Contents
- 1 Class 10 Science Chapter 9 Important Questions with Answers Heredity and Evolution
- 1.1 Heredity and Evolution Class 10 Important Questions Very Short Answer Type
- 1.2 Heredity and Evolution Class 10 Important Questions Short Answer Type I
- 1.3 Heredity and Evolution Class 10 Important Questions Short Answer Type II
- 1.4 Heredity and Evolution Class 10 Important Questions Long Answer Type
Solved the very best collection of Heredity and Evolution Class 10 Science Important Questions and Answers Chapter 9 Pdf from the latest NCERT edition books, It will help you in scoring more marks in CBSE Exams.
Class 10 Science Chapter 9 Important Questions with Answers Heredity and Evolution
Class 10 Chemistry Chapter 9 Important Questions with Answers Heredity and Evolution
Heredity and Evolution Class 10 Important Questions Very Short Answer Type
Question 1.
What is speciation? (2013 D, 2015 D)
Answer:
The process by which new species develop from the existing species is known as speciation.
Question 2.
List any two factors that could lead to speciation. (2013 D)
Answer:
Two factors that could lead to speciation:
- Geographical isolation of a population caused by various types of barriers (such as mountain range, rivers and sea). This leads to reproductive isolation due to which there is no flow of genes between separated groups of population.
- Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
Question 3.
Why is DNA copying necessary during reproduction? (2013 OD)
Answer:
DNA copying is essential during reproduction for the inheritance of features from parents to the next generation.
Question 4.
Give the respective scientific terms used for studying: (2014 D)
(i) the mechanism by which variations are created and inherited and
(ii) the development of new type of organisms from the existing ones.
Answer:
(i) Reproduction
(ii) Speciation
Question 5.
Name the information source for making proteins in the cells. (2014 D)
Answer:
DNA – (Deoxyribo Nucleic Acid) is the information source for making proteins in the cells.
Question 6.
Write the contribution of Charles Darwin in the field of ‘evolution’. ( 2014 D)
Answer:
- Charles Robert Darwin gave the theory of evolution in his famous book “The Origin of Species”.
- The theory of evolution proposed by Darwin is known as “The Theory of Natural Selection”.
- This theory suggests that the best adapted organisms are selected by nature to pass on their characteristics to the next generation.
Question 7.
What is gene? (2014 OD)
Answer:
A gene is a unit of DNA on a chromosome which governs the synthesis of one protein that controls a specific character of an organism. Thus genes are actually units of heredity which transfer characteristics from parents to their offsprings during reproduction.
Question 8.
What is heredity? (2014 OD)
Answer:
The transmission of characters from the parents to their offspring is called heredity.
Question 9.
No two individuals are absolutely alike in a population. Why? (2013, 2014 OD)
Answer:
DNA copying is an essential part of the process of reproduction for the inheritance of features from parents to the next generation. The process of DNA copying brings some variation each time.
The surviving cells are similar to but subtly different from each other. This in built tendency for variation during reproduction brings variations among individuals of the same species. Thus, no two individuals are absolutely alike in a population.
Question 10.
Where is DNA found in a cell? (2015 OD)
Answer:
DNA is found in the nucleus of the cell.
Question 11.
What is DNA?
Answer:
DNA. Deoxyribonucleic acid is a genetic material found in all the living organisms.
It is the carrier of hereditary information from parents to the next generation.
Heredity and Evolution Class 10 Important Questions Short Answer Type I
Question 1.
“DNA copies generated during reproduction will be similar but may not be identical to the original.” Justify the statement. (2012 OD)
Answer:
A basic event in reproduction is the creation of a DNA copy. This is necessary to produce organisms which are similar to their parents. DNA copying is accompanied by the creation of an additional cellular apparatus. When two DNA copies separate, each with its own cellular apparatus by cellular division, so from one cell, two cells are produced.
The process of copying of DNA brings some variations each time. Thus the surviving cells are similar to but subtly different from each other. This inbuilt tendency for variation during reproduction brings variations among the individuals of the same species.
Question 2.
“The chromosomals number of the sexually reproducing parents and their offspring is the same.” Justify this statement. (2013 D, 2014 OD)
Answer:
In sexual reproduction, though the genetic material DNA (in the form of chromosomes) from two gametes, male and female gametes, combines together to form a new cell ‘zygote’ but the amount of DNA (the number of chromosomes) in the zygote does not get doubled because gametes are the special type of cells called reproductive cells which contain only half the amount of DNA (or half the number of chromosomes) as compared to the normal body cells of an organism.
So when a male gamete (having half number of chromosomes of the organism) combines with a female gamete (which also contain half the number of chromosomes) during sexual reproduction, then the new cell zygote will have the normal amount of DNA or normal number of chromosomes in it.
Question 3.
State the importance of chromosomal difference between sperms and eggs of humans. (2013 OD, 2014 OD)
Answer:
A male has one X chromosome and one Y chromosome. Thus half the sperms will have X chromosomes and the other half will have Y chromosome.
A female has two X chromosomes. So all the female gametes will have only X chromosomes.
If a sperm carrying X chromosome fertilizes an ovum then the child born will be a girl. If a sperm carrying Y chromosome fertilizes an ovum then the child born will be a boy.
Thus the chromosomal difference between sperms and eggs of humans determines the sex of the child.
Heredity and Evolution Class 10 Important Questions Short Answer Type II
Question 1.
Define homologous and analogous organs. (2011 D)
Classify the following as homologous or analogous organs:
(i) Wings of an insect and wings of bat.
(ii) Forelimbs of a man and forelimbs of a frog.
Answer:
Homologous organs: Those organs which have the same basic structure or same basic design but different functions, are called homologous organs.
Analogous organs: Those organs which have different basic structure or different basic design but have similar appearance and perform similar functions are called analogous organs.
- These are analogous organs.
- These are homologous organs.
Question 2.
Explain how equal genetic contribution of male and female parents is ensured in the progeny. (2011 D)
Answer:
Both the parents contribute equal DNA material to progeny. Every sexually reproducing organism bears two sets of all genes, one inherited from each parent. Each germ cell must have only one gene set. Thus the male gamete and female gamete carry one gene for each characteristic from the gene pairs of parents. But when a male gamete fuses with a female gamete during fertilisation, they make a new cell called zygote with a full set of genes. Thus zygote grows and develops to form a new organism having equal characteristics from both the parents which it has inherited through genes.
Question 3.
Explain the terms: (i) Speciation; (ii) Natural selection. (2011 D; 2015 OD)
Answer:
(i) Speciation: The process by which new species develop from the existing species is known as speciation.
The important factors which could lead to the formation of new species are:
- Geographical isolation of a population caused by various types of barriers like mountain ranges, rivers, sea etc. The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of population.
- Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
- Variations caused in individuals due to natural selection.
(ii) Natural selection. Natural selection is the process of evolution of a species whereby characteristics which help individual organisms to survive and reproduce are passed on to their offsprings and those characteristics which do not help are not passed on.
Question 4.
Explain with examples how the following are evidences in favour of evolution in organisms.
(i) Homologous organs (ii) Analogous organs (iii) Fossils (2011 D, 2015 OD)
Answer:
(i) Homologous organs. Those organs, which have the same basic structure but different functions, are called homologous organs.
For example: The forelimbs of a man, a lizard, a frog, a bird and a bat have the same basic design of bones but they perform different functions.
The presence of homologous organs in different animals provides evidence for evolution that they are derived from the same ancestor who has the basic design of the organ on which all the homologous organs are based.
(ii) Analogous organs. Those organs, which have different basic structure but have similar appearance and perform similar functions are called analogous organs.
For example: The wings of an insect and a bird have different structures but they perform the same function of flying.
Analogous organs provide evidence for evolution that the organisms from different ancestors perform similar functions to survive, flourish and keep on evolving in prevailing environment.
(iii) Fossils. The remains of dead animals or plants that lived in the remote past are known as fossils. The fossils provide evidence for evolution.
For example: A fossil of a bird called Archaeopteryx looks like a bird but it has many other features found in reptiles. Therefore Archaeopteryx is a connecting link between the reptiles and birds and hence suggests that the birds have evolved from the reptiles.
Question 5.
Explain Mendel’s view of a dominant trait. Give an example. (2011 D)
Answer:
According to Mendel’s view of dominant trait, the traits of an Tall pea plant Dwarf pea plant organism are determined by internal factors which occur in pairs. Out of two contrasting traits only one expresses itself in an individual. This trait is called dominant, while the other which has not shown its effect in the presence of dominant trait is called recessive.
Example, When true bred tall pea plants are crossed with true bred dwarf plants, the plants that appeared in F1 generation are tall, although they have received a factor (trait) from dwarf plant. So trait of tallness is dominant one. However this recessive hidden character reappeared, unchanged in F2 generation.
Question 6.
Describe any three ways in which individuals with a particular trait may increase in population. (2011 OD)
Answer:
The three ways in which individuals with a particular trait may increase in population:
- Geographical isolation of a population caused by various types of barriers such as mountain ranges, rivers and seas, etc. The geographical isolation leads to reproductive isolation and the individuals with a particular trait may increase in population.
- The struggle for survival within populations eliminates unfit individuals. Fit individuals (i.e., favourable trait) survive and reproduce. In other words, the variation if given survival advantage, it will be naturally selected.
- Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
Question 7.
State the evidence we have for the origin of life from inanimate matter. (2011 OD)
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 an apparatus to create an early earth like atmosphere which was supposed to consist of gases like methane, ammonia and hydrogen sulphide but no oxygen, over water. This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning.
At the end of a week, 15% of the carbon (from methane) had been converted to complex compounds of carbon including amino acids which make up protein molecules in the living beings.
Question 8.
(a) “The sex of the children is determined by what they inherit from their father and not their mother.” Justify.
(b) Give an example where environmental factors like temperature determines the sex of the offspring. (2011 OD)
Answer:
(a)
- A male has one X chromosome and one Y chromosome.
- A female has two X chromosomes.
- If a sperm carrying X chromosome fertilises an ovum, then the child bom will be a girl.
- If a sperm carrying Y chromosome fertilises an ovum, then the child born will be a boy.
Thus, the sperm determines the sex of the child.
(b) In some reptiles, the temperature at which the fertilised egg is incubated before hatching plays a role in determining the sex of the offspring.
Example: In a turtle, high incubation temperature leads to female offspring.
Question 9.
Explain various stages of evolution? (2011 OD)
Answer:
Various stages of evolution:
- Complex organs may have evolved because of the survival advantages of the intermediate stage.
- Complex organs like eyes are created bit by bit over generations through the changes in the DNA sequences.
- The structure of the eye in all organisms is different enough to have separate evolutionary origin.
- Organs may be adapted to new functions during the course of evolution, e.g., feathers are thought to have evolved for warmth and later adapted for flight. ,
- Some dissimilar looking structures also evolved from a common ancestor, e.g., different vegetation like cauliflower, cabbage, broccoli, kale, etc. are generated by artificial selection from wild cabbage.
- Changes in DNA during reproduction are the basic events of evolution.
Question 10.
Give an example of body characteristics, used to determine how close two species are in terms of evolution and explain it. (2011 OD)
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 11.
What are homologous organs? Can the wings of a butterfly and the wings of a bat be regarded as homologous? Why? (2011 OD)
Answer:
Those organs which have the same basic structure but different functions are called homologous organs. The wings of a butterfly and the wings of a bat cannot be regarded as homologous because they have different basic design though they are used for the same purpose of flying. They are rather analogous organs.
Question 12.
(a) Name any four varieties of vegetables which have been produced from ‘wild cabbage’ by the process of artificial selection.
(b) Give one example of an evolutionary change produced in an organism for one purpose which later on becomes more useful for a different function. (2012 D)
Answer:
(a) Cabbage, broccoli, kale, kohlrabi are evolved from wild cabbage by artificial selection.
(b) Sometimes an evolutionary change produced in an organism for one purpose later on becomes more useful for an entirely different function. For example: Birds have evolved feathers as a means of providing insulation to their bodies in cold weather but later on these feathers became more useful for the purpose of flying.
Question 13.
A blue colour flower plant denoted by BB is crossbred with that of white colour flower plant denoted by bb.
(a) State the colour of flower you would expect in their F2 generation plants.
(b) What must be the percentage of white flower plants in F2 generation if flowers of F1 plants are self-pollinated?
(c) State the expected ratio of the genotypes BB and Bb in the F2 progeny. (2012 D, 2013 OD, 2015 OD)
Answer:
(a)
All the flowers in the F1 generation are blue
(b) If flowers of F1 plants are self-pollinated
Genotype ratio of BB and BW in F2 progeny is BB : BW : 1 : 2.
Question 14.
What is meant by the term speciation? List four factors which could lead to speciation. (2012 D)
Answer:
The process by which new species develop from the existing species is known as speciation.
Important factors which could lead to the formation of a new species are as follows:
- Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
- Geographical isolation of a population caused by various types of barriers like mountain ranges, river, sea etc. The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of population.
- Variation caused in individuals due to natural selection.
- Sometimes the sub-population becomes reproductively isolated by ecological barriers. Therefore it occurs within the same geographical area and within the original population.
Question 15.
Distinguish between homologous organs and analogous organs. In which category would you place wings of a bird and wings of a bat? Justify your answer giving a suitable reason. (2012 D)
Answer:
Difference between Homologous organs and Analogous organs
Homologous organs:
- Homologous organs are those organs which are different in appearance and perform different functions but have similar basic structure and developmental origin.
- Presence of homologous organs confirms com-mon ancestry and evolutionary relationship.
- Example: Forelimbs of vertebrates
Analogous organs:
- Analogous organs are those organs which are different in their basic structure and developmental origin but appear similar and perform similar function.
- Presence of analogous organs shows that all the similarities are not necessary because of common ancestry.
- Example: Wings of an insect and a bird
Reason. Wings of a bird and wings of a bat are homologous organs because they have similar basic design.
Question 16.
Define the term ‘evolution’. “Evolution cannot be equated with progress.” Justify this statement. (2012 D)
Answer:
Evolution. Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years in which new species are produced.
Evolution cannot be equated with progress. More and more complex body designs have emerged and evolved over time, but this does not mean that the older designs are inefficient. One of the simplest life for bacteria came into being very early in evolution is still surviving in the present conditions.
Bacteria inhabits the most inhospitable habitats like hot springs, deep sea, thermal vents and ice in Antarctica. But human beings, have a body design which is best suited to their environment and supports their existence only in limited favourable conditions.
Question 17.
If we cross pure-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant we will get pea plants of F1 generation. If we now self-cross the pea plant of F1 generation, then we obtain pea plants of F2 generation.
(a) What do the plants of F1 generation look like?
(b) State the ratio of tall plants to dwarf plants in F2 generation.
(c) State the type of plants not found in F1 generation but appeared in F2 generation, mentioning the reason for the same. (2012 OD)
Answer:
(a) The plants of F1 generation are all Tall.
(b) Tall plants : Dwarf plants – 3:1
(c) Dwarf plants: This is because in F1 generation, tall is a dominant trait whereas in F2 generation, two copies of ‘tt’/recessive traits made the plant dwarf.
Question 18.
How are fossils formed? Describe, in brief, two methods of determining the age of fossils. (2012 OD)
Answer:
When organisms (plants or animals) die, their bodies will decompose by the action of micro-organisms in the presence of oxygen, moisture, etc.
Sometimes in the lack of such conditions (oxygen, moisture, etc.), their body does not decompose completely and is preserved as fossil with the passage of time in the rocks. In many cases the soft parts of the organism get decomposed and hard parts (like bones etc.) become fossil. Sometimes even the soft parts (like leaf etc.) remain preserved as fossils in the form of their impressions inside the rocks.
Methods to determine the age of fossils:
1. Relative method. The fossils which we find in layers closer to the surface of the earth are more recent;
the fossils which are found in deeper layers are older.
2. Carbon dating. Fossils were once living objects and all living objects contain some carbon-14 atoms which are radio-active. When a living object dies and forms fossil, its carbon-14 radioactivity goes on decreasing gradually. The age of the fossil is found by comparing the carbon-14 radioactivity left in the fossil with the carbon-14 radio-activity present in the living objects today.
Question 19.
List in tabular form two distinguishing features between acquired traits and inherited traits, with one example of each. (2012 OD)
(Or)
State the meaning of inherited traits and acquired traits. Which of the two is not passed on to the next generation? Explain with the help of an example. (2012 OD, 2013 D, 2015 D, 2016 D)
Answer:
Difference between Acquired traits and Inherited traits
Acquired traits:
1. A trait of an organism which is not inherited but develops in response to the environment is called an acquired trait.
2. The acquired traits of an organism cannot be passed on to the future generation.
Example: If a beetle does not get sufficient food for a considerable time, its weight will be reduced due to starvation. The low weight of this beetle is an acquired trait.
3. Acquired traits can not direct evolution.
Example, “low weight” of beetle, “cut tail” of a muse.
Inherited traits:
1. A trait of an organism which is caused by a change in its gene is called an inherited trait.
2. Inherited traits can be transmitted to future generations because the changes have occurred in the genes of sex gametes. Example: If in a group of red beetle a colour variation arises during reproduction so that there is a beetle which is green in colour. This green colour of the beetle is an inherited character which can pass on to the next generation.
3. Inherited traits can direct evolution.
Example “red colour of beetles, “fur coat” of guinee pigs.
Question 20.
“The father is responsible for the sex of a child, not the mother.” Justify this statement. (2012 OD)
Answer:
- A male has one X-chromosome and one Y-chromosome. Thus half the male gametes have X- chromosomes and the other half have Y-chromosomes.
- A female has two X-chromosomes. Thus all female gametes have only X-chromosomes.
- If a sperm carrying Y-chromosome fertilises an ovum carrying X-chromosome, then the child born will be a boy.
- If a sperm carrying X-chromosome fertilises an ovum carrying X-chromosome, then the child born will be a girl.
Therefore it is the sperm from the father which determines the sex of the child.
Question 21.
“The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it.” Justify this statement with the help of a flow chart showing determination of sex of a newborn. (2013 D, 2014 OD)
Answer:
Sex determination flow chart:
- A male has one X-chromosome and one Y-chromosome. Thus half the male gametes have X- chromosomes and the other half have Y-chromosomes.
- A female has two X-chromosomes. Thus all female gametes have only X-chromosomes.
- If a sperm carrying Y-chromosome fertilises an ovum carrying X-chromosome, then the child born will be a boy.
- If a sperm carrying X-chromosome fertilises an ovum carrying X-chromosome, then the child born will be a girl.
Therefore it is the sperm from the father which determines the sex of the child.
Thus in human beings, the sex of the baby is determined by the type of sperm that fuses with ovum. As human male produces two types of sperms in equal proportion, so there are 50% chances of a male baby and 50% chances of a female baby.
Question 22.
What are fossils? State their importance in the study of evolution with the help of a suitable example. (2011 OD, 2013 D)
Answer:
The remains or impressions of extinct animals or plants that lived in the remote past are known as fossils. Importance of fossils:
1. Fossils provide evidence for evolution, e.g., a fossil bird called Archaeopteryx looks like a bird but it has many features which are found in reptiles. Archaeopteryx has feathered wings like birds but teeth and tail like those of reptiles. Therefore Archaeopteryx is a connecting link between the reptiles and birds and hence suggests that the birds have evolved from the reptiles.
2. Habits and behaviour of extinct species can be inferred. For example, the estimation of age of dinosaur fossils have told that they first appeared on earth about 250 million years ago and became extinct about 65 million years ago.
3. Fossils provide direct evidence of past life.
4. With the help of fossils broad historical sequence of biological evolution can be built up.
Question 23.
Explain with the help of suitable examples why certain traits cannot be passed on to the next generation? What are such traits called? (2013 OD, 2014 OD)
Answer:
A trait (or characteristic) of an organism which is ‘not inherited’ but develops in response to the environment is called an acquired trait.
The acquired traits of an organism cannot be passed on to its future generations.
For example, Tow weight’ of beetle, ‘cut tail’ of a mouse.
Changes brought in the non-reproductive tissues cannot be passed on to the DNA of the germ cells. So the experiences of an individual during its lifetime cannot be passed on to its progeny. Thus acquired characters of an individual cannot he inherited.
Question 24.
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: (2013 OD)
(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:
When plants of two different traits of character are crossbred to get a progeny (F1 generation), only the dominant trait is visible in this generation. But when plants of F1 generation are selfbred then the two traits of character get separated and the recessive trait also appears in the plant of F2 generation. This is known as Law of Segregation (separation) of traits.
Flow Chart
Question 25.
How are fossils formed? State two methods of determining the age of fossils. (2013 OD)
Answer:
Formation of a fossil: Usually when organisms die, their bodies get decomposed by the action of micro-organisms in the presence of oxygen, moisture, etc. Sometimes, the conditions in the environment like oxygen, moisture, etc. are absent which do not let the body of the organism decompose completely. So fossils are such remains or impressions of dead animals or plants that lived in the remote past but which were not decomposed completely.
For example, if a dead leaf gets caught in mud, it will not decompose quickly. The mud around the leaf will set around it as a mould and gradually harden to form a rock and retain the impression of the whole leaf. This forms a leaf fossil which can be dug out from the earth a long time after.
Determination of age of the fossil.
- Fossils closer to the surface are more recent compared to those found in the deeper layers of the earth’s surface.
- Another way is by detecting the ratio of different isotopes of the same element in the fossil material and comparing their values with the present form of living beings.
Question 26.
A cross was made between pure breeding pea plants, one with round and green seeds and the other with wrinkled and yellow seeds. (2014 D)
(a) Write the phenotype of F1 progeny. Give reason for your answer.
(b) Write the different types of F2 progeny obtained along with their ratio when F1 progeny was selfed.
Answer:
(a) The cross was made between round, green seeds and wrinkled, yellow seeds. In the given cross, two traits were taken into account, which is a dihybrid cross.
Yellow colour and round shape is dominant over green colour and wrinkled shape.
The above cross shows round and yellow seeds in F1 generation. It occurs because dominant traits (round and yellow) express themselves, whereas recessive traits (wrinkled and green) get suppressed.
(b) On selfing of F1 progeny, different types of F2 progeny were obtained.
F2 progeny along with their ratios obtained in F2 generation:
Question 27.
(a) Mendel crossed tall pea plants with dwarf pea plants in his experiment. Write his observations giving reasons on the F1 and F2 generations.
(b) List any two contrasting characters other than height that Mendel used in his experiments in pea plants. (2014 D)
Answer:
(a) In Mendel’s experiments with pea plants, when he crossbred a tall pea plant with a dwarf pea plant, he found that the first generation F1 was of only tall plants. In the F1 progeny, no dwarf plants were obtained. However in F2 generation, both tall and dwarf plants were obtained in the ratio of 3 : 2 respectively. In the F2 progeny both traits tallness and dwarfness were inherited where the tall character was the dominant trait and dwarf character was the recessive trait.
Flow chart depicting Mendel’s experiment.
(b) Contrasting characters of pea plant
- Round and green seeds.
- Wrinkled and yellow seeds.
Question 28.
(a) Mendel in one of his experiments with pea plants crossed a variety having round seeds with one having wrinkled seeds. Write his observations, giving reasons, of F1 and F2 progeny.
(b) List any two contrasting characters other than roundness of pea plants that Mendel used in his experiments with pea plants. (2014 D)
Answer:
(a) In Mendel’s experiment with pea plants, when he crossbred a round seed plant with a wrinkled seed plant, he found that the first generation (F1) was only round seed plants. In the F1 progeny, no wrinkled seed plants were obtained. However, in the F2 progeny both traits round seed and wrinkled seed were obtained in the ratio 3 : 1 respectively. The trait which is obtained in F1 generation is dominant trait, therefore round seed character was dominant and wrinkled seed trait is recessive.
Flow chart:
(b)
- Tallness and dwarf ness.
- Green seed and yellow seed. These are the two contrasting characters that Mendal used in his experiment with pea plants.
Question 29.
what is the effect of DNA copying, which is not perfectly accurate, on the reproduction process? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals? (2014 OD)
Answer:
DNA coping is not perfectly accurate. During reproduction, no chemical reaction is absolutely reliable so the process of copying the DNA will hare some variations each time. As a result, the DNA copies generated will te similar but may not be identical to the original. Thus the surviving newborn cells are similar to but subtly different from each other. This inbuilt tendency for variation during reproduction is the basic for evolution.
In sexual reproduction, though the genetic material DNA (in the form of chromosomes) from two gametes, male and female gametes, combines together to form a new cell ‘zygote’ but the amount of DNA (the number of chromosomes) in the zygote does not get doubled because gametes are the special type of cells called reproductive cells which contain only half the amount of DNA (or half the number of chromosomes) as compared to the normal body cells of an organism.
So when a male gamete (having half number of chromosomes of the organism) combines with a female gamete (which also contain half the number of chromosomes) during sexual reproduction, then the new cell zygote will have the normal amount of DNA or normal number of chromosomes in it.
Question 30.
List three main factors responsible for the speciation and briefly describe each one of them. (2014 OD)
Answer:
The process by which new species develop from the existing species is known as speciation.
important factors which could lead to tJiefirrnation of a new species are as follows:
- Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
- Geographical isolation of a population caused by various types of barriers like mountain ranges, river, sea etc. The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of population.
- Variation caused in individuals due to natural selection.
- Sometimes the sub-population becomes reproductively isolated by ecological barriers. Therefore it occurs within the same geographical area and within the original population.
Question 31.
What is DNA copying? State its importance. (2015 D)
Answer:
A process in which a DNA molecule produces two similar copies of itself in a reproducing cell through chemical reaction is called DNA copying.
- It transmits the characteristics from parents to the next generation (offspring).
- It causes the variations in the population.
Question 32.
“We cannot pass on to our progeny the experiences and qualifications earned during our life time”. Justify the statement giving reason and examples. (2015 D)
Answer:
All traits of the parent cannot be transmitted to the offspring because all traits are not inherited traits, some of the characteristics are acquired. The experiences and qualifications earned during our lifetime are examples of acquired traits.
A trait of an organism which is ‘not inherited’ but develops in response to the environment is called an acquired trait. The acquired traits of organisms cannot be passed on to their future generations. Only those traits can be transmitted to future generations in which changes have occurred in the genes present in the reproductive cells of parent organisms.
For example, If we breed some mice, all the progeny of mice will have tails, just like parents. Now, if we cut the tails of these first generation mice surgically and breed them, we will get new mice, all with full tails. Despite the cutting of tails of mice for a number of generations, a tailless mouse is never born.
This is because the cut tail of mice is an acquired trait which is never passed on to their progeny. This is because cutting the tails of mice does not change the genes of their reproductive cells.
Question 33.
(a) Planaria, insects, octopus and vertebrates all have eyes. Can we group eyes of these animals together to establish a common evolutionary origin? Justify your answer. (2014 D, 2015 D)
(b) “Birds have evolved from reptiles”. State evidence to prove the statement.
Answer:
(a) The eyes seen in planaria, insects, octopus and vertebrates vary greatly in their structure. These organisms can be used for studying evolution of eyes as the eyes of planaria are simple without lens, insects have compound eyes and vertebrates have highly specialised eyes. However, all of them perform the same function, that is, vision. Thus, a common evolutionary origin can be established.
(b) Birds have evolved from reptiles as the connecting link between reptiles and birds is Archaeopteryx (flying dinosaur). Also, there are sonie similarities in birds and reptiles. Birds have a four-chambered heart, which is also a feature of sonw reptiles. Both birds and reptiles have separate sexes and internal fertilization occurs in both.
Question 34.
What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained. (2015 OD)
Answer:
Chromosomes are thread-like structures made up of DNA and proteins. They are found in the nucleus at the time of cell division.
During gamete formation meiosis occurs and the original number of chromosomes becomes half. Hence, when two gametes combine the zygote formed contains the full set of chromosomes and the original number of chromosomes gets restored in the progeny.
Question 35.
How do organisms, whether reproduced asexually or sexually maintain a constant chromosome number through several generations? Explain with the help of suitable example. (2016 D)
Answer:
When organisms reproduce asexually, a basic event in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell, and they will need to be separated from each other.
However, keeping one copy of DNA in the original cell and simply pushing the other one out would not work, because the copy pushed out would not have any organised cellular structure for maintaining life processes. Therefore, DNA copying is accompanied by the creation of an additional cellular apparatus, and then DNA copies separate, each with its own cellular apparatus. Effectively, a cell divides to give rise to two cells. Thus, chromosome number remains unchanged. For example, reproduction of amoeba by binary fission.
In sexual reproduction, organisms produce gametes through a special type of division, meiosis reductional division, in which the original number of chromosomes becomes half. These two gametes then combine to form the zygote and the original number of chromosomes is restored as in the case of human beings.
Question 36.
In one of his experiments with pea plants Mendel observed that when a pure tall pea plant is crossed with a pure dwarf pea plant, in the first generation, F1 only tall plants appear.
(a) What happens to the traits of the dwarf plants in this case?
(b) When the F1 generation plants were self-fertilised, he observed that in the plants of second generation, F2 both tall plants and dwarf plants were present. Why it happened? Explain briefly. (2016 Delhi)
Answer:
(a) Mendel first crossed pure-bred tall pea plants with pure-bred dwarf pea plants and found that only tall pea plants were produced in the first generation or F1 generation. No dwarf pea plants were obtained in the first generation of progeny. From this Mendel concluded that the F1 generation showed the traits of only one of the parent plants: tallness being the dominant trait. The trait of other parent plant, dwarfness, being recessive did not show up in the progeny of first generation.
(b) In the F2 generation, both the tall and dwarf traits are present in the ratio of 3 :1. This showed that the traits for tallness and dwarfness are present in the F1 generation, being the recessive trait does not express itself in the presence of tallness, the dominant trait.
Question 37.
In a monohybrid cross between tall pea plants (TT) and short pea plants (tt) a scientist obtained only tall pea plants (Tt) in the F1 generation. However, on selfing the F1 generation pea plants, he obtained both tall and short plants in F2 generation. On the basis of above observations with other angiosperms also, can the scientist arrive at a law? If yes, explain the law. If not, give justification for your answer. (2016 D)
Answer:
Law of Segregation:
When plants of two different traits of character are crossbred to get a progeny (F1 generation), only the dominant trait is visible in this generation. But when plants of F1 generation are selfbred then the two traits of character get separated and the recessive traits also appears in the plant of F2 generation. This is known as Law of Segregation (separation) of traits.
Law of Dominance:
According to this law, the characteristics (or traits) of an organism are determined by internal ‘factors’ which occur in pairs. Only one of a pair of such factors can be presented in a single gamete. This law explains expression of only of the parental character which is dominant trait in F1 generation and expression of both in F2 generation.
Question 38.
“Two areas of study namely ‘evolution’ and ‘classification’ are interlinked”. Justify this statement. (2016 OD)
Answer:
Classification of organisms is based on relative similarities and differences in their internal and external structures. Similarities among organisms will allow us to group them and study the groups and classify them. Some basic characteristics will be shared by most organisms.
The more characteristics the two species will have in common, the more closely they are related. The more closely they are related, the more recently they have had a common ancestor. So we can say that classification of a species is in fact a reflection of their evolutionary relationship.
Question 39.
With the help of an example justify the following statement: (2014; 2016 OD)
“A trait may be inherited, but may not be expressed.”
Answer:
In Mendel’s experiment with pea plants, when he cross-bed a tall pea plant with a short plea plant, he found that the first generation (F1) was of only tall plants. In the F1 progeny, no short plants were obtained. However, in the F2 generation, both tall and short plants were obtained in the ratio 3 :1 respectively. In the F2 generation, both traits – tallness and shortness were inherited where the tall character was the dominant trait and short character was the recessive trait.
Flow Chart:
Conclusion. Reappearance of dwarf character in F2 generation proves that the dwarf trait was inherited but not expressed in the F1 generation.
Question 40.
Explain with the help of an example each how the following provide evidences in favour of evolution:
(a) Homologous organs
(b) Analogous organs
(c) Fossils (2017 D)
Answer:
(a) Homologous organs. Those organs which have same basic structure among different types of living beings but perform different functions are called Homologous organs. For example, arms of human beings and forelegs of horse, lion, etc. are Homologous organs. Their same basic structure shows that these have been evolved from some common ancestors.
(b) Analogous organs. Those organs which have different basic structure but perform same functions in different types of living beings are known as Analogous organs. For example, wings of birds and wings of bat are analogous organs. Similarity in these organs is superficial and the design and structure of these organs is very different.
(c) Fossils. Fossils are the dead remain parts of the extinct form of living beings. They provide the missing link between the species, e.g., Fossils of dinosaurs with feathers/ fossils of prehistoric horse, etc.
Heredity and Evolution Class 10 Important Questions Long Answer Type
Question 1.
How many pairs of chromosomes are present in human beings? Out of these how many are sex chromosomes? How many types of sex chromosomes are found in human beings?
“The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it”. Draw a flow chart showing determination of sex of a newborn to justify this statement. (2015 D)
Answer:
- There are 23 pairs of chromosomes present in human beings.
- There is 1 pair of sex chromosomes present in human beings.
- The chromosomes which determine the sex of a person are called sex chromosomes. There are two types of sex chromosomes, one is called X chromosome and the other is called Y chromosome. Males contain one X chromosome and one Y chromosome (XY), while females contain two X chromosomes (XX).
- Flow chart showing determination of sex of a child.
Sex determination flow chart:
- A male has one X-chromosome and one Y-chromosome. Thus half the male gametes have X- chromosomes and the other half have Y-chromosomes.
- A female has two X-chromosomes. Thus all female gametes have only X-chromosomes.
- If a sperm carrying Y-chromosome fertilises an ovum carrying X-chromosome, then the child born will be a boy.
- If a sperm carrying X-chromosome fertilises an ovum carrying X-chromosome, then the child born will be a girl.
Therefore it is the sperm from the father which determines the sex of the child.
Thus in human beings, the sex of the baby is determined by the type of sperm that fuses with ovum. As human male produces two types of sperms in equal proportion, so there are 50% chances of a male baby and 50% chances of a female baby.
Question 2.
How do Mendel’s experiments show that the
(a) traits may be dominant or recessive, (2016 D)
(b) traits are inherited independently? (2015, 2016 OD)
Answer:
(a) Mendel’s experiments show that:
- In Mendel’s experiment with pea plants, when he crossbred a pure tall pea plant with a pure dwarf pea plant, he found that the first generation F1 was of only tall plants. Tallness is the dominant trait.
- Then he produced F2 generation by selfing of hybrids F1
- In the F1 progeny, no dwarf plants were obtained. However in F2 generation, both tall and dwarf plants were obtained in the ratio 3 : 2 respectively.
- The trait which remains hidden in F1 generation, i.e., dwarfness is the recessive trait.
- He observed that even when not expressed in the first generation, alternate forms of a trait could retain their identify in the hybrid and could re-emerge in the next generation.
Flow Chart:
(b) Traits are inherited independently. Mendel cross-bred pea plants showing two different characteristics, rather than just one. When he cross-bred pea plants of round green seeds with wrinkled yellow seeds, he got F1 generation with all such seeds which were yellow and round. So, it was concluded that round and yellow character of seeds were dominant traits in the pea plant. On selfing of F1 progeny, different types of F2 progeny were obtained.
F2 progeny along with their ratios obtained in F2 generation:
So traits of two different characters were inherited independent of each other and made new combination characteristics independent of their previous combinations.
Question 3.
What are fossils? How are they formed? Described in brief two methods of determining the age of fossils. State any one role of fossils in the study of the process of evolution. (2015 OD)
Answer:
When organisms (plants or animals) die, their bodies will decompose by the action of micro-organisms in the presence of oxygen, moisture, etc.
Sometimes in the lack of such conditions (oxygen, moisture, etc.), their body does not decompose completely and is preserved as fossil with the passage of time in the rocks. In many cases the soft parts of the organism get decomposed and hard parts (like bones etc.) become fossil. Sometimes even the soft parts (like leaf etc.) remain preserved as fossils in the form of their impressions inside the rocks.
Methods to determine the age of fossils:
1. Relative method. The fossils which we find in layers closer to the surface of the earth are more recent; the fossils which are found in deeper layers are older.
2. Carbon dating. Fossils were once living objects and all living objects contain some carbon-14 atoms which are radio-active. When a living object dies and forms fossil, its carbon-14 radioactivity goes on decreasing gradually. The age of the fossil is found by comparing the carbon-14 radioactivity left in the fossil with the carbon-14 radio-activity present in the living objects today.
Question 4.
What is meant by speciation? List four factors that could lead to speciation. Which of these cannot be a major factor in the speciation of a self-pollinating plant species. Give reason to justify your answer. (2016 D)
Answer:
Speciation. The process by which new species develop from the existing species by evolution or any genetic modification of previous species is known as speciation.
The important factors which could lead to the formation of new species are:
- Geographical isolation of a population caused by various types of barriers like mountain ranges, rivers, sea etc. The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of population.
- Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
- Variations caused in individuals due to natural selection.
- Drastic change in the genes or DNA called mutation is also a cause of speciation.
Reproductive isolation can not be a major factor for the speciation of a self-pollinating plant species as it does not depend on any other plant for its reproduction process.
Question 5.
Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution. (2016 OD)
Answer:
Evolution. Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years in which new species are produced.
How it occurs:
- It is through the constant process of evolution taking place in the organisms since the origin of life that such an enormous variety of plants and animals have come to exist on this earth at present.
- There is an inbuilt tendency to variation during reproduction due to errors in DNA copying and as a result of sexual reproduction.
Relationship between fossils and evolution:
Fossils are the remains of impressions of dead plants or animals which died millions of years ago. The study of fossils helps us to know about the evolution of species. Fossils tell us how new species are developed from the old. Fossils provide evidence of evolution by revealing characteristics of past organisms and the changes that have occurred in these organisms to give rise to present organisms. Therefore, fossils have an importance in deciding evolutionary relationship.
For example, a fossil called Archaeopteryx has feathered wings like birds but teeth and tail like reptiles hence suggesting that birds and reptiles had a common ancestor and birds have been evolved.