Important Questions Class 10 Science Chapter 9

Important Questions Class 10 Science Chapter 9 – Heredity And Evolution

Chapter 9 of CBSE Class 10 Science covers Heredity and Evolution. The concepts of sexual reproduction, heredity, how evolution occurs, etc., are all covered in this important chapter. In this chapter, students will learn about the process by which variations are produced and passed down in many living species.Students will have a deeper understanding of the effects of these variances as well as the evolutionary process. The Griffith experiment, Mendel’s law, the Lamarckist and Darwinism views, and other concepts will also be covered with students.

Extramarks is one of the most trusted platforms where students get online learning resources for their studies and exam preparation from Class 1 to Class 12. 

Our academic subject experts understand how important it is to solve problems in order to understand scientific concepts on a regular basis.Questions from many sources, such as the NCERT textbook, NCERT examples, previous year’s test questions, other reference books, etc., have been compiled by us. Students can obtain these questions and their answers by consulting our important questions Class 10 Science Chapter 9.

In order to assist students in answering these questions, our science faculty members have created step-by-step guidelines. Students can access the Chapter 9 Class 10 Science important questions question bank by registering on our website.

Students can find a variety of additional study materials on our website in addition to the Important Questions Class 10 Science Chapter 9, such as NCERT chapter-by-chapter solutions, CBSE revision notes, previous year test questions, etc.

CBSE Class 10 Science Important Questions 2022-23

CBSE Class 10 Science Important Questions are also available for the following chapters:

Important Questions Class 10 Science Chapter 9 – With Solutions

Regularly practising questions has proven helpful for a lot of students in subjects such as Science. 

Extramarks’ expert team of science teachers has collated questions from various sources so that students can rely on only one source. We strongly recommend students refer to our question bank of Science Class 10 Chapter 9 important questions. Since ,the questions cover all topics from the chapter and the solutions come with detailed step-by-step instructions, students are able to revise the chapter while solving these questions. 

Below are a few questions and their answers from our Important Questions Class 10 Science Chapter 9.

Question 1. The exchange of genetic material takes place in

(a) budding 

(b) asexual reproduction

(c) sexual reproduction

(d) vegetative reproduction

Answer 1 : (c)

Explanation:

Apart from sexual reproduction, other options include types of asexual reproduction in which only one parent is involved. Hence, the exchange of the genetic material takes place in the sexual mode of reproduction.

Question 2. A crossing between the tall plant (TT) and the short pea plant (tt) resulted in a progeny that was all tall plants because

(a) tallness is the dominant trait

(b) height of the pea plant is not governed by the gene ‘T’ or ‘t’

(c) tallness is the recessive trait

(d) shortness is the dominant trait

Answer 2: (a)

Explanation:

In a monohybrid cross, only dominant characters are expressed in the first progeny.

Question 3. Which of the following statements is incorrect?

(a) For the production of every enzyme, there is a gene.

(b) For every protein, there is a gene.

(c)  For every hormone, there is a gene.

(d) For every molecule of a fat, there is a gene

Answer 3: (d)

Explanation: There is a specific gene for each protein, enzyme, and hormone, but there is no gene for fats.

Question 4. If the round, green-seeded pea plant (RR yy) is crossed with any wrinkled, yellow-seeded pea plant (rr YY), then the seeds thus produced in the next F1 generation are

(a) round and yellow

(b) wrinkled and yellow 

(c) wrinkled and green

(d) round and green

Answer 4: (a)

Explanation: Since round and yellow are the dominant characteristics, all seeds from the first generation will have these characteristics.

Question 5. The maleness of a child is determined by

(a) sex is determined by chance

(b) the Y chromosome in the zygote

(c) the X chromosome in the zygote

(d)  the cytoplasm of the germ cell, which determines the sex

Answer 5: (b) 

Explanation:

The zygote will mature into a male offspring if the egg is fertilised by sperm that has a copy of the Y chromosome. If X-chromosome-carrying sperm fertilises the egg, the zygote will give rise to a female offspring.

Question 6. A basket full of vegetables that contains carrot, radish, potato,  and tomato. Which of these represents the correct homologous structures?

(a) Radish and Potato 

(b) Carrot and tomato

(c) Radish and carrot

(d) Carrot and potato

Answer 6: (c) 

Explanation: Both the radish and carrot have a similar structure, and they both grow beneath the earth (roots).

Question 7. Select the correct statement.

(a) Tendril of any pea plant and the phylloclade of Opuntia are homologous

(b) Tendril of any pea plant and the phylloclade of Opuntia are analogous

(c) Wings of the birds and wings of the bats are homologous

(d) Wings of birds and limbs of lizards are analogous

Answer 7: (a)

Explanation: The tendril of the pea plant and the phylloclade of Opuntia are homologous because they have similar designs and origins.

Question 8. When the fossil of an organism is found in the deeper layers of the earth,  we can assume that

(a) the fossil position in the deep layers of the earth is not related to its time of extinction 

(b) the extinction of the organism occurred thousands of years ago

© the extinction of the organism occurred recently

(d) time of extinction cannot be determined

Answer 8: (b) The extinction of the organism occurred thousands of years ago

Explanation: Older fossils are always found deep in the earth. 

Question 9. Which of the following statements is not true with respect to the variation?

(a) All variations in any species have an equal chance of survival

(b) Variation is the minimum in asexual reproduction

(c) Selection of the variants by  environmental factors forms the basis of the evolutionary processes

(d) Change in genetic composition results in variation

Answer 9: (a)

Explanation: Statement a) is wrong because nature chooses the fittest variation to survive.

 and the only useful variations have a chance of survival.

Question 10. Select the group which shares the most number of common characters

(a) two individuals of the species

(b)  two genera of two families

(c) two genera of a family

(d) two species of a genus

Answer 10: (a) 

Explanation:

Since species is the lowest level of taxonomy, people who belong to the same species have most of the same characteristics.

Question 11.  According to evolutionary theory, the emergence of new species is generally the result of

(a) movement of the individuals from one habitat to another

(b) the accumulation of the variations over several generations

(c) clones formed during  an asexual reproduction

(d) sudden creation by nature

Answer 11: (b)

Explanation:

Variations in DNA over numerous generations lead to the emergence of new species. Since there are no gametes involved, asexual reproduction will not produce variety. Individuals moving from one habitat to another won’t cause their DNA to alter, so this cannot be the correct response.

Question 12. From the list given below, select the character that can be acquired by organisms but not inherited

(a) nature of hair

(b) colour of skin

(c) size of body

(d) colour of eye

Answer 12: (c)

Explanation:

The type of a person’s body is determined by their eating habits. A muscular body can be developed through regular exercise. Body size is not inherited because body nature is not passed down to offspring.

Question 13. The two versions of a trait (character) when  brought in by the male and female gametes are situated on

(a) any chromosome 

(b) two different chromosomes

(c) copies of the same chromosome

(d) sex chromosomes

Answer 13: (b)

Explanation: This is the reason behind the expression of one progeny in one version and other versions in another progeny.

Question 14. How many pairs of sex chromosomes are there in a human zygote?

(a) one

(b)  four

(c) three

(d)two

Answer 14: (a) one

Explanation: The 23rd pair of chromosomes, sometimes known as the sex chromosome, control the sex of the progeny.

Question 15. The theory of the evolution of the species by natural selection was given by

(a) Lamarck

(b) Darwin

(c) Morgan

(d) Mendel

Answer 15: (b)

Explanation:

Mendel proposed the laws of heredity.

Morgan discovered a mutation in Drosophila.

Lamarck proposed the use and disuse theory.

Question 16. Some dinosaurs had feathers, but they could not fly; birds have feathers that help them to fly. In the context of evolution, this means that

(a) feathers are homologous structures in both organisms

(b) there is no evolutionary connection between the reptiles and the birds

(c) reptiles have evolved from birds

(d) birds have evolved from reptiles

Answer 16: (d) 

Explanation:

Dinosaurs were reptiles. Despite having feathers, some dinosaurs were unable to fly. Dinosaurs’ feathers were originally used as insulation in frigid climates; subsequently, birds modified them to allow for flight. In light of evolution, this implies that birds descended from reptiles.

Question 17. 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 makeup of the tall parent can be depicted as

(a) TTWW

(b) TTww

(c) TtWW

(d) TtWw

Answer 17:(c)

The tall parent’s genetic makeup may be TtWW. All progenies bore violet flowers, further indicating that violet colour is dominant over white, and the fact that half the progenies are short suggests that the parent plant likewise will have a collection of short genes.

Question 18. An example of homologous organs is

(a) Our arm and a dog’s foreleg.

(b) Our teeth and an elephant’s tusks.

(c) Potato and runners of grass.

(d) All of the above.

Answer 18:(d)

Despite having diverse roles, homologous organs share the same origin as the aforementioned organs. The term “homologous organs” refers to organs from different species that share basic structural similarities but perform diverse functions. For instance, the forelimbs of a frog, a man, and a whale all have similar basic architecture but  different purposes; for this reason, they are referred to as homologous organs.

Question 19. In the evolutionary terms, we have more in common with

(a) A Chinese schoolboy.

(b) A chimpanzee.

(c) A spider.

(d) A bacterium.

Answer 19: (a)

Since they both belong to the same family and order (Primates), humans and chimpanzees are linked (Hominidae). However, a student is still a Homo sapiens regardless of race.

Question 20. 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 either dominant or recessive? Why or why not?

Answer 20: To determine whether a trait is dominant or recessive, one must have knowledge of at least three generations.As a result, the dominant or recessive nature of the given characteristic cannot be determined.

Question 21: How are evolution and classification related to one another?

Answer 21:

Two areas of biology that are related are classification and evolution. Classification deals with determining the relationships between different species, while evolution deals with how creatures evolve. Australopithecus afarensis, for instance, is thought to be one of our oldest ancestors, according to evolution and fossil evidence. Additionally, classification informs us that Australopithecus afarensis is a member of the Homo genus, the same genus as contemporary humans.

Question 22. Give an example of the main characteristics being used to determine how close two species are in  evolutionary terms.

Answer 22:

Take chimpanzees and humans as an example. It was formerly believed that only humans could display a wide range of emotions, such as laughing or smiling, although chimpanzees are also capable of doing so. The orbicularis oculi muscle spontaneously contracts and lifts the cheekbones when the limbic system of the brain is activated, causing wrinkles to appear around the eyes. This suggests that the smile is real and sincere. The Duchenne smile is a moniker for this peculiar reaction. In addition, studies have revealed that chimps and humans share 98.6% of our DNA. This indicates that long ago, chimpanzees and humans shared a common ancestry. It’s crucial to remember that chimpanzees are our closest surviving cousins.

Question 23. Can the wings of the butterfly and the wings of the bat be considered homologous organs? Why or why not?

Answer 23:

As they do not have the same ancestor, the wings of the butterfly and the bat cannot be regarded as homologous organs. Although both structures are useful for flying, they have independently evolved. This is demonstrated by the difference between the wings of a butterfly and a bat, which are made up of two chitinous membranes and a bony skeleton with blood vessels, respectively. As a result, these are analogous organs rather than homologous organs.

Question 24. What are the fossils? What do they tell us about the process of evolution?

Answer 24:

The preserved remains of extinct animals, plants, or other species that perished millions of years ago are known as fossils. These fossils provide information on numerous extinct organisms as well as clues as to how evolution may have taken place. It is possible to infer an organism’s possible appearance and lifestyle from fossils. More crucially, we can compare current and fossilised organisms to learn how they relate to one another. For instance, the protein sequences of the T-rex dinosaur, which established its avian ancestry, have been recovered by scientists. This indicates that birds are the living descendants of (avian) dinosaurs. Additionally, the distribution of fossils provides us with a general idea of the historical period during which various species were created or went extinct.

Question 25. Why are human beings who look completely different from each other in terms of colour and looks said to belong to the same species?

Answer 25:

Humans differ in colour and look in general, although they all share the same genetic foundation. One theory put forth for our radical alterations is that they are the result of evolutionary pressure, where the necessity to be quickly recognised caused us to have quite distinct faces.

Question 26. In the evolutionary terms, can we say which among bacteria,  fish, spiders, and chimpanzees have a ‘better’ body design? Why or why not?

Answer 26:

Environmental demands and pressure have an impact on how bodies are designed. As a result, we cannot draw the conclusion that one organism has a superior body to another. For instance, because it is best suited for an aquatic environment, fish have evolved a streamlined design. A spider or chimpanzee, on the other hand, might not be able to survive in such aquatic environments.

Question 27. Explain the terms “analogous” and “homologous” organs with suitable examples.

Answer 27:

Homologous organs are those that share the same basic anatomical makeup and place of origin but have unique uses. For instance, the anatomy of human forelimbs and bat wings is comparable.

Organs that perform similar functions but have a different structural makeup or origin are said to be analogous organs. For instance, insect and bird wings.

Question 28. Explain the importance of the fossils in deciding the evolutionary relationships.

Answer 28: Fossils give evidence about:

(a)Evidence concerning the organism and its paleobiology can be found in fossils.

(b) Even an organism’s behaviour can be inferred to some extent. Palaeontologists, for example, have discovered a site containing over 10,000 Hadrosaurus dinosaur skeletons.This suggests that the dinosaurs were herd animals.

(c) Fossils can shed light on how animals and plants have evolved over time (for instance, palaeontologists have discovered that whales evolved from goat-sized land-dwelling animals called Pakicetus).

Question 29. What evidences do we have for the origin of life from the inanimate matter?

Answer 29: The experiment carried out in 1953 by Stanley L. Miller and Harold C. Urey proved that life originated from inanimate elements. They made an artificial atmosphere that resembled that of the early planet; it contained ammonia, hydrogen, and other gases believed to have existed during the prehistoric era of the world.

The temperature of this mixture of gases was  just below 100 ° C. In addition, sparks were produced to mimic lightning, which was also considered to occur frequently at the time. At the conclusion of the test, he was able to produce 11 of the 20 amino acids needed for life.

Question 30. Explain how  sexual reproduction gives rise to  more viable variations than  asexual reproduction. How does this idea affect the evolution of  organisms that reproduce sexually?

Answer 30: Because of the following factors, sexual reproduction leads to numerous viable variations:

(a) A mistake in DNA copying (though it was rare)

At the moment sex cells develop, paternal and maternal chromosomes are randomly segregated.

(c) When gametes are formed, homologous chromosomes exchange genetic material.

(d) Variations accumulated as a result of reproduction over many generations, and extensive diversity was naturally produced by choice.

(e) Because there is only one parent engaged in asexual reproduction, variation is highly constrained. As a result, the offspring shares the parent’s genetic makeup.

Question 31. How is the equal genetic contribution of the male and female parents ensured in the progeny?

Answer 31: By inheriting an equal number of chromosomes from both parents, kids are guaranteed to have genetic contributions from both male and female parents. The chromosomes come in 23 pairs, however not all of them are coupled. The 22 pairings are known as autosomes, while the final pair, which consists of one pair, is known as the sex chromosomes (represented as X and Y).

Males have only one X and one Y chromosome, while females have two sets of X chromosomes.

Fertilisation, which occurs during the reproductive process and involves the union of the male and female gametes, produces a diploid zygote. Additionally, both parents contribute the same amount of genetic material to the zygote. One X or Y chromosome and 22 autosomes are contributed by the man. One X chromosome and 22 autosomes are contributed by the female.

Question 32. Only the 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:The statement is accurate: Only differences give particular species a chance to thrive in a community. For instance, if a bacterium finds itself in a setting with a sudden rise in ambient temperature, changes that increase its heat resistance are particularly helpful for survival. For the bacteria, this will mean the difference between life and death.

Question 33. All the variations in a species do not have  equal chances of survival. Why?

Answer 33: In the habitat they live in, not all varieties have an equal chance of surviving. Depending on the type of modifications, different people may benefit in different ways.The organisms that are best suited to their surroundings will endure.

Question 34: A Mendelian experiment consisted of breeding  pea plants bearing violet flowers with pea plants bearing  white flowers. What will be the result of the F1 progeny?

Answer 34: The Mendelian experiment indicates that white colour (ww) is a recessive trait and violet colour (VV) is a dominant trait. Consequently, the F1 progeny’s blossom will be violet in colour (Vw).

Question 35: Name the information source for making proteins in the cells.

Answer 35:The information needed to make proteins comes from the deoxyribonucleic acid (DNA) found in the chromosomes of the cell nucleus.

Question 36: What is a gene? 

Answer 36: A gene is a piece of DNA located on a chromosome that directs the production of a certain protein that controls a particular trait (or set of characteristics) in an organism.

Question 37: What is heredity? 

Answer 37: The inheritance of characters (or trials) from the parents to their offspring is called heredity.

Question 38: Why is the progeny always tall when a tall pea plant is crossed with a short pea plant?

Answer 38: Because tall is the dominant trait and short is the recessive trait, when a tall pea plant crosses with a short pea plant, the offspring is always tall. As a result, the children display the dominant trait.

Question 39: Write one difference between the  inherited traits and the acquired traits, giving one example of each trait.

Answer 39: An acquired trait is the trait (or characteristic) of the organism that is “not inherited” but instead arises in reaction to the environment. For instance, all of a bunch of mice offspring will have tails if they are naturally bred. Now, if these mice’s tails are surgically removed after each generation, tailless mice won’t be born. This is true since losing one’s tail is an acquired behaviour.

A trait (or feature) of an organism that results from a change in its genes (or DNA) is referred to as an inherited trait. Because inherited qualities have altered the organism’s genes (or DNA), they can be passed on to the organism’s offspring. Take human skin colour as an example.

Question 40.(a) Why did Mendel carry out an experiment to study the inheritance of two traits in the garden peas?

(b) What were the findings with respect to the inheritance of traits in the F1 and F2 generations?

(c) State the ratio obtained in the F2 generation in the above-mentioned experiment.

Answer 40:

(a) Mendel performed crosses between two qualities to observe how they interacted and how their inheritance patterns differed. Mendel conducted a dihybrid cross, and it was found that each character exhibited itself independently of the other when two pairs of characters were taken into account.

(b) An example of a cross between parents would be a round yellow and wavy green hybrid.

All plants of the F1 generation have spherical yellow seeds. The F2 generation, on the other hand, contains a wide variety of plants, including round yellow, round green, wrinkled yellow, and wrinkled green.

F2 generation ratio : Round-yellow = 9 : Round- green = 3 : Colour of stem in the F1 progeny Wrinkled- yellow = 3 : Wrinkled-green = 1

Question 41: How did Mendel explain the possibility that atrait is inherited but not expressed in the organism?

Answer 41: Mendel started by choosing two pure-line plants. Then he crossed such plants with disparate personalities. He saw that just one of the two opposing characters—which he labelled dominant—appeared in the F1 generation, while the other was recessive. Later, when he selfed the F1 plants, he noticed that both features did indeed arise, but in a certain proportion. This is how Mendel explained the possibility thata trait might be inherited but not expressed in the plant.

Question 42.How did Mendel interpret the result to show that the traits may be either dominant or recessive? Describe it in brief. 

Answer 42: Mendel made a pea plant with two opposing traits in mind and crossed them. It was recessive to have a characteristic that did not manifest in the F1 generation and dominant to have one that did. He later selfed the F1 generation plants, and the F2 generation displayed both parental characteristics in a clearly defined proportionMendel concluded from his findings that the characteristic was dominant when it manifested itself in the F1 generation and recessive when it did so in the F2 generation. The subsequent cross serves as evidence for this claim.

Question 43: Explain Mendel’s experiment with peas on the inheritance of the  characters considering only one visible contrasting character. 

Answer 43: The pure tall pea plant and the pure dwarf pea plant were crossed by Mendel. Every F1 generation plant harvested was tall.Mendel obtained both tall and dwarf plants in the ratio of 3:1 in the F2 generation when he selfed plants from the F1 generation. This explains why there are two alleles for each set of opposing characteristics. A dominant allele controls the trait that is expressed in the first generation (F1), whereas a recessive gene regulates the trait that is not expressed in the first generation (F1). When both opposing alleles are present in F1 individuals, there is no mixing of the alleles; instead, they segregate once more during the production of the gamete. Recessive traits therefore resurface in the F2 generation as a result of the combination of the recessive genes.

Question 44: “It is a matter of chance if a couple will have a male or a female child.” Justify this statement by illustrating it in a flow chart. 

Answer 44: When male and female gametes unite during fertilisation, sex is established. Gametes with an X or Y chromosome are produced by males, while gametes with an X chromosome are produced by females. When male and female gametes combine to form a zygote during fertilisation, the sex of the child is established.

The offspring will be a girl if a sperm (male gamete) with an X chromosome fertilises an egg or an ovum (female gamete) with an X chromosome. This is due to the fact that the children will have XX  chromosome combinations.

The offspring will be a boy if a sperm (male gamete) with a Y chromosome fertilises an egg or ovum (female gamete) with an X chromosome. This is due to the fact that the children will have XY sex chromosome combinations.

Therefore, there is a 50% chance of having a male child and a 50% chance of having a female child.

Question 45: A cross was made between the two pure-breed pea plants,  one with round and green seeds and the other with wrinkled and yellow seeds.

(a) Write the Phenotype of the F1 progeny. Give a reason for your answer.

(b) Write the different types of the F2 progeny obtained along with their ratio when the F1 progeny was selfed. 

Answer 45:

(a) The cross in question was created using two pea plants only used for breeding, one with round, green seeds and the other with wrinkled, yellow seeds.

Green seed colour and wrinkled seed shape are subordinate to yellow seed colour and spherical seed shape. Recessive features are stifled in the F1 generation, while dominant traits are expressed.

As a result, the F1 progeny phenotype is spherical and yellow.

(b) The offered cross might serve as an example of the various F2 progeny types and their ratio when F1 progeny were selfed.

Ratio of phenotypes: 9: 3: 3: 1

Round yellow seeds – 9 ; Round green seeds – 3;

Wrinkled yellow seeds – 3; Wrinkled green seeds – 1

Question 46: A blue colour flowering plant denoted by BB is cross-bred with that of a white colour flower plant denoted by bb.

(a) State the colour of the flower you would expect in their F1 generation plants.

(b) What must be the percentage of the white flower plants in the F2 generation if the flowers of F1 plants are self-pollinated?

(c) State the expected ratio of the genotypes BB and Bb in the F2 progeny. 

Answer 46:

(A) The F1 generation blossom will be blue in colour.

(b) If the F1 generation flowers self-pollinate, then 25% of the F2 generation’s blossoms must be white.

(c) A 1:2 ratio between the genotypes BB and Bb is anticipated in the progeny of the F2 generation.

The cross shown above could represent the outcomes mentioned above:

Question 47: If we cross pure-breed tall (dominant) pea plants with pure-breed dwarf (recessive) pea plants, we will get pea plants of the F1 generation.

If we now self-cross the pea plant of the F1 generation, then we obtain pea plants of the F2 generation.

(a) What do the plants of the F1 generation look like?

(b) State the ratio of  tall plants to  dwarf plants in the F2 generation.

(c) State the type of plant that is not found in the F1 generation but appeared in the F2 generation, mentioning the reason for the same.

Answer 47:

(a) The F1 generation of plants will all be tall plants.

(b) The F2 generation has a 3:1 ratio of tall to dwarf plants.

(c) Dwarf plants first arose in the F2 generation and were not present in the F1 generation. This is because only the dominant trait (tall) expresses itself in the F1 generation, while the recessive trait (dwarf) is inhibited. Due to the separate inheritance of characteristics, whether dominant or recessive, the dwarf plants first appeared in the F2 generation. To put it another way, a single copy of (T) is sufficient to make the plant tall, whereas both copies of (T) are required to make the plant dwarf.

Question 48: How is the sex of the child fixed during the fertilisation step in  human beings? Explain. 

Answer 48: Human beings have 23 pairs of chromosomes (22 pairs of autosomes +1 pair of sex chromosomes). A male has only one X chromosome and one Y chromosome, whereas the female has two X chromosomes. The sex of a child depends on the two conditions which take place during fertilisation. The two conditions are given below:

• If a sperm carrying an X chromosome fertilises an ovum which carries an X chromosome, then the child born will be a girl.
• If a sperm carrying a Y chromosome fertilises an ovum which carries an X chromosome, then the child born will be a boy.

Question 49: How do Mendel’s experiments show that

(a) the traits may be dominant or recessive?

(b) inheritance of the two traits is independent of each other? 

Answer 49: (a) Mendel discovered that only tall pea plants were created in the first generation when he crossed the pure-bred tall pea plants with the pure-bred dwarf pea plants (F1). The tall plants and dwarf plants were produced in the second generation, or (F2), in a ratio of 3:1. He then self-crossed the tall pea plants of the F1 generation. Mendel said that the dwarfness of one of the parent pea plants had not been lost, but rather had been suppressed or hidden in the first generation before resurfacing in the second. He described the expressed characteristic of tallness as the “dominant trait,” and the suppressed feature of dwarfism as a “recessive trait.” Mendel’s studies on tall and dwarf pea plants demonstrated that the qualities might be dominant or recessive in this way.

Thus, the suggested cross could provide an explanation for this:

(b) Round-yellow and wrinkled-green were two of the distinctive combinations Mendel saw in seeds, while round-green and wrinkled-yellow were two novel combinations that had emerged in the F2 generation. In a cross, more than one pair of traits is taken into account at once, and the variables causing each pair of features are dispersed independently to the gametes, in accordance with Mendel’s second law of inheritance.

The cross presented below, which depicts a dihybrid cross, demonstrates how two qualities can be inherited independently of one another.

Question 50: Give the respective scientific terms used for studying:

(a) the mechanism by which the variations are created and inherited, and

(b) the development of  new types of organisms from the existing ones. 

Answer 50:

(a) The process by which variants are produced and passed down is through heredity.

(b) Evolution is the process through which a new form of organism develops from the ones that already exist.

Question 51: Write about the contribution of Charles Darwin in the field of evolution.

Answer 51: Charles Darwin made a significant contribution to the field of evolution by stating that only organisms that can adapt to changing environmental conditions can survive. He also asserted that natural selection is a process that plays a significant role in the evolution of plants and animals by choosing organisms that have traits that are advantageous to the environment.

Question 52. How is the sex of a newborn determined in humans?

Answer 52:The genes a person inherits from their parents determine their sex. A newborn will have a feminine gender if it inherits X chromosomes from the father and a male gender if it inherits Y chromosomes.

Question 53. Do the genetic combination of the mothers play a significant role in determining the sex of a newborn?

Answer 53: No, the father’s chromosomal donation will decide the gender of the newborn. Fathers have X and Y in their 23rd chromosomal pair while mothers have XX in theirs and always donate One X. The child will be a girl if the father donates X, and a boy if the father donates Y.

Question 54. Mention the three important features of fossils which help in the study of evolution.

Answer 54:

• Ancient species are preserved in fossils.
• The evolutionary distinctions between creatures and their ancestors are shown by fossils.
• The age of a particular species is determined by its fossil record.

Question 55. Why do all the gametes formed in  human females have an X chromosome?

Answer 55: Of their 23 pairs of chromosomes, females have XX. All female gametes have X chromosomes because one X chromosome enters each one during meiosis.

Question 56. A very small population of a species faces a greater threat of extinction than the larger population. Provide a suitable genetic explanation.

Answer 56:

Because of the following factors, a species with a relatively small population is more likely to go extinct than one with a higher population:

A small population encourages inbreeding. Reduced variety is the outcome of inbreeding.

Genetic drift: A small population is susceptible to an abrupt environmental change. Genetic drift increases the risk of extinction for species with small populations.

Negative population growth caused by inbreeding depression is harmful to the survival of  species with a smaller population.

Question 57. What are the homologous structures? Give an example. Is it necessary that  homologous structures always have a common ancestor?

Answer 57: Homologous structures are ones that have a similar fundamental structure but carry out various tasks. For instance, consider the forelimbs of mammals, amphibians, and reptiles. They are referred to as similar structures if they don’t share a common ancestor.

Question 58. Does the occurrence of the diversity of the animals on  earth suggest their diverse ancestry also? Discuss this point in the light of  evolution.

Answer 58:

Although animals have a wide range of diverse structures, they do not share a common ancestor. This is due to the possibility that variety may be severely constrained by common ancestry. Since many creatures share a habitat, it is unlikely that they have evolved through geographical isolation or speciation. Therefore, it is unlikely that all animals share a common ancestor.

Question 59. Give the pair of the contrasting traits of the following characters in the pea plant and then mention which one is dominant and recessive.

(i) yellow seed (ii) round seed

Answer 59:

1. Yellow-dominant
2. Green-recessive
3. Round-dominant
4. Wrinkled-recessive

Question 60. Why did Mendel choose the pea plant for his experiments?

Answer 60: Mendel decided to conduct his experiments on the pea plant for the following reasons:

• Pea plants are simple to grow
•  yet only live a brief time.
• They have flowers that are larger.
• The pea plant self-pollinates.

Question 61. A woman has only daughters. Analyse the given situation genetically and provide a suitable explanation.

Answer 61:

When a woman only bears daughters, the X chromosomes from the sperm are always transferred to the egg. A female kid will be born if the sperm gives X chromosomes, and a male child will be born if the sperm donates Y chromosomes.

Question 62. Does the geographical isolation of the individuals of a species lead to the formation of a new species? Provide a suitable explanation.

Answer 62: Genetic drift is caused by the isolation of a species’ members from one another geographically. This restricts the separated population’s ability to reproduce sexually. As a result, individuals that are isolated from one another begin to reproduce. A new variant is created as a result of this. New species will emerge as a result of the accumulation and transmission of these variations over generations.

Question 63. Bacteria have a simpler body plan in comparison to human beings. Does it mean that human beings have  evolved more than bacteria? Provide a suitable explanation.

Answer 63:

This is a contentious subject. Depending on how we assess evolution. If body complexity is a parameter, then humans are significantly more advanced than microbes. Humans have organ-level organisation, whereas bacteria are organised at the cellular level.

However, when it comes to adaptability, germs have advanced more than people have. The only requirement for human habitation is artificial protection. Bacteria can exist anywhere on the planet, whereas humans cannot survive in harsh climates. They can endure even extreme environments, like sulphur springs and hydrothermal vents.

Question 64. All the human races, like Africans,Europeans, Asians, Americans, and others, might have evolved from a common ancestor. Provide a few pieces of evidence in support of this view.

Answer 64:

Despite their apparent differences, all human races share a common ancestor. The evidence supporting this opinion is as follows:

• A similar size of the brain
• Bipedal locomotion
• Hair on the body
• Ability to handle tools
• Ability to communicate using language
• Highly complex social behaviour
• Same body design

Question 65. Evolution has exhibited greater stability of the molecular structure when compared with the morphological structures. Comment on the statement and justify your opinion.

Answer 65: Morphological structures are those that are visible to our sight. The biomolecules that make up molecular structures are essential to all living things. We are surrounded by a wide range of diversity. The variety in morphological structures makes this diversity feasible. The least stable structures are morphological ones, as this demonstrates. On earth, life first appeared as simple forms, but it is today made up of several complex forms.

Although basic macromolecules like DNA have undergone millions of years of evolution, their structure has not changed. Humans and mice share the same DNA. The structure of a protein is the same in a fungus and a bird. The molecular foundation of life has not changed over the years. This demonstrates that, relative to the morphological structure, the molecular structure has shown stronger evolutionarily-related stability.

Question 66. Give the basic features of the mechanism of inheritance.

Answer 66:

The following are some of the fundamental components of the inheritance mechanism:

• Characters are controlled by genes
• Genes can take two or more different forms.
• Genes are found on chromosomes, and one type of gene may be dominant over another.
• There are two possible versions of a single gene, which may or may not be similar.
• At the time of gamete creation, the gene splits into two forms.
• In the zygote, two gene forms come together.

Question 67. Give reasons for the appearance of new combinations of characters in the F2 progeny.

Answer 67:

Round, yellow seeds are found in F1 plants. In the F2 generation, generational crosses with the colours round-yellow, round-green, wrinkled yellow, and wrinkled green in the ratio 9:3:3:1 can produce novel combinations.

This demonstrates that a pea seed’s likelihood of being round or wrinkled is independent of whether it will be yellow or green. Allele pairs are, therefore, independent of one another. This is an independent assortment.

Question 68. If  trait A exists in 10% of a given population of an asexually reproducing species and trait B exists in 60% of the same population, which of these traits is likely to have arisen earlier?

Answer 68:

Compared to trait A, trait B is more likely to emerge early because it has been present and is replicating in a larger proportion of the population.

Question 69:  How does the creation of the variations within a species promote survival?

Answer 69:The species can better adapt to environmental changes thanks to genetic variety. Furthermore, it is a crucial force in evolution because it enables natural selection to alter the frequency of alleles. These differences will determine whether the species survives or goes extinct.

Question 70. How do Mendel’s experiments show that the traits may be either dominant or recessive?

Answer 70: Mendel’s tests on the monohybrid cross showed that the traits might either be dominant or recessive. He conducted the experiment by crossing tall (TT) and dwarf (TT) pea plants. The F1 (or filial) generation was represented by the plants that emerged as a result of fertilisation. The F1 plants were all very tall. Mendel continued by self-pollinating the plants from the filial generation, and as a result, one-fourth of the plants produced by the F2 generation were dwarfs. Mendel deduced from this experiment that the tall F1 plants were not true-breeding. Instead, they possessed traits of both tall and dwarf heights. Because the characteristics for tallness predominated over the traits for dwarfness, some of the plants were tall. The idea that traits can either be dominant or recessive is thus confirmed.

Question 71. How do Mendel’s experiments show that traits are inherited independently?

Answer 71:

Mendel’s dihybrid cross experiment demonstrates that characteristics are inherited separately. He used two characteristics in the experiment: seed shape and seed colour. While the round shape (RR) predominates over the wrinkled shape, the colour yellow (YY) dominates over green (YY) (rr). There were nine plants with round yellow (RRYY) seeds, three plants with round green (RRyy), three plants with wrinkled yellow (rrYY), and one plant with wrinkled green seeds among the F2 progeny of the dihybrid cross (rryy). He also noted that while the round green and wrinkled yellow are new, the wrinkled greens and round yellow are parental combinations. Four different types of gametes were produced by a dihybrid cross between two seeds with dominant traits (RRYY) and non-dominant traits (rryy) (RY, Ry, rY and ry). By segregating independently of one another, each gamete occurs at a frequency of 25% of the total number of gametes generated.

Question 72. 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 72:

The information provided does not allow us to determine if blood group A or O traits predominate. In ABO blood, blood type A is consistently dominant, and blood type O is consistently recessive. In this case, the mother’s blood group could be OA or OO, while the father’s blood group could be genotypically AA (homozygous) or AO (heterozygous).

Question 73. How is the sex of the child determined in human beings?

Answer 73:

In humans, the men decide the sex of the infant. In contrast to females, who have XX chromosomes, males have XY chromosomes. Therefore, if the mother gives birth to a girl  when the X chromosomes of the male and female join. When the X chromosome of the female and the male combine, a boy is born as a result.

Question 74. Why are the traits acquired during the lifetime of an individual individual and not inherited?Answer 74: Since changes do not reflect in the DNA of the germ cells, traits acquired over the course of a lifetime cannot be passed down through future generations. A football player, for example, cannot pass on his talents to his progeny because they are solely inherited by non-reproductive cells.

Question 75. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer 75: The genetic diversity of the species declines along with the size of the tiger population. This has the effect of limiting the genetic variants that can be introduced into tiger populations. There will be significant ramifications from this lack of diversity. For instance, if a disease spreads among the tiger population, it could possibly obliterate the entire population and lead to their extinction.

Question 76. Will the geographical isolation be a major factor in the speciation of the self-pollinating plant species? Why or why not?

Answer 76: Geographical isolation often has a minor role in the pollination of plant species because a self-pollinating plant species won’t acquire any new traits. However, it’s possible that some environmental changes will lead to certain variances.

Question 77. Will the geographical isolation be the major factor in the speciation of an organism that reproduces asexually? Why or why not?

Answer 77:Geographic isolation cannot be taken into account in the case of asexually reproducing organisms. Meiosis does not take place during asexual means of reproduction, which accounts for this.

Question 78: Why do mice whose tails were surgically removed just after birth for generations continue to produce mice with tails?

Answer 78: Typically, a bunch of mice will breed, and each of their offspring will have a tail. Now, these mice won’t create tail-less offspring if their tails are surgically removed after each generation. This is the case because removing the tail during the mouse’s life cycle is an acquired trait that is not passed on to the next generation. The genes of the mice’s germ cells cannot be altered by the removal of the tail.

Question 79: Define genetics. Why is the decrease in the number of  surviving tigers a cause for concern from the point of view of genetics? Explain briefly.

Answer 79: The area of biology known as genetics is concerned with the investigation of heredity and variation. William Bateson first used the word “genetics” in 1906. Small populations have fewer and narrower variances, which results in less variety and less variation in attributes. From a genetics perspective, the fact that there are so few remaining tigers is concerning for the following reasons:

• If they were to die, the gene pool would also die, meaning that many genes would be removed from the gene pool.
• Due to the genetic drift phenomena, tigers only survive in small populations; therefore, if a natural disaster wipes out this small population of tigers, they will abruptly go extinct..

• If a disease is contagious throughout the entire population, the remaining people may be wiped out. This could result in the quick extinction of the tiger species and the permanent loss of their DNA, which would be detrimental to nature’s diversity.

Question 80: With the help of two suitable examples, explain why the experiences and traits earned by people during their lifetimes are not passed on to the next generations. When can such traits be passed on?

Answer 80: Because these features are gained by the man during his lifetime, certain experiences and traits acquired by humans during their lifetimes are not passed on to the next generation. These qualities are not innate in man, and he cannot pass them on to his offspring. The following examples could clarify these more clearly:

(i) A really talented swimmer’s child might not be able to swim. This is the case because each person must learn how to swim on their own; it is not something that is passed down from parents.

(ii) Someone may have a scar on their face from an accident-related cut. Another example of an acquired characteristic that cannot be passed on to the following generation is this one.

Future generations may inherit traits for which alterations have been made to the genes found in the parent species’ reproductive cells. These characteristics are referred to as inherited qualities.

Question 81: “An individual cannot pass on to its progeny the experiences of its life-time”. Justify the statement with the help of a suitable example and also give a reason for it.

Answer 81: If we breed some mice, every mouse that is born will have a tail like its parents. Now, if we surgically remove the tails and then breed the mice once more, we will continue to produce mice with tails. This is due to the fact that removing a mouse’s tail does not alter the genes in its reproductive cells (or gametes). Additionally, since the gene structure of mice is not altered by the acquired property of having severed tails, this trait cannot be handed down to succeeding generations. This leads us to the conclusion that since acquired traits are not the result of a change in genes, they cannot be passed down to a person’s offspring and, therefore, cannot be the cause of evolution.

Question 82: What is the speciation? Explain in brief the role of natural selection and  genetic drift in this process. 

Answer 82: Speciation is the process by which  new species arise from existing species. In the process of speciation, both genetic drift and natural selection are crucial. Natural selection is the process through which nature chooses features that are advantageous to the species in the environment.

For instance, beetles change their colour when they reproduce. In the offspring, one beetle, instead of developing its typical red colour, acquires a green one. This beetle may pass on this colour variation to its offspring, ensuring that all of them are green in hue. Crows continue to consume red beetles, which are easily seen on green leaves, even though they can’t easily spot green-colored beetles on the green leaves of bushes. As a result, each generation sees a rise in the number of green beetles.

When a portion of the population perishes in a natural disaster or migrates to another area, genetic drift occurs, eradicating the genes for certain traits from the tiny population.

 The remaining population’s gene frequency changes as a result.Imagine that one red beetle develops a blue body colour instead of red in a community of sexually reproducing red beetles. This beetle has the ability to pass on this colour variation to its young, resulting in an entire generation of blue beetles. There would initially be a small number of blue beetles amid the vast majority of red beetles as the population of beetles grew. An elephant passes by at this point and stamps on the bushes that the beatles are living in. As a result, the majority of the beatles perish. By happenstance, the majority of the remaining beetles are blue. Over time, this population will once again steadily increase and primarily consist of blue-colored insects. Over time, the colour characteristic changed from the usual red to blue as more blue beetles persisted in the population. Accidents can alter the frequency of some genes in a small population, even if the possessors do not benefit in terms of survival.

Question 83:List and briefly describe the three main factors responsible for speciation.

Answer 83: The process by which new species arise from existing ones is known as speciation.

(i) Geographic isolation of a population due to various sorts of barriers, including mountain ranges, rivers, and seas, is one of the three key causes of speciation. Geographical isolation, which results in reproductive isolation and obstructs the transfer of genes between isolated populations through gametes, is a crucial determinant in the speciation of sexually reproducing animals.

(ii) Genetic drift is the loss of a small population’s genes for specific traits as a result of migration or natural disasters that cause a portion of the population to perish. The remaining population’s gene frequency changes as a result.

(iii) Variations introduced by  random mating and hybridisation. The random fusionof the gametes adds new alleles and results in the formation of new species.

Question 84:  Explain, with the help of an example each, how the following will be providing evidence in favour of evolution:

(a) Homologous organs

(b) Analogous organs

(c) Fossils

Answer 84: (a) Although they have a similar fundamental structure and embryonic origins, homologous organs serve diverse purposes in other animals. For instance, the basic structure of the forelimbs of a frog, reptile, a bird, and a human being is comparable. The underlying commonality in the forelimbs of these many vertebrates implies common ancestry, despite the fact that these organs serve radically distinct tasks. This demonstrates how these vertebrates have evolved over time in response to the unique requirements of succeeding generations.

(b) Comparable organs have a different underlying structure and embryonic genesis from one another, yet seem alike and serve the same purposes. Insect and bird wings, for instance, have differing architecture but serve the same purpose of enabling flight. The fact that these organs are present indicates that they do not have a common ancestor, but they can still evolve to carry out similar functions in order to survive, thrive, and continue to evolve in the current environment. This offers an evolutionary mechanism.

(c) Fossils are the remains or imprints of deceased plants and animals that once existed in the distant past. The fossils offer proof of evolution. For instance, the fossilised bird Archaeopteryx exhibits traits shared by both reptiles and birds. It had features that are unique to birds, such as feathers, fused bones, and a beak, as well as those that reptiles have, such as teeth in the jaws, claws on the fingers, a long tail, etc. Thus, Archaeopteryx serves as a transitional fossil between reptiles and birds, indicating that birds diverged from reptiles through a process known as continuous evolution.

Question 85: “Evolution and classification of organisms are interlinked”. Give reasons to justify this statement.

Answer 85:The process of evolution is how different types of organisms evolve from already existing ones. The organisation of organisms into a number of groups based on physiologic, biological, anatomical, or other links is known as classification. All classification schemes follow a hierarchy. The more recently two species share an ancestor, the closer their relationship. Organisation of organisms into several groups based on shared and unique traits is a necessary component of classification. It aids in understanding the fundamental configuration of a hierarchical structure among many species. It readily enables investigations or research on a large range of related organisms. As a result, we may claim that evolution and categorisation are related and that how species are classified actually reflects how they evolved.

Question 86: (a) Planaria, insects, octopuses, and vertebrates all have eyes. Can we group the eyes of these animals together to establish their common evolutionary origin? Justify your answer.

(b) “Birds have evolved from reptiles.” State the evidence to prove the statement.

Answer 86: (a) The eye cannot be used to classify vertebrates, insects, octopuses, or planaria. Invertebrates, octopuses, planarians, and insects all have similar eyes that have evolved over several generations as an adaptation for related tasks. They are examples of convergent evolution, in which populations that are not closely related evolve similar functional structures as an adaptation to a shared function.

(b) Archaeopteryx, a fossil bird, has feathers, fused bones, and a beak, which are traits that distinguish birds from other animals. Additionally, it possessed traits common to reptiles, such as long tails, claws on free fingers, and jaws with teeth. As a result, it serves as a link between reptiles and birds. This illustration offers evidence that birds descended from reptiles.

Question 87: Distinguish between homologous  and analogous organs. In which category would you place the wings of a bird and the wings of a bat? Justify your answer by giving a suitable reason.

Answer 87: Homologous organs are those with diverse functions but the same fundamental structure and embryonic origin.

These organs develop according to the same basic organisational structure, but as adults, they have undergone modifications to perform diverse tasks in order to adapt to various situations. Analogous organs are those that perform comparable activities but have different fundamental architectures and developmental origins.

The basic construction or architecture of a bird’s and a bat’s wings is different, yet they both serve the same purpose when it comes to flight, making them equivalent organs.

Question 88: How are the fossils formed? Describe, in brief, the two methods of determining the age of fossils.

Answer 88: When animals or plants die, their remains are broken down by microbes in the presence of oxygen, moisture, etc. Sometimes, due to environmental factors (such as a lack of oxygen or moisture, for example), an organism’s body cannot entirely degrade. When we excavate the earth, we find an organism’s body (or a portion of its body) preserved as a fossil. In many instances, the soft parts of the animals dissolve, leaving behind fossilised skeletons of the hard components (such as teeth, bones, etc.).

Even the delicate, swiftly decomposing portions of plants and animals can occasionally be retained as fossils in the form of their imprints in rocks. For instance, a dead leaf that gets stuck in mud won’t decay right away. The mud will harden around the leaf, creating a mould that will eventually become a rock while still leaving an impression of the leaf. After a considerable amount of time, the earth can be excavated to reveal a fossilised leaf.

The age of the fossils can be determined in primarily two ways, as given below:

(i) By the relative method: At various depths in the earth, fossils can be found through digging. The fossils that are found in layers of the earth are closer to the surface, and  are therefore more recent, while those found in deeper layers are older. The oldest fossils are those that are found in the earth’s deepest strata.

(ii) Carbon dating method: When a living thing perishes and turns into a fossil, its carbon-14 radioactivity continues to gradually decline. By analysing and comparing the carbon-14 radioactivity left in the fossils with the carbon-14 radioactivity present in  living things today, this technique determines the age of the fossils.

Question 89: Explain how the evolutionary relationships can be easily traced by the study of the homologous organs.

Answer 89: Anatomical and morphological proof of evolution is provided by homologous organs. Different types of animals or plants have a variety of organs that share a fundamental structure but serve various functions. We refer to these as homologous organs. For instance, the basic structure of the forelimbs of frogs, reptiles, birds, and humans is identical. The fundamental resemblance of these various animals’ forelimbs suggests that they all descended from a common ancestor that possessed five digits of pentadactyle limbs, which were modified during the course of evolution in response to the unique requirements of succeeding generations. Homologous organs therefore represent divergent evolution or adaptive radiation.

Question 90: Define evolution. How does it occur? Describe how the fossils provide us with evidence in support of evolution. 

Answer 90: The progressive transition from simple to complex living forms, or from ancient organisms that lived millions of years ago to contemporary species, is known as evolution. Simple life forms undergo changes, improvements, and modifications during evolution. The remains or imprints of species that existed in the distant past are known as fossils. The existence of fossils demonstrates that the current animal descended from earlier species through ongoing evolution. An organism’s evolutionary history can be traced using fossils. The fossil distribution pattern reveals that the most recent fossils discovered in the top strata are more highly evolved than the older fossils found in the bottom rocks.

This indicates that as we move from the oldest to most recent rocks, fossils emerge and become increasingly complicated. It provides us with a general picture of the historical period during which certain species were created or went extinct. As a result, fossils give us proof that evolution is true.

Benefits of Solving Important Questions Class 10 Science Chapter 9

Class 10 Science is crucial for students pursuing the science stream in Class 11 and Class 12. Having clear concepts about each topic is important as the Class 10 chapters would form the basis for many chapters that would be covered in Class 11 and Class 12. We suggest students solve questions from our question bank of  Important Questions Class 10 Science Chapter 9.Our team has collected exam-oriented questions and prepared step-by-step solutions. 

Below are a few of the benefits of solving questions from our Important Questions Class 10 Science Chapter 9:

• Our team has sourced the questions from the NCERT textbook and exemplar books, other Science reference books, and past years’ question papers. They are carefully chosen so as to cover all the topics in the chapter. Students can confidently rely on our comprehensive question bank as it would save them a lot of time searching for questions from different. By solving questions, they would be able to fully revise the chapter.
• While solving the questions from our Important Questions Class 10 Science Chapter 9, students will be able to self-assess their weak and strong points. Based on it, they can plan their revisions and improve their exam preparation.
• The step-by-step solutions are prepared by Science subject matter experts with years of experience to provide credible study material based on the NCERT books. Hence, students can fully rely on and trust these solutions.

All of the chapter topics are adequately covered in our question bank of  Important Questions Class 10 Science Chapter 9. 

Extramarks make learning fun and engaging for students. Our website has a wealth of materials in addition to important questions and answers. Students can access some of these resources by clicking on the links provided below:

• NCERT books
• CBSE Revision Notes
• CBSE syllabus
• CBSE sample papers
• CBSE’s previous year’s question papers
• Important formulas 
• CBSE extra questions