Heredity And Evolution Class 10 Science Important Questions

Please refer to Chapter 9 Heredity And Evolution Class 10 Science Important Questions with solutions provided below. These questions and answers have been provided for Class 10 Science based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 10 Science for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 10.

Class 10 Science Important Questions Heredity And Evolution Chapter 9

Very Short Answer

Question. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Answer: Trait B is likely to have arisen earlier as it occurs in more number.

Question. How do Mendel’s experiments show that traits may be dominant or recessive?
Answer: Mendel took pea plants of two different characters i.e., tall plants and short plants.
The first generation of F₁ progeny formed were all tall. This shows that traits may be either dominant or recessive, there is no way in between traits obtained.

Question. 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: The given information is not enough to tell us which of the traits-blood group A or O – is dominant. In blood heredity, bood type A is always dominant and blood type O is always recessive. Here, father’s Blood group can be I^AI^A (homozygous) or I^Ai (heterozygous) genotypically, whereas that of mother is ii. For daughter to be born with blood group O, she must receive i type gene one each from father and mother.
For this father must have heterozygous I^Ai blood group and mother must have homozygous blood group ii.

Question. What are the different ways in which individuals with a particular trait may increase in a population?
Answer: The ways in which individual with a particular trait may be increased in a population are:
(a) If it can survive in the adverse condition i.e., naturally selected.
(b) It can also be increased by the inheritance.

Question. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer: The small number of tigers are causing a worry for the genetics because if they become extinct then the genes of this species will be lost forever. There will be no scope of again getting this species back to life without their genes.

Question. Will geographical isolation be a major factor in the speciation of a self-pollinating plant species. Why or why not?
Answer: No, geographical isolation cannot be a major factor in the speciation of self-pollinating plant species.
It is because such plants do not depend on other plants for its further reproduction to be carried out.

Question. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer: Two organisms with similar characteristics have genes with similar DNA codes.
Whereas the organisms with different characteristics will have different genes, different DNA structures.

Question. What are fossils? What do they tell us about the process of evolution?
Answer: Preserved traces of living or dead organisms on solid hard surface is called fossil.
Fossils help us to know the evolution. If a fossil is found closer to the surface of earth, then it is more recent in origin than the fossils we find in deeper layers.
Fossils, like Archaeopteryx, help us to find evolutionary relation between organisms.

Question. In evolutionary terms, we can say which among bacteria, spiders, fish and chimpanzees have a better body design? Why or why not?
Ans. Evolution shows that body design changed from simple to complex. Hence, bacteria has the simplest body design and chimpanzee has the most complex and better body design.

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. All the variations in a species do not have equal chances of survival. Why?
Answer : Some variations are caused by environmental changes and they do not bring out any change in DNA.
Therefore, all the variations do not have equal chances of survival.

Question. A Mendelian experiment consisted of breeding pea plants bearing violet flowers with pea plants bearing white flowers. What will be the result in Fj progeny?
Answer : All will bear violet flowers.

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

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. 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 indication do we get by reappearance of dwarf plant in F₂ generation?
Answer : After obtaining progeny in F₂ generation in a dihybrid cross, Mendel concluded that when two pairs of traits are combined in a hybrid, one pair of character segregates independently of the other pair of character.

Question. How many pairs of chromosomes are present in human beings?
Answer : 23 pairs.

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. An organism which is a worm, has very simple ‘eyes’, that are really eye spots which detect light. Name that organism.
Answer : Planaria.

Question. Why is it that asexual reproduction produces exact copies but sometimes minor variations are also seen in next progeny?
Answer : Since no biochemical reaction is reliable, therefore, in copying of DNA, it may cause slight difference which causes these variations.

Question. How can the chromosomes be identified?
Answer : In human beings, the individual chromosomes are identified by their lengths, position of centromere and banding pattern on staining.

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. A normal baby girl receives her X chromosome from whom : mother, father, both mother and father or either from mother or father?
Answer : 
From both mother and father. 

Question. No two individuals are absolutely alike in a population. Why?
Answer : All individuals have different kind of DNA. So all individuals are not alike to each other.

Question. What is a gene?
Answer : It is a functional piece of DNA that is responsible for expression of a trait in the organisms.

Question. Write the sex of the baby that inherits Y-chromosomes from the father.
Answer : Male.

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

Question: Name the information source for making proteins in the cells. 
Answer: Deoxyribonucleic acid (DNA) present in the chromosomes of cell nucleus is the information source for making proteins. 

Question: What is heredity? 
Answer: The inheritance of characters (or traits) from the parents to their offsprings is called heredity.

Question: Why is the progeny always tall when a tall pea plant is crossed with a short pea plant?
Answer: When a tall pea plant is crossed with a short pea plant, the resultant progeny is always tall because tall is dominant trait and short is recessive trait. Therefore, dominant trait expresses itself in the progeny.

Question: What is a gene?
Answer: A gene is a unit of DNA on a chromosome which governs the synthesis of particular protein that controls specific characteristics (or traits) of an organism.

Short Answer:

Question: Why is variation beneficial for the species, but not necessarily for the individual?
Answer: Due to presence of variation, few individuals in population may survive under extreme conditions such as change in temperature, water level, etc. Due to drastic change in niche, population except few individuals with variations can be wiped out.This inbuilt tende ncy for variation is the basis of evolution and over time, such variations are useful for the survival of the species.

Question: Define variation in relation to a species. Why is variation beneficial in the species?
Answer: The differences in the traits or characters shown by the individuals of a species are referred to as variations. Variations appear during reproduction whether organisms multiply asexually or sexually.
Minor variations arise during asexual reproduction due to small inaccuracies in DNA copying. Sexual reproduction however, generates greater variations because of the following reasons:
(i) Chance separation of chromosomes during gamete formation (gametogenesis).
(ii) Crossing over during meiosis.
(iii) Chance coming together of chromosomes during fertilisation.
(iv) Mutations, i.e., alterations in the genetic material. Some variations among individuals of a species are favourable and helpful in better survival.
Depending upon the nature of variations, different individuals would have different kinds of advantages. For example, bacteria that can withstand heat will survive better in a heat wave than others.

Question: What are fossils? What do they tell about the process of evolution?
Answer: Fossils are the remains or impressions of the dead animals and plants that lived in the remote past.The fossils provide evidence for evolution.
For example, a fossil bird called Archaeopteryx have characters of both reptiles and birds. It had feathers, fused bones and beak which are exclusive characters of birds and had teeth in the jaws, claws on fingers, a long tail, etc like reptiles.Thus, Archaeopteryx is a connecting link between the reptiles and birds, and hence suggests that the birds have evolved from the reptiles through the process of continuous evolution.

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 : 

	Acquired Trait	Inherited Trait
1.	Experiences of an individual during its lifetime.	Genetically inherited
2.	It cannot be passed on from one generation to the next.	They can be passed on from one generation to the next.
3.	Example: power to lift weights and reading French	Example: Eye colour or height

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. 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. Tails of some mice were amputated and they were allowed to breed. The mice that were produced also had their tails amputated and it was repeated for many generations. What is the reason of tail appearing again and again?
Answer : Such traits are acquired traits. Traits acquired during the life-time of an individual are not inherited as these changes are not in the genes of reproductive tissues.
The changes in the non-reproductive tissues cannot be passed on to the DNA of the germ cells, hence such acquired changes are not inherited by the progeny.
Example: tailless mice (if tail is removed by surgery)cannot produce tailless progeny.

Question. a. “Recent fossils are found closer to the earth’s surface”. Comment on the statement stating reason.
b. List two factors which could lead to the rise of new species.
Answer : 
a. This statement is correct as the fossils found closer to the surface of earth are more recent and those found in deeper layers are older ones.
b. Natural selection and genetic drift.

Question. “Experience of an individual during its lifetime cannot be passed on its progeny and cannot direct evolution”.
Justify this statement giving an example.
Answer : Since acquired characters are not inherited over generations. Change in non-reproductive tissues cannot be passed on to the DNA of the germ cells.

Question. What are sex chromosomes? Which sex chromosomes are found in male and female human beings? State the chromosome responsible for the development of male child in human beings?
Answer : Sex chromosomes are set of chromosomes present in human beings which help in sex determination.
XX and XY.
Y chromosome.

Question. How are fossil studies important in working out evolutionary relationships. How would the age of fossils be determined?
Answer : Fossils are impressions of the body/ body parts or the remains of organisms living in the past, which got preserved in sediments of earth. Any remains of an organism that has been preserved in the earth’s crust.
Study of fossils helps in working out evolutionary relationships. Age of fossils can be determined by time dating using isotopes of carbon (carbon dating).

Question. A tall pea plant was crossed with a dwarf one. F₁ generation was allowed to self pollinate and F₂ generation was also obtained.
Answer the following questions:
a. What would be the phenotype of plants in F₁ generation?
b. What would be the phenotypic ratio in F₂ generation?
c. Give reason for your observation in F₁ generation.
Answer : 
a. all tall
b. 3:1
c. Reason: The tall trait of pea plant is dominant trait over short trait, a recessive trait.

Question. What is a dominant trait with respect to height in pea plant. Give any two examples.
Answer : Characters/Traits like ‘T’ are called dominant trait (because it express itself) ‘t’ are recessive trait
(because it remains supressed). 

Character	Dominant Trait	Recessive Trait
Seed shape	Round	Wrinkled
Pod shape	Inflated	Constricted
Pod colour	Green	Yellow
Height of plant	Tall	Dwarf

Question. Variations are important for the survival of species overtime. Justify this statement with reasons.
Answer : 
a. It causes adaptations,
b. It promotes 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 violet pea plant [VV] was crossed with a white one[vv]. F₁ generation was allowed to self pollinate and F₂ generation was also obtained,
Answer the following questions:
a. What would be the phenotype of plants i white flowers in F₂ generation?
c. What would be the ratio of vv: Vv in F₂ generation.
Answer : a. all violet flowers
b. 25%
c. 1 : 2.

Question. a. Do eyes of octopus, insect and human show relation in their evolutionary process?
b. How can we say that birds have evolved from reptiles?
Answer :
a. No, eyes of these animals do not show any evolutionary relationship as they are analogous organs.
b. The presence of feathers both in dinosaurs and birds indicate birds have evolved from reptiles.
Some organs may be adapted to perform new functions during evolution, e.g., feathers which were meant for providing insulation in cold weather, slowly became adapted for flight. Hence birds are closely related to reptile as dinosaurs had feathers, though could not fly.

Question. From the set of figures given below, make a pair of homologous and analogous organs each and give one reason in case of both, to justify your answer. 

Answer : Organs:
a. Bird wing and Bat wing – Analogous organs.
Structures are different but functions are same.
b. Human forelimb and Bird wing — Homologous organs.
Structure are same but functions are different.

Question. Why do human beings look different from each other? What do you mean by species?
Answer : Human beings are sexually reproducing organisms.
Genetic recombination occurs during gamete formation in the sex organs followed by union of two gametes coming from two parents with different genetic combination. Thus it ensures more diversity in characteristics in terms of colour, size, and looks.
Inspite of this, they are able to reproduce among themselves to produce fertile offsprings. A species is a group of individuals which have some common characters and they are able to reproduce among themselves to produce fertile offsprings.

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: “Only variations that confer an advantage to an individual organism will survive in a population.” Justify this statement.
Answer: Variations are the structural, functional or behavioural changes from the normal characters developed in the living organisms. Inheritable variations participate in evolution. According to Darwin, natural selection sorts out individuals with favourable variations. Such organism will survive, reproduce more and thus, will leave more progenies. Hence, useful variations get established in nature.

Question: How did Mendel’s experiments show that different traits are inherited independently? Explain.
Answer: In a dihybrid cross given by Mendel, it was observed that when two pairs of traits or characters were considered, each trait expressed independent of the other. us, Mendel was able to propose the Law of Independent Assortment which says about independent inheritance of traits. This could be explained clearly from the given cross: 

F₂ generation ratio : Round-yellow = 9, Roundgreen = 3 Wrinkled-yellow = 3; Wrinkled-green =1

Question: How did Mendel explain that it is possible that a trait is inherited but not expressed in an organism?
Answer: Mendel first selected two pure line plants. He then crossed such plants having contrasting characters. In the F₁ generation, he observed that only one of the two contrasting character appeared, he called it dominant and the one which does not get expressed in F₁ was recessive. He later selfed the F₁ plants and observed that both the traits appear but in a definite proportion. It can be explained by the following cross :

This is how Mendel explained that a trait may be inherited but not expressed in the plant.

Question: List two difierences in tabular form between dominant trait and recessive traits. What
percentage/proportion of the plants in the F₂ generation/progeny were round, in Mendel’s cross between round and wrinkled pea plants?
Answer: Difierences between dominant traits and recessive trait are given below:

Out of total 4 genotypes possible in F₂ generation 31 genotypes result in phenotypic expression of round seeds. So, the percentage of plants with round seeds will be 75%. is can be illustrated as follows:

Question: In one of his experiments with pea plants Mendel observed that when a pure tall pea plant is crossed with a pure dwarf pea plant, in the First generation, F₁ only tall plants appear.
(a) What happens to the traits of the dwarf plants in this case?
(b) When the F₁ generation plants were selffertilised, he observed that in the plants of second generation, F₂ both tall plants and dwarf plants were present. Why it happened? 
Answer: (a) Mendel’s monohybrid cross indicated that out of two contrasting traits only one appears in the progeny of first generation.this implies that the trait which appears in F₁ generation is dominant and the trait which does not express is recessive. We can also say that gene controlling thedominant trait is dominant gene or allele and gene controlling the recessive trait is recessive gene or allele.
In F₁ progeny although the dominant trait is expressed but genes for both dominant and
recessive traits are present in a heterozygous condition.The recessive trait has a chance to express in next generation only if recessive genes come in homozygous condition. This can be illustrated by the given cross:

(b) Appearance of suppressed recessive trait in individuals of F₂ generation in Mendelian cross indicates that the characters of recessive traits are not lost even when they are not expressed. When the F₁ generation plants were allowed to selffertilise, both the parental traits were expressed in definite proportion in F₂ generation.This could be explained by the given cross by selfing the gametes obtained in F₁ generation. 

Question: (a) Mendel crossed tall pea plants with dwarf pea plants in his experiment. Write his observations giving reasons on the F₁ and F₂ generations.
(b) List any two contrasting characters other than height that Mendel used in his experiments in pea plants.
Answer: (a) The possible cross of Mendel’s experiment is : 

Hence, tall (T) is dominant whereas dwarf (t) is recessive. In F₁ generation, only dominant trait expresses itself, whereas recessive trait gets suppressed. In F₂ generation, both traits, i.e., dominant and recessive express themselves . In this way, Mendel’s experiment showed that the traits (tall and dwarf) are inherited independently.
(b) The two contrasting characters other than height that Mendel used in his experiment in pea plants are round/wrinkled seeds and violet/white flowers.

Question: The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it”. Justify this statement with the help of flow chart showing determination of sex of a new born.
Answer: Sex is determined at the time of fertilisation when male and female gametes fuse. Male produces two types of gametes, i.e., having X or Y chromosome and female produces same type of gametes containing X chromosomes. The sex of the child is determined at the time of fertilisation when male and female gametes fuse to form zygote.
If a sperm (male gamete) carrying X chromosome fertilises an egg or ovum (female amete) carrying X chromosome, then the offspring will be a girl (female). This is because the offspring will have XX combination of sex chromosomes.
If a sperm (male gamete) carrying Y chromosome fertilises an egg or ovum (female gamete) which has X chromosome, then the offspring will be a boy (male). This is because the offspring will have XY combination of sex chromosomes.
Therefore, there are 50% chance of a male child and 50% chance of a female child.

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: (a) The colour of the flower in F₁ generation will be blue.
(b) If the flowers of F₁ generations are self pollinated, then the percentage of white flowers in F₂ generation must be 25%.
(c) THe expected ratio of the genotypes BB and Bb in the F₂ generation progeny is 1 : 2.
The above results could be depicted by the given cross:

Question: If we cross pure-breed tall (dominant) pea plant with pure-breed dwarf (recessive) pea plant we will get pea plants of F₁ generation.
If we now self-cross the pea plant of F₁ generation, then we obtain pea plants of F₂ generation.
(a) What do the plants of F₁ generation look like?
(b) State the ratio of tall plants to dwarf plants in F₂ generation.
(c) State the type of plants not found inF₁ generation but appeared in F₂ generation, mentioning the reason for the same.
Answer: (a) The plants of F₁ generation will be all tall plants.
(b) The ratio of tall plants to dwarf plants in F₂ generation is 3 : 1.
(c) Dwarf plants are not found in F₁ generation but appeared in F₂ generation. is is so because in F₁ generation only dominant trait (tall) expresses itself and recessive trait (dwarf) gets suppressed. The dwarf plants appeared in F₂ generation, because the traits whether dominant or recessive are independently inherited. In others words, a single copy of (T) is enough to make the plant tall, while both copies have to be (t) for the plant to be dwarf.

Question: How is the sex of the child fixed during the fertilisation step in human beings? Explain.
Answer: Human beings have 23 pairs chromosomes (22 pairs of autosomes +1 pair of sex chromosome).
A male has one X chromosome and one Y chromosome whereas a female has two X
chromosomes. Sex of a child depends on the two conditions which takes place during fertilisation.
The two conditions are given below:
(i) If a sperm carrying X chromosome fertilises an ovum which carries X chromosome, then the child born will be girl.
(ii) If a sperm carrying Y chromosome fertilises an ovum which carries X chromosome, then the child born will be a boy.

Question: “A trait may be inherited, but may not be expressed”. Justify this statement with the help of a suitable example.
Answer: A trait may be inherited but may not beexpressed, this could be explained by the given example. When a tall pea plant was crossed with adwarf pea plant, then F₁ generation plants were all tall. When F₁ plants were selfed, then F₂ generation plants were both tall and dwarf.This shows that the F₁ plants had inherited both the parental traits but did not express dwarfness or recessive trait in the presence of the trait for tallness or dominant trait. This could be explained by the given cross :

Question: With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of sex of a child? 
Answer: Sex is determined at the time of fertilisation when male and female gametes fuse. Male produces two types of gametes, i.e., having X or Y chromosome and female produces same type of gametes containing X chromosomes. The sex of the child is determined at the time of fertilisation when male and female gametes fuse to form zygote.
If a sperm (male gamete) carrying X chromosome fertilises an egg or ovum (female gamete) carrying X chromosome, then the offspring will be a girl (female). THis is because the offspring will have XX combination of sex chromosomes.
If a sperm (male gamete) carrying Y chromosome fertilises an egg or ovum (female gamete) which has X chromosome, then the offspring will be a boy (male). This is because the offspring will have XY combination of sex chromosomes.
Therefore, there are 50% chance of a male child and 50% chance of a female child.

Question: Distinguish between the acquired traits and the inherited traits in tabular form, giving one example for each. 
Answer: Difierences between the inherited traits and acquired traits are as follows : 

Question: Explain how the sex of the child is determined at the time of conception in human beings.
Answer: Human beings have 23 pairs chromosomes (22 pairs of autosomes +1 pair of sex chromosome).
A male has one X chromosome and one Y chromosome whereas a female has two X
chromosomes. Sex of a child depends on the two conditions which takes place during fertilisation.
The two conditions are given below:
(i) If a sperm carrying X chromosome fertilises an ovum which carries X chromosome, then the child born will be girl.
(ii) If a sperm carrying Y chromosome fertilises an ovum which carries X chromosome, then the child born will be a boy.

Question: List three distinguishing features, in tabular form, between acquired traits and the inherited traits.
Answer: Differences between the inherited traits and acquired traits are as follows :

Question:“Two areas of study namely ‘evolution’ and ‘classification’ are interlinked”. Justify this statement.
Answer: Evolution is the process by which newer types of organisms are developed from the pre-existing ones through modifications. Classification is the arrangement of organisms into a series of groups based on physiological, biological, anatomical or other relationships. All systems of classification are hierarchial. The more closely two species are related, the more recently they have a common ancestor. Classification of organisms necessarily involves organising them in difierent groups, based on the similarities and difierences of
characteristics. It helps in the recognisation of the basic arrangement of a hierarchical structure among diverse species. It facilitates studies or research of wide variety associated with organisms effortlessly. Thus, classification of species is infact a reflection of their evolutionary relationship or we can say that evolution and classification are interlinked.

Long Answer:

Question: Define evolution. How does it occur? Describe how fossils provide us evidences in support of evolution.
Answer:  Evolution is the sequence of gradual changes, from simple life forms to complex life form, i.e., from primitive organisms that lived over millions of years ago to new organisms that exist today. Evolution occurs by changes, improvement and modification of simple life forms. Fossils are the remains or impressions of organisms that lived in the remote past. Fossils provide the evidence that the present animal have originated from previously existing ones through the process of continuous evolution. Fossils can be used to reconstruct evolutionary history of an organism.
The distribution pattern of fossils shows that the ancient fossils present in the bottom rocks are simple, while the most recent fossils found in the upper strata are more highly evolved. It means fossils form and become more and more complex as we proceed from earliest to recent rocks. It gives us an idea of time in history when different species were formed or became extinct. Thus, fossils provide us evidences in support of evolution.

Question: What are fossils? How are they formed? List two methods of determining the age of fossils. Explain in brief the importance of fossils in deciding the evolutionary relationships
Answer: When organisms like plants or animals die, their bodies get decomposed by the action of microorganisms in the presence of oxygen, moisture, etc. Sometimes the conditions in the environment are such (like absence of oxygen, moisture, etc.), which do not let the body of the organism to get decompose completely. It is the body (or body part) of an organism which we get as fossil on digging the earth. In many cases the
so parts of the organisms get decomposed and we get skeleton of hard parts (like teeth, bones, etc.) as fossil. Even the soft parts of the plants and animals (which usually decompose quickly) are sometimes preserved as fossils in the form of their impressions inside the rocks. For example, if a dead leaf gets caught in mud, it will not decompose
quickly. The mud around the leaf will set around it as a mould, gradually harden to form a rock and retain the impression of the leaf. This forms a leaf fossil which can be dug out from the earth a after a long time period.
The age of fossils can be determined in two ways as given below :
(i) By the relative method : When we dig into the earth, we find fossils at difierent depths. Te fossils which wefind in layers closer to the surface of the earth are more recent and those fossils which are found in deeper layers are older; whereas the fossils found in the deepest layers of earth are the oldest ones.
(ii) Carbon dating method : When a living object dies and forms fossil, its carbon-14 radioactivity goes on decreasing gradually. By this method, the age of fossils is found by comparing the carbon-14 radioactivity le in fossils with the carbon-14 radioactivity present in living objects today.