Heredity And Evolution Class 10 Science Important Questions

Please refer to Heredity And Evolution Class 10 Science Important Questions given below. These solved questions for Heredity And Evolution have been prepared based on the latest CBSE, NCERT and KVS syllabus and books issued for the current academic year. We have provided important examination questions for Class 10 Science all chapters.

Class 10 Science Heredity And Evolution Important Questions

Question. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as           
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw

Question. An example of homologous organs is       
(a) our arm and a dog’s fore-leg.
(b) our teeth and an elephant’s tusks.
(c) potato and runners of grass.
(d) all of the above.

Question. In evolutionary terms, we have more in common with           
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.

Question. With whom we associate theory of evolution?         
(a) Charles Darwin
(b) Mendel
(c) Stanley Miller
(d) Harold Urey

Question. Which one of the following is not one of the direct conclusions that can be drawm from Mendel’s experiment?           
(a) Only one parental trait is expressed
(b) Two copies of each trait is inherited in sexually reproducing orgainsm
(c) For recessive trait to be expressed, both copies should be identical.
(d) Natural selection can alter frequency of an inherited trait.

Question. Fossils helps           
(a) To study evolution
(b) To understand climatic conditions in past
(c) For a hierarchy of organisms (classification)
(d) They help in all the above

Question. How can we know how old fossils are:             
(a) Fossils found closer to surface are recent than those found much below
(b) Detecting ratios of isotopes
(c) Studying its characteristics
(d) All of these

Question. Which one is a possible progeny in F2 generation of pure bred tall plant with round seed and short plant with wrinkled seeds?         
(b) Tall plant with wrinkled seeds
(c) Short plant with round seed
(d) All of the above

Question. Which of the following is controlled by genes?         
(i) Weight of a person
(ii) Height of a person
(a) only 1 (i)
(b) only (ii)
(c) both (i) and (ii)
(d) Sometimes (i) and sometimes (ii)

Question. Which one of the following is present in the nucleus?             
(a) Gene
(b) DNA
(c) Chromosomes
(d) All of these

Question. Amongst which of the following animals, sex of the offsprings not genetically determined?   
(a) Humans
(b) Snails
(c) Birds
(d) Dogs

Question. Which of the following is a totally impossible outcome of Mendel’s Experiment (cross breeding pure bred tall and short pea plants)           
(a) 3 tall 1 short plant
(b) 24 tall and 8 short plants
(c) 8 tall and 0 short plants
(d) 4 tall plants and 1 medium-height plant.

Question. What is the probability that a human progeny will be a boy?             
(a) 50%
(b) 56%
(c) 47.34%
(d) It varies

Question. Who have a perfect pair of sex chromosomes?           
(a) Girls only
(b) Boys only
(c) Both girls and boys
(d) It depends on many other factors

Question. If we breed a group of squirrels and surgically remove their tails, then amongst the progeny of these tailless squirrels–       
(a) All have no tail
(b) All have a tail
(c) Some of them have tails
(d) Cannot be determined.

Question. A section of DNA providing information for one protein is called—         
(a) Nucleus
(b) Chromosomes
(c) Trait
(d) Gene

Question. Organism A recently came into existence while B was formed millions of years ago. What does this indicate?           
(i) A is more efficient than B
(ii) A is more complex than B
(a) Only (i)
(b) Only (ii)
(c) Both (i) and (ii)
(d) Either (i) or (ii)

Question. Formation of 2 independent species due to genetic drift, geographical isolation, natural selection is specifically referred as–         
(a) Evolution
(b) Classification
(c) Speciation
(d) Reproduction

Question. Homologous organs have             
(a) Same structure, same function
(b) Different structure, different function
(c) Same structure, different function
(d) Same function, different structure

Question. Analogous organs have         
(a) Same structure, same function
(b) Different structure, different function
(c) Same structure, different function
(d) Same function, different structure

Question. Which one of the following strongly indicates that bird and dinosaurs are closely related?     
(a) They both have feathers
(b) They both respire
(c) They both reproduce
(d) They both have eyes

Question. There is an inbuilt tendency of variation during reproduction because of–             
(i) Errors in DNA copying
(ii) Sexual reproduction
(a) only (i)
(b) only (ii)
(c) both (i) and (ii)
(d) none of them

Question. Which one of the following gives a survival advantage and thus alters frequency of inherited trait.       
(i) natural selection
(ii) genetic drift
(a) only (i)
(b) only (ii)
(c) both (i) and (ii)
(d) none of these

Question. Wild cabbage is being cultivated for thousands of years and humans have generated broccoli, cauliflower, kala etc. from it. This is an example of             
(a) Natural selection
(b) Genetic drift
(c) Geographic isolation
(d) Artificial selection

Question. Which of the following can be called a characteristic?           
(a) Plants can photosynthesise
(b) We have 2 eyes
(c) Mango tree is multicellular
(d) All of these

Question. If A and B have n characteristics common while A and C have n/2 characteristics common, then which of the two organisms are more closely related?             
(a) A and C
(b) A and B
(c) Characteristics need to be known
(d) None of these

Very Short Answer Type Questions :

Question. What is environmental selection?
Answer : It is the selection within a population resulting from the influence exerted by the environment. It leads to a change in the composition of genes within a population.

Question. Why is the progeny always tall when a tall pea plant is crossed with a short pea plant?
Answer : The trait which represents the tallness in a pea plant is dominant over the another trait, shortness (dwarf).

Question. What is the phenotypic ratio of a dihybrid cross in F2 generation?
Answer : 9 : 3 : 3 : 1.

Question. Give an example where sex determination is regulated by environmental factors.
Answer : In snail, sex is determined by environmental factors (temperature).

Question. Define speciation.
Answer : Speciation means origin of new species from the existing one.

Question. What is the effect of DNA copying which is not perfectly accurate on the reproduction process?
Answer : It will result in less variations which may further lead to less adaptation to changing environment, thus, giving less chances of survival.

Question. Name the plant on which Mendel performed his experiments.
Answer : Garden pea (Pisum sativum).

Question. What are the basic events in evolution?
Answer : The changes in DNA during reproduction are the basic events in evolution.

Question. What is genetic drift?
Answer : The change in the frequency of certain genes in a population over generations.

Question. What are fossils?
Answer : Preserved traces of living organisms.

Question. What are analogous organs?
Answer : The organs which have similar functions but different structures are called analogous organs.

Question. “The chromosome number of the sexually producing parents and their offspring is the same”. Justify this statement.
Answer : In sexual reproduction, both the gametes (male and female) contain half the number of chromosomes (haploid or n) and by the fusion of these gametes, the zygote have full set (diploid 2n) chromosomes.

Question. The human hand, cat paw and the horse foot, when studied in detail show the same structure of bones and point towards a common origin.
a. What do you conclude from this?
b. What is the term given to such structures?
Answer :
a. They have common origin/ancestory.
b. Homologous organs.

Question. When a tall and dwarf pea plant were crossed, Fx showed only tall plants but in F₂ generation, some plants were dwarf. What does it mean?
Answer : It means reappearance of the dwarf character, a recessive trait in B’2 generation shows that the dwarf trait/ character was present in individuals of F* but it did not express (due to the present of tallness, a dominant trait / character)

Question. How is the age of fossil determined?
Answer : The age of fossil fuels is determined through carbondating or time dating method.

Question. What is evolution?
Answer : Gradual unfolding of organisms from pre-existing organisms through change is called evolution.

Question. In a beetle population, the number of green beetles is more than blue and red beetles. Give a reason behind this situation.
Answer : Variation/Natural selection.

Question. What are fossils? What is their significance in the study of evolution?
Answer : Fossils are impressions of the body/ body parts or the remains of organisms living in the past, which got preserved in sediments of earth.
a. Study of fossils helps in working out evolutionary relationships.
b. Fossils provide one of the most acceptable evidences in support of evolution, because we can study the evolutionary past of individuals in the form of their fossils.
c. Age of fossils can also be found by time dating using isotopes of carbon! carbon dating.
d. By studying fossils occurring in different strata of rocks, geologists are able to reconstruct the time course of evolutionary events.

Question. (a) On what rules inheritance is based?
(b) Is each trait influenced by both paternal and maternal DNA?
Answer :
a. The rules of inheritance is based on the fact that the traits in the progeny are carried out by DNA’s of both the parents (mother and father). These rules are known s ‘Mendel’s Laws of Inheritance’.
The rules are:
(i) Law of dominance,
(ii) Law of segregation, and
(iii) Law of independent assortment.
b. Yes, it is true that each trait is influenced by both paternal and maternal DNA.

Question. a. What is the genetic constitution of human sperm?
b. Mention the chromosomes pair present in zygote determining the sex of a male child.
Answer :
a. 22 + Y or 22 + X
b. (22 + Y + 22 + X)

Question. a. How many gene sets should a germ cell have?
b. Mention two factors causing evolution.
Answer :
a. One gene set.
b. (i) Reproduction isolation (ii) Natural selection

Question. What term did Mendel use for genes? Where are the genes located?
Answer : Mendel used the term ‘factors’ for genes. Genes are portions of DNA which code for a single protein.

Question. How many pairs of chromosomes do human beings have, specify the types of chromosomes also?
Answer : Human beings have 23 pairs of chromosomes the first 22 pairs are called autosomes are similar in males and females. The 23rd pair is called the sex chromosome. In males it is XY and in females it is XX.

Question. Define heredity.
Answer : Heredity deals with the inheritance of characters from one generation to the next.

Question. What are homologous organs? Explain with an example.
Answer : Homologous organs are those organs in different plants or animals which have the same basic structural design and origin but may have different functions. Example., hand of human and fore-limb of frog.

Question. What are analogous organs? Explain with an example.
Answer : Analogous organs have the same function but have different structural design and origin. For example, wings of birds and insects have the same function but have different structural design and origin.

Question. State the importance of variations.
Answer : Variations are the differences in the characters among the individuals of a species. Variations enable the organisms to adapt themselves in the changing environmental conditions. Variations form the raw materials for evolution and formation of new species.

Question. What is evolution?
Answer : Evolution is the sequence of gradual changes which take place in living organisms over millions of years to give rise to new species.

Question. What type of reproduction gives rise to more number of successful variations?
Answer : Sexual reproduction.

Question. Which of the following are homologous and analogous organs?
(a) Wings of birds and insects.
(b) Flippers of whale and fins of fish.
(c) Flippers of whale and wings of bat.
(d) Our teeth and elephants tusks.
(e) Potato and runners of grass.
Answer : (a) — Analogous organs
(b) — Analogous organs
(c) — Homologous organs
(d) — Homologous organs
(e) — Homologous orgAnswer :

Question. How do traits or characters get expressed?
Answer : Genes control the expression of a trait or a character in an organism. Genes produces proteins. The proteins act as enzymes which can directly control a character or help in the formation of a hormone which can control the expression of a particular character.

Question. A true breeding tall plant is crossed with a true breeding short plant. All the offsprings of the F1 generation are tall. Of these two characters which one is dominant and which is recessive.
Answer :

Question. In Q14. on previous page the tall plant of the F1 generation is selfed. What is the outcome or ratio of the F2 progeny?   
Answer : 

Question. Which of the two sperm or egg–decides the sex of the child?
Answer : The sperm decides the sex of the child.

Question. How is the sex of the child determined in human beings?
Answer : Human beings have 23 pairs of chromosomes. 22 pairs are autosomes and the 23rd pair is the sex chromosome. The males have XY and the females have XX. All the gametes formed in the females are of one type i.e., X. In males there are two types of sperms that are formed –X and Y. If the sperms having X fertilizes with the egg the zygote formed is XX. This will form female child. If the sperm having Y fertilizes with the egg then the zygote formed is XY and the offspring will be male child. So basically it’s the male gametes that decide the sex of the unborn child.

Question. What is genetic drift?
Answer : Accidents in small populations can change the frequency of some genes in a population even if they give no survival advantage. This is genetic drift, which provides diversity without any adaptations. So, it is the random change in the frequency of alleles in a population over successive generation.

Question. What is a trait?
Answer : A characteristics feature is called a trait.

Question. Name two human traits that show variations.
Answer : Colours of eyes and shape of external ears.

Short Answer Type Questions :

Question. What is meant by the term speciation? List four factors which could lead to speciation.
Answer: Speciation is the evolution of reproductive isolation among once interbreeding population.
Factors which can lead to speciation are:
1. Genetic drift: Over generations, genetic drift may accumulate which leads to speciation.
2. Natural selection: Natural selection may work differently in different location which may give rise to speciation.
3. Severe DNA change.
4. A variation may occur which does not allow sexual act between two groups.

Question. A blue colour flower plant denoted by BB is cross bred with that of white colour flower plant denoted by bb.
(a) State the colour of flower you would expect in their F1 generation plants.
(b) What must be the percentage of white flower plants in F₂ generation if flowers of F₁ plants are self-pollinated?
(c) State the expected ratio of the genotypes BB and Bb in the F₂ progeny. 
Answer:

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

Wings of a bird and wings of a bat are analogous organs as they have different basic structural design but have similar appearance and perform similar functions.

Question. Define the term ‘evolution’. “Evolution cannot be equated with progress”. Justify this statement.
Answer: Evolution is the sequence of gradual change which takes place in primitive organisms over millions of years and new organisms are formed. Evolution cannot be equated to progress from lower forms to higher forms. It seems to have given rise to more complex body designs even while the simpler body designs continue to flourish. For example, human beings have not evolved from chimpanzees, but both have common ancestor.

Question. If we cross pure-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant we will get pea plants of F₁ generation. If we now self-cross the pea plant of F₂ generation, then we obtain pea plants of F₂ generation.
(a) What do the plants of F₂ generation look like?
(b) State the ratio of tall plants to dwarf plants in F2 generation.
(c) State the type of plants not found in F₂ generation but appeared in F₂ generation, mentioning the reason for the same.
Answer: (a) All plants of F₁ generation will be tall plants.
(b) 3:1
(c) Dwarf trait is recessive trait which was not expressed in the F₁ generation, the recessive trait gets expressed in the F₂ generation after self pollination.

Question. Give one example each of characters that are inherited and the ones that are acquired in humans. Mention the difference between the inherited and the acquired characters.
Answer: Eye colour or hair colour of a person is an example of inherited character whereas, body weight is an example of acquired character.
The basic difference between inherited and acquired character is that inherited character is passed on from parent to offspring and acquired characters are acquired by an individual during his lifetime depending upon his lifestyle.

Question. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer: During sexual reproduction, a female gamete or egg cell fuses with a male gamete or sperm cell which are haploid to form zygote. Zygote is diploid which contains 23 chromosomes from mother and 23 from father. In this way, an equal genetic contribution of male and female parents is ensured in the progeny.

Question. How are fossils formed? Describe, in brief, two methods of determining the age of fossils.
Answer: When organisms die, their bodies decompose due to action of micro organisms. However, sometime the body or at least some parts of the body may be in such an environment that does not let it decompose completely. All such preserved traces of living organisms are called fossils.
The age of fossils can be estimated by the following two methods:
1. If we dig into the earth and start finding fossils, it can be assumed that the fossils closer to the surface are more recent to those found in deeper layers.
2. By detecting the ratios of different isotopes of the same element in the fossil material.

Question. Define ‘evolution’. Describe Darwin’s theory of evolution.
Answer: Evolution is the sequence of gradual changes which take place in the primitive organisms over millions of years and new species are produced. Since, the evolution is of the living organisms, so it is called ‘Organic Evolution’.
Darwin’s theory of Evolution: Charles Robert Darwin gave the theory of evolution in his famous book, ‘The Origin of Species’. The theory of evolution proposed by Darwin is known as ‘The Theory of Natural Selection’. It is also called ‘Darwinism’.
According to Darwin’s theory of evolution:
1. There is natural variation within any population and some individuals have more favourable variations than others.
2. Population remains fairly constant even though all species produce a large number of off springs.
3. This is due to ‘competition’ or struggle for existence between same and different species.
4. The struggle for survival within population eliminates the unfit individuals and those with ‘favourable variations’ survive and pass on these variations to their progeny to continue. This is called natural selection.
5. The favourable variations are accumulated over a long time period leading to the origin of a new species.

Question. Define variation in relation to a species. Why is variation beneficial to the species? 
Answer: Variation refers to the differences in the characters or traits among the individuals of a species.
Variations are beneficial to the species because:
1. They enable the organisms to adapt themselves in changing environment.
2. Variations form the basis of heredity.
3. They form the raw materials for evolution and development of new species.

Question.”An individual cannot pass on to its progeny the experiences of its lifetime.” Justify the statement with the help of an example and also give reason for the same. 
Answer: Experience achieved during the lifetime of an individual does not make any change in the gene of the individual.
For example, if a person reads a book on birds, the knowledge he earns by reading the book does not make any change in the gene, hence, this knowledge will not get automatically transmitted to his next generation. Such a trait is called acquired trait.

Question. State the meaning of inherited traits and acquired traits. Which of the two is not passed on to the next generation? Explain with the help of an example.
Answer: Inherited traits are the characteristics transmitted from parents to their offspring.Acquired traits are characteristics which are developed during the lifetime of an individual.Acquired traits are not passed on to the next generation. For example, if we breed a group of mice, all their progeny will have tails. Now, if the tails of these mice are removed by surgery and allowed to breed, the next generation mice will also have tails. If these tails are also removed and allowed to breed, the progeny of mice will again have tails. Removal of tail by surgery is an acquired trait and do not change the genes of germ cells and hence, are not passed on to the next generation.

Question. What is meant by analogous organs? Taking a suitable example, explain how they support the theory of Organic Evolution. 
Answer: Analogous organs are those organs which I have different basic structural design and developmental origin but have similar appearance and perform similar functions.
Example: The wings of birds and bats look similar but have different design in their structure. They have a common function of flying but their origins are not common. So, birds and bats are not closely related.

Question. Discuss the role of variations in evolution. What is natural selection and genetic drift? 
or
Explain the following:
(a) Speciation (b) Natural Selection
Answer :
a. The members of a population have minor differences among them which is called variations.
b. Two sources of variations are sexual reproduction and environmental factors.
c. Sexual reproduction has greater chances of producing variation.
d. Variations with some advantage has greater chances of surviving, for example, long neck of giraffe.
e. Natural selection and genetic drift lead to formation of new species hence evolution.
Natural Selection: Some variations may have survival advantage hence they happen to gain over others so that they can propagate more than others. Ultimately such variations are selected and propagated among all members of the population.
This is called adaptation of the species which help them to cope well in their surroundings.
In course of time, it could lead to accumulation of adaptation. In geographically separated populations of a species and development of reproductive barrier among them may lead to the formation of a new species.
Genetic Drift: Some variation may not givesurvival advantage to members of population. 
But if by chance other variations are wiped out from populations, the remaining variations get propagated in next generations.

Question. Explain how gene expresses itself in a cell? Why are we somewhat similar to our parents yet not identical to them?
Answer : Genes are functional segments of DNA. They are units of heredity that gets passed on through reproduction
from parents to progeny. It is the blue print of life.
DNA expresses itself through synthesis of proteins.
Proteins make structures in our body and also controls the functioning. In other words cells, tissues, organs and hence a living body expresses the traits inherited as genes/ DNA. Since we inherit the DNA, half from one and half from other parents, hence we somewhat resemble them. At the same time we show mixed traits of both so can not be identical to either of them.

Question. In a pea plant, find the contrasting trait if:
a. the position of flower is terminal.
b. the flower is white in colour.
c. shape of pod is constricted.
Answer :
a. Axial position of flower.
b. Purple colour of flower.
c. Inflated shape.

Question. Some of the traits are acquired while others are inherited. Explain. Which of two will not be passed on to next generation?
Answer : Acquired traits are those features which are present in an organism due to experiences during its life time, for example, swimming and knowledge of a language in human beings.
Inherited traits are those features which are transferred from one generation to the next through DNA or genes present in the cells of a reproductive tissue. For example, colour of eyes and hair in human beings.
Traits acquired during the life time of an individual can not be inherited because the information of this feature is not ingrained in the DNA of individual.

Question. An angiosperm plant having red coloured flowers when crossed with the other having the same colour produced 40 progenies, out of which 30 plants were with red coloured flowers, 10 plants were with white coloured flowers. Find out:
a. What is the possible genotype of parent plants?
b. Which trait is dominant and recessive?
c. What is this cross called as and what is its phenotypic ratio?
Answer :
a. Rr and Rr.
b. Red colour of flowers is the dominant trait while white colour is the recessive trait.
c. Monohybrid cross, phenotypic ratio is 3 : 1.

Question. What is DNA copying? State its importance.
Answer : A process where a DNA molecule produces two similar copies of itself in a reproducing cell.
Importance –
a. It makes possible the transmission of characters
from parents to the next generation.
b. It causes variation in the population.

Question. “We cannot pass on to our progeny the experiences and qualifications earned during our lifetime”. Justify the statement giving reason and examples.
Answer : Acquiring knowledge / skill in one’s lifetime such as learning dance, music, physical fitness or any other suitable example.
Reason:
a. Such characters / experiences acquired during one’s lifetime do not bring any change in the DNA of the reproducing c$ll/germ cell.
b. Only germ cells are responsible for passing on the characters from the parents to the progeny.

Question. a. Insects, octopus and vertebrates all have eyes.
Can we group eyes of these animals together to establish a common evolutionary origin? Justify your answer.
b. “Birds have evolved from reptiles”. State evidence to prove the statement.
Answer :
a. No, the structure of the eye in each of the organisms is different.
b. Fossils of certain dinosaurs/reptiles show imprints of feathers along with their bones but they could not fly presumably using the feathers for insulation.
Later they developed / evolved and adapted feathers for flight, thus becoming the ancestors of present day birds. (OR any other suitable evidence/example)

Question. What are chromosomes ? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.
Answer : Chromosomes – Thread like structures made up of DNA found in the nucleus. The original number of chromosomes becomes half during gamete formation.
Hence, when the gametes combine, the original number of chromosomes gets restored in the progeny.
(or same thing explained in the form of a flow chart).

Question. Explain with an example for each, how the following provides evidences in favour of evolution in organisms:
a. Homologous organs
b. Analogous organs
c. Fossils
Answer :
a. Homologous organs – study of homologous organs suggests that the organs having same structure but performing different functions have evolved from a common ancestor. Example: forelimbs of a frog, lizard, bird and man.
b. Analogous organs – show adoption of organs for common use. Example: wings of butterfly and wings of bat.
c. Fossils – provide the missing links between two species. Example: – Archeopteryx / fossils of some dinosaurs with feathers.

Question. How do Mendel’s experiments show that the a. traits may be dominant or recessive, b. traits are inherited independently?
Answer :
a. When Mendel cross pollinated pure tall pea plants with pure dwarf pea plants, only tall plants were obtained in F1 generation. On self pollinating the F1 progeny, both tall and dwarf plants appeared in F2 generation in the ratio 3 : 1.
Appearance of tall character in both the F1 and F2 shows that it is a dominant character.
The absence of dwarf character in F1 generation and its reappearance in F2 shows dwarfness is the recessive character.
b. When Mendel conducted a dihybrid cross having two sets of characters, he obtained only one set of parental characters in F1 generation whereas in F2 generation he obtained both the set of parental characters now recombined in the ratio of 9 : 3 : 3 : 1.
The appearance of new recombinants in the F2 generation along with parental type shows that traits are inherited independently.

Question. What is the difference between homologous and analogous organs? Give one example each.
Answer :
a. Homologous organs: Structures in animals share a common ancestry. The structure, which has similar basic structure and developmental origin but perform different functions.
For example: Fore limbs in vertebrates.
Homologous organs give an evidence of common ancestory and evolutionary relationship between apparently different species.
b. Analogous organs: Analogous organ are the organs in different organisms which have different basic structure but have similarity in shape and function. However, these organs do not provide an evidence in support with common ancestory, e.g., Wings of bat and bird.

Question. What is speciation? Discuss any two factors that lead to speciation.
Answer : Speciation means creation of new species from pre exiting ones.
The two main factors which could lead to the formation of a new species are natural selection leading to accumulation of adaptation in geographically separated populations of a species and development of reproductive barrier among them.
Complete separation of sub-populations of a spices (Genetic drift) and difference in way of Natural selection in them for many generations results in speciation i.e. formation of new species that cannot interbreed under natural conditions.

Question. a. “Chromosomes are heredity carriers.” Why do we say so?
b. Which vital function is not controlled by autosomes?
Answer :
a. Chromosomes are made-up of DNA. Genes are located on the chromosomes. It is the DNA copy which transfers from both the parents to their offspring. Therefore, chromosomes made-up of DNA and containing genes are said to be the heredity carriers.
b. Sex of the child is not controlled by autosomes.

Question. a. During evolution some changes may have occurred for a reason but proved to be useful for some other purpose. Cite one such example.
b. Has the evolutionary changes took place all of sudden. Elaborate.
Answer :
a. Evolutions of feathers: Functional Advantage: A change that is useful for one property to start with can become useful later for quite a different function. Feathers, for example, can start out as providing insulation in cold weather. But later, they might become useful for flight. In fact, some dinosaurs had feathers, although they could not fly using the feathers. Birds seem to have later adapted the feathers to flight. This, means that birds are very closely related to reptiles, since dinosaurs were reptiles. Birds have evolved from reptile.
b. Evolution changes has not took place all of sudden. Evolution takes place in stages, i.e., bit by bit over generations. Even an intermediate stage, such as a rudimentary eye, can be useful to some extent. This might be enough to give a fitness advantage. In fact, the eye seems to be a very popular adaptation.
Insects have them, so does an octopus, and so do vertebrates. And the structure of the eye in each of these organisms is different – enough for them to have separate evolutionary origins.

Question. a. What function is performed by human arms, forelimbs of dog and forelimbs of whales?
b. Which type of organs are these?
c. Why do we call them so?
Answer :
a. Human arm : holding things Forelimbs of dog :
running Forelimbs of whales : paddles
b. Homologous,
c. Same origin, different functions.

Question. (a) Identify the organism shown in the above figure.

(b) Name one incipient feature selected by the nature.
(c) Mention any other primitive feature of birds.
Answer :
a. Planaria.
b. Eyes which were there only for detecting light.
c. Birds developed feathers for insulation.

Question. (a) Explain giving examples how artificial selection has helped in the formation of newer varieties of cauliflower.
(b) List the steps involved in the formation of new species.
(c) How different races of human beings belong to the same species?
Answer :
a. Formation of newer varieties, e.g., Broccoli, cauliflower, red cabbage, etc. by man.
b. Migration, gene flow, natural selection, new species.
c. Capable of interbreeding among themselves.

Question. (a) Which type of organs are shown in the figure below?

(b) Which type of origin and structure do these organs have?
Answer :
a. These are organs which help in flying (wings of insects and wings of birds).
b. The structure and components of these wings are different. They look similar because they have a common use for flying, but their origins are not common, i.e., they are analogous.

Question. A pea plant with blue colour flower denoted by BB is cross-breed with a pea plant with white flower denoted by ww.
a. What is the expected colour of the flowers in their F1 progeny?
b. What will be the percentage of plants bearing white flower in F₂ generation, when the flowers of F₁ plants were selfed?
c. State the expected ratio of the genotypes BB and Bw in the F₂ progeny.
Answer :
a. F1 generation — blue.
b. 25%
c. BB : Bw = 1 : 2.

Question. How are fossils formed? Describe, in brief, two methods of determining the age of fossils.
Answer : Fossils are formed when dead organisms are not completely decomposed. The organisms may get trapped in resins of tree, lava of volcanoes or hot mud which when hardens, retains the animal’s parts thus, forming fossils.
Two methods of determining the age of fossils:
a. Relative method: By estimating the age of the layer of earth’s crust where the fossil is found.
Fossils near the surface are recent and those in the deeper layers are more ancient.
b. Radio-carbon dating method: By detecting the ratios of different isotopes of carbon in the fossils.
Fossils help in determining the connecting links between various groups and their origin from their primitive ones, e.g., Archaeoptyrx.

Question. Explain the term homologous organ with an example.
Answer : The organs which have similar basic structure and mode of origin but perform different functions in different animals are called homologous organs. E.g., Forelimbs of amphibians, reptiles, birds and mammals.
Homologous organs give an evidence of common ancestory and evolutionary relationship between apparently different species.

Question. How green beetles had colour advantage over red beetles? Explain.
Answer : Green beetle merge with green background of vegetation which give survival advantage to a species from elimination.
a. in the population of beetles, the new variation (green colour) get survival benefit / advantage to green beetles whereas other (red) perishes.
b. It is because of Natural selection — some variations are advantageous for an organism to adapt better in the prevailing conditions of habitat. It makes it easy to obtain food and mating partner by them.
In this manner they are able to propagate more, transmitting their genes to next generation and producing more individuals with similar genetic makeup and phenotype.

Question. “Only variations that confer an advantage of an individual organism will survive in a population”. Comment.
Answer : According to Theory of Natural Selection, some variations are advantageous for an organism to adapt better in the prevailing conditions of habitat.
It makes it easy to obtain food and mating partner by them. In this manner they are able to propagate more, transmitting their genes to next generation and producing more individuals with similar genetic makeup and phenotype.
Though according to Genetic Drift Theory, even those not having a variation that confers an advantage also get to 5 survive but only in a small population. If due to an accident most of the individual with other variation get removed, the organisms with leftover variation get to propagate and survive under such circumstances.
Hence it is wrong to say that only variations that confer an advantage of an individual organism will survive in a population.

Question. Give reasons for the following:
a. Traits acquired during lifetime of an individual are not inherited.
b. All the human beings belong to a single species.
c. Variations keep on accumulating during reproduction and do not disappear in next generation.
Answer :
a. These are acquired traits that do not make any change to the DNA of an organism.
b. Homo sapiens originated in Africa and spread across the globe in stages. The humans with different colours in different regions have come into being as an accident of evolution, so that they could live their lives the best they could. So all belong to the same species.
c. Inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation. So the changes keep on accumulating generations after generations.

Long Answer Type Questions :

Question. Woman are often blamed for bearing daughters. As a student with knowledge in science how will you explain it to your fellow students that the sex of the child is not determined by mother’s genetic contribution?
Ans : Sex of the child is not determined by mother’s genetic contribution. The sex is determined by a specific pair of 7 chromosomes called sex-chromosomes. In female, this pair consists of two similar (homologous) chromosomes denoted as XX. Hence, females produce only one type of gametes (Ova/eggs) each having an ‘X’ chromosome.
Whereas male human being has two different types of sex chromosomes i.e., X, Y (heterologous) having different sizes and shapes. Hence male produces two different kinds of gametes (sperms). Half of them have “X’ chromosome and half have ‘Y’ chromosome.
If a sperm with ‘X’ fuses with the ovum, female child is born and if a sperm with ‘Y’ chromosome fuses with the ovum, male child is bom as shown below in the cross. Therefore, the father’s genes is responsible for the determination of the sex of the child.

Question. Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution.
Answer : Evolution is the formation of more complex organisms from pre-existing simpler organisms over a certain period. Accumulation of variation in genetic material forms the basis of evolutionary processes.
Fossils provide a unique view into the history of life by showing the forms and features of life in the past. Fossils tell us how species have changed across long periods of the Earth’s history.
Importance of fossils in the evolutionary process:
a. Some invertebrates living on the sea bed died and were buried in the sand.
b. More sand was accumulated and formed , sandstone under pressure.
c. After millions of years, dinosaurs living in the area died and their bodies were buried in the mud.
d. The mud got compressed into the rock, just above the rock containing earlier invertebrate fossils.
e. Again millions of years later, the bodies of horselike creatures dying in the area were fossilised in the rocks above the earlier rocks.
f. Much later, because of erosion and water flow, some rocks wore out and exposed the horse-like fossils.

Question. Give five points to show the significance of variations.
Answer :
a. Variations help an organism to get adapted to the changing environment.
b. Variations lead to evolution through natural selection and adaptation.
c. During sudden change in the environment only those variants will make the population of that particular species which can withstand such changes.
d. Variations result in more genetic vigour, i.e., organism emerges as a strong species maintaining its large population.
e. Variations make an organism to be resistance to diseases and environmental fluctuations.

Question. a. “Evolution has occurred in stages.” Justify the statement.
b. Differentiate between eye and eyespots. Which animal possesses eyespots?
Answer :
a. “Evolution has occurred in stages” it is said because the process of evolution has took place over a long period of time. The complex organs are created bit-by-bit over generations.
There was increasing complexity of the organs. For example, eye was present in the earliest organism as eyespot which got developed into a more complex and evolved eye.
Further there are some organs in the human body which are present in the reduced form and do not perform any function, e.g., nictitating membrane of the eye, vermiform appendix, third pair of molars etc.
Similarly, during the course of evolution, some structures changed their function. So we can see that evolution has occurred in stages over a long period of time.
b. Eye is a complex structure made-up of different tissues which can see image as well as light whereas eyespots are merely dot-like structure to sense light.

Question. What is speciation? List four factors that could lead to speciation. Which of these cannot be major factors in the speciation of a self pollinating plant species? Explain.
Answer : Speciation – formation of new species from pre-existing ones.
Factors – (1) Mutations (2) Natural selection (3) Genetic drift (4) Geographical Isolation Geographical isolation cannot be a major factor in the speciation of a self pollinating plant species.
Reason – physical barrier cannot be created in self pollinating plants.