Bihar Board Class 10 Science Solutions Chapter 9 Heredity and Evolution

 

Bihar Board Class 10 Science Chapter 9 Heredity and Evolution InText Questions and Answers

Intext Questions (Page 143)

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 A is likely to have arisen earlier because traits reduce from one generation to the next generation.

Question 2.
How does the creation of variations in a species ensure survival?
Answer:
All the variations in the species do not have equal chances of surviving in the environment. The survival of the Variations depend on the nature of variations. Different individuals have different chances. Selection of variants by the environmental factors forms the’bases for evolutionary process.

Intext Questions (Page 147)

Question 1.
How do Mendel’s experiments show that traits may be dominant or recessive ?
Answer:
Mendel took pea plants having different characteristics, like a tall plant and a short plant. He produced progeny from them and calculated the percentages of tall or short progeny. There was no halfway characteristics in the first generation. All plants were tall. This meant that only one of the parental traits was seen, not the other. Here, the trait of tallness is dominant while shortness is the recessive characteristic.

Question 2.
How do Mendel’s experiments show that traits are inherited independently ?
Answer:
Mendel performed an experiment in which he took two different traits, like tall and short plant, and round and wrinkled seeds. In 2nd (F2) generation, some plants were tall with round seeds and some were short with wrinkled seeds. There would also be short plants having round seeds. Thus, the tall/short traits and round/wrinkled seed traits are independently inherited.

Question 3.
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:
Yes, this information is enough to tell that trait A is dominant. It is because only dominant traits are expressed from one generation to next generation.

Question 4.
How is the sex of a child determined in human beings ?
Answer:
There are 23 pairs of chromosomes in the cell of human body. Out of these, 22 pairs do not take part in sex-determination in human beings. The 23rd pair in gonadal cell called sex chromosome which is not always a perfect pair. Women have a perfect pair having XX – chromosomes. But men have a pair having XY-chromosomes.

This cell is divided meiotically in both men and women to form gametes. All children will inherit an X-chromosome from mother and an X – or Y- chromosomes from their father. Thus, the sex of children is determined by the chromosomes they inheriting from their father. A child inheriting X – chromosome from father will be a girl and one inheriting Y- chromosome from him will be a boy.

Intext Questions (Page 150)

Question 1.
What are the different ways in which individuals with a particular trait may increase in a population ?
Answer:
There are following ways in which individuals with a particular trait may increase in a population :
(i) By natural selection.
(ii) By inheritance.

Question 2.
Why are traits acquired during the lifetime of an individual not inherited ?
Answer:
The germ cells of sexually reproducing populations are made in specialised reproductive tissue. The acquired traits cannot change the DNA of the germ cells. Therefore, the acquired traits cannot be inherited over generations during the lifetime of an individual.

Question 3.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics ?
Answer:
Genetics is the science of heredity and variations. It explains how the traits are inherited from generation to generation. The small numbers of surviving tigers is the cause of worry from the point of view of genetics because the diversity and the traits are reduced gradually. This fact wants explanation and genetics should answer it.

Intext Questions (Page 151)

Question 1.
What factors could lead to the rise of a new species ?
Answer:
Following factors could lead to the rise of a new species :

• Natural selection.
• Processes of genetic drift.
• Mutation (sudden change in genetic makeup).
• Environmental factors.
• Local factors.

Question 2.
Will geographical isolation be a major factor in the speciation of a self-pollinating plant species ? Why or why not?
Answer:
No, geographical isolation will not be a major factor in the speciation of a self-pollinating plant species. It is due to the fact that new genes do not enter in the population, so new species is not produced or formed.

Question 3.
Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually ? Why or why not ?
Answer:
Yes, geographical isolation is a major factor in the speciation of an organism. It is due to the fact that migrant organism will reproduce with the local population. This will result in the genes of migrant organism entering a new population. This kind of gene flow is bound to happen between populations that are partly but not completely separated.

Intext Questions (Page 156)

Question 1.
Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer:
Forelimbs of human and birds show the closeness between these species. The basic structure of the limbs is similar, though it has been modified to perform different functions.

Question 2.
Can the wing of a butterfly and the wing of a bat be considered homologous organs ? Why or why not ?
Answer:
The wing of a butterfly and the wing of a bat cannot be considered homologous because they have a common use for flying but their origins and structure are not common. Rather, they are analogous organs.

Question 3.
What are fossils ? What do they tell us about the process of evolution ?
Answer:
The remains of dead plants and animals which were buried under the rocks millions of years ago are called fossils. Fossils tells us about the process of evolution. The fossils of different organisms have some features similar to one species,

Intext Questions (Page 150)

Question 1.
What are the different ways in which individuals with a particular trait may increase in a population ?
Answer:
There are following ways in which individuals with a particular trait may increase in a population :
(i) By natural selection.
(ii) By inheritance.

Question 2.
Why are traits acquired during the lifetime of an individual not inherited ?
Answer:
The germ cells of sexually reproducing populations are made in specialised reproductive tissue. The acquired traits cannot change the DNA of the germ cells. Therefore, the acquired traits cannot be inherited over generations during the lifetime of an individual.

Question 3.
Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics ?
Answer:
Genetics is the science of heredity and variations. It explains how the traits are inherited from generation to generation. The small numbers of surviving tigers is the cause of worry from the point of view of genetics because the diversity and the traits are reduced gradually. This fact wants explanation and genetics should answer it.

Intext Questions (Page 151)

Question 1.
What factors could lead to the rise of a new species ?
Answer:
Following factors could lead to the rise of a new species :

• Natural selection.
• Processes of genetic drift.
• Mutation (sudden change in genetic makeup).
• Environmental factors.
• Local factors.

while some matures are similar to the other species. In this way, they show the link between two species. They tell us that one species evolves from the other species.

Intext Questions (Page 158)

Question 1.
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:
The human beings are different from each other in terms of size, colour and looks but they are said to belong to the same species. It is due to their fundamental characteristics. The fundamental characteristics of one species are more closdr. among these organisms than the other organisms of other species. All human have same fundamental characteristics. So thev belongs to the same species.

Question 2.
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 a better body design because they .have a well-developed body system, well-developed brain, and the thumb opposite to the finger to catch very small and minute things.

Bihar Board Class 10 Science Chapter 9 Heredity and Evolution Textbook Questions and Answers

Question 1.
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 makeup 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.
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 traits is dominant or recessive ? Why or why not ?
Answer:
We can say fhat light eye colour trait is dominant because only dominant traits are transferred from the parents to the children in the first generation.

Question 5.
How are the areas of study – evolution and classification – interlinked ?
Answer:
Evolution and classification are interlinked with each other. Classification is the most important term to explain evolution. Classification is based on the similarities and differences between two- species or among two organisms. More closer the characteristics are, the more closer is the evolution and more chances are to remain in the same group of classification. We can appreciate that classification of species is in fact a reflection of their evolutionary relationship.

Question 6.
Explain the terms analogous and homologous organs with examples.
Answer:
Analogous organs : The organs having the same functions but different in structure, origin and components are called analogous organs. For example, the wings of a bat and the wings of an insect are analogous organs.
Homologous organs : The organs having the same structure, origin and components but different functions are called homologous organs. For example, the forearms of a horse and the hands of a human.

Question 7.
Outline a project which aims to find the dominant coat colour in dogs.
Answer:
Select a homozygous black (BB) male dog and a homozygous white (bb) female dog. Allow them to mate and produce offspring (Fx generation). If all of the F2 offspring are black, we can conclude that black coat cover is dominant than white coat in dog.

Question 8.
Explain the importance of fossils in deciding evolutionary relationship.
Answer:
Fossils are the remains of dead plants or animals which died millions of years ago. The study of fossils helps us to know about the evolution or the link between two species. Fossils tells us how new species are developed from the old. So fossils have an importance in deciding evolutionary relationship.

Question 9.
What evidence do we have for the origin of life from inanimate matter ?
Answer:
An experiment conducted by Stanley L. Miller and Harold C. Urey in 1953 proved that origin of life takes place from inanimate matter. They assembled the atmosphere containing NH3, CH4 and H2S but no O2 over water. This was maintained at a temperature just below 100°C, and sparks were passed through the mixture of gases. At the end of a week, 15% carbon from methane had been converted to simple compounds of carbon like amino acids, which make up protein molecules. So life arose afresh on earth.

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 asexually ?
Answer:
Sexual reproduction gives rise to more viable variations than asexual. It is because the genes of the traits are trans mitted from one generation to the next generation and dominant characters are expressed. While in asexual reproduction, gene cannot be separated from the parental organisms. So no more variations occur. This cause of variation affects the evolution of those organisms that reproduce sexually. By this process, more and more variations are produced in the next generations. In this way, the genetic drift will accumulate, which causes the formation of new species.

Question 11.
How is the equal genetic contribution of male and female parents ensured in the progeny ?
Answer:
There are 23 pairs of chromosomes. Most human chromosomes have maternal and a paternal copy. We have 22 such pairs. These pairs contain half chromosomes from mother and half from father. One pair is called sex chromosomes. At the time of sex determination, the egg cell fuses with the sperm cell which are haploid to form zygote. Zygote is diploid which contains 23 chromosomes from mother and 23 from father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.

Question 12.
Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement ? Why not ?
Answer:
We agree with this statement that only variations that confer an advantage will survive in a population. All the variations do not have an equal chance of surviving in the environment in which they find themselves. The chances of surviving depend on the nature of variations. Different individuals would have different kinds of advantages. A bacteria that can withstand heat will survive better in a heat wave. Selection of variants by environmental factors forms the basis for evolutionary processes.

Bihar Board Class 10 Science Chapter 9 Heredity and Evolution Textbook Activities

Activity 9.1 (Page 143)

Observe the ears of all the students in the class. Prepare a list of students having free or qttached earlobes and calculate the percentage of students having each (Fig. 9.2). Find out about the earlobes of the parents of each student in the class. Correlate the earlobe type of each student with that of their parents. Based on this evidence, suggest a possible rule for the inheritance of earlobe types.
Answer:
Students observe the ears of all the students and make a chart as given below.
Write F for free earlobes and A for attached earlobes.

On the basis of the findings, suggest a possible rule for the inheritance of earlobe type based on Mendel’s law of inheritance.

Tite lowest part of th ear, called the earlobe, is closely attached to the side of tite head in some of u..,and not in others. Free and attached eariobes are two variants found in human populations

Activity 9.2 (Page 144)

Question 1.
In Fig. 9.4, what experiment would we do to confirm that the F2 generation did in fact have a 1: 2 : 1 ratio of , Tt and tt trait combinations ?

Answer:
We took seeds of plant of F x generation and grew them. In F2 generation, we found that the ratio between tall and short plants is 3 : 1. To confirm that the ratio is in fact 1 : 2 : 1, we should take more than two traits.

Bihar Board Class 10 Science Chapter 9 Heredity and Evolution NCERT Exemplar Problems

Short Answer Type Questions

Question 1.
How is the sex of a newborn determined in humans?
Answer:
The sex of the individual genetically determined i.e., genes inherited from parents decide whether the new-born will be a boy or a girl. A new-born who inherits an ‘X’ chromosome from father will be a girl and one who inherits a ‘Y’ chromosomes ‘ will be a boy.

Question 2.
Do genetic combination of mothers play a significant role in determining the sex of a new-born?
Answer:
No, because mothers have a pair of X’ chromosomes. All children will inherit an X’ chromosome from their mother regardless of whether they are boys or girls.

Question 3.
Mention three important features of fossils which help in the study of evolution.
Answer:
(a) Fossils represent modes of preservation of ancient species.
(b) Fossils help in establishing evolutionary traits among organisms and their ancestors.
(c) Fossils help in establishing the time period in which organisms lived.

Question 4.
Why do all the gametes formed in human females have an X chromosome?
Answer:
Human females have two X’ chromosomes called sex chromosomes. During meiosis at the time of gamete formation, one X’ chromosome enters each gamete. Hence all the gametes possess an X’ chromosome.

Question 5.
In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.
Answer:
The sex of an infant is determined by the type of sex chromosome contributed by the male gamete. Since the ratio of male gametes containing X chromosome and those containing Y chromosome is 50 : 50, the statistical probability of male or a female infant is also 50 : 50.

Question 6.
A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.
Answer:
Fewer individuals in a species impose extensive inbreeding among them. This limits the appearance of variations and puts the species at a disadvantage if there are changes in the environment. Since the individuals fail to cope up with the environmental changes, they may become extinct.

Question 7.
What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?
Answer:
Structures which have a common basic structure but perform different functions are called homologous structures, e.g., fo^e limbs of reptiles, amphibians and mammals. Yes, they have common ancestor but variously modified to carry out different activities.

Question 8.
Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Answer:
Though animals have a vast diversity in structures, they probably do not have a common ancestry because common ancestry may greatly limit the extent of diversity. As many of these diverse animals are inhabiting the same habitat, their evolution by geographical isolation and speciation is also not likely. Thus, a common ancestry for all the animals is not the likely theory.

Question 9.
Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive
(i) yellow seed
(ii) round seed
Answer:
(i) yellow – dominant
green – recessive
(b) round – dominant
wrinkled – recessive

Question 10.
Why did Mendel choose pea plant for his experiments?
Answer:
Due to the following characteristics of pea plant, Mendel chose it or his experiments.
(а) Easy to grow
(b) Short life span
(c) Easily distinguishable characters
(d) Larger size of flower
(e) Self-pollinated

Question 11.
A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
Answer:
Genes inherited from parents decide whether the new born will be a boy or a girl. Females have a pair of ‘X’ chromosomes. All children inherit an X’ chromosome from their ; mother and ‘X’ or X chromosome from their father. A new – born who inherits an X’ chromosome from father becomes a girl and \ one who inherits a X chromosome becomes a boy. Thus, if a woman has only daughters it means every time egg of that woman got fertilised by X’ chromosome of her male partner.

Long Answer Type Questions

Question 12.
Does geographical isolation of individuals of a species lead to formation of a new species? Provide a y suitable explanation.
Answer:
Yes, geographical isolation gradually leads to genetic drift. This may impose limitations to sexual reproduction of the separated population. Slowly the separated individuals will reproduce gmong themselves and generate new variations. Continuous accumulation of those variations through a few generations may ultimately lead to the formation of a new species.

Question 13.
Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Provide a suitable explanation.
Answer:
This is a debatable issue. If appearance of complexity is concurrent with evolution then, human beings are certainly more evolved than bacteria. But if we take the totality of life characteristics into account, then it is hard to label either organism as the most evolved.

Question 14.
All the human races like Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor. Provide a few evidences in support of this view.
Answer:
Characteristics are details of appearance or behaviour; s in other words, a particular form or a particular function. The more characteristics two species will have in common, the more closely they are related. And the more closely they are related, the more recently they will have had a common ancestor. All the human races like Africans, Asians, Europeans, Americans and others have common body plan, structure, physiology and metabolism. All the humans have constant chromosome number and common genetic blue print. Besides, freely inter-breeding is possible in them. Thus, it is clear that all human races have many common characteristics. Hence, it may be considered that all the humans races might have evolved from a common ancestor.

Question 15.
Differentiate between inherited and acquired characters. Give one example for each type.
Answer:
Characters that are passed on from parents to offspring are inherited characters e.g., colour of seeds, colour of eyes.
Characters appearing in an individual’s life time but cannot be transmitted to next generation are acquired characters e.g., obese body, loss of a linger in an accident etc.

Question 16.
Give reasons why acquired characters are not inherited.
Answer:
Acquired characters do not produce change in the DNA of gerfn. cells. So they cannot be inherited. Only those characters which have a gene for them can be inherited.

Question 17.
Evolutidp has exhibited a greater stability of molecular structure When compared with morphological structures. Comment on the statement and justify your opinion.
Answer:
We see immense diversity.in size, form, structure and morphological features in the living ‘dopld. But at the molecular level, these diverse types of organisms exhibit unbelievable similarity. For instance, the basic biomolecules like DNA, RNA, carbohydrates, proteins etc. exhibit remarkable similarity in all organisms.

Question 18.
In the following crosses write the characteristics of the progeny

Answer:
(a) Round, yellow
(b) Round, yellow
Round, green
Wrinkled, yellow
Wrinkled, green
(c) Wrinkled, green
(d) Round, yellow

Question 19.
Study the following cross and showing self pollination in F, fill in the blank and answer the question that follows

Answer:
Rr Yy Round, yellow

Question 20.
In previous question, what are the combinations of character in the Fg progeny? What are their ratios?
Answer:

• Round yellow – 9
• Round green – 3
• Wrinkled yellow – 3
• Wrinkled green – 1

Required ratio – 9 : 3 : 3 : 1

Question 21.
Give the basic features of the mechanism of inheritance.
Answer:

• Characters are controlled by genes.
• Each gene controls one character.
• There may be two or more forms the gene.
• One form may be dominant over the other.
• Genes are present on chromosomes.
• An individual has two forms of the gene whether similar or dissimilar.
• The two forms separate at the time of gamete formation.
• The two forms are brought together in the zygote.

Question 22.
Give reasons for the appearance of new combinations of characters in the F2 progeny.
Answer:
Mendel performed an experiment in which he took two different traits, like tall and short plants, and round and wrinkled seeds. In 2nd (F2) generation, some plants were tall with round seeds and some were short with wrinkled seeds. There would also be short plants having round seeds. Thus, the tall/short traits and round/wrinkled seed traits are independently inherited. I It is clear from the above discussion that traits are inherited independently. That is why the hew combinations of characters i appear in the F2 progeny.