Class 10 Science Chapter 9 Board Questions

Class 10 Science Chapter 9 Board Questions of Heredity and Evolution. It contains previous years questions, last 10 years important board questions and last five years CBSE Board questions with answers. All the questions are divided into 1 mark, 2 marks, 3 marks and 5 marks questions. Answers of questions are according to their marks. We are updating the question bank as per suggestions of users by adding new questions every year. Previous years questions give just an idea about what type of questions are asked in Board examination. For the preparation of school test or board exams, these board questions are extremely helpful for all the students.

UP Board students can also use these previous year questions for practicing the chapter 9 of Class 10 Science. There are variety of questions covering all the important topics of Class 10 Science NCERT Books.

Class 10 Science Chapter 9 Board Questions for Exams

Class: 10Science
Contents:10th Science Chapter 9 Board Questions

Class 10 Science Chapter 9 Board Questions for 2020-21

Prepare your school test and final exams with the help of Class 10 Science Chapter 9 Board Questions answers. All the important questions from last 10 years CBSE papers and all the questions from last 5 years CBSE Examination papers are given with answers. These Sets of questions 10th Science are helpful for UP Board students also.

10th Science Chapter 9 Board Questions Set – 1 (1 Mark)

What is the effect of DNA copying which is not perfectly accurate on the reproduction process? [CBSE 2008]

DNA copying cannot be perfectly accurate always. This leads to accumulation of variation, which results in evolution.

What is genetic drift? [CBSE 2008]

Gene migration or gene flow from a population to a new area is known as genetic drift.

What are the basic events in evolution? [CBSE 2008]

Natural selection and variation are the basic events in evolution.

How do we know how old a fossil is? [CBSE 2008]

Age of the fossil can be estimated by:
(a) Digging the layer of the earth- deeper the fossil, older it is and nearer the surface would be more recent ones.
(b) Studying the amount of C14 (radioactive isotope of C) in the fossils. Since it has half life, therefore by quantitative analysis we can give approximate time period when that organisms would have existed.

Write the sex of the baby that inherits Y chromosome from the father. [CBSE 2013]

Such a baby will have XY, therefore will be a male.

Organic Evolution

Process of accumulation of variations/changes in DNA, leading to formation of new species, is organic evolution.

10th Science Chapter 9 Board Questions Set – 2 (1 Mark)

Give an example where sex determination regulated by environmental factors. [CBSE 2012]

In snail and garden lizard, sex is determined by outside temperature.

What is the phenotypic ratio of a dihybrid cross in F2 generation? [CBSE 2013]

9:3:3:1.

Name the scientist who gave the theory of evolution. [CBSE 2013]

Theory of evolution was given by Charles Darwin.

Define species. [CBSE 2013]

Group of individuals that have similar features and are capable of interbreeding, are said to belong to a species.

Write two factors that could lead to rise of new species. [CBSE 2011]

(i) Geographical isolation.
(ii) Genetic drift.
(iii) Natural selection.

Heredity

Transmission of traits from one generation to next through genes is termed as heredity.

10th Science Chapter 9 Board Questions Set – 3 (1 Mark)

Identify analogous and homologous organs amongst the following: Wings of an insect, wings of bat, forelimbs of lizard, forelimbs of bird. [CBSE 2012]

Homologous organs- Forelimbs of lizard and forelimbs of bird. Both have same structure but different functions.
Analogous organs- Wings of an insect and wings of a bat. Both have different structure but same function.

Give one example of an evolutionary change produced in an organism for one purpose which later on become more useful for different functions. [CBSE 2012]

Birds developed features, as they evolved to become warm blooded animals to protect them from cold. But slowly, these features also helped them to evolve for aerial mode of life in search of food, shelter etc.

Which of the following fossils is invertebrate and which one is vertebrate? (i) Dinosaur (ii) Ammonite [CBSE 2012]

(i) Dinosaur is vertebrate.
(ii) Ammonite is an invertebrate.

There are certain changes that are small though they are very sufficient. What is this process is known as? [CBSE 2013]

Variations are these changes and process is evolution.

Give the respective scientific terms used for studying: (i) the mechanism by which variations are created and inherited. (ii) the development of new type of organisms from the existing ones. [CBSE 2014]

(i) Evolution.
(ii) Speciation.

Mutation

Sudden changes in the genetic make-up of an organisms, which are capable of expressing and are inheritable are called mutation.

10th Science Chapter 9 Board Questions Set – 4 (1 Mark)

“Our teeth and an elephant’s tusks are homologous organs.” Justify this statement. What do the analogous organs indicate? [CBSE 2012]

Our teeth and elephant’s tusks are homologous organs as both have same basic structure but different functions. We use ours for chewing while elephants use theirs to hold things.
Analogous organs indicate that even the organisms having different structures can adapt to perform similar functions for their survival under given similar environmental conditions.

Sometimes accidently a dead body or its parts get buried under depositing sediments and are preserved. These are fossils. How can the estimation of the age of fossils be done? [CBSE 2013, 2017, 2018, 2019]

It can be done in many ways:
(a) The fossils found in upper layer are recent and the ones that are deeper are older.
(b) By radio-active carbon dating.

Mendel took tall pea plants and short pea plants and produced F1 progeny through cross-fertilization. What did Mendel observe in the F1 progeny? [CBSE 2017, 2018]

On crossing pure tall and pure short pea plants, the F1 generation was tall (but not pure). It was heterozygous for tall.

Define heredity? [CBSE 2011]

The process by which traits and characteristic are reliable inherited or passed from the parents to the offspring is called heredity.

Define genetics. [CBSE 2011]

The branch of biology which deals with heredity and variations is known as genetic.

Gene

Gene is function segment of DNA on a chromosomes occupying specific positions which carries out a specific biology function.

10th Science Chapter 9 Board Questions Set – 5 (3 Mark)
How did Mandel explain that it is possible that a trait is inherited but not expressed in an organism? [CBSE 2017]

Gregor Johann Mandel, through consistence studies on garden pea arrived that laws of inheritance.
He used plants that were pure breeding for a trait and considered contrasting character like- tall and short size, round and wrinkled seeds, white and violet flower etc.
In his experiment he crossed plants with contrasting character, studied the progeny of first generation(F1) and second generation(F2) and calculated ratios of plants with contrasting that were original paternal type or different.
For example, he crossed a tall pea plant with a dwarf pea plant. He found that in first generation(F1) all the plants produced were tall. Since F1 plants are all tall and genotypically are “Tt” they have inherited “t” from one parent which is not expressed, as it results in dwarf plant.

Name the organisms Mandel used for his experiment. Explain about F1 and F2 progeny obtained by Mandel when he bred the tall and the short variation of the organism he experimented with. [CBSE 2010]

Organisms used by Mandel for his experiment was pea plant. Mandel took a pure tall plant (TT) and crossed with a pure dwarf (tt) plant. The progeny thus obtained was called F1 progeny.
Then he self-pollinated the F1 progeny to obtained F2 generation. In F2 generation He found that 75% were tall and 25 were dwarf. 1TT: 2Tt:1tt.

Write the full form of DNA. Name the part of cell where it is located. Explain it role in the process of reproduction of the cell. [CBSE 2010]

DNA id Deoxyribonucleic acid. It is generally located within the nucleus. It is the basic structure that make up the chromosome. It carries complete information for that organism. DNA is capable of replicating thus making its own copies for reproduction it is mandatory that the cell must pass on the information to the next generation since DNA is capable of dividing so it plays most important role in reproduction.

How can we say that change in genes can be brought about by change in DNA? [CBSE 2013]

(a) A gene is specific portion of DNA occupy a specific location.
(b) It provide information for protein synthesis.
(c) It also provides stability to the species.
Thus any change in genes will bring about change in DNA.

In the following crosses, write the characteristics of progeny: (a) RrYy x RrYy (b) rryy x rryy (c) RRYY x rryy [CBSE 2012]

(a) Round yellow:9
Round green:3
Wrinkle yellow:3
Wrinkle green:1
(b) All wrinkled and green.
(c) All round and yellow.

Natural selection

Nature selects the best traits in a species, leading to survival of fittest ad evolution of species. This phenomenon is known as natural selection.

10th Science Chapter 9 Board Questions Set – 6 (3 Mark)
Mention the factors which is responsible for inherited traits. State the two outcomes of Mendel’s experiments. [CBSE 2012]

DNA that contains all the information is the main factor responsible for inherited trait.
Outcomes of Mendel’s experiments.
(a) Both parent contribute equally toward progeny.
(b) Trait may be either dominant or recessive.
(c) A dominant trait will be expressed in both heterozygous and homozygous conditions while recessive traits will be expressed only in homozygous condition.
(d) The traits are inherited independent of each other.

In fruits flies the sex chromosomes in males are XY and in females are XX. (i) Does a male fly inherit X chromosome from his mother or father? (ii) How many types of gametes can be a female fly produce? (iii) How many types of gametes can a male fly produce? [CBSE 2012]

(i) Since females have XX, so the male fly inherits X chromosome from his mother only.
(ii) A female fly produces only one type of gamete all with X chromosome.
(iii) Male fly produces two types of gametes 50% with X and 50% with Y.

Briefly explain the role of natural selection and genetic drift in speciation by citing an example. [CBSE 2011, 2017, 2018]

Let us study the example of beetles. Let the original beetle population be red. If due to variation a green beetle was produced it would have survival advantage over red beetle. Thus, green beetles would be naturally selected, and will grow in number.
If few of these green beetles move to some other area, adapt to changed environment and after few generations, would vary greatly from the original population of red beetles. These two populations may not be able to interbreed due to accumulation of variation.
Thus, due to Natural selection and Genetic Drift, a new species of beetles is formed.

Explain the method of sex determination in humans. [CBSE 2013]

Human beings have 22 pairs of autosomes and one pair of sex chromosome. This pair is XX in females and XY in males. Thus, if parents are.
This cross shows that females produce all similar gametes, carrying X chromosome. While males produce two types of gamete 50% with X and 50% with Y chromosome.
Hence, when a female gamete fuses with sperm with X chromosome, a female child is produced and when it fuses with sperm with Y chromosome, a male child is produced.
So, it is male that determine the sex of the child.

Explain how new species are produced. [CBSE 2012]

Let us study the example of beetles. Let the original beetle population be red. If due to variation a green beetle was produced it would have survival advantage over red beetle. Thus, green beetles would be naturally selected, and will grow in number.
If few of these green beetles move to some other area, adapt to changed environment and after few generations, would vary greatly from the original population of red beetles. These two populations may not be able to interbreed due to accumulation of variation.
Thus, due to Natural selection and Genetic Drift, a new species of beetles is formed.

Reproduction isolation

It refers to the mechanism which checks the organisms of two different groups from interbreeding.

10th Science Chapter 9 Board Questions Set – 7 (3 Mark)
“Only father is responsible for the sex of a new born child”. Explain. [CBSE 2011]

Human beings have 22 pairs of autosomes and one pair of sex chromosome. This pair is XX in females and XY in males. Thus, if parents are.
This cross shows that females produce all similar gametes, carrying X chromosome. While males produce two types of gamete 50% with X and 50% with Y chromosome.
Hence, when a female gamete fuses with sperm with X chromosome, a female child is produced and when it fuses with sperm with Y chromosome, a male child is produced.
So, it is male that determine the sex of the child.

“It is a matter of chance whether a couple will give birth to a boy or a girl”. Justify the statement. [CBSE 2013]

Human beings have 22 pairs of autosomes and one pair of sex chromosome. This pair is XX in females and XY in males. Thus, if parents are.
This cross shows that females produce all similar gametes, carrying X chromosome. While males produce two types of gamete 50% with X and 50% with Y chromosome.
Hence, when a female gamete fuses with sperm with X chromosome, a female child is produced and when it fuses with sperm with Y chromosome, a male child is produced.
So, it is male that determine the sex of the child.

Give reasons for your answer: Define speciation. Mention factors due to which this can happen. [CBSE 2012, 2013, 2016, 2017]

Speciation- It is the process of formation of new species from an existing one. Factors that can lead to speciation are
(i) Natural selection.
(ii) Geographical isolation.
(iii) Migration- Genetic drift.

Describe any three methods of tracing evolutionary relationships amongst organisms. [CBSE 2011]

(i) Homologous organs: Homologous organs are those organs which are formed on the same fundamental structural plan but they differ in their shapes because they have to function differently.
Examples: Forelimbs of frog and bird.
(ii) Analogous organs: Such organs which perform similar function but are different in structure and origin.
Example: Wings of a bird and a bat.
(iii) Fossils- These are imprints or dead remains of plants and animals. They indicate how one kind of organisms may have evolved from previously existing ones.
Examples: Archaeopteryx- a fossil dinosaur that had wings.
This shows that birds would have evolved from reptiles.

List and describe any two evidences for evolution. [CBSE 2012]

(i) Homologous organs: Homologous organs are those organs which are formed on the same fundamental structural plan but they differ in their shapes because they have to function differently.
Examples: Forelimbs of frog and bird.
(ii) Analogous organs: Such organs which perform similar function but are different in structure and origin.
Example: Wings of a bird and a bat.
(iii) Fossils- These are imprints or dead remains of plants and animals. They indicate how one kind of organisms may have evolved from previously existing ones.
Examples: Archaeopteryx- a fossil dinosaur that had wings.
This shows that birds would have evolved from reptiles.

These are CBSE Board questions with solutions. If you need more questions for practice, see the Important Questions on Class 10 Science Chapter 9. Important Questions sets covers the entire NCERT Books.

10th Science Chapter 9 Board Questions Set – 8 (3 Mark)
Mention some of the tools of tracing evolutionary relationship amongst species. [CBSE 2013]

(i) Homologous organs: Homologous organs are those organs which are formed on the same fundamental structural plan but they differ in their shapes because they have to function differently.
Examples: Forelimbs of frog and bird.
(ii) Analogous organs: Such organs which perform similar function but are different in structure and origin.
Example: Wings of a bird and a bat.
(iii) Fossils- These are imprints or dead remains of plants and animals. They indicate how one kind of organisms may have evolved from previously existing ones.
Examples: Archaeopteryx- a fossil dinosaur that had wings.
This shows that birds would have evolved from reptiles.

How has the method of artificial selection by humans helped in the evolution of different vegetables? Explain in brief giving an example. [CBSE 2011]

Human beings have artificially selected certain variants that arose in nature by chance. This led to evolution of different species.
For example, wild cabbage was cultivated and its variants were selected due to different advantages, by artificial selection.
(a) Short distances between leaves- led to formation of modern day cabbage.
(b) Arrested flowers development- Broccoli.
(c) Sterile flowers- Cauliflowers.
(d) swollen pats- Kohlrabi.
(e) Large leaves- Kale.

Why did human race spread from Africa to other parts of the world? [CBSE 2013]

The earliest evidence for human race were found in Africa.
Some of our ancestors left Africa in search of food and shelter, in other areas and stayed on. Slowly, we migrated to most parts of the world.
They settled in different parts and adapted. There was mixing in these populations so they evolved as different races.

(a) If we cut the tail of a mouse, will tail occur in next generation of that mouse? Give reason to support your answer. (b) What are the features that Archaeopteryx had in common to the reptiles? [CBSE 2013, 2016]

(a) Even after cutting tail of a mouse its progeny continues to have tail. This is because ‘no tail’ is an acquired trait. The mouse continuous to have information for presence of tail in its DNA and hence the progeny will have tail.
(b) Archaeopteryx has reptilian features as presence of tail, vertebrate, teeth etc.

(a) What will be the consequence when a small population of individuals is separated due to a large barrio in between them? (b) DNA has a property that it is used as a tool in genetic engineering. Mention the property. [CBSE 2013]

(a) When a small group of individuals move away and there is a large barrier between them this smaller group will accumulate variation. This may ultimately lead to formation of new species. Thus, this leads to speciation due to geographical isolation.
(b) DNA is self-replicating i.e., it can make its copies. This is the property used as a tool in genetic engineering.

Genetic Drift

Sudden change in the frequency of a particular gene, due to migration, selection, mutation etc., is known as genetic drift.

10th Science Chapter 9 Board Questions Set – 9 (3 Mark)
Name two homologous structure in vertebrates. Why are they named so? What is the significance of these structure in the study of evolution? [CBSE 2012, 2016, 2017]

(i) Homologous structure in vertebrates are wings in birds and forelimbs in lizard.
(ii) They are so named as they have same structural design but different function.
(iii) Such structure gives us idea about common ancestry.

Give two uses of fossils. How does the study of fossils provide evidence in favour of organic evolution? [CBSE 2012, 2008, 2016, 2017]

Two uses of fossils are:
(a) To help study evolution of plant and animals.
(b) To know past climatic conditions.
(c) To help calculate geological time etc.
Evidence of favour of organic evolution:
(i) Fossils help to identify an evolutionary relationship between apparently
different species.
(ii) The older fossil present deeper, are simpler in body design as compared to those present in upper layers which are more recent.
This clearly provides evidence in favour of organic evolution.

What are acquired traits? Why are these traits generally not inherited over generation? Explain. [CBSE 2017, 2018]

The traits that a person acquires during one’s life time and not by virtue of his/her genes are known as acquired traits.
These traits are not present on our genes in reproductive cells. Hence they cannot be inherited. Since these changes are in the non-reproductive cells and thus cannot be passed on to the germ cells hence are not inheritable by the future generation. An organism requires them for himself in his life time due to his environment.

What is speciation. List four factor responsible for secretion? [CBSE 2017, 2018]

Speciation is the formation of new species from the pre-existing ones due to accumulation of changes in such a way that group of individuals of one species can no longer inherited. This result in formation of two new independent species.
Factors responsible for speciation are:
(i) Natural selection- Nature select due to survival advantages.
(ii) Genetic drift- Due to accumulation of changes over generation in sub-population.
(iii) Geographical isolation- In different geographical locations the natural selection acts differently on different sub-population because of varying abiotic/biotic factors.
(iv) Mutation- DNA changes can be severe and hence the germ cells of two cannot fuse giving rise to new species.

Define variation in relation to a species. Why is variation beneficial to a species. [CBSE 2008]

Variation are relatively small changed that occur due to error during DNA copying in asexual reproduction or fusion of gametes in sexual reproduction. These changes are subtle, maintaining the basic body design. Sometime these variations may be such that they give an advantage during adverse condition and hence help I survival. This is how variation helps in continuation of species.

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10th Science Chapter 9 Board Questions Set – 10 (3 Mark)
Mention the information source of making proteins in the cell. What is the basic event in reproduction? [CBSE 2008]

DNA is the basic source of making proteins in the cells. The basic event in reproduction or fusion of gametes in asexual reproduction is the creation of a DNA copy. Cells use chemical reaction to build copies of their DNA. This creates two copies of the DNA in a reproducing cell and they will need to be separate from each other. DNA copying occurs accompanied by the creation of an additional cellular apparatus. The DAN copies then separate each having its own cellular apparatus for maintaining life process.

Give one example each of the characters that are inherited and the ones that are acquired in humans. Mention the difference between the inherited and the acquired character. [CBSE 2010, 2013]

Inherited character are blood group, eye colour etc., whereas acquired character are being sportsman, dancer or scientist etc. Inherited character is transmitted from parent to the progeny as they are present on our genes. While acquired traits are those which a person acquires during his life time. Thus they are not inheritable.

How can a change in colour give survival advantage to a specie? Explain it by giving suitable example. [CBSE 2013]

Change in colour is an inherited trait so it is transmitted to the next generation and can provide survival advantages to the species. For example, in population of green and red beetles, green beetles protect themselves from crows that feed on them by hiding un green leaves. But red beetles can be easily spotted. Thus over a period of time only green beetles grow in number as their rate of survival will be higher and red beetles with decreasing population will be under threat.

Explain with the help of example where the colour change gives no survival advantages to a species. [CBSE 2014]

Colour change needs not always give survival advantages. For example, if there is a population of red and blue beetles in an area. An elephant who happens to pass by may step on this population. Thus survival is only chance and not due to selection. Hence survival here is due to chance and no advantages due to change in body colour.

(a) Give the evidence that the birds have evolved from reptiles. (b) Insect, octopus, planaria and vertebrates possess eyes. Can we group these animals together on the basic of eyes that they possess? Justify your answer and giving reason. [CBSE 2014, 2015]

(a) Fossils are important evolutionary evidence to show what kind of organisms existed earlier. Archeopteryx is a fossil dinosaur with wings. This proves that it has features of both reptiles as well as birds. Hence we can say that birds evolved from reptiles.
(b) These organisms cannot be grouped together as the structure of eye in each is very different. This means that they have separate evolutionary origin.

Revise first 10th Science NCERT Textbook and go through the solutions of Chapter exercises given at the end of the chapter. After doing these practices with important questions and board questions.

10th Science Chapter 9 Board Questions Set – 11 (5 Mark)
Define variation in a species. How does it increase the survival chance of a species? Why does environmentalist get worried due to small population of a species? [CBSE 2013, 2017, 2018]

Any division from original trait in a species is variation. Sometimes these variations may give added advantage of being of the nature so as to give better adaptability in changed conditions. Hence it increases the chances of survival. Smaller population of species would enforce inbreeding with the population which would result in fewer variations. This would also result in inbreeding depression and expression of recessive traits, thereby making it prone to diseases or extinction. Hence environmentalists are worried about smaller population.

Define the term evolution? “Evolution cannot be equating with process” Justify this statement. [CBSE 2012, 2013, 2016]

The process by which we know how various life forms have come into being from the previously existing ones is known as evolution.
Evolution cannot be equating with progress this is because
(i) Evolution is caused due to variation in original form.
(ii) This may lead to formation of new species. But it does not mean that original type may not exist.
(iii) It only leads to more complex body designs.
(iv) The simplest life form i.e., bacteria exist till day and are found in all types of habitats from hot water springs to cold temperature regions etc. Bacteria are also one of the oldest life form known. So we can safely say that evolution cannot be equate with progress.

Why is it more appropriate to compare the process of evolution with branches of a tree rather than with a ladder? [CBSE 2013]

While studying evolution of various life forms it is observed that from a single point or ancestor there may be originated different lines, each leading to formation of a new species.
For example, both the humans and chimpanzee have many common feature which suggests that both would have had a common ancestor. Also it is not as if one species is eliminated to give rise to new one. Homologous organs explain this well. Forelimbs of a frog, lizard, bird and horse have common design but different function. This clearly suggest that all these organisms belonging to different group originated from a common ancestor. They evolved in their own way to perform and adapt to their mode of life to give rise to current forms. Hence it is more appropriate to compare the process of evolution with branches of a tree than with a ladder.

(a) Green and red of seeds are recessive and dominant traits respectively. Out of F1 and F2 in which generation will the green seed appear if both parent is not hybrid. Explain with reason (b) Dead remain of two pieces A and B were buried. Later only A’s body was found to be a fossil but not B’s Give reason to explain it. (c) Species A shares ten character with B species, species C shares fifteen character with D. Which of the two pair shares closer relation? (d) After the death of the two insects, one of the insects was buried in hot mud and the other in usually found mud. Which of the two is more likely to be preserved better and why? [CBSE 2013]

(a) Since it is given that green is recessive and red seeds are dominant hence green colour of seeds will reappear only in F2 generation. This is because both parent are not hybrid for this trait and hence the two recessive gene will come together only in F2.
(b) Fossil are formed only when the dead part are hard and get buried immediately without getting decomposed. In case of A may be left its imprints as fossil while B may be decomposed and hence has not formed fossil.
(c) Since more characteristic are shared between C and D therefore they are more closely related.
(d) The insect buried in hot mud is more likely to be preserved better because it will not decompose quickly. Also the mud will harden on cooling retaining the impression of body parts of the insect.

What is Chromosomes? Explain how in sexually organisms the number of chromosomes in the progeny is maintained. [CBSE 2016, 2017]

Chromosomes are long DNA stands present in nucleus carrying gene for a trait. Hence they are hereditary material. In an organism each cell has two copies of a chromosomes one each from a male and female parent. In sexually reproducing organisms where fusion of gamete take place one chromosomes from each pair is taken up in formation of a germ cell by a special cell division called meiosis. When two germ cell fuse they restore the original number of chromosomes in the progeny.

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10th Science Chapter 9 Board Questions Set – 12 (5 Mark)
Define evolution. How does it occur? Explain hoe fossils provide evidences in support of evolution. [CBSE 2016, 2017]

The inbuilt tendency of variation either due to error in DNA copying due to sexual reproduction both result in some changes in the existing population of an organism. This continuous change ultimately leads to evolution. It occurs due to change in DNA which keep accumulating generation ultimately giving rise to new species.
Fossil provide evidence for evolution as they are preserved traces of living organisms. The fossils are formed when on death of an organism the body does not decompose instead it get trapped in an environment where it gets preserved. For example, an organism getting trapped in volcanic lava will not decompose. On cooling the lava will harden and retain the impression of the body parts of that organisms as fossil.

(a) Why do we say that homozygous plants produce pure progeny? (b) Define heterozygous. (c) Explain how the process of speciation take place. [CBSE 2013]

(a) Homozygous plants whether for dominant or recessive trait have both is genes for that trait. Thus they always produce similar gametes resulting in pure breeding plants.
(b) When the two chromosomes in the homologous pair are different that’s why one is dominant and other recessive such that pair is said to be heterozygous.
(c) Speciation can be defined as the formation of new species in term of evolution take place. Reproductive isolated is a collection of behavior, mechanism and physiological process they prevent the member of two different species which cross or mate from producing offspring or which ensure that may be produce is not fertile. Speciation is isolated as a genetic change in the new speciation between two previously interbreeding population of the same species.

Mandel crossed a pea plant having green pod with a constricted yellow pod. (a) What type of cross is it (b) What type of plants are obtained in F1 (c) In F2 generation the Phenotype ratio is 9:3:3:1. State the rule for the inheritance of traits observed by Mendel. [CBSE 2013]

(a) This a dihybrid cross.
(b) All plant is inflated with yellow pod plants.
(c) In F2 generation new combatants are produced as a traits are assorting independently. The law given by Mandel is Law of Independent Assortment which states that in a dihybrid cross where two different character are being studied which may be present together in an individual are inherited independently of each other in next generation.

(a) Define the gene of a particular protein. (b) How may speciation take place? [CBSE 2013]

(a) Gene is a particular segment of DNA on a chromosome that is capable of a codding for a polypeptide.
(b) Speciation may take place by
(i) Migration
(ii) Mutation
(iii) Genetic drift
(iv) Natural selection

(a) What is meant by natural selection? Explain. (b) Why are thorn of Bougainvillea plants and a tendril of passiflora plant consider homologous. [CBSE 2013, 2016]

(a) Natural selection: It is selection of certain trait in nature in an individual in a population of a particular species. This leads to survival advantage and hence variation leading ultimately to speciation.
(b) Thorn of Bougainvillea and tendril of Passiflora both are modified stem i.e., both have similar structure but doddering function. Thorn of Bougainvillea protests plants from being grazed while tendril of passiflora helps the plant to climb up a support. Hence they are homologous organs.

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