CESSF L U UT - Universal Tutorials€¦ · Chapter 09: Heredity and Evolution 3 Volume 2 of 2 Universal Tutorials – X CBSE – Science 3 Every organism reproduces either sexually

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Entrance

X - CBSE - SCIENCEVOLUME 2

Table of Contents

Volume 2 of 2 Universal Tutorials – X CBSE – Science

Table of Contents CHAPTER 09: HEREDITY AND EVOLUTION .......................................................... 1

CHAPTER MAP: ........................................................................................................................................... 1 A) INTRODUCTION: ...................................................................................................................................... 1 B) ACCUMULATION OF VARIATION DURING REPRODUCTION: ......................................................................... 2 C) HEREDITY: ............................................................................................................................................. 3

Inherited Traits: ................................................................................................................................. 3 The Basic Similarities (In Human): ............................................................................................... 3 Differences: .................................................................................................................................. 3

Mendel’s Contribution: ....................................................................................................................... 3 Mendel’s Laws of Heredity: .......................................................................................................... 4

Expression of Traits: .......................................................................................................................... 6 Sex Determination: ............................................................................................................................ 7

Sex Determination in Humans: .................................................................................................... 7 D) EVOLUTION: ........................................................................................................................................... 7

Variations in Beetle Population: ........................................................................................................ 8 Acquired and Inherited Traits: ........................................................................................................... 9

Origin of life on earth: ................................................................................................................... 9 E) SPECIATION:......................................................................................................................................... 10

Geographical Isolation: .............................................................................................................. 10 Genetic Drift: .............................................................................................................................. 10 Natural Selection: ....................................................................................................................... 10 Reproductive Isolation: ............................................................................................................... 11 Factors Causing Speciation ....................................................................................................... 11

F) EVOLUTION AND CLASSIFICATION: ......................................................................................................... 11 Classification: ............................................................................................................................. 12

Tracing Evolutionary Relationships: ................................................................................................ 12 Fossils: ....................................................................................................................................... 13

Evolution by Stages: ........................................................................................................................ 13 Artificial Selection: ...................................................................................................................... 13

G) EVOLUTION CANNOT BE EQUATED WITH PROGRESS: .............................................................................. 14 Human Evolution: ............................................................................................................................ 14

Diversity in Human Forms: ......................................................................................................... 15 Origin of Human beings: (Africa) ................................................................................................ 15

PREVIOUS BOARD QUESTIONS: ................................................................................................................. 15 NCERT EXERCISE: ................................................................................................................................... 18 REVIEW EXERCISE: ................................................................................................................................... 22 WORKSHEET ............................................................................................................................................. 23

CHAPTER 10: LIGHT – REFLECTION AND REFRACTION .................................. 25

CHAPTER MAP: ......................................................................................................................................... 25 A) LIGHT: ................................................................................................................................................. 25

Introduction: ..................................................................................................................................... 25 Optical media: ............................................................................................................................ 26

Reflection of Light: ........................................................................................................................... 26 Characteristics of the image formed by a plane mirror: .................................................................. 27

B) REFLECTION AT SPHERICAL SURFACES: ................................................................................................ 27 Types of spherical mirrors: .............................................................................................................. 27 Terms and definitions: ..................................................................................................................... 28 Mirror Formula: ................................................................................................................................ 29

SOLVED EXAMPLES:.................................................................................................................................. 32

Universal Tutorials – X CBSE – Science Volume 2 of 2

REVIEW QUESTIONS: ................................................................................................................................. 34 REFRACTION OF LIGHT: ............................................................................................................................. 36

Introduction: ..................................................................................................................................... 36 Refraction through a Glass slab: ..................................................................................................... 37

REFRACTION THROUGH LENSES: ................................................................................................................ 38 Image formed by concave and convex lenses: ............................................................................... 39 Sign conventions (Lenses): ............................................................................................................. 40 Lens Formula: ................................................................................................................................. 40 Power of a Lens (P): ........................................................................................................................ 41

APPENDIX: ................................................................................................................................................ 41 PREVIOUS BOARD QUESTIONS: ................................................................................................................. 45 NCERT QUESTIONS: ................................................................................................................................ 52 SOLVED EXAMPLES:.................................................................................................................................. 54 REVIEW QUESTIONS: ................................................................................................................................. 56 WORK SHEET: .......................................................................................................................................... 58

CHAPTER 11: THE HUMAN EYE AND THE COLOURFUL WORLD .................... 77

CHAPTER MAP: ......................................................................................................................................... 77 A) EYE: .................................................................................................................................................... 77

Least distance of distinct vision, near point and far point .......................................................... 78 Defects of vision: ............................................................................................................................. 78

Myopia or short-sightedness: ..................................................................................................... 78 Hypermetropia or long-sightedness: .......................................................................................... 79 Presbyopia: ................................................................................................................................ 79

Prism: .............................................................................................................................................. 79 B) DISPERSION OF LIGHT: ......................................................................................................................... 80

Atmospheric Refraction: .................................................................................................................. 81 Twinkling of stars........................................................................................................................ 81 Advanced sunrise and delayed sunset ...................................................................................... 81 Scattering of Light (Blue colour of the sky): ............................................................................... 82

Red colour of sky: ............................................................................................................................ 82 Tyndall effect: .................................................................................................................................. 83

APPENDIX: ................................................................................................................................................ 83 PREVIOUS BOARD QUESTIONS: ................................................................................................................. 85 NCERT QUESTIONS: ................................................................................................................................ 86 REVIEW QUESTIONS: ................................................................................................................................. 87 WORK SHEET: .......................................................................................................................................... 89

CHAPTER 12: ELECTRICITY ................................................................................. 95

CHAPTER MAP: ......................................................................................................................................... 95 A) INTRODUCTION: .................................................................................................................................... 95 B) CURRENT ELECTRICITY: ........................................................................................................................ 96

Classification of Substances: .......................................................................................................... 96 Electric Potential and Potential Difference: ..................................................................................... 96

C) ELECTRIC CIRCUITS: ............................................................................................................................. 97 D) OHM’S LAW: ........................................................................................................................................ 98

Verification of Ohm’s Law: ......................................................................................................... 98 E) RESISTANCE (R): .................................................................................................................................. 99

Concept of resistance: ..................................................................................................................... 99 Combination of Resistors: ............................................................................................................. 100

Resistors in Series: .................................................................................................................. 100 Resistors in Parallel: ................................................................................................................ 101

Table of Contents


F) HEATING EFFECT OF ELECTRIC CURRENT: ........................................................................................... 101 Joule’s law for heating effect of electric current: ........................................................................... 101 Applications of heating effect of current: ....................................................................................... 102

Electric bulb: ............................................................................................................................. 102 Electric Fuse: ............................................................................................................................ 102

Electric Power: .............................................................................................................................. 103 Useful Conversions: ................................................................................................................. 103

APPENDIX: .............................................................................................................................................. 103 PREVIOUS BOARD QUESTIONS: ............................................................................................................... 106 QUESTIONS BASED ON PRACTICAL EXPERIMENTS FROM DIFFERENT SETS. .................................................. 116 NCERT QUESTIONS: .............................................................................................................................. 121 SOLVED EXAMPLES:................................................................................................................................ 123 REVIEW QUESTIONS: ............................................................................................................................... 126 ANSWERS TO UNSOLVED EXERCISES: ...................................................................................................... 131 ANSWERS TO QUESTIONS BASED ON PRACTICAL EXPERIMENTS: ............................................... 133 WORK SHEET: ........................................................................................................................................ 134

CHAPTER 13: MAGNETIC EFFECTS OF ELECTRIC CURRENT ....................... 139

CHAPTER MAP: ....................................................................................................................................... 139 A) INTRODUCTION: .................................................................................................................................. 139 B) MAGNETIC EFFECTS OF ELECTRIC CURRENT: ...................................................................................... 140

Oersted’s Experiment: ................................................................................................................... 140 Magnetic field due to a straight wire carrying electric current: ...................................................... 140

Factors affecting the magnetic field produced due to current: ................................................. 141 Magnetic field due to a Solenoid: .................................................................................................. 141

C) EFFECTS OF EXTERNAL FIELD ON A WIRE CARRYING CURRENT: ............................................................ 142 Fleming’s Left hand Rule: .............................................................................................................. 142 Factors to increase the force: ........................................................................................................ 142

D) ELECTRIC MOTOR: ............................................................................................................................. 143 E) ELECTROMAGNETIC INDUCTION: .......................................................................................................... 143

Fleming’s Right Hand Rule: ........................................................................................................... 144 Factors to increase the strength of induced current: ................................................................ 144

Domestic Electric Circuits: ............................................................................................................. 145 APPENDIX: .............................................................................................................................................. 146 PREVIOUS BOARD QUESTIONS: ............................................................................................................... 149 NCERT QUSESTIONS: ............................................................................................................................ 152 SOLVED EXAMPLES:................................................................................................................................ 154 REVIEW QUESTION: ................................................................................................................................. 154 ANSWERS TO UNSOLVED EXERCISES: ...................................................................................................... 158 WORK SHEET: ........................................................................................................................................ 159

CHAPTER 14: SOURCES OF ENERGY ............................................................... 166

CHAPTER MAP: ....................................................................................................................................... 166 A) INTRODUCTION: .................................................................................................................................. 166

A good source of energy: .............................................................................................................. 167 Conventional Sources of Energy: ............................................................................................. 167

B) FOSSIL FUELS: ................................................................................................................................... 167 Disadvantages: ......................................................................................................................... 167 Pollution Control: ...................................................................................................................... 168

C) TRADITIONAL SOURCES OF ENERGY: ................................................................................................... 168 Thermal Power Plant: .................................................................................................................... 168 Hydro Power Plants: ...................................................................................................................... 168

Universal Tutorials – X CBSE – Science Volume 2 of 2

D) IMPROVEMENTS IN TECHNOLOGY FOR USING CONVENTIONAL SOURCES OF ENERGY: ............................ 169 Bio-Mass: ....................................................................................................................................... 169

Bio gas and bio gas plant: ........................................................................................................ 169 Wind Energy: ................................................................................................................................. 170

E) NON–CONVENTIONAL SOURCES: ......................................................................................................... 171 Solar Energy: ............................................................................................................................ 171

F) ENERGY FROM SEA: ............................................................................................................................ 173 Forms of energy from Sea: ...................................................................................................... 173

Geothermal Energy: ...................................................................................................................... 174 Nuclear Energy: ............................................................................................................................. 174 Environmental Consequences: ..................................................................................................... 175 How long will an energy source last us? ....................................................................................... 175

PREVIOUS BOARD QUESTIONS ................................................................................................................. 175 NCERT QUESTIONS: .............................................................................................................................. 177 REVIEW QUESTION: ................................................................................................................................. 178 APPENDIX: .............................................................................................................................................. 180 ANSWERS TO THE UNSOLVED EXERCISE: ................................................................................................. 182 WORK SHEET: ........................................................................................................................................ 184

CHAPTER 15: OUR ENVIRONMENT ................................................................... 186

CHAPTER MAP: ....................................................................................................................................... 186 A) INTRODUCTION: .................................................................................................................................. 186

Pollution and Pollutants: ................................................................................................................ 186 Classification of Pollutants: ...................................................................................................... 187

B) ECOSYSTEM: ...................................................................................................................................... 187 Components of Ecosystem: .......................................................................................................... 188

Abiotic Components: ................................................................................................................ 188 Biotic Components: .................................................................................................................. 188

Food Chains and Food Webs:....................................................................................................... 190 Food Chain: .............................................................................................................................. 190 Food Web: ................................................................................................................................ 190 Trophic Levels: ......................................................................................................................... 191 Energy Flow: ............................................................................................................................ 191

C) ENVIRONMENTAL PROBLEM: ............................................................................................................... 192 Depletion of Ozone Layer: ............................................................................................................. 192

Effects of Ozone Depletion: ..................................................................................................... 193 Waste Disposal: ............................................................................................................................ 193

PREVIOUS BOARD QUESTIONS: ............................................................................................................... 194 NCERT QUESTIONS: .............................................................................................................................. 196 REVIEW EXERCISE: ................................................................................................................................. 198 WORKSHEET ........................................................................................................................................... 199

CHAPTER 16: MANAGEMENT OF NATURAL RESOURCES ............................. 202

A) INTRODUCTION: .................................................................................................................................. 202 B) REDUCE, RECYCLE, REUSE: ............................................................................................................... 203 C) MANAGEMENT OF RESOURCES: .......................................................................................................... 203

Natural Resources: .................................................................................................................. 203 Resource Planning: .................................................................................................................. 204 Conservation of Resources: ..................................................................................................... 204

D) FOREST AND WILD LIFE: ..................................................................................................................... 205 Forest: ........................................................................................................................................... 205

Conservation of Forests: .......................................................................................................... 206

Table of Contents


Wild Life: ........................................................................................................................................ 206 Conservation of Wild Life: ........................................................................................................ 206

Stakeholders: ................................................................................................................................ 207 Sustainable Management: ............................................................................................................. 208

Chipko Andolan (‘Hug the Trees Movement’): ......................................................................... 208 E) WATER: ............................................................................................................................................. 209

Dams: ............................................................................................................................................ 211 Watershed Management: .............................................................................................................. 211

Rain Water Harvesting: ............................................................................................................ 213 F) COAL AND PETROLEUM: ...................................................................................................................... 213

Management of Fossil Fuels: ................................................................................................... 213 G) OVERVIEW OF NATURAL RESOURCES MANAGEMENT: .......................................................................... 214 PREVIOUS BOARD QUESTIONS: ............................................................................................................... 214 NCERT QUESTIONS: .............................................................................................................................. 215 REVIEW EXERCISE: ................................................................................................................................. 218 WORKSHEET ........................................................................................................................................... 219

MCQ BASED ON PRACTICAL SKILLS ............................................................... 222

Chapter 09: Heredity and Evolution 1

Volume 2 of 2 Universal Tutorials – X CBSE – Science 1

Chapter 09: Heredity and Evolution

Chapter Map:

→ Introduction

→ Accumulation of variation during Reproduction

→ Heredity

→ Inherited Traits

→ Mendel’s Contributions

→ Expression of Traits

→ Sex Determination

→ Evolution

→Variation in Beetle Population

→ Acquired and Inherited Traits

→ Speciation

→ Evolution and Classification

→ Tracing Evolutionary Relationships

→ Evolution by Stages

→ Evolution is not equated with progress

→ Human Evolution

A) Introduction: In asexual reproduction variation are less limited whereas in sexual reproduction distinct variations can be seen among different individuals.

The accumulation of variation in long term gives rise to new species.

Definitions: (Not in syllabus but given for information)

Genetics: It is the study of heredity and variations. It deals with the mechanism of transmission of heredity materials (genes) and their expression from generation to generation.

Gene: Chemically specific segment of DNA which determines the inheritance and expression of a particular character.

Factor or Determiner: It is something which was presumed by Mendel as functional unit of heredity present in the gametes (now called gene) which determines the character of the organism. It was designated by Mendel with letters,e.g. T (tallness), t (dwarfness), R (redness), r (whiteness) etc.

Trait: It is the specific character of a particular species for e.g., colour, length, shape, size of pea plant.

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2 Universal Tutorials – X CBSE – Science Volume 2 of 2

Alleles or Allelomorphs: A pair of contrasting characters or related factors controlling a single trait, e.g. height (tall-T and dwarf-t), colour (red-R and white-r) etc.

Dominant: One of the two contrasting characters of a single trait, which appears first in F1 hybrid.

Recessive: One of the two contrasting characters of a single trait, which is suppressed in F1 hybrid.

Homozygous: An organism with identical ‘determiners or genes; TT, tt or homologous chromosomes.

Heterozygous: An organism with dissimilar “determiners” or genes; Tt, Rr or heterozygous chromosomes.

Pure breed: A homozygous individual formed by the parents with identical characters and breed true to the species atleast for three consecutive generations, e.g. TT (pure tall), tt (pure dwarf).

Hybrid: A heterozygous individual formed by the parents having contrasting characters e.g. Tt (hybrid tall), Rr (hybrid round) etc.

Progeny: Total number of offsprings produced through successive crosses. F1 generation or first filial generation: It is the first generation of hybrid individuals

obtained by crossing homozygous parents with contrasting characters. F2 generation or second filial generation: It is the generation resulting by selfing of

F1 hybrids. Phenotype: External appearance of an individual; tall, dwarf, red, white etc. Genotype: Genetic makeup or constitution of an organism; TT (pure tall), Tt (hybrid

tall), tt (pure dwarf) etc. Offsprings: These are the individuals produced by the parents. Monohybrid ratio: In crossing of two pure individual plants when one pair of

contrasting characters is considered, the phenotypic ratio obtained in F2 generation is called monohybrid ratio.

Dihybrid ratio: In crossing if two pairs of contrasting characters or two alleles are concerned, the phenotypic ratio which one gets in F2 generation is called dihybrid ratio.

Germ cells: The cells which produce gametes by process of cell division are called germ cells.

Somatic cells: These are body cells that don’t take part in reproduction.

B) Accumulation of Variation during Reproduction: Variations are differences between individuals of the same species. Variations are prerequisite and progressive factor in evolution. Without variation there won’t be any evolution.

Inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation.

When this new generation reproduces the second generation will have differences that they inherit from the first generation as well as newly created differences.

Although children resemble their parents and their siblings, no two individuals exactly resemble each other (except identical twins) or there is some degree of variation even within the same progeny. No two organisms, even brothers and sisters look alike because they show differences which has occurred due to inaccuracies in DNA copying.



Every organism reproduces either sexually or asexually to produce offsprings which are similar to their parents. In asexual reproduction variations are less and in sexual reproduction variations are more.

According to law of nature the useful variations are preserved and passed on to their offsprings and promotes the survival of the species.

Depending on the nature of variations different individuals would have different kinds of advantages. For e.g. Bacteria that can withstand heat will survive better in heat wave.

C) Heredity: Heredity is defined as the transmission of characteristics from one generation to the successive generations or resemblances among individuals related by descent.

Heredity information is present in the zygote, which develops into an organism of a particular type. Children resemble their parents or grandparents not due to coincidence but due to inheritance or heredity.

Inherited Traits: All organisms of the world possess common building blocks and life processes indicating that they

have developed from common ancestors. Asexual reproduction preserves the similarities among individuals of a given line of descent.

In sexual reproduction, both similarity and variation are clearly observed even among offspring. Human population shows a great deal of variation. For eg. Free and attached ear lobes are two

variants found in human population.

The Basic Similarities (In Human): Protoplasm is made up of similar types of macromolecules and macromolecules in all the

organisms. Metabolism in same. All organisms take in matter and energy from outside. Organisms maintain homeostasis. All organisms reproduce new individuals of similar kind.

Differences: Although the organisms reproduce similar kind of offspring but lot of differences can be seen in

their character, size, shape of body organ for e.g. son and father may have similar face but the texture of hair may change, eyes might be slightly different.

Mendel’s Contribution: Gregor Johann Mendel (1822–1884) put forth his results about the contrasting characters he

observed in the garden pea plant, (Pisum sativum). His results led him to interpret that these contrasting characters are controlled by “factors”. He considered every character to be a unit controlled by a factor.

Gregor Johann Mendel is also called father of genetics. Johanssen named Mendel’s factors (the carriers of heredity information) as ‘genes’. Discovery of the process of sexual reproduction including gamete formation and fertilisation put

forth the transmission of genetic material for the continuity of life.

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Mendel’s Laws of Heredity: Law of dominance: The law of dominance states that, out of the contrasting characters of a

pair, the one which expresses itself in the F1 generation is called a dominant character and the other which is prevented from expressing itself is called a recessive character.

Law of segregation (Purity of gametes): It states that when a pair of contrasting characters occurs together in a hybrid, they remain together without mixing with each other and segregate during the formation of gametes.

Law of independent assortment: It states that when two parents differing from each other in two or more pairs of contrasting characters are crossed, then the inheritance of one pair of characters is independent of that of the other pair of characters.

Based on his experimental data, Mendel proposed that for every character, there were two factors controlling it. For height of a plant (tall and dwarf), there were two factors controlling the expression whether the plant would be tall or dwarf.

Each character in organism has two contrasting traits eg.:

Dominant × Recessive Tall plants × Dwarf plants

Yellow seeds × Green seeds

Round seeds × Wrinkled seeds

Violet flowers × White flowers

Green pods × Yellow pods

Axial flower × Terminal flower

Inflated pods × Constricted pods

After hybridization (crossing of parents with contrasting traits), the next generation resembled only one parent i.e. only one trait is expressed.

For each of the crosses that Mendel carried out, he found that the F1 hybrids resembled only one parent.

1. Example: (Law of Dominance) TT tt Parent Tall × Dwarf

F1 generation (All heterozygous tall plants)

(selfing F1) Tt × Tt F2 generation TT Tt Tt tt

Homozygous Tall Heterozygous Tall Homozygous Dwarf 1 2 1

Conclusion:

T represents Tall trait and t represent dwarfness

T t

Tt



When a tall plant is crossed with a dwarf plant, the F1 generation shows plant which are Heterozygous Tall. (Tt)

This indicates that both the tallness and shortness traits were inherited in the F1 plants, but only the tallness trait was expressed. Thus, two copies of the trait are inherited in each sexually reproducing organism.

When F1 plants were selfed, the F2 generation showed plants in the ratio 1 : 2 : 1.

Dominant:

An allele that influences the appearance of the phenotype even in the presence of an alternative allele.

Recessive:

An allele that influences the appearance of the phenotype only in the presence of another identical allele.

2) Example: (Law of Segregation) Parents PP × pp (Violet flower) (White flower) Gametes F1 generation heterozygous violet

F2 generation (selfing F1) Pp × Pp PP Pp Pp pp

Homozygous violet Heterozygous violet Homozygous white 1 2 1

Conclusion:

The reappearance of the recessive trait in the F2 generation proves that the factor for white coloured flowers was present in the F1 hybrid and was not contaminated by the dominant factor

Thus, the factors maintain their individuality in F1 generation and segregate during gamete formation.

3) Example: (Law of Independent assortment) This law can be explained by a dihybrid cross (considering two traits at the same time) The Dominant characters chosen was yellow colour and round shape of pea seeds The recessive characters chosen was green colour and wrinkled seeds

P p

Pp

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Tall plant with round seeds and short plant with wrinkled seeds

Parent (RRYY) × (rryy) (Round yellow) (Wrinkled green) Gametes F1 generation (All hybrid round yellow)

F2 (selfing F1) generation RrYy RrYy

Female gametes → RY Ry rY ry

Mal

e ga

met

es

↓

RY RR YY Yellow round

RR Yy Yellow round

Rr YY Yellow round

Rr Yy Yellow round

Ry RR Yy Yellow round

RR yy Green round

Rr Yy Yellow round

Rr yy Green round

rY Rr YY Yellow round

Rr Yy Yellow round

rr YY Yellow wrinkled

rr Yy Yellow wrinkled

ry Rr Yy Yellow round

Rr yy Green round

rr Yy Yellow wrinkled

rr yy Green wrinkled

F2 generation Yellow round–9 Yellow wrinkled–3 Green round–3 Green wrinkled–1

Phenotypic ratio 9:3:3:1

Conclusion:

Yellow and roundness are dominant traits Green and wrinkled are recessive traits Yellow/green trait and the round seed/wrinkled seed trait are independently inherited.

Expression of Traits: Traits are expressed due to Genes. Genes are units of heredity that determine particular traits (e.g. colour of hair, blood group etc.) Each gene is a segment of DNA that carries instructions for making all or part of a specific protein.

E.g. Height of a plant. Plant hormones are responsible to trigger the growth. Plant height can thus depend on the amount

of a particular plant hormone. The amounts of plant hormones depend on efficiency of the enzymes processing it. If this

enzymes work efficient a lot of hormones will be made and the plant will be tall. If the gene for that enzyme has an alternation that make the enzyme less efficient, the amount of

hormone will be less and the plant will be short. Thus, gene controls characteristic or traits.

How do germ cells make a single set of genes from normal two copies? Ans: Each gene set is present as separate independent pieces called chromosome. Thus, each cell

will have two copies of each chromosome one each from the male and female parents.

RY ry

RrYy



Every germ cell will take one chromosome from each pair and these may be either from maternal or paternal origin. When two germ cells combine, they will restore the normal number of chromosomes in the progeny, ensuring the stability of the DNA of the species.

Sex Determination: There are two types of chromosomes in an organism i.e. Sex chromosomes and Autosomes. In a diploid organism, there is one pair of chromosome, which is responsible for determination of

sex. They are called sex chromosomes. All the other chromosomes are called autosomes. In some animals, the temperature at which fertilised eggs are kept determines whether the

animals developing in the eggs will be male or female.eg alligators and turtles. In other animals, such as snails, individuals can change sex, indicating that sex is not genetically

determined. However, in human beings, the sex of the individual is largely genetically determined.

Sex Determination in Humans: In humans, the females have two X chromosomes whereas; the males have one X

chromosome and one Y chromosome. The Y chromosome is smaller in size than the X chromosome, yet pairs with X chromosome during meiosis.

In human males → 44 Autosomes + 1X chromosome + 1Y chromosome (44 + XY) In human females → 44 Autosomes + 2X chromosomes (44 + XX) During meiosis or at the time of gametes formations, homologous chromosomes separate and

go to different gametes. Same is true for the chromosomes in males and females. So, each sperm will have only either X chromosome or Y chromosome. The sex of a child depends on which sperm is fertilizing the egg – the X chromosome

containing sperm, or the Y-chromosomes containing sperm. A child who inherits an X chromosome from her father will be a girl and one who inherits a Y

chromosome from him will be a boy. The probability of producing a male child or a female child is equal i.e. 50%.

Parent Female Male Genotype XX XY

Gametes Egg X Sperm X Y Fertilisation Offsprings

XX XY Female Male 50% 50%

D) Evolution: The process of gradual and orderly changes. Which lead to the development of present day complex forms of life from pre-existing simple ones is called organic evolution.

All organisms, which we see today, have descended from pre-existing simple ancestors. The science which deals with the gradual unfolding of organisms from pre-existing ones through change from the beginning of life is referred to as evolution.

In the words of Darwin, “evolution is descent with modification”.

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Variations in Beetle Population:

Situation Occurrence Interpretation Group of red beetles were fed on

green leaves

Crows eat beetles Population of beetles reduces

First Situation

One green coloured beetle suddenly appears instead of red.

Caused due to variation during reproduction.

Green colour passed on to next generation

All the progenies of the green coloured beetles are green in colour.

Green beetles could not be seen on green leaves by crows.

So green beetle’s survived and red beetle’s population reduced.

Second situation

One blue coloured beetle suddenly appears instead of red.

Caused due to variation during reproduction.

Blue colour passed on to next generation

All the progenies of the blue coloured beetles are blue in colour.

Blue and red coloured beetles were seen on green leaves

Crow ate blue and red beetles and population reduced

Few blue beetles are left and most of them are red

Initially population of red beetles was more

Elephant stamps on the bush where beetle lives.

Most of the red beetles are killed and luckily blue beetles survive

Later few beetles were red and most were blue

After stamping majority of population was blue. As the population expands slowly again blue beetles survive and are maximum.

Third Situation

Plants were affected by some disease. Beetle population went down as they were undernourished. Those surviving were weighing less. But genetic composition was same

Plant disease was eliminated after few years

Lot of food was available and the weight of beetles increased.

Since Genes control traits the frequency of certain genes in a population changed over generations.

This is the idea of evolution.

Conclusion: In the first situation natural selection is directing evolution in the beetle population. Natural Selection is exerted by the crows. The green color variation gave a survival advantage. It results in adaptations in the beetle population to fit their environment better. In the second situation it was accidental survival of the beetles. If the population was large it would not have made much difference but since the population

was small and elephant stamped on it only few survived.

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E) Speciation: In micro–evolution the changes are very small but significant. They don’t explain how new species come into existence.

Speciation is the formation of new species from preexisting simple species. The formation of new species (speciation) may occur by gradual drifting apart of two or more populations of a single species until such time when they stop to interbreed.

Geographical Isolation: Population of species may be isolated by geographical barriers. E.g. If the bushes the beetles feed on are spread widely over a mountain range. The beetle

population will increase, individual beetles will feed on a few nearby bushes, throughout their life time. They will not travel far to feed.

So, in this huge population of beetles, there will be sub-populations in neighbourhoods. Since male and female beetles have to meet for reproduction to happen, most reproduction will be within these sub-populations.

However, if a river comes into existence between two sub-populations they will be further isolated and gene flow between them will decrease.

Over generations, genetic drift will accumulate different changes in each sub–population. Also, natural selection may also operate differently in these different geographic locations.

Total number of genes present in a population is called gene pool. Free flow of genes occurs between the members during sexual reproduction. Any change in gene pool leads to speciation. E.g. If any adventurous beetle goes from one site to another to mate or if any beetle is picked

up by crow and is left in other population without being eaten will reproduce with the local population. This results in the genes of the migrant beetle entering a new population.

This kind of gene flow is bound to happen between populations that are partly, but not completely separated.

Genetic Drift: An important factor in evolution is the effect of change, on very small populations. This effect is

called as genetic drift. It is a chance variation in frequencies from one generation to another. The smaller the population the greater the genetic drift.

Natural Selection: This theory was proposed by Charles Robert Darwin in his book “The origin of species”. Basis of his theory was his observations of nature during his voyage on the ship HMS Beagle

and the population theory of Malthus. The main postulates of the theory are:

There is struggle between members of same species and different species for food, space and mate.

The unfit individuals are eliminated. The fit organisms possess some variations, which are favourable. There organisms leave the progeny to continue the favourable variations. This phenomenon is known as ‘natural selection’. These inherited variations over a long period of time lead to origin of a new species.

The main drawback of this theory is that it could not explain cause of variations.



E.g. New variation emerges in which green females will not mate with red males, but only with green males. This allows very strong natural selection for greenness.

Reproductive Isolation: Two different species are incapable of interbreeding with one another because of reproductive

isolation, even if they happen to meet. It is further divided into following three types:

Genetic Isolation: It refers to interspecific sterility or if the DNA changes are severe enough such as a change

in the number of chromosomes, eventually the germ cells of the two groups cannot fuse with each other.

Temporal Isolation: It refers to the structural differences in genitalia (reproductive organs) of individuals

belonging to different animal species.

Behavioral Isolation The males of one animal species are unable to recognize the females of another species as

potential mates. It prevents interbreeding of two groups due to differences in mating behaviour.

E.g. If a green female beetle meets a red male beetle from the other group, her behaviour will ensure that there is no reproduction between them.

Factors Causing Speciation Other than the above mentioned reasons speciation can be caused by following ways:

Change in genetic makeup of an organism Recombination of genes Hybridization

F) Evolution and Classification: Characteristics: They are the details of appearance or behaviour, or in other words particular form or particular function.

Examples of same common basic characteristics in living organisms Cell is the basic unit of life in all organisms Human beings or other vertebrates have four limbs Plants perform photosynthesis

12

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The design of the wings, their structure and components are thus very different, but look similar because they have a common function of flying.

Example: The wings of birds and insects, leaves of opuntia and peepal, potato and sweet potato

Fossils: Fossils are the remains of organisms which are not decomposed completely but are caught in

strata of the earth and retain impressions of their body parts. These preserved traces of living organisms are called fossils.

These are Palaeontological evidences:

How old are the Fossils? The age of fossils can be estimated by two ways: (i) Relative (ii) Dating fossils.

Relative estimation: We dig into the earth and start finding fossils, it is reasonable to suppose that the fossils we find closer to the surface are more recent than the fossils we find in deeper layers.

The fossil records of geological time scale shows that fossils of only simple forms are found in lower or old strata while those of complex forms appear in upper or recent strata of the earth.

This indicates that complex forms have gradually evolved from pre-existing simple ones. Dating fossils: It is done by detecting the ratios of different isotopes of the same

element in the fossil material. Age of fossil can be done by using uranium lead method and radioactive carbon method.

Importance of Fossils

Study of fossil record helps to build a historical sequence of biological evolution of complex organisms from simple ancestors.

Analysis of organ structure in fossils allows us to make estimates of how far back evolutionary relationships go.

Evolution by Stages: Evolution occurred step by step. Example Planaria; Planaria has simple eyes that are really just eye–spots which detect light. Even intermediate stage such as rudimentary eye can be useful to some extent. Different organisms have different structure of eye which will have separate evolutionary origins.

E.g. octopus, insects, vertebrates.

How can we say that birds are closely related to reptiles? Ans: Dinosaurs which were reptiles had feathers which acted as insulation in cold weather but those

feathers were not used for flight. Later on birds adapted the feathers to flight. So this means birds are very closely related to reptiles.

Artificial Selection: Very dissimilar looking structures evolve from a common ancestral design. It is true that analysis of the organ structure in fossils allows us to make estimates of how far

back evolutionary relationships go. But those are guesses about what happened in history. Latest example is Wild cabbage plant. Man some 2000 years ago cultivated wild cabbage as

a food plant and generated different vegetables from it by artificial selection.

14


Conclusion:

As a result 6 different vegetables were produced by selecting various characteristics.

Changes in DNA during reproduction:

Changes in DNA during reproduction are the basic events in evolution. This is done by comparing the DNA of different species which gives direct estimate of

how much DNA has changed during the formation of these species. This method is now extensively used to define evolutionary relationships.

G) Evolution cannot be equated with Progress: We cannot say that evolution is progress because evolution is the generation of diversity and the shaping of diversity by environmental selection.

Eg. Beetle population: Few beetles are eliminated by natural selection. The beetles that survive will give rise to new

species. It is not necessary that new species are ‘better’ as compared to old ones. A new population is

formed because of Natural Selection and Genetic drift. Eg. Human beings and Chimpanzee:

Human beings have evolved from chimpanzee is not true. Both chimpanzee and human beings had a common ancestor long ago, but that common

ancestor was not chimpanzee or human being. So we can conclude that chimpanzee and human being have evolved in their own separate

ways. In fact from the above examples, there is no real ‘progress’ in the idea of evolution. The only progressive trend in evolution seems to be that more and more complex body designs have emerged over time. While simpler body designs continue to flourish.

However, again it is not as if the older designs are inefficient. Eg. Bacteria:

Bacteria which exhibits the simpler body design inhabits in hot springs, deep sea, thermal vents and ice in Antarctica.

In other words, human being is not the pinnacle or top most form of evolution cycle, but simply yet another species in the teeming spectrum of evolving life.

Human Evolution: Tools used for studying human evolution are as follows:

Excavating

WILD CABBAGE PLANT

KaleKohlrabi

Swollen partsLarger leavesRed cabbage

Colour

Short distance between leaves

Cabbage Arrested flower development

Broccoli

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Time–dating Fossils Determining DNA sequences

Diversity in Human Forms: Races were identified by skin colour. The races were called like yellow, black, white and

brown.

Have these races evolved from common ancestor or differently? Ans: There is no biological basis to the notion of human races. All humans are a single species.

Origin of Human beings: (Africa) Study of the evolution of human beings indicates that all of us belong to a single species that

evolved in Africa and spread across the world in stages. Earliest members of the human species. Homo sapiens can be traced in Africa. Genetic footprints can be traced in Africa’s roots. Some of our ancestors left Africa while few stayed back. Migrants spread over the planet from Africa to West Asia and then Central Asia, Eurasia, South

Asia, Indonesia, Philippine, Australia and crossed the Bering land Bridge to America. They went forwards and backwards with groups sometimes separating from each other and

sometimes coming back to mix with each other, even moving in and out of Africa. Like all other species on the planet, they had come into being as an accident of evolution, and

were trying to live their lives the best they could.

PREVIOUS BOARD QUESTIONS:

Very Short Answers type Questions: [1 Mark] 1) A basket of vegetables contains potato, onion, turnip and sweet potato. Which of them

represent the correct homologous structure? [2014] a) potato, onion b) potato, sweet potato c) onion, beetroot d) onion, sweet potato

2) The leaves of Banyan tree and the spines of a cactus plant are homologous in nature as: a) They have a similar function b) They store water c) Spines provide mechanical support c) Spines are modified leaves [2014]

3) Given below is the list of vegetables available in the market. Select from these the two vegetables having homologous structures:

a) Potato and sweet potato b) Radish and carrot c) Okra and sweet potato d) Potato and tomato [2014]

4) Define ‘evolution’. [2007] 5) What is the function of genes in an organism? [2005] 6) Write the scientific term used for ‘science of heredity and variation’. [2005] 7) Define inheritance [2004]

Short Answers type Questions: [2 Marks]

1) What are fossils? What do they tell us about the process of evolution [2005/08] 2) Define variation in relation to a species. Why is variation beneficial to the species? [2008] 3) Define the terms:

i) Analogous organs ii) Sex chromosome [2007]

16

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18


NCERT EXERCISE:

1) i) 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 suggest that the genetic make-up of the tall parent can be depicted as

a) TTWW b) Ttww c) TtWW d) TtWw ii) An example of homologous organs is a) our arm and dog’s fore-leg b) our teeth and an elephant’s tusks c) potato and runners of grass d) all of the above iii) In evolutionary terms, we have more in common with a) a Chinese school boy b) a chimpanzee c) a spider d) a bacterium Ans: (i–c) (ii–d) (iii–a) 2) 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? Ans: In a population of asexually reproducing species, the chances of appearance of new traits (that

is variation) is very low, so the trait which is already present in the population in higher percentage will arise earlier. As the trait B is present in 60% of the population thus, this trait is likely to have arisen earlier.

3) How does the creation of variations in a species promote survival? Ans: Variations take place in response to the changes in the environment. Such variations enable a

species to cope with the new changes. Thus, variations help a species to survive. 4) How do Mendel’s experiments show that traits may be dominant or recessive? Ans: When Mendel first crossed pure tall pea plants (TT) with

pure dwarf pea plants (tt) and found that only tall plants (Tt) were produced in the F1 generation. The expressed allele T for the tallness is dominant over unexpressed allele t for dwarfness. Thus Mendel experiment show that traits may be dominant or recessive.

5) How do Mendel’s experiments show that traits are inherited independently? Ans: When Mendel first crossed pure-bred pea plants having round-yellow seeds with pure-bred pea

plants having wrinkled-green seeds and found that only round-yellow seeds were produced in the F1 generation.

When the F1 generation pea plants were cross-bred by self-pollination then four types of seeds having different combinations of shape and colour were obtained in second generation (F2). These were round-yellow, round-green, wrinkled-yellow and wrinkled-green seeds.

Gametes RY Ry rY ry

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ry RrYy Round yellow

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rrYy Wrinkled yellow

rryy Wrinkled green

RRYY x rryy (Round, yellow seeds) (Wrinkled, green seeds) Gametes RY ry F1 (1st filial generation) RYry (Round yellow) F2 (selfing F1 generation) RYry x RYry

Chapter 0

Volume 2

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20


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

Ans: No, geographical isolation will not be a major factor for the speciation of a self-pollinating plant species because it does not depend on other plants for the process of reproduction to be carried out.

13) Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?

Ans: No, geographical isolation will not be a major factor in the speciation of an organism that reproduces asexually because it does not require any other organism to carry out reproduction.

14) Give an example of characteristics being used to determine how close two species are in evolutionary terms.

Ans: Forelimbs of humans and wings of birds show the closeness between these two species. Since, the forelimbs of a human and wings of birds have similar structure but perform different functions.

Thus the presence of homologous organs in different animals provides evidence for evolution by telling us that they have evolved from the same ancestor (divergent evolution).

15) Can the wing of butterfly and the wing of a bat be considered homologous organs? Why or why not?

Ans: The wings of a butterfly are made up of chitinous membrane, whereas the wings of a bat are made of fold of skin. Hence, this cannot be considered as homologous organs because they have different basic designs even though they perform similar functions rather they are referred as analogous organs.

16) What are fossils? What do they tell us about the process of evolution? OR Explain the importance of fossils in deciding evolutionary relationship. Ans: Fossils are the remains of organisms which are not decomposed completely but are caught in

strata of the earth and retain impressions of their body parts. These preserved traces of living organisms are called fossils.

The fossils indicate the following about the process of evolution: i) It helps to identify an evolutionary relationship between apparently different species. ii) Study of fossil record helps to build a historical sequence of biological evolution of complex

organisms from simple ancestors. iii) Analysis of organ structure in fossils allows us to make estimates of how far back

evolutionary relationships go. iv) Fossils tell us about many extinct animals and plants and give insights into how they would

have evolved. 17) Why are human beings who look so different from each other in terms of size, colour and

looks said to belong to the same species? Ans: The human beings different from each other in terms of size, colour and looks are said to be of

the same species (Homo sapiens) because they can interbreed to produce fertile offsprings. 18) In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees

have a ‘better’ body design? Why or why not? Ans: It depends on our perception of ‘better’ design. If complexity of body design is the criterion, then

chimpanzee is obviously better than bacteria. But if ability of survival in almost inhospitable habitats is a criterion then bacteria are far ahead than any other group of organisms.

In real sense all organisms have a better body design which suits to adapt themselves best in their ecological niche.

19) 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 dominant or recessive? Why or why not?

Ans: Nothing can be said about the eye colour trait on the basis of the given information. In case the trait is dominant:



The genotype of the parents will be: LL So, Parents LL × LL ↓ Children LL In case the trait is recessive: The genotype of the parents will be: ll So, Parents ll × ll Children ll All the children will have light–coloured eyes in both the cases. 20) How are the areas of study–evolution and classification–interlinked? Ans: Characteristics of organisms refer to the details of their external and internal appearance or

behaviour that distinguish them from one another. These characteristics of organism also form the basis for the classification of organisms. The

more characteristics two species will have in common, the more closely they are related. And the more closely they are related the more closer is the evolution and chances to be in the

same group of classification ancestor. By identifying hierarchies of characteristics between species, we can work out the evolutionary

relationships of the species we see around us. Thus, we can appreciate that classification of species is in fact reflection of their evolutionary

relationship. 21) Explain the terms analogous and homologous organs with examples. Ans: Analogous organs: Those organs which have different basic structural design and

developmental origin but have similar appearance and functions are called analogous organs. Example: The wings of birds and insects, leaves of opuntia and peepal, potato and sweet potato. Homologous organs: Those organs which have the same basic structural design and

developmental origin but different appearance and functions are called homologous organs. Example: The forelimb of a frog, a lizard, a bird and a man and pitcher plant, cactus leaves. 22) Outline a project which aims to find the dominant coat colour in dogs. Ans: Select a homozygous black male dog (BB) and a homozygous white female dog (bb). Cross –

breed them, if all the offsprings in the F1 generation are black, we can conclude that black coat colour is dominant over white coat colour and if all the offsprings are white, the dominant coat colour will be white.

23) What evidence do we have for the origin of life from inanimate matter? Ans: An experiment conducted by Stanley L. Miller and Harold C. Urey in 1953 proved that origin of

life takes place from inanimate matter. They assembled an apparatus to create an early atmosphere of earth, which was supposed to be made up of gases like methane, ammonia and hydrogen sulphide but no oxygen or water.

This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to stimulate lightning. At the end of a week, 15% of the carbon (from methane) had been converted to simple compounds of carbon including amino acids which make up protein molecules.

Protein molecules were precursor of life on earth. 24) Explain how sexual reproduction gives rise to more viable variations than asexual

reproduction. How does this affect the evolution of those organisms that reproduce sexually?

Ans: In asexual reproduction, the offspring’s are almost identical to their parents because they have the same genes as of their parents. Thus, much genetic variation is not possible and thus further evolution of the organism is slowed down.

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In sexual reproduction, the offspring although similar to their parents, are not identical to them or to one another. This is because the offsprings receive some genes from the mother and some from the father.

Because of the mixing of genes of mother and father in various different combinations, all the offsprings will exhibit genetic variations. In this way, sexual reproduction leads to greater variations in the population.

Thus, genetic variation leads to the continuous evolution of various species to form better organisms.

25) How is the equal genetic contribution of male and female parents ensured in the progeny?

Ans: In case of human beings, 23 pairs of chromosomes have maternal and a paternal copy. These pairs contain half chromosomes from mother and half from father which separate out during gamete formation.

At the time of fertilization, the egg cell (n) fuse with the sperm cell which is haploid (n) to form diploid zygote (2n). In this way, an equal genetic contribution of male and female parents is ensured in the progeny.

26) Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?

Ans: No, We don’t agree with this statement that only variations that confer an advantage will survive in a population.

All the variations need not be advantageous to the individual as seen in the case of beetles. The green beetle had survival advantage in terms of camouflage whereas the blue beetle did not have any such survival advantage still it evolved and continue to survive.

REVIEW EXERCISE:

Very Short Answers type Questions: (1 Mark) 1) Define evolution in least possible words. 2) Name the following:

i) Science that deals with the study of inheritance ii) Father of Genetics iii) Carriers of genes.

3) What are autosomes? 4) List any three structures of animals as example of homologous organs. 5) The human palm, cat paw and the horse foot when studied in detail show the same structure of

bones and point towards a common origin. i) What do you conclude from this? ii) What is the term given to such structures?

6) What is the ultimate source of organic variation? 7) Evolution is descent with modification. Explain. 8) What is a sex chromosome? 9) Distinguish between acquired and inherited traits.

10) Explain geographical isolation. 11) What are the factors responsible for speciation? 12) Give an example of artificial selection.

Short Answers type Questions: (2–3 Marks) 13) What are homologous organs? How do they provide evidence in support of evolution?

Long Answers type Questions: (5 Marks) 14) Define genetics. What is the contribution of Mendel in this branch of biology? 15) How is sex determined in human beings?



16) Explain reproductive isolation. 17) A couple got five sons and a daughter. The husband thinks that he produces more of Y-bearing

sperms. Give your views giving scientific reason. 18) A certain woman produced four daughters in successive pregnancies. How would you explain

on the basis of genetics that this lady did not bear a son? What are the prospects of her getting a son in fifth pregnancy if it occurs sure or again a chance? Schematically, explain sex determination (chromosomal) in XY organisms.

19) Describe in brief the morphological evidence in support of organic evolution.

WORKSHEET

1) Which of the two, sperm or ovum, decides the sex of the child? Ans: _________________________________________________________________________

_________________________________________________________________________

2) State whether the following statement is true of false: The sex of an infant is not a case of inheritance of characteristics. Ans: _________________________________________________________________________

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3) a) What are genes? Where are they located in our body? b) What is meant by dominant genes and recessive genes? Give one example of each. c) Explain how, characteristics (or traits) are inherited through genes. Ans: _________________________________________________________________________

_________________________________________________________________________

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4) State one characteristic which shows that the birds are very closely related to dinosaurs. Ans: _________________________________________________________________________

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5) Name the ancestor of the following: Brocoli, Kohlrabi, Kale Ans: _________________________________________________________________________

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6) Out of the wing of a bird, wing of an insect and the wing of a bat: a) which two are homologous organs? b) which two are analogous organs? Ans: _________________________________________________________________________

_________________________________________________________________________

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7) X, Y and Z are three animals. The animal X can fly but animal Y can only run on ground or walls. The forelimbs of animals X and Y have the same basic design but they are used for different purposes such as flying and running respectively. The animal Z became extinct a long time ago. The study of fossils of Z tells us that it had some features like those of X and some like those of Y. In fact, Z is said to form a connecting link in the evolutionary chain of X and Y.

a) What could the animals X, Y and Z be? b) What name is given to the forelimbs like those of X and Y which have the same basic design

but different functions? c) Name one feature in which Z resembled X. d) Name one feature in which Z resembled Y. e) Which is the correct evolutionary chain involving X, Y and Z: X → Z → Y or Y → Z → X? _________________________________________________________________________

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CESSF L U UT - Universal Tutorials€¦ · Chapter 09: Heredity and Evolution 3 Volume 2 of 2 Universal Tutorials – X CBSE – Science 3 Every organism reproduces either sexually