CHPATER 5 :- ORIGIN AND EVOLUTION OF LIFE 

Q.:  What is paleontology?

Ans. The study of forms of the life existing in the past geological periods is known as paleontology. It deals with fossil study.

Q.:  Define fossils, explain various types of fossils.

Ans.: (A) The fossils can be defined as remains or impressions of the hard parts of the past individuals in the strata of the earth.

(B) Different types of fossils can be explained as follows:

Actual remains:

1) It represents the most common type of fossils.

2) These are generally found in deep oceans.

3) After death of an organism i.e. either plant or animal their dead bodies sink at the bottom.

4) These parts or entire body gets deposited by the minerals forming hard stony structure.

5) It is also observed that dead body or parts of dead body gets deposited by ice and preserved in the form of fossils.

II) Mould:

I) it is an impression of the body part left on the soft mud of the oceanic floor.

II) Casts: When the cavities of the Mould get filled with minerals it hardens into stones and forms cast.

III) Compressions:- internal structure is absent but a thin film of carbon indicates the outline of external features.

Q.: Give the significance of fossil record.

Ans.: 1) It is useful in reconstructing the phylogeny. I.e. it help to study evolutionary history of the organism.

2)   It help in studying various other forms and the structure of extinct animals.

3)  These serve as important tool in understanding the habit of extinct organism.

4) It provides connecting links between different groups.

Q.:  What are the different types of evidences which support the process of evolution?

Ans.  Paleontology, comparative anatomy, Embryology and Genetics are the evidences in support of evolution.

Q.:  Describe paleontological evidences of evolution.

Ans. 1) Paleontological evidences is the study of fossil record of organism.

2) Fossils are considered as witness of document of past period and are more reliable than any other type of evidence from different other branches of biology.

3) The primitive life forms existed on the earth are fossilized into lower strata of earth whereas advanced or recent forms are found in upper strata.

4) Most of the fossil record is available from the sedimentary rocks other types are amber, volcanic gas, ice, peat bags and soil, etc.

5) the most significant point of paleontological evidences is that they provide evolutionary details of a particular group and connecting links between the organisms or their groups.

6) Connecting link is intermediate or transitioned stage between two organisms, showing combination of characters from both the groups.

It is also called as missing link.

7) The different examples can be given as under:

a) Seymouria: 350 million years old, forms connecting link between amphibians and reptiles.

b) Archeopteryx: Connecting link between reptiles and aves.

c) Ichthyostegia: It forms the missing link between Pisces and amphibians.

8) Helps to study pedigree of individuals.

Q.: Write a short note on connecting link.

Ans.: 1) A connecting link is defined as intermediate or transitional stage between two organisms.

2) These are also called as missing link or transitional forms.

3) These links possess the characters of two distinct groups in combination.

4) The different examples of missing links can be given as follows:

a) Seymouria: 350 million years old, connecting link between amphibians and reptiles.

b) Archeopteryx: connecting link between reptiles and birds.

c) Ichthyostegia: Missing link between Pisces and amphibians.

d) Lycaenops: It was mammal like reptile, and consider as link between reptiles and mammals.

e) Cynognathus: (Dog Jaw): Possessed characters of reptiles and mammals and most ancient form.

f) Basilosaurus: Fossile whale with hind limbs and link aquatic mammals with their terrestrial ancestors.

g) Duck billed platypus: Shows hair and mammary glands but lay eggs, presence of cloaca, Thus forms connecting link between reptiles and aves.

Q.: Explain, Archeopteryx as the connecting link between reptiles and Aves.

  Give various reptilian and avian characters of fossil bird or archaeopteryx.

Ans. 1) Archeopteryx is the connecting link between Reptiles and Mammals.

2) The different characters of archaeopteryx are as follows:

A) Reptilian characters:

1) Body axis is more or less like lizard.

2) Presence of long tail.

3) No pneumatic bones.

4) Jaws are provided with similar teeth.

5) Hand bears a typical reptilian plan with each finger terminating into a claw.

6) Presence of weak sternum.

7) Presence of free caudal vertebrae same as lizards.

B) Avian Characters of Archeopteryx:

1) Presence of feathers over body.

2) The two jaws modified into beak.

3)  Forelimbs modified into wings.

4) Hind limbs are built on typical avian plan

5) An intimate fusion between skull bones as seen in birds.

3) From the above characters, it is clear evident that reptiles are ancestors of birds.

Hence, Huxley called birds as glorified retiles.

Q. Write an account of various evidences from comparative anatomy in support of evolution.

Ans.: 1) The study of different structures from various groups indicates common origin of life.

2) The different evidences from comparative anatomy are as follows:

A) Homologous organs:

1) The organs which have the same fundamental structure but are different   in functions are called as homologous organs.

2) These organs follow the same basic plan of organization during their development but in adult forms these get modified to perform different functions as an adaptation to their environment.

3) Homology indicates common ancestry.

4) The homologous structures develop as a result of divergent evolution.

5) The different examples can be given as follows:

a) Fore limbs of terrestrial vertebrates such as frog lizard, bird, man. In this case, limbs are constructed on same basic plan but functionally hopping, in lizards crawling, in birds flying and in man gripping the objects.

b) Homology of organs is seen in mouth parts of insects, like cockroach, honey bee, mosquitoes, and butterfly, adapted to different functions.

B) Analogous organs:

1) The organs which have similar function but are different in their structural details and origin are called as analogous organs.

2) Analogous organs develop as result of convergent evolution due to same habitat.

3) These organs do not help to find out evolutionary relationship among the organisms and thus plays no significant role in evolution.

4) The different examples are as under:-

a) Wings of birds and insects, both are useful in flight, but structurally both are different. The wings of insects are expansions of exoskeleton whereas wings of birds are modified forelimbs.

b) Pectoral fins of shark and flippers of dolphin pectoral fins are not pentadactly in shark as seen in dolphin. Structurally both are different but help in same function i.e. swimming.

C) Vestigial organs:

1) These are functional less organs in animals and their presence is not required in animal.

2) They continued to exist before they degenerate and disappear in the process of evolution.

3) The vestigial organs were well developed in ancestors, functional and indicates evolution and line.

4) The different examples of vestigial organs in human body are as follows:

a) Caecum and vermiform appendix:  It is still seen in humans as functionless organ. It helps in cellulose digestion in herbivores animals.

b) Nictitating membrane: It is present in the eyes of humans and is a remnant of the third eyelid.

c) Coccyx and fail vertebrae: It is a remnant of tail in man.

Q.: Write a note a molecular evidences.

Ans.: 1) Cell forms the structural and functional unit in all living organisms.

2) Cytoplasmic organelles like Golgi apparatus, endo plastic reticulum, mitochondria are found in all cells.

3) Proteins and genes perform same type of functions in all living organisms.

4) DNA forms the common ubiquitous genetic material.

5) DNA replication, protein synthesis, respiration follow same mechanisms in all living organisms.

6) All organisms use ATP as source of any for different physiological activities.

Thus, all these facts indicate common origin of life.

FOR DIAGRAMS REFER STATE BOARD BOOK PAGE NO. 107 AND 108

 CHAPTER 5 :- ORIGIN AND EVOLUTION OF LIFE

Q.: Explain the action of Natural selection with reference to industrial mechanism.

Ans. 1) Industrial melanosis the best example of natural selection.

2) The development of dark coloured Month in response to air pollution during industrial revolution in Britain was reported by Kettle well.

The result is due to random mutation in Month.

3) Before industrial revolution light coloured peppered month Biston betularia were in high number on trunk of trees.

4) They were camouflaged well with the lichen covered trees which helped them to escape from birds, their predators.

5) On the contrary, black coloured Moth i.e. Biston carbonaria were Conspicuous and become easy prey for birds.

6) After industrial revolution, release of smoke and soot killed lichens on trees due to which white moth became prominent or conspicuous.

7) Thus, natural selection has resulted in the establishment of a phenotypic trait in changing the environmental conditions.

Q.: How will you explain that natural selection is differential reproduction?

Ans.: 1) The difference in the rate and frequency of reproduction in the members of population is known as differential reproduction.

2) The better adapted individuals show high Rae of reproduction while less adapted individual breed at slower rate.

3) Due to this, proportionally more genes are contributed to the gene pool by better adapted highly reproducing organisms than the others.

4) If the differential reproduction continues for several generations the individual reproducing at the higher rate will become predominant with maximum contribution in the gene pool.

5) Any organism survive by producing, more off spring favourable variation  are preserved  by natural selection because of differential reproduction.

Q.: Define isolation. Explain different types of isolation in detail.

Ans.: 1) Isolation is the prevention of mating amongst the interbreeding groups due to geographical, ecological, physiological, behavioral, mechanical and genetic barriers.

2) Any factor which prevents interbreeding is known as isolating mechanism.

3) The two main types of isolation are as follows:

A) Geographical isolation:

1) The process takes place when the population is divided into subunits due to different factors like oceans, rivers, mountains, canyons, valleys deserts, forests etc.

2) This result in preventing individuals from interbreeding.

3) Geographical isolation or spatial isolation has played significant role in evolution and speciation.

4) In course of time, recombination and mutations occurring in the two groups may be incorporated in the gene pool of different groups.

5) The differences may become so much that the separated groups cannot interbreed when they come in contact again.

6) The two groups are considered as two different species.

7) For example, Darwin’s finches at Galapagos island. Different species of finches with varied feeding habit are found on different islands. The ancestral forms were from the mainland of South America 600 miles away.  These birds, perhaps blown by storms, evolved into different species on various islands.

B) Reproductive isolation:

1) The gene pool of a species is separate from all other. This is known as reproductive isolation and serves as a barrier to inter breeding.

2) It prevents breeding even of related populations present in same geographical area.

3) Reproductive isolation shows following types:-

A) Prezygotic or premating isolation: The main factors operating under this are as follows:

1) Mechanical Isolation: The morphology of genitalia or reproductive organs of both male and female of the two populations may be very complicated, unlike with the result of failure in mating.

2) Psychological isolation: The behaviors differences restrict random mating between male and female individuals in different species.

3) Seasonal isolation: Breeding period of mating individuals is different for members of different species.

4) Gametic Isolation: In free living aquatic forms where the fertilization is external the gametes produced by the different species usually do not  attract each other and this kind barrier is known as gametic isolation.

b) Post zygotic or post mating isolation:

The main factors operating under this mechanism are as follows:

I) Gamete mortality : Mating occurs i.e. sperm is transferred but egg is not fertilized.

II)  Zygote, mortality : Formed: Egg is fertilized but zygote dies.

III) Hybird mortality : Formed hybrid reaches maturity but fails to reproduce due to sterility.  E.g. Mule – Produced from male donkey and female horse.

Henny Produced from male horse and female donkey.

 CHAPTER 5 :- ORIGIN AND EVOLUTION OF LIFE

Q.: Write a note on genetic drift?

Ans.: 1) The term refer to the elimination of certain fruits when a section of       population migrates or dies due to natural calamity.

2) It is also known as Sewall Right effect as it was explained by Sewall right.

3) It alters the gene frequency of remaining population which causes    variation.

4) All populations show genetic drift but its marked effect is seen in small sized population.

5) The genetic drift is explained two effects

a) Founder effects: Formation of different genotype in a new settlement is called as founder effect. (New species may develop).

b) Bottleneck effect: Reduction in the allele frequency is called as bottle check effect which often prevents species from extinction.

6)  Significance:

1) It is an evolutionary force.

2) It helps the populations to become different because of the probability that each population fixes different population by chance.

Q.: Name the mechanism by which new alleles appear in a population.

Ans.: Mutation is the mechanism by which new alleles appear in a population.

Q.:  Explain various factors that can alter gene frequency.

Ans.: The theory is based on three main concepts which can be explained as follows:-

Genetic variations: 1) the group of interbreeding organism in a specific geographical area is known as population and considered as unit of evolution.

2) Genetic variations actually act as raw material in the process of evolution.

3) The different reasons for genetic variations can explained as follows:-

I) Gene mutation or point mutation: 1) Changes in the chemical makeup of a gene is known as gene mutation or point mutation.

2)  Point mutation bring about variation in gene pool and change the gene frequency.

II) Gene Flow: 1) Transfer of genes between two genetically different populations from one another is called as gene flow.

2) Migration of animals to different regions transfer genes to the gene pool of new area altering the gene frequency.

III) Genetic recombination:

1) It is the result of exchange of genetic material between two homologous chromosomes by the process of crossing over.

In sexual reproduction, gametogenesis brings about new genetic recombination.

2) These genetic recombination are responsible for variations.

VI) Genetic drift / Sewall Right effect: 

1) Any alteration in frequency of an allele in the natural population by pure chance is genetic drift.

2) Sewall Right proposed this concept of genetic drift.

3) Due to genetic drift addition of elimination of specific can occur in a population.

4) Smaller populations have greater chances of genetic drift. These small population under favourable conditions can give barge number of variations.

V) Chromosomal aberrations:

1)  It refers to structural alteration in chromosomes changing the arrangement of genes.

2) The different process like deletion, duplication translocation and inversion can bring about changes in Mendelian population also.

Q.: Explain the role of gene flow in evolution?

Ans.: 1) Gene Flow is also known as gene migration and defined as the movement of individuals from one place to another.

2) It the migrating animals breed with the new population the immigrated animals will add new gene to local gene pool of the hosts. This is gene migration.

3) Many times two isolated populations of the same species come close due to migration.

4) The genes of two district populations intermix through breeding and produce variation in off springs.

Thus gene flow brings about genetic variability in the off spring and helps in evolution.