organs
(c) – Homologous organs
(d) – Homologous organs
(e) – Homologous organs

Question 11.
How do traits or characters get expressed?
Answer:
Genes control the expression of a trait or a character in an organism. Genes produces proteins. The proteins act as enzymes which can directly control a character or help in the formation of a hormone which can control the expression of a particular character.

Question 12.
Define variation in relation to a species: Why is variation beneficial is the species.
Answer:
Variations are differences that occur between the organisms of the same species in spite of the same basic features. Variation in species promotes survival of an organism in changing environment by increasing the adaptability.

Question 13.
A true breeding tall plant is crossed with a true breeding short plant. All the offsprings of the F₁ generation are tall. Of these two characters which one is dominant and which is recessive.
Answer:

Question 14.
In Question 14. on previous page the tall plant of the F₁ generation is selfed. What is the outcome or ratio of the F₂ progeny?
Answer:

Question 15.
How is the sex of the child determined in human beings?
Answer:
Human beings have 23 pairs of chromosomes. 22 pairs are autosomes and the 23rd pair is the sex chromosome. The males have XY and the females have XX. All the gametes formed in the females are of one type i.e., X. In males there are two types of sperms that are formed -X and Y. If the sperms having X fertilizes with the egg the zygote formed is XX.

This will form female child. If the sperm having Y fertilizes with the egg then the zygote formed is XY and the offspring will be male child. So basically it’s the male gametes that decide the sex of the unborn child.

Question 16.
What is genetic drift?
Answer:
Accidents in small populations can change the frequency of some genes in a population even if they give no survival advantage. This is genetic drift, which provides diversity without any adaptations. So, it is the random change in the frequency of alleles in a population over successive generation.

Question 17.
Which is gene flow?
Answer:
It is the exchange of genetic material by interbreeding between populations of the same species. Gene flow increases the variations in a population.

Question 18.
How do we know how old fossils are?
Answer:
We can find the relative of the fossil by the depth at which the fossil is found. The ones that are found near the surface are more recent than the fossils found in the deeper layer. The second way of dating fossils in detecting the ratios of different isotopes of the ‘ same element in the fossils material.

Question 19.
What is speciation? How does it occur?
Answer:
Formation of new species from the existing ones over the period of time is called speciation. Speciation takes place due to gene flow, genetic drift, reproductive isolation and finally natural selection.

Question 20.
What is natural selection?
Answer:
According to Darwin, natural selection is the process which brings about evolution of new species of plants and animals.

It consists of the following processes:

• He noted that the size of population tends to remain constant despite the fact that more offsprings are produced than needed.
• Variations provide adaptations.
• The best adopted survive in the changing environment (survival of the fittest).
• Nature selects the best organisms with better adaptations and after many generations new species are formed (natural selection).

Question 21.
Define Genetics. What did Mendel’s contribution to genetics?
Answer:
The science of heredity and variation is called Genetics. Mendel conducted breeding experiments in a plant called garden pea (pisum sativum) with contrasting pair of characters, found that only one character of the pairs appeared in the first generation but both the characters appeared in the subsequent generation.

On the basis of these results of his experiments he put forth the various principals of inheritance. He also suggested that each character is controlled by a pair of factors which are now called as genes.

Question 22.
Explain the Monohybrid Cross.
Answer:
The cross in which just two contrasting characters are studied is called monohybrid cross. Mendel did monohybrid cross for his first experiment. He selected a pair of contrasting characters. For example cross between tall plants and short plants.

TT represents the genotype of tall plant and tt represents the genotype of short plants. In the F₂ generation, all plants were tall but their genotype was Tt; which means they were not pure tall plants. This could be established by the appearance of the character of shortness in the F₂ generation; in which most of the plants were tall and some of the plants were short.

This experiment showed that the character of shortness was recessive in F₁ generation and hence could not be observed. The ratio of number of tall plants to that of short plants in F₂ generation was 3:1.

Question 23.
State Mendel’s first law.
Answer:
Mendel’s first law is Law of segregation. Every individual possesses a pair of alleles for a particular trait. During gamete formation, a gamete receives only one trait from the alleles. A particular trait can be dominant or recessive in a particular generation.

Question 24.
What are alleles?
Answer:
When two or more alternative forms of a gene arise by mutation and are found at the same place on a chromosome.

Question 25.
State the second law of Mendel.
Answer:
Law of independent assortment: the alleles of different character separate independently from each other during gamete formation.

Question 26.
Define Genotype and Phenotype.
Answer:
Genotype: The complete set of genes in an organism’s genome is called genotype. Phenotype: The observable characters in an organism make the phenotype. Phenotype is a result of genotype’s interaction with the environment. Due to this reason, many phenotypes are not inheritable.

Question 27.
Discuss how the variation is seen/accumulated during different types of reproduction.
Answer:
Asexual reproduction involves a single parent and is hence not ideal for facilitating variations. Some minor variations do occur due to inaccuracies in DNA replication, mutations. But the variations would be too little and would take too many years to show distinctive effect.

Sexual reproduction, on the other hand, is ideal for facilitating variations because two parents are involved in it. The offspring’s genotype is contributed by two parents and hence chances of variations are very high.

Question 28.
List down the reasons for the choice of pea plant by Mendel for his experiment.
Answer:
Reasons for choosing pea plant:

• Pea can be termed as biennial plant, i.e. two generations of a pea plant can grow in a given year.
• This means that Mendel could get enough time to observe a larger number of generations.
• Many easily identifiable and contrasting characters are present in pea plants.
• Cross pollination can be easily induced in pea plants.

Question 29.
State the result of Mendel’s experiment.
Answer:
Mendel conducted experiments on pea plants and proposed the rules of inheritance; based on his observations. Mendel observed that characters are often present in pairs. A pair of contrasting characters is called allele

Question 30.
What is classification?
Answer:
It is the arrangement of organism into series of groups based on the similarity of characters on physiology, anatomy, morphology and other relationships.

Question 31.
State the importance of variations.
Answer:
Variations are the differences in the characters among the individuals of a species. Variations enable the organisms to adapt themselves in the changing environmental conditions. Variations form the raw materials for evolution and formation of new species.

Long Answer Type Questions

Question 1.

1. What is genetics?
2. Give the common name of the plant on which Mendel performed its experiments.
3. What for did Mendel use the term factors and what are these factors called now?
4. What are genes? Where are the genes located?

Answer:

1. Science which deals with the study of heredity and variations is called genetic.
2. Pea plant.
3. Mendel used the term factors for ‘genes’.
4. Genes is the unit of inheritance. It is a part of the chromosome which controls the appearance of a set of hereditary character. Genes are located on the chromosome.

Question 2.
Define ‘evolution’. State Darwin’s theory of evolution.
Answer:
Evolution is a change in the genetic composition of a population.

Darwin’s theory:

• The size of population remains the same, constant despite the fact that more offsprings are produced than needed.
• Variations provide adaptations.
• The best adapted organism survive in the changing environment (survival of the fittest).
• Nature selects the best organisms with better adaptations and after many generations new species are formed (natural selection).

Question 3.
What are various evidences in factors of evolution?
Answer:
Evidences are:

• Homologous organs – Organs which have same structure but different function. Example : wings of a bat, hands of man and limbs of monkey.
• Analogous organ – Organs which perform similar function but are structurally different are called analogous organ. Example : wings of bat, insects, birds.
• Vestigial organs -These organs are those which appear in an organism but are functionless e.g., vermiform appendix, nictitating membrane in eye is present in human beings but has no function.
• Embryological evidence – The study of embryos of vertebrates shows that all of them have same origin as their structure at initial stage is same. Embryo of frog, fish, man looks alike.
• Fossils as evidence -Archaeopteryx fossils shows a link between bird and reptiles as this fossil has some feature of bird and some of reptile.

Question 4.

1. What are traits?
2. Explain the inherited trait and acquired traits.
3. Define speciation. What are the factors which could lead to the rise of a new species?

Answer:

1. Traits: A characteristic feature is called trait.
2. Inherited and acquired trait (given in notes on page 112).
3. Speciation and factors (given in notes on page 112).

Questions On High Orderer Thinking Skills (Hots)

Question 1.
Study the given diagram and answer the questions.

Creation of diversity over succeeding generations. The original organism at the top will give rise to, say, two individuals, similar in body design, but with subtle differences. Each of them, in turn, will give rise to two individuals in the next generation. Each of the four individuals in the bottom row will be different from each other. While some of these differences will be unique, others will be inherited from their respective parents, who were different from each other.
(i) Why do we find all bottom row individuals different from each other?
(ii) What is similar in all the individuals?
Answer:
(i) The differences can be due to inheritance of acquired traits. When respective parents are different from each other the variation occurs due to inheritance.

(ii) Body design.

Question 2.
Male individual has 23 pairs of chromosomes, female individual has 23 pairs of chromosomes. Then why don’t an offspring have 46 pairs of chromosomes which is obtained by the fusion of these two eggs.
Answer:
Male individual has 23 pairs of chromosomes but the gamete that is formed by the meiotic cell division contain only half the number of chromosomes i.e., 23 chromosomes in male sperm and 23 chromosomes in female egg.

It is the fusion of this sperm and egg which leads to an offspring with 23 pairs of chromosomes.

Question 3.
Study the given figure and say what information it gives you.

Answer:
Do it yourself.

Question 4.
Dead remains of two species A and B were buried. Later only A’s body was found to be a fossil but not B’s given reason.
Answer:
B’s body did not have hard tissues, like bones.

Question 5.
Species A shares ten characteristics with species B, species C share fifteen characteristics with D which of the two pairs share closer relation.
Answer:
C and D.

Question 6.
After the death of two insects, one of the insect was hurried in hot mud and the other in usually found mud. Which of the two is more likely to be preserved better and why?
Answer:
The insect hurried in hot mud. The body will not get decomposed in hot mud and the impression of the body will remain.

Question 7.
Green and red coloured seeds are recessive and dominant trait respectively. Out of F₁ and F₂, in which generation will the green seed appear, if both parents are not hybrid.
Answer:
F₂ generation.

Question 8.
With the help of an example explain how “Genes control characteristics or traits”?
Answer:
Tallness of a plant is a characteristic. Height of a plant depend on the amount of hormone secreted by the plant responsible for its tallness. The gene has the coding for the amount of hormone released. If the gene for that hormone has an alteration and makes its efficiency low, then the plant will be short. Thus, this shows that traits are controlled by gene.