Students should refer to Worksheets Class 10 Science Heredity And Evolution Chapter 9 provided below with important questions and answers. These important questions with solutions for Chapter 9 Heredity And Evolution have been prepared by expert teachers for Class 10 Science based on the expected pattern of questions in the class 10 exams. We have provided Worksheets for Class 10 Science for all chapters on our website. You should carefully learn all the important examinations questions provided below as they will help you to get better marks in your class tests and exams.
Heredity And Evolution Worksheets Class 10 Science
Question. 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
Question. 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
B
Question. 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
Very Short Answer Type Questions :
Question. What is micro evolution? Does it explain speciation?
Answer :
a. In micro evolution, the changes are small which occurs in lower categories and change the common characteristics of a particular species.
b. It does not properly explain speciation.
Question. In an area A, the leaf materials available to beetles were very less. What are the two consequences seen in case of beetles?
Answer :
a. Due to poor nutrition, the average weight of adult beetles decreases.
b. The number of beetles (population) decreases due to starvation.
Question. How are characters or traits controlled?
Answer : Characters or traits of an organism are controlled by the genes /DNA.
Question. Mendel observed a contrasting trait in relation to position of flowers. Mention the trait.
Answer : Axial flower position (dominant), terminal flower position (recessive).
Question. A violet pea plant [VV] was crossed with a white one[vv]. F1 generation was allowed to self pollinate and F2 generation was also obtained, Answer the following questions:
a. What would be the phenotype of plants in F1 generation?
b. What would be the percentage of plants with white flowers in F2 generation?
c. What would be the ratio of vv: Vv in F2 generation.
Answer :
a. all violet flowers
b. 25%
c. 1 : 2.
Question. A tall pea plant was crossed with a dwarf one. F1 generation was allowed to self pollinate and F2 generation was also obtained. Answer the following questions:
a. What would be the phenotype of plants in F1 generation?
b. What would be the phenotypic ratio in F2 generation?
c. Give reason for your observation in F1 generation.
Answer :
a. all tall
b. 3:1
c. Reason: The tall trait of pea plant is dominant trait over short trait, a recessive trait.
Question. What is F2 generation?
Answer : The generation produced by the offsprings of F1 generation i.e., first generation as parent is called F2 or second generation.
Question. Tails of some mice were amputated and they were allowed to breed. The mice that were produced also had their tails amputated and it was repeated for many generations. What is the reason of tail appearing again and again?
Answer : Such traits are acquired traits. Traits acquired during the life-time of an individual are not inherited as these changes are not in the genes of reproductive tissues.
The changes in the non-reproductive tissues cannot be passed on to the DNA of the germ cells, hence such acquired changes are not inherited by the progeny.
Example: tailless mice (if tail is removed by surgery) cannot produce tailless progeny.
Question. If YYRR is round yellow, what do the following represent?
yyrr yyRR
Answer :
yyrr – Wrinkled, green seeds
yyRR — Round, green seeds
Question. What indication do we get by reappearance of dwarf plant in F2 generation?
Answer : After obtaining progeny in F2 generation in a dihybrid cross, Mendel concluded that when two pairs of traits are combined in a hybrid, one pair of character segregates independently of the other pair of character.
Question. Give the respective scientific terms used for studying:
a. the mechanism by which variations are created and inherited, and
b. the development of new type of organisms from the existing ones.
Answer :
a. Heredity
b. Species
Question. How did Mendel explain that it is possible that a trait is inherited but not expressed in an organism?
Answer : Yes, it is possible.
Example – When pure tall pea plants are crossed with pure dwarf pea plants, only tall pea plants are obtained in F1 generation.
On selfing tall plants of F1 both tall and dwarf plants are obtained in F2 generation in the ratio 3:1.
Reappearance of the dwarf character, a recessive trait in F2 generation shows that the dwarf trait/ character was present in individuals of F1 but it did not express (due to the present of tallness, a dominant trait / character)
Question. What is a gene?
Answer : It is a functional piece of DNA that is responsible for expression of a trait in the organisms.
Question. a. “Recent fossils are found closer to the earth’s surface”. Comment on the statement stating reason.
b. List two factors which could lead to the rise of new species.
Answer :
a. This statement is correct as the fossils found closer to the surface of earth are more recent and those found in deeper layers are older ones.
b. Natural selection and genetic drift.
Question. “Experience of an individual during its lifetime cannot be passed on its progeny and cannot direct evolution”. Justify this statement giving an example.
Answer : Since acquired characters are not inherited over generations. Change in non-reproductive tissues cannot be passed on to the DNA of the germ cells.
Question. What is a dominant trait with respect to height in pea plant. Give any two examples.
Answer : Characters/Traits like ‘T’ are called dominant trait (because it express itself) ‘t’ are recessive trait (because it remains supressed).
Question. What are sex chromosomes? Which sex chromosomes are found in male and female human beings? State the chromosome responsible for the development of male child in human beings?
Answer : Sex chromosomes are set of chromosomes present in human beings which help in sex determination.
XX and XY.
Y chromosome.
Question. How are fossil studies important in working out evolutionary relationships. How would the age of fossils be determined?
Answer : Fossils are impressions of the body/ body parts or the remains of organisms living in the past, which got preserved in sediments of earth. Any remains of an organism that has been preserved in the earth’s crust.
Study of fossils helps in working out evolutionary relationships. Age of fossils can be determined by time dating using isotopes of carbon (carbon dating).
Question. What is a gene?
Answer: Gene is the unit of inheritance. Gene is the part of a chromosome which controls the appearance of a set of hereditary characteristics.
Question. What is the importance of DNA copying in reproduction? Why is variation beneficial to the species but not necessary for the individual? Explain.
Answer : DNA copying is essential part of reproduction because it ensures that same blueprint of the body design is maintained. Variation for the species is beneficial for adaptation and better survival. It may result in new species formation.
Short Answer Type Questions :
Question. Explain the manner in which sex is determined in human beings?
or
Explain how equal genetic contribution of male and female parents is ensured in progeny?
Answer : The sex of the child is determined at the time of fertilization when male and female germ-cells (gametes) are fused to form a zygote. The sex is determined by a specific pair of chromosomes called sex-chromosomes.
In female human being, this pair consists of two similar (homologous) chromosomes denoted as XX. Hence, females produce only one type of gametes (Ova/ eggs) each having an “X’ chromosome.
Whereas male human being has two different types of sex chromosomes i.e., X, Y (heterologous) having different sizes and shapes. Hence male produces two different kinds of gametes (sperms). Half of them have ‘X’ chromosome and half have Y” chromosome.
If a sperm with “X’ fuses with the ovum, female child is born and if a sperm with ‘Y’ chromosome fuses with the ovum, male child is born as shown below in the cross.
Hence, we find that the sex of the child is actually determined by the type of sperm that fuses with ovum at the time of fertilization.
In this manner we can justify that the sex of the children is determined by what they inherit from their father and not their mother.
Question. Rekha is very dark in colour. She stays very quiet at home and in her class also. She is always seeing for the beauty products which can help her to become fair. Her friend Lila talks to her about excessive use of beauty products and tells her that they are very harmful and colour comes by birth and she is not responsible for her dark colour.
a. What might have caused Rekha’s colour to be dark?
b. Is it possible that all the family members of Rekha’s family were dark?
c. What value do you learn?
Answer :
a. Her dark colour may be due to the genetic inheritance.
b. All may not be dark, depending upon the genes inherited and the environmental conditions that each one of them living in.
c. Awareness, logical thinking, scientific temperament.
Question. A cross was carried out between a pure bred tall pea plant and a pure bred dwarf pea plant and F1 progeny was obtained. Later, the F1 progeny was selfed to obtain F2 progeny. Answer the following questions:
a. What is the phenotype of the F1 progeny and why?
b. Give the phenotypic ratio of the F2 progeny.
c. Why is the F2 progeny different from the F1 progeny?”
Answer :
a. Tall, because genes responsible for tallness are dominant over dwarf trait.
b.
c. Because in F2 generation, recessive genes got expressed in homozygous condition.
Question. If a population of red beetles, living on green bushes, is being eaten by crows. During sexual reproduction,
a green beetle is found in progeny:
a. What is the future of new trait?
b. Will it survive in the new habitat?
Answer :
a. Among progeny, when green beetle is found, it escaped attack of crows as it merged with green colour. Green beetles increased, red decreased.
b. New trait will survive.
Question. a. State any two factors that could lead to the rise of a new species.
b. How do analogous organs provide evidence in favour of evolution?
Answer :
a. Natural Selection, Genetic drift, Mutations, Variations.
b. The organs which are similar in function but are structurally different suggest that although these two organs may look alike superficially giving an idea of common ancestory but the different in structure and origin suggests that organisms having these organs have a distant ancestor but such organs have developed during the course of evolution as an adaptation to similar mode of life.
Question. (a) Differentiate between:
1. Homologous organs and Analogous organs.
2. Pollination and Fertilization
(b) What do fossils tell us about the process of evolution?
Answer :
a. (i) Organs in different organisms with same origin with different function/ different origin, same function.
(ii) Transfer of pollen from the stamen to the pistil of the flower/fusion of male and female gametes.
b. Help in establishing links and act as evidence of evolution.
Question. (a) “Each organism has its own identity”. Explain.
(b) What is speciation?
Answer :
a. (i) The DNA of each organism is different from others.
(ii) The DNA of each organism is specific within the same species with specific number of chromosomes/genes.
b. Emergence of new species from pre-existing forms through natural selection/artificial selection/ genetic drift/evolution, etc.
Question. An organ like a wing in birds are an advantage to an organism. Did they appear in different stages or were formed due to a single sudden change in them.
Answer : Feathers in dinosaur were long and they could not fly using feathers. It gave them protection from cold weather and warmth. Birds seem to have later adapted the feathers to flight.
Question. Fore limbs of amphibians, reptiles, birds and mammals show similarity in their bones but Wings of bat and bird don’t. What conclusion can be drawn from such observation regarding their ancestry?
Answer : The organs which have similar basic structure and mode of origin but perform different functions in different animals are called homologous organs, e.g., forelimbs of amphibians, reptiles, birds and mammals.
Homologous organs give an evidence of common ancestory and evolutionary relationship between apparently different species.
Analogous organ are the organs in different organisms which have different basic structure but have similarity in shape and function, e.g., wings of bat and bird. These organs do not provide an evidence in support with common ancestory.
Question. a. What are fossils?
b. Explain the importance of fossils in evolutionary relationship.
Answer :
a. Impressions of the body parts of the organisms and preserved traces of the living organisms are called fossils.
b. The presence of fossilized remains of the organism is the evidence of existence of organisms million years ago which have now become extinct. Fossil also help in determining the connecting links between various groups and their origin from their primitive ones.
Question. What are fossils? What do they tell about the process of evolution?
Answer : The fossils can be defined as remains or impressions of the hard parts of the past individuals in the strata of the earth. Fossils helps in working out evolutionary relationships. Fossils provide one of the most acceptable evidences in support of evolution, because we can study the evolutionary past of individuals in the form of their fossils. By studying fossils occurring in different strata of rocks, geologists are able to reconstruct the time course of evolutionary events.
Age of fossils can also be found by time dating using isotopes of carbon (carbon dating).
Question. Variation is useful for the useful over long time. But the variants have unequal chances of survival. Explain this statement.
or
Define variation in a species. How does it increases the survival chances of a species?
a. Identify the organism shown in the above figure.
b. Name one incipient feature selected by the nature.
c. Mention any other primitive feature of birds.
Answer : Variation are minor differences among members of a population. They are useful for the process of evolution which take place over long time. But some of the variants find it more advantageous in the present environmental conditions to survive than others variants by virtue of the variation possessed by them hence they have unequal chances of survival. Thus some get selected and others get eliminated. Those which survive pass their genes to next generation therefore frequency of genes possessed by them increase in frequency in the population. Example – in a population of beetles, a new variation (green colour) get survival benefit/advantage to green beetles whereas other (red) perishes.
Question. a. Why traits such as intelligence and knowledge cannot be passed on to the next generation?
b. How can we say that birds are closely related to reptiles and have evolved from them?
Answer :
a. Traits such as intelligence and knowledge are not heritable traits, which do not bring upon any changes in the DNA of the germ cells and, therefore, cannot be passed on to the progeny.
b. This can be said because traits such as feathers were first seen in reptiles like Dinosaurs, which performed the function of providing insulation to them in cold weather although they could not fly using the feathers but later birds adapted the feathers for flight. This means that birds are very closely related to reptiles, as dinosaurs were reptiles.
Question. A group of grasshoppers — some green and some brown lived in a grassland having dry bushes and dry grass.
a. Which one would normally be picked up by predatory birds and why?
b. Population of which grasshopper will increase?
c. Name this phenomenon.
Answer :
a. Green grass hopper, because they stand out, against brown background of dry bushes.
b. Brown
c. Natural selection.
Question. (a) Explain why the wing of a bat and the wing of bird are considered to be analogous organs.
(b) List two factors that lead to the formation of a new species.
Answer :
a. Design, structure and components are different.
Origins are not common.
b. Genetic drift and natural selection.
Question. a. Name the scientist who gave the idea of evolution of species by natural selection.
b. What conclusion did Mendel draw from his experiments about traits?
c. Arrange the following according to evolution.
Cockroach, Mango tree, Gorilla, Fish
Answer :
a. Darwin
b. Traits are inherited independently.
c. Mango tree — Cockroach – Fish — Gorilla.
Question. 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. Outline a project which aims to find the dominant coat colour in dogs.
Answer : Dominant → WW (white colour)
Question. Explain the importance of fossils in deciding evolutionary relationships.
Answer : Fossils help us to know the following:
(a) Fossils help to trace the racial history of organisms.
(b) They help to measure the geological time.
(c) Older fossils lie at the depth and young fossils are at the upper surface of the earth. Complex organisms are present at top and simple organisms are present at the bottom.
(d) Fossil like—Archaeopteryx-show the link between two different types of species.
Question. 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. 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. 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.
Question. 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. 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. 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. 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 F1 progeny formed were all tall. This shows that traits may be either dominant or recessive, there is no way in between traits obtained.
Question. 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. 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 tell us about the process of evolution. The fossils of different organisms have some features similar to one species while some features 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.
Question. Distinguish between acquired and inherited traits by giving one example of each. Why are traits acquired during the lifetime of an individual not inherited?
Answer: Acquired trait is a particular characteristic that is developed during the lifetime of an individual. Such characteristics are not genetically controlled and cannot be passed on to the next generation. Example: Loss of weight due to starvation.
Inherited trait is the transmission of particular characteristics from parents to their off springs, generation to generation. Such traits are genetically determined characteristic that distinguishes a person.
Example: Colour of skin.
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. The human beings who look so different from each other in terms of colour, size and looks are said to belong to the same species. Why?
Answer: Human beings are said to belong to the same species because of the following reasons:
1. DNA studies.
2. Number of chromosome is same,
3. All have a common ancestor.
4. They interbreed among themselves to produce fertile young ones of their own kind.
Question. Explain the mechanism of sex determination in humans.
Or
With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of sex of a child?
Answer: Mechanism of Sex Determination in Human Beings:
In human beings, the sex of the individual is genetically determined.
Sex determination is the process by which sex of a new born individual can be determined.
Human beings have 1 unpaired sex chromosome. Sex chromosome of male is XY and of female is XX.
Sex of a child depends on what happens at fertilisation.
Thus, father is responsible for the determination of the sex of a child.
Question. With the help of suitable examples explain natural selection.
Answer: Let us assume that there exist a group of red beetles in some green bushes. Due to variation during sexual reproduction one green beetle evolved among them. This green beetle can pass the colour to its progeny which are green beetles.
Crows cannot see green beetles in green bushes and therefore, cannot eat them. The progeny of green beetles are not eaten while the progeny of red beetles continued to be eaten. As a result there are more and more green beetles in the beetle population. The progeny of green beetles increase due to natural selection which gives survival advantage.
Question. Explain the terms: (i) Speciation (ii) Natural selection
Answer: (i) Speciation is the evolution of reproductive isolation among once-interbreeding populations, i.e. the development of one or more species from an existing species.
(ii) Natural selection is the process, according to Darwin, which brings about the evolution of new species of animals and plants.
Question. Explain with examples how the following are evidences in favour of evolution in organisms. (i) Homologous organs (ii) Analogous organs (iii) Fossils
Answer: (i) Forelimb of human and bird are homologous organs. They have same structural design and developmental origin but they have different functions and appearance. Homologous organs help us to understand that the organism has evolved from a common ancestor. The more common characteristics the two species have, the more closely they are related.
(ii) Analogous organs are those organs design and developmental origin but have similar appearance and perform similar functions.
Example: The wings of birds and bats look similar but have different design in their structure. They have a common function of flying but their origins are not common. So, birds and bats are not closely related.
(iii) Fossils and their study is useful in knowing about the species which are no longer alive. They provide evidence and missing links between two classes. They are helpful in forming a sequence of organisms in the pathway of evolution. Thus, fossils have an importance in deciding evolutionary relationship. Archaeopteryx is a fossil bird. It had feathers, fused bones and beak which are exclusively bird structures. It also had some features which are found in reptiles, e.g. teeth in jaw, claws on free fingers and a long tail. This fossil provides a clue that birds have evolved from reptiles.
Question. Describe briefly four ways in which individuals with a particular trait may increase in a population.
Answer: The four ways in which individuals with a particular trait may increase in a population are as follows:
1. Sexual reproduction results into variations.
2. The individuals with special traits survive the attack of their predators and multiply while the other will perish.
3. Genetic drift provides diversity without any adaptation.
4. Variations in the species may lead to increased survival of the individuals.
Question. What is a sex chromosome?
Answer: Sex chromosome is a chromosome that operates in the sex-determining mechanism of a species. Many animals have two different types of sex chromosomes. For example, in human there is a large X chromosome and a much smaller Y chromosome.
Question. What evidence do we have for the origin of life from inanimate matter?
Answer: Stanley L. Miller and Harold C. Urey provided evidence regarding origin of life from inanimate matter. They assembled an atmosphere similar to that existed on early earth. The atmosphere had molecules like ammonia, methane and hydrogen sulphide, but no oxygen and kept over water at temperature just below 100°C. 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.”The sex of the children is determined by what they inherit from their father and not their mother.” Justify.
Answer: It is because a child who inherits an X chromosome from her father will be a girl and one who inherits a Y chromosome from his father will be a boy. But all children inherit a X chromosome from their mother regardless of whether they are boys or girls.
Question. Give an example of body characteristics used to determine how close two species are in terms of evolution and explain it.
Answer: Homologous organs help to identify the relationship between organisms. These characteristics in different organisms would be similar because they have inherited from a common ancestor. For example, forelimbs of human and wings of birds show closeness between the two species because the organs have similar basic structural design of limbs though it has been modified to perform different functions.
Question. What are homologous organs? Can the wing of a butterfly and the wing of a bat be regarded as homologous? Why?
Answer: Homologous organs are those organs which have the same basic structural design and developmental origin but have different functions and appearance.
Example: The forelimb of a frog, a lizard, a bird and a man seem to be built from the same basic design of bones, but they perform different functions.
No, the wing of a butterfly and the wing of a bat cannot be considered homologous organs because they have a common function for flying but their origin and structure are not common. So, they are analogous organs.
Question. 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 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.
LONG ANSWER TYPE QUESTIONS
Question. (i) What is genetics?
(ii) Give the common name of the plant on which Mendel performed its experiments.
(iii) What for did Mendel use the term factors and what are these factors called now?
(iv) What are genes? Where are the genes located?
Answer : (i) Science which deals with the study of heredity and variations is called genetic.
(ii) Pea plant.
(iii) Mendel used the term factors for ‘genes’.
(iv) 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. A group of class X students prepared a street play to educate masses on gender disparity to stop sex determination of girl child and abort it. (a) In human being, what is the chance of giving birth to a girl child? (b) Who is responsible for the birth of a female child and why? (c) What value is depicted among the group members of class X?
Answer : (a) The chance of giving birth to a girl child is 50%. (b) Male (father) is responsible for the birth of a female child as only the male individual is a carrier both of X and Y chromosomes which will determine the sex of the foetus. (c) The group members show team work, collaborative leadership, participating citizenship etc.
Question. Define ‘evolution’. State Darwin’s theory of evolution.
Answer : Evolution is a change in the genetic composition of a population. Darwin’s theory
1. The size of population remains the same, constant despite the fact that more offsprings are produced than needed.
2. Variations provide adaptations.
3. The best adapted organism survive in the changing environment (survival of the fittest).
4. Nature selects the best organisms with better adaptations and after many generations new species are formed (natural selection).
Question. What are various evidences in factors of evolution?
Answer : Evidences are:
(a) Homologous organs: Organs which have same structure but different function. E.g., wings of a bat, hands of man and limbs of monkey.
(b) Analogous organ. Organs which perform similar function but are structurally different are called analogous organ. E.g., wings of bat, insects, birds.
(c) 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.
(d) 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. (e) 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. Study the given diagram and answer the questions. (img 129) 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. 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.
Question. Explain the analogous organs and homologous orgAnswer : Identify the analogous and homologous organ amongst the following: Wings of an insect, wings of a bat, forelimbs of frog, forelimbs of human.
Answer : Analogous organs are those organs that have same function but have different structural design and origin. E.g., wings of birds and insects. Homologous organs are those organs in different plants or animals which have the same basic structural design and organ but have different appearance and functions. Analogous—Wings of an insect, wings of a bat Homologous–Forelimbs of frog, forelimbs of human and wings of bat.
Question. 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. 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. 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. After the death of two insects, one of the insect was burried 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 burried in hot mud. The body will not get decomposed in hot mud and the impression of the body will remain.
Question. How do Mendel’s experiments show that traits are inherited independently?
Answer : When Mendel crossed pure bred tall pea plants with pure bred 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. Why are traits acquired during the life-time of an individual not inherited?
Answer. This happens because an acquired trait involves change in non-reproductive tissues (somatic cells) which cannot be passed on to germ cells or the progeny. Therefore, these traits cannot be inherited.
Question. How do Mendel’s experiments show that traits are inheritedindependently?
Answer. Mendel crossed pea plants having round green seeds (RRyy) with pea plants having wrinkled yellow seeds (rrYY).
An example of dihybrid crosses
Since the F1 plants are formed after crossing pea plants having green round seeds and pea plants having yellow wrinkled seeds, F1 generation will have both these characters in them. However, as we know that yellow seed colour and round seeds are dominant characters, therefore, the F1 plants will have yellow round seeds.
Then this F1 progeny was self-pollinated and the F2 progeny was found to have yellow round seeds, green round seeds, yellow wrinkled seeds, and green wrinkled seeds in the ratio of 9:3:3:1.
Independent inheritance of two different traits
In the above cross, more than two factors are involved, and these are independently inherited.
Question. 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. No. This information is not sufficient to determine which of the traits − blood group A or O − is dominant. This is because we do not know about the blood group of all the progeny. Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.
Question. What factors could lead to the rise of a new species?
Answer. Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.
Question. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species ? Why or why not?
Answer. Geographical isolation can prevent the transfer of pollens among different plants. However, since the plants are self-pollinating, which means that 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, geographical isolation cannot prevent speciation in this case.
Question. 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. In asexual reproduction, the reproducing cells produce a copy of their DNA through some chemical reactions. However, this copying of DNA is not accurate and therefore, the newly formed DNA has some variations.
It can be easily observed in the above figure that in asexual reproduction, very few variations are allowed. Therefore, if a trait is present in only 10% of the population, it is more likely that the trait has arisen recently. Hence, it can be concluded that trait B that exists in 60% of the same population has arisen earlier than trait A.
Question. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer. Geographical isolation prevents gene flow between populations of a species whereas asexual reproduction generally involves only one individual. In an asexually reproducing organism, variations can occur only when the copying of DNA is not accurate. Therefore, geographical isolation cannot prevent the formation of new species in an asexually reproducing organism.
Question. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer. Small numbers of tigers means that fewer variations in terms of genes are available. This means that when these tigers reproduce, there are less chances of roducing progeny with some useful variations . Hence, it is a cause of worry from the point of view of genetics.
Question. How is the sex of the child determined in human beings?
Answer. In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY.
The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.
Type of male gametes: 22+X OR 22+ Y.
However, since the females have XX sex chromosomes, their gametes can only have X sex chromosome.
Type of female gamete: 22+X
Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.
Question. What are the different ways in which individuals with a particular trait may increase in a population?
Answer. Individuals with a particular trait may increase in a population as a result of the following:
(i) Natural selection: When that trait offers some survival advantage.
(ii) Genetic drift: When some genes governing that trait become common in a population.
(iii) When that trait gets acquired during the individual’s lifetime.
Question. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer. The presence of feathers in dinosaurs and birds indicates that they are evolutionarily related. Dinosaurs had feathers not for flying but instead these feathers provided insulation to these warm-blooded animals. However, the feathers in birds are used for flight. This proves that reptiles and birds are closely related and that the evolution of wings started in reptiles.
Question. Find out, from Table, the medium having highest optical density. Also find the medium with lowest optical density.
Answer. Highest optical density = Diamond
Lowest optical density = Air
Optical density of a medium is directly related with the refractive index of that medium. A medium which has the highest refractive index will have the highest optical density and vice-versa.
It can be observed from table 10.3 that diamond and air respectively have the highest and lowest refractive index. Therefore, diamond has the highest optical density and air has the lowest optical density.
Question. What are fossils? What do they tell us about the process of evolution?
Answer. Fossils are the remains of organisms that once existed on earth. They represent the ancestors of plants and animals that are alive today. They provide evidences of evolution by revealing the characteristics of the past organism and the changes that have occurred in these organisms to give rise to the present organisms.
Question. 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. A species is a group of organisms that are capable of interbreeding to produce a fertile offspring. Skin colour, looks, and size are all variety of features present in human beings. These features are generally environmentally controlled. Various human races are formed based on these features. However, there is no biological basis to this concept of races. Therefore, all human beings are a single species as humans of different colour, size, and looks are capable of reproduction and can produce a fertile offspring.
Question. A study found that children with light-coloured eyes are likely to have parents with lightcoloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Answer. Let us assume that children with light-coloured eyes can either have LL or Ll or ll genotype. If the children have LL genotype, then their parents will also be of LL genotype.
LL × LL
↓
LL
If the children with light-coloured eyes have ll genotype, then their parents will also have ll genotype.
ll × ll
↓
ll
Therefore, it cannot be concluded whether light eye colour is dominant or recessive.
Question. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer. In human beings, every somatic cell of the body contains 23 pairs of chromosomes. Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosomes represented as X and Y.
Females have two X chromosomes and males have one X and one Y chromosome. The gamete receives half of the chromosomes. Therefore, the male gametes have 22 autosomes and either X or Y chromosome.
The female gamete, on the other hand, has 22 autosomes and X chromosome. During reproduction, the male and female gametes fuse and thus the progeny receives 22 autosomes and one X or Y chromosome from male parent and 22 autosomes and one X chromosome from the female parent.
Question. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Answer. Evolution cannot always be equated with progress or better body designs. Evolution simply creates more complex body designs. However, this does not mean that the simple body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms found on earth. They can survive hot springs, deep sea, and even freezing environment.
Therefore, bacteria, spiders, fish, and chimpanzees are all different branches of evolution.
Question. 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. In species, variations that offer survival advantages are naturally selected. Individuals adjust to their environments with the help of these selected variations and consequently these variations are passed on to their progeny. Evolution of organisms occurs as a result of this natural selection.
However, there can be some other variations, which do not offer any survival advantage and arise only accidentally. Such variations in small populations can change the frequency of some genes even if they are not important for survival.
This accidental change in the frequency of genes in small populations is referred to as genetic drift.
Thus, genetic drift provides diversity (variations) without any survival advantage.
Question. Explain the terms analogous and homologous organs with examples.
Answer. Homologous organs are similar in origin (or are embryologically similar) but perform different functions. For example, the forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar. It means that their origin is similar (as wings in birds are odifications of forearm) but functions are different – the wings help in flight whereas human forearm helps in various activities.
Analogous organs, on the other hand, have different origin but perform similar functions. For example, the wings of a bird and a bat are similar in function but this similarity does not mean that these animals are more closely related. If we carefully look at these structures, then we will find that the wings of a bat are just the folds of skin that are stretched between its fingers whereas the wings of birds are present all along the arm. Therefore, these organs are analogous organs.
Question. 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. In sexual reproduction, two individuals having different variations combine their DNA to give rise to a new individual. Therefore, sexual reproduction allows more variations ,whereas in asexual reproduction, chance variations can only occur when the copying of DNA is not accurate.
Additionally, asexual reproduction allows very less variations because if there are more variations, then the resultant DNA will not be able to survive inside the inherited cellular apparatus.
However, in sexual reproduction, more variations are allowed and the resultant DNA is also able to survive ,thus making the variations viable.
Variation and Evolution: Variants help the species to survive in all the conditions. Environmental conditions such as heat, light, pests, and food availability can change suddenly at only one place. At that time, only those variants resistant to these conditions would be able to survive. This will slowly lead to the evolution of a better adapted species. Thus, variation helps in the evolution of sexually reproducing organisms.
Question. How are the areas of study − evolution and classification − interlinked?
Answer. Classification involves grouping of organism into a formal system based on similarities in internal and external structure or evolutionary history.
Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor.
For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation.
With subsequent generations, the variations make organisms more different than their ancestors.
This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.
Question. Explain the importance of fossils in deciding evolutionary relationships.
Answer. Fossils are the remains of the organism that once existed on earth. They represent the ancestors of the plants and animals that are alive today. They provide evidences of evolution by revealing the characteristics of the past organisms and the changes that have occurred in these organisms to give rise to the present organisms. Let us explain the importance of fossils in deciding evolutionary history with the help of the following example.
Around 100 million years ago, some invertebrates died and were buried in the soil in that area. More sediment accumulated on top of it turning it into sedimentary rock.
At the same place, millions of years later, some dinosaurs died and their bodies were buried on top of the sedimentary rock. The mud containing dinosaurs also turned into a rock.
Then, millions of years later, some horse-like creatures died in that area and got fossilized in rocks above the dinosaur fossils.
Some time later, due to soil erosion or floods in that area, the rocks containing horselike fossils are exposed.
If that area is excavated deeper, then the dinosaur and invertebrates fossils can also be found. Thus, by digging that area, scientists can easily predict that horse-like animals evolved later than the dinosaurs and the invertebrates.
Thus, the above example suggests that the fossils found closer to the surface of the earth are more recent ones than the fossils present in deeper layers.
Question. How do Mendel’s experiments show that traits may be dominant or recessive?
Answer. Mendel selected true breeding tall (TT) and dwarf (tt) pea plants. Then, he crossed these two plants. The seeds formed after fertilization were grown and these plants that were formed represent the first filial or F1 generation. All the F1 plants obtained were tall.
Then, Mendel self-pollinated the F1 plants and observed that all plants obtained in the F2 generation were not tall. Instead, one-fourth of the F2 plants were short.
Self-pollination of F1 plants
From this experiment, Mendel concluded that the F1 tall plants were not true breeding. They were carrying traits of both short height and tall height. They appeared tall only because the tall trait is dominant over the dwarf trait.
Question. Outline a project which aims to find the dominant coat colour in dogs.
Answer. Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog.
A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown. Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb)
In this case, all the offsprings will be heterozygous (Bb).
Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles.
If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offsprings.
Question. How does the creation of variations in a species promote survival?
Answer. Sometimes for a species, the environmental conditions change so drastically that their survival becomes difficult. For example, if the temperature of water increases suddenly, most of the bacteria living in that water would die. Only few variants resistant to heat would be able to survive. If these variants were not there, then the entire species of bacteria would have been destroyed. Thus, these variants help in the survival of the species. However, not all variations are useful. Therefore, these are not necessarily beneficial for the individual organisms.
Question. What evidence do we have for the origin of life from inanimate matter?
Answer. A British scientist, J.B.S. Haldane, suggested that life originated from simple inorganic molecules. He believed that when the earth was formed, it was a hot gaseous mass containing elements such as nitrogen, oxygen, carbon, hydrogen, etc. These elements combined to form molecules like water (H2O), carbon dioxide (CO2), methane (CH4), ammonia (NH3), etc.
After the formation of water, slowly the earth surface cooled and the inorganic molecules interacted with one another in water to form simple organic molecules such as sugars, fatty acids, amino acids, etc. The energy for these reactions was provided by solar radiations, lightning, volcanic eruptions, etc.
This was proved by the experiment of Stanley L. Miller and Harold C. Urey in 1953. They took a mixture of water (H2O), methane (CH4), ammonia (NH3), and hydrogen gas (H2) in a chamber and sparks were passed through this mixture using two electrodes. After one week, 15% of the carbon from methane was converted into amino acids, sugars, etc. These organic molecules are polymerized and assembled to form protein molecules that gave rise to life on earth.
