MP Board Class 12th Biology Solutions Chapter 7 Evolution

MP Board Class 12th Biology Solutions Chapter 7 Evolution

Evolution NCERT Textbook Questions and Answers

Question 1.
Explain antibiotic resistance observed in bacteria in light of Darwinism selection theory.
Answer:
Darwinism theory of natural selection states that environment selects organisms with favourable variations and these organisms thus, survive and reproduce. It is observed when bacterial populations are exposed to certain antibiotic, the sensitive bacteria could not tolerate and hence, died due to the adverse environment. Whereas some bacteria that developed mutation became resistant to the particular antibiotic and survived. As a result such resistant bacteria survive and multiply quickly as compared to other sensitive bacteria. So, the whole population is regained by multiplication of resistant variety and antibiotic resis¬tant gene becomes widespread in the bacterial population.

Question 2.
Find out from newspapers and popular science articles any new fossil dis-coveries or controversies about evolution.
Answer:
Fossils of dinosaurs have revealed the evolution of reptiles in Jurassic period. As a result of this evolution of other animals such as birds and mammals has also been discovered. However, two unusual fossils recently unearthed in China have ignited a controversy over the evolution of birds confiiciusomis is one such genus of primitive birds that were crow sized and lived during the Cretaceous period in China.

Question 3.
Attempt giving a clear definition of the term species.
Answer:
Species is a morphologically distinct and reproductively isolated one or more natural populations of individuals which resemble one another closely and interbreed freely amongst themselves.

Question 4.
Try to trace the various components of human evolution (Hint: Brain size and function, skeletal structure, dietary preference, etc.)
Answer:
The various components of human evolution are as follows:

1. Brain capacity.
2. Posture
3. Food/Dietary preference and their important features.

Name brain capacity, posture, and food features:

• Dryopithecus Africans: Knuckle walker, walked similar to Gorillas and Chimpanzees (was more apelike) soft fruit and leaves; canines large, arm and legs are of equal size.
• Ramapithecus: Semi-erect (more manlike) seeds, nuts canines were small while molars were large.
• Australopithecus africanus: Australopithecus africanus 450 cm3 full erect posture, height (1 -05m) Herbivorous (ats fruits). Hunted with stone weapons, lived as trees, canines and incisors were small.
• Homo habilus: Homo habilus 735 cm3 fully erect posture, height (1 -5m) carnivo¬rous canines were small. They were first tool makers.
• Homo erectus: Homo erectus 800-1100 cm3 fully erect posture, height (1-5- l-8m) omnivorous. They used stone and bone tools for hunting games.
• Homo neanderihalensis: Homo neanderthalensis 1300 – 1600 cm3 fully erect posture, height (1-5 – l-6m) omnivorous cave dwellers, used hiles to protect their bodies and buried their dead.
• Homo sapiens fossils: Homo sapiens fossils 1650 cm3 fully erect posture with height (l -8m) omnivorous. They had a strong jaw with teeth close together. They were cave dwellers, made painting and carvings in the caves. They developed a culture and were called first modem man.
• Homo sapiens sapiens : Homo sapiens sapiens 1200 – 1600 cm3 fully erect pos¬ture, height (1-5 – l-8m) omnivorous. They are the living modem men with high intelligence. They developed art, culture, language, speech, etc. They cultivated crops and domes¬ticated animals.

Question 5.
Find out through the internet and popular science articles whether animals other than man have self-consciousness.
Answer:
There are many animals other than humans, which have self-consciousness. An example of an animal being self-conscious is dolphins. They are highly intelligent. They have a sense of self and, they also recognize others among themselves and others. They communicate with each other by whistles, tail-slapping, and other body movements, not dolphins, there are certain other animals such as Crow, Parrot, chimpanzees, Gorilla, Orangutan, etc., which exhibit self-consciousness.

Question 6.
List 10 modern-day animals and using the internet resources link them to a corresponding ancient fossil. Name both.
Answer:
Modern and Ancient corresponding animals :

Question 7.
Practice drawing various animals and plants.
Answer:

Question 8.
Describe one example of adaptive radiation.
Answer:
Darwin’s finches in the Galapagos Island once had a common ancestor but with evolution, they modified into different types according to their food habitat.

Question 9.
Can we call human evolution adaptive evolution?
Answer:
No, because parent species of homosapiens have evolved by progressive evolution
(Homo habilis —Homoerectus lineage)

Question 10.
Using various resources such as your school library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal, say horse.
Answer:
The evolution of horse started with Eohippus during the Eocene period. It involved the following evolutionary stages :

• Gradual increase in body size
• Elongation of head and neck region
• Increase in the length of limbs and feet
• Gradual reduction of lateral digits
• Enlargement of third functional toe
• Strengthening of the back
• Development of brain and sensory organs
• Increase in the complexity of teeth for feeding on grass

• Eohippus: It had a short head and neck. It had four functional toes and a splint of 1 and 5 on each hind limb and a splint of 1 and 3 on each forelimb. The molars were short crowned that were adapted for grinding the plant diet.
• Mesohippus: It was slightly taller than Eohippus. It had three toes in each foot.
• Merychippus: It had the size of approximately 100 cm. Although it still had three toes in each foot, it could run on one toe. The side toe did not touch the ground. The molars were adapted for chewing the grass.
• Pliohippus: It resembled the modern horse and was around 108 cm tall. It had a single functional toe with a splint of 2nd and 4th in each limb.

Equus: Pliohippus gave rise to Equus or the modern horse with one toe in each foot. They have incisors for cutting grass and molars for grinding food.

Evolution Other Important Questions and Answers

Evolution Objective Type Questions

1. Choose the Correct Answer.

Question 1.
These are found in the atmosphere of earth before evolution:
(a) Water vapour, CH₄, NH₃ and Oxygen
(b) CO₂, NH₃, H₂ and Water vapour
(c) CH₄, NH₃, H₂ and Water vapour
(d) CH₄, O₃, O₂ and Water vapour.
Answer:
(c) CH₄, NH₃, H₂ and Water vapour

Question 2.
Which gas is absent in the atmosphere of the earth at the time of origin of the earth:
(a) NH₃
(b) H₂
(c) O₃
(d) CH₄
Answer:
(c) O₃

Question 3.
Which gaseous mixture are used and found the amino acid by Miller:
(a) Methane, Ammonia, Hydrogen and Water vapour
(b) Methane, Ammonia, Nitrogen and Water vapour
(c) Methane, Nitrogen, Hydrogen and Water vapour
(d) Ammonia, Carbon dioxide, Nitrogen and Water vapour.
Answer:
(a) Methane, Ammonia, Hydrogen and Water vapour

Question 4.
Who gave the theory “Survival of the fittest” :
(a) Charles Darwin
(b) Herbert Spencer
(c) Lamarck
(d) Hugo de Vries.
Answer:
(b) Herbert Spencer

Question 5.
Who gave the theory of inheritance of acquired, characters :
(a) Charles Darwin
(b) Lamarck
(c) Valles
(d) de Vries.
Answer:
(b) Lamarck

Question 6.
Who wrote origin of species:
(a) Oparin
(b) Beajman
(c) Lamarck
(d) Darwin.
Answer:
(d) Darwin.

Question 7.
What is the name of Darwin’s ship:
(a) Gangotri
(b) Beagle
(c) Atlantic
(d) Seagull.
Answer:
(b) Beagle

Question 8.
‘Atmosphere is a factor of variation’ who gave this theory :
(a) Mendel
(b) Darwin
(c) Lamarck
(d) Laplace.
Answer:
(c) Lamarck

Question 9.
Darwinism explains it:
(a) Characters are grown by heredity
(b) Species are changed into structural form with time.
(c) Nature selected the animals which are adapted
(d) Origin of evolution due to effect of environment.
Answer:
(c) Nature selected the animals which are adapted

Question 10.
Which antibiotic is used to Replica planting experiment of Ladderberg:
(a) Penicillin
(b) Streptomycin
(c) Erythromycin
(d) Neomycin.
Answer:
(a) Penicillin

Question 11.
Which is the basic unit of natural selection:
(a) Species
(b) Community
(c) Genous
(d) Solitary organism.
Answer:
(c) Genous

Question 12.
Who gave the theory of natural selection :
(a) Lamarck
(b) de Vries
(c) Darwin
(d) Mendel.
Answer:
(d) Mendel.

Question 13.
Darwinism is based on:
(a) Segregation
(b) Independent assortment
(c) Quantitative heredity
(d) Natural selection.
Answer:
(b) Independent assortment

Question 14.
Who discover the uses and experiment of organs:
(a) Valles
(b) Lamarck
(c) Darwin
(d) de Vries
Answer:
(a) Valles

Question 15.
The unit of natural selection :
(a) Solitary animal
(b) Family
(c) Community
(d) Species.
Answer:
(d) Species.

Question 16.
Mule is a product of:
(a) Mutation
(b) Reproduction
(c) Inter-species hybridization
(d) Intra-species hybridization
Answer:
(b) Reproduction

Question 17.
Who use first the word ‘species’:
(a) Linnaeus
(b) John
(c) Aristotle
(d) Darwin
Answer:
(b) John

Question 18.
Homologus organs are :
(a) Similar in origin
(b) Similar in function
(c) Similar in evolution
(d) Similar in behaviour.
Answer:
(a) Similar in origin

Question 19.
Which era are called as the golden period of Reptilia or Dinosaurs:
(a) Mesozoic
(b) Cenozoic
(c) Palaeozoic
(d) Cenozoic.
Answer:
(a) Mesozoic

Question 20.
Dinosaurs are distinct in this era:
(a) Jurassic
(b) Triassic
(c) Cretaceous
(d) Permian.
Answer:
(c) Cretaceous

Question 21.
Vestigial organs of human’ are:
(a) Wisdom teeth, Coccyx, Nail, Eyelids, Vermiform appendix
(b) Wisdom teeth, Coccyx, Vermiform appendix, Pancreas
(c) Wisdom teeth, Coccyx, Vermiform appendix, Nictating membrane
(d) Coccyx, Wisdom teeth, Nail, Auricular muscle.
Answer:
(c) Wisdom teeth, Coccyx, Vermiform appendix, Nictating membrane

Question 22.
How made fossils:
(a) Animals are naturally buried inland after death
(b) Animals are decomposed by decomposers
(c) Animals are eaten by their hunter species
(d) Animals are destroyed due to environmental conditions.
Answer:
(d) Animals are destroyed due to environmental conditions.

Question 23.
Species which are similar in shape and different in reproduction are called :
(a) Sub-species
(b) Sibling
(c) Isotopic
(d) Allopatric species.
Answer:
(c) Isotopic

Question 24.
Name the ship which had been used by Darwin for the journey:
(a) Ciloge
(b) Beagle
(c) Seagull
(d) Atlantic.
Answer:
(b) Beagle

Question 25.
Life is not in this era :
(a) Mesozoic
(b) Palaeozoic
(c) Cenozoic
(d) Azoic.
Answer:
(d) Azoic.

Question 26.
Which factor is responsible for evolution due to New-Darwinism theory:
(a) Mutation
(b) Useful variation
(c) Hybridization
(d) Mutation and Natural selection.
Answer:
(d) Mutation and Natural selection.

Question 27.
Found the age of fossils by which :
(a) By quantity of calcium ions
(b) By quantity of organic radioactive components
(c) By struggle from other mammals
(d) By the structure of bones.
Answer:
(d) By the structure of bones.

Question 28.
Darwin finches are related to which of the following evidence:
(a) Fossils
(b) Embryology
(c) Anatomy
(d) Geographical distribution.
Answer:
(d) Geographical distribution.

Question 29.
Who gave Recapitulation theory :
(a)Weizmann
(b) Haeckel
(c) Darwin
(d) Malthus.
Answer:
(b) Haeckel

Question 30.
Which definition of organic evolution is correct:
(a) Evolutionary history of a species
(b) History of species with the variations in the species
(c) Embryonal history of species
(d) Development of species.
Answer:
(a) Evolutionary history of a species

Question 31.
What is the perfect sequence of development of human:
(a) Peking man, Heidelberg man, Neanderthal Cro-Magnon
(b) Peking man, Homo sapiens, Cro-Magnon, Neanderthal
(c) Peking man, Neanderthal,.Homo sapiens, Heidelberg
(d) Peking man, Cro-Magnon, Homo sapiens, Neanderthal.
Answer:
(a) Peking man, Heidelberg man, Neanderthal Cro-Magnon

Question 32.
Which of the following is the most primitive ancestor of man :
(a.) Australopithecus
(b) Ramapithecus
(c) Homo habilis
(d) Homo neanderthalensis.
Answer:
(b) Ramapithecus

Question 33.
Ancestral amphibians were tetrapods that evolved during :
(a) Jurassic period
(b) Cretaceous period
(c) Devonian period
(d) Carboniferous period.
Answer:
(c) Devonian period

2. Fill in the Blanks:

1. Earth is a member of …………….
2. ……………. wrote ‘Origin of life’.
3. Oxygen is found on the earth because photo-synthetic organisms are present on the earth, this phenomenon is called …………….
4. ………….. is the connecting link between Reptiles and Aves.
5. …………………. is the ancesters of horse.
6. The evolution of ……………. molecule set the stage for the evolution of autotrophs.
7. Evolution of birds and mammals were ……………. era.
8. Golden era of Dinosaurs is ……………. period.
9. ……………. fossil man has been known from Shivalik hills in India.
10. Book of Charles Darwin “Origin of life” has been explained of …………….
11. ……………. be change of hareditary characters.

Answer:

1. Solar system
2. Oparin
3. Oxygen revolution
4. Archaeopteryx
5. Eohippus
6. Chlorophyll
7. Jurassic
8. Mesozoic
9. Ramapithecus
10. Natural selection
11. Mutation.

Question 3.
Match the Following :

Answer:

1. (d)
2. (a)
3. (e)
4. (c)
5. (b)

Answer:

1. (d)
2. (c)
3. (e)
4. (a)
5. (b)
6. (f).

4. Answer in One Word / Sentence:

1. The matter which gave rise to the universe 15 billion years ago.
2. The matter is a link between acellular and cellular systems.
3. The island at which Darwin studies the organisms for his theory of evolution.
4. Origin of two or more unlike species from a common ancestor.
5. The whole process of development at changes from embryo to adult organism.
6. The process of changes in the course of origin of a new species.
7. The theory of organic evolution proposed by Darwin.
8. The permanent, heritable, and spontaneous changes in organisms.
9. The remains of ancient organisms.
10. The organs which are different in their origin but have a similar function.

Answer:

1. Ylem
2. Coacervates
3. Galapagos
4. Adaptive radiation
5. Ontogeny
6. Phytogeny
7. Natural selection
8. Mutation
9. Fossils
10. Homologous organs.

Evolution Very Short Answer Type Questions

Question 1.
What is abiogenesis?
Answer:
It is the process of the appearance of the first form of life slowly from non-living molecules.

Question 2.
Name the theory which tells about the milky way and the formation of a star.
Answer:
Big Bang.

Question 3.
What is evolutionary biology?
Answer:
Science deals with the study of the history of life forms on earth.

Question 4.
Which planet has the possibility of the origin of life other than earth?
Answer:
ars.

Question 5.
Define homologous organs.
Answer:
The organs have similar embryonic origin but they perform different functions.

Question 6.
What is the art of limitation, which is practiced the world over from annoying siblings or plant resembles another creature to gain other advantages?
Answer:
Mimicry.

Question 7.
Define homology.
Answer:
Homology refers to the similarities in the fundamental anatomy and embryology of organs of different groups of plants and animals.

Question 8.
What is the collection of different genes within an interbreeding population?
Answer:
Gene pool.

Question 9.
What is the analogy?
Answer:
It refers to structurally different organs evolving for the same function in a different groups of plants and animals.

Question 10.
Who proposed the theory of natural selection?
Answer:
Darwin.

Question 11.
Why are the wings of a butterfly and of a bat called analogous? (CBSE 1996, 2009)
Answer:
They are of different embryonic origin but similar function.

Question 12.
The astronomical distance measured in?
Answer:
The astronomical distance measured in Light years.

Question 13.
Give 2 examples of evolution due to anthropogenic activities.
Answer:
DDT resistance in mosquitoes and Antibiotic resistance in microbes.

Question 14.
What is a fossil?
Answer:
Fossils are the remains or impressions of ancient organisms preserved in sedimentary rocks or other media.

Question 15.
Name the fossil animal which serves as a connecting link believers reptiles and birds. (CBSE 1995)
Answer:
Archaeopteryx – fossil bird.

Question 16.
Name the scientist who tells the spontaneous theory is wrong.
Answer:
Louis Pasteur’s.

Question 17.
Name the placental mammal corresponding to the Austrian “Spotted cuscus” and Tasmanian “tiger cat”. Which have evolved as a result of convergent evolution (CBSE 2008)
Answer:
Lemur and Bobcat.

Question 18.
In which ship Darwin studied nature?
Answer:
Beagle.

Question 19.
Name any two vertebrates’ body organs which are homologus organs of the human forelimb.
Answer:

1. Flipper of Whale
2. Wing of birds

Question 20.
What is the scientific name of modern man?
Answer:
Homo sapiens.

Question 21.
What is meant by gene pool?
Answer:
The sum total of all the genes pooled by the members of a population.

Question 22.
Who are the early human and sub-human?
Answer:
Ramapithecus is early human and Australopithecus is early human.

Question 23.
Name the immediate ancestor of lycopods.
Answer:
Zosterophyllum.

Question 24.
Which type of human was ‘Cro-Magnon’ on the basis of food intake?
Answer:
Cro-Magnon was carnivorous.

Question 25.
Darwin’s theory is known as the “Theory of Natural selection”. How is Lamark’s theory know? (CBSE 1995)
Answer:
Theory of inheritance of acquired characters.

Question 26.
Give the name of apelike ancestors of humans
Answer:
Apelike ancestors of humans are Dryopithecus.

Question 27.
Define genetic drift.
Answer:
Random changes in the allelic frequencies of a population, occurring only by chance events, constitute genetic drift.

Evolution Short Answer Type Questions

Question 1.
Describe the theory of abiogenesis.
Answer:
According to this theory, the first form of life arose slowly through evolutionary forces from non-living molecules.

• The reducing atmosphere and high temperature favoured the formation of diverse organic compounds from inorganic molecules.
• Then the first non-cellular forms of life i.e. self duplicating molecules like RNA evolved.

Question 2.
What is oxygen revolution? Explain.
Answer:
Oxygen revolution: Evolution of 02 in photosynthesis during primitive environmental conditions is very important because, it is required in the evolution of organism and conversion of reducing environment into oxidizing environment hence, it is called oxygen revolutioa Oxygen evolution should cause the following changes in the environment:

• Oxygen evolution should cause the conversion of reducing environment into oxidizing environment
• Ozone layer is formed 15 miles above from the earth which absorbs the ultraviolet light of the sunlight and thus, prevents the entry of uv light in the atmosphere.
• O₂ present in the environment dissociates methane (CH₄) into CO₂ and O₂. This CO₂ is used in photosynthesis.
• NH₃ of the primitive environment is dissociated into H₂O.and nitrogen.
  CH₄ + 2O₂2 → CO₂ + 2H₂O
  4NH₃ + 3O₂ → 2N₂ + 6H₂O.

Question 3.
Amongst pea tendrils, opuntia spines, lemon thorns and cucurbit tendrils. Which ones are homologous structures? Why do you call them homologous? (CBSE 1999)
Answer:

• Pea tendrils and opuntia spines are homologous.
• Lemon thorm and cucurbit tendrils are homologous.

Reason:

• Pea tendrils and Opuntia spines are modified leaves (same orign) but perform different functions.
• Lemon thorns and cucurbit tendrils are modified stems. Both arise from axillary positions. Both perform different functions.

Question 4.
Mention the names of discoveries and principles given by the following scientists:

1. Louis Pasteur
2. A. I. Oparin
3. Urey and Miller
4. Francesco Redi
5. Faux.

Answer:

1. Louis Pasteur: He proved that air contains spores of microorganisms and the Biogenesis theory was supported by him.
2. A. I. Oparin: He presented the biochemical explanation of the origin of life in his book “The Origin of Life on Earth”.
3. Urey and Miller: They supported the evidence of the Oparin-Haldane theory of Origin of life.
4. Francesco Redi: He by conducting experiments proved that abiogenesis cannot exist but biogenesis theory can exist i.e., Life arises from pre-existing life.
5. Faux: He has been experimentally supporting the organic substances as described by Oparin.

Question 5.
Write down the difference between:

1. Ozone and Oxygen
2. Micro-molecules and Macro-molecules.

Answer:
1. Differences between Ozone and Oxygen :

2. Differences between Micro-molecules and Macro-molecules :

Question 6.
What are homologous organs?
Or
What is homology?
Answer:
Organs which are similar in structure and origin but different in appearance and functions are called homologous organs and the phenomenon is called homology.
Examples: Forelimbs of bat, wings of bat, hands of man, forelimbs of horse. These are examples of homologous organs because, they are made up of similar bones, hu¬merus, radius-ulna, carpals, metacarpals and fingers.

Question 7.
How do Darwin’s finches illustrate adaptive radiation? (AI2008)
Answer:
Darwin finches are varieties of small blackbirds found in the Galapagos Islands. They all must have evolved on the island itself. From the original seed-eating birds, many other forms evolved, with altered beaks enabling them to become insectivorous and vulgarian habits. This process of evolution of different species in the same geographical area starting with one species and radiated to other areas is called adaptive radiation.

Question 8.
What is the difference between homologous and analogous organs? Give two examples of each of them.
Answer:
Differences between Homologous and Analogous organs :

Question 9.
State Hardy – Wein berg principle of genetic equilibrium knowing that genetic drift disturbs this equilibrium. Mention what does this disturbance in genetic equilibrium leads to?
Answer:
Hardy Weinberg’s principle states that allele frequencies in a population are stable and remain constant from generation to generation.

• Genetic drift refers to a change in allele frequencies of a population acquiring by chance.
• Such a change in allele frequency may be so different that the population becomes a different species.
• The original drifted population is called founder and the effect is called the founder effect.

Question 10.
What is connecting link? Also, explain the significance of connecting links.
Answer:
Connecting link: Certain organisms which share characters with two different groups. Such organisms are called connecting links.
Examples: Some fossils present in nature like Archaeopteryx is known as fossils connecting link and it is the connecting link of birds and reptiles. Neopilina, Platypus, Protopterus, etc. Neopilina is a mollusk and is the connecting link of Mollusca and Annelida.
Significance of Connecting links: It proves the process of organic evolution and helps in the identification of organisms closely related.

Question 11.
Write down the demerits of Darwinism.
Answer:
Some of the demerits of Darwinism are:

• Darwinism stresses upon small fluctuating variations which has no role in evolution.
• Does not satisfactorily explain effect of use and disused and presence of vestigial organs:
• It did not differentiate somatic and germinal variations.
• It explains survival of the fittest but not arrival of the fittest. .

Question 12.
Differentiate between Lamarckism and Darwinism.
Answer:
Differences between Lamarckism and Darwinism:

Question 13.
Explain Lamarckism in short
Or
Explain Lamarckism of organic evolution in brief.
Answer:
Lamarckism: In 1809, Lamarck has proposed a theory to explain organic evolution, which is known, as the “Theory of inheritance of acquired characters.” According to Lamarck, organisms acquire certain characters during their lifetime due to changes in the environment and these acquired characters are heritable. According to this theory, new species are originated as follows:

• New requirements and wills are produced in the organisms due to the effect of changing environment
• New requirements and wills of organisms resulting in the production of new habits.
• Changes in the habit bringing about modifications of the organ.
• New habits resulting in the use or disuse of the organs:
• Use of organ resulting in the development of acquired characters.
• These acquired characters are heritable.
• Inheritance of acquired characters resulting in the development of new species.

Evolution Long Answer Type Questions

Question 1.
Draw a well-labelled diagram of Miller and Urey’s experiment
Answer:

Experimental evidence of Chemical evolution or Miller’s experiment:

• Experiment was performed by S.L. Miller and H.C. Urey in 1953.
• Experimental set-up: In a closed flask containing CH4, H2, NH3 and water vapoiy at 800°C, electric discharge was create. The conditions were similar to those in primitfve atmosphere.
• Observations: After a week, they observed presence of amino acids and complex molecules like sugars, nitrogen bases, pigments and fats in the flask.
• Conclusions : (i) It provides experimental evidence for the theory of chemical origin.
  (ii) It showed that the first non-cellular form of life was created about 3 billion years ago.
  (iii) It showed that non-cellular biomolecules exist in the form of DNA, RNA, polysaccharides and protein.

Question 2.
Write an essay on modern concepts of origin of life.
Or
Explain the role of non-living in origin of life.
Answer:
Modern concept of origin of life : The modem concept of origin of life was postulated by a Russian biochemist A.I. Oparin in 1936. According to this theory, after the formation of earth various chemicals played important role in the formation of atmosphere. Life originated and first organism came into existence from certain molecules when atmospheric conditions became suitable. According to Oparin, life originated in the following steps:

1. Formation of earth and its atmosphere: Earth is believed to be originated some 4,500 million years ago by the condensation and cooling of the clouds of cosmic dust and gases called ylem. The heavier elements collected at the core and lighter elements around the core. Outermost layer contains H, C, O and N. Oxygen was found only in combination of other elements. These four elements reacted with each other forming H₂, H₂O, CH₄, NH₃, CO₂ and HCN.

2. Formation of small organic molecules: The mixture of methane, ammonia, water and hydrogen comes in contact of solar energy. Cosmic rays and electric discharge could produce some simple organic compounds. These simple organic compounds formed in such a way and accumulated in primitive atmosphere and oceans were responsible for synthesis of complex micro molecules as follows :

3. Formation of polymers : It is clearly understood from the above description that a large number of micro molecules such as hydrocarbons, amino acids, fatty acids, purine and pyrimidines and simple sugars accumulated in the oceans. When atmospheric water condensed on further cooling, the inorganic precursors collided, reacted and aggregated to form new molecules of increasing size and complexity. Thus, by polymerization macromolecules were formed. The chemical reactions for the formation of macromolecules can be summarized as follows:

• Sugar + Sugar → Polysaccharides
• Fatty acid + Glycerine → Lipids
• Amino acid + Amino acid → Protein
• Nitrogenous base (Adenine) + Sugar + Phosphate → Adenosine phosphate
• Nitrogenous base + Sugar → Nucleoside
• Nucleoside + Phosphate → Nucleotide
• Nucleotide + Nucleotide → Nucleic acid.

4. Formation of molecular aggregates and primitive cells: Over a vast of time, these molecules became associated with one temporary complex. Ultimately, it leads to the formation of a coacervate. A coacervate is a solution of high molecular weight of chemicals, i.e., proteins and carbohydrates, which become bounded by lipid membrane, which is selectively permeable. The coacervate grows by absorbing molecules from its environment. The substances which got accumulated in the coacervates underwent reactions and resulted in the molecular reorganization of some proteins into enzymes. A coacervate having nucleoprotein surrounded by various nutritive organic substances and covered by surface membrane is considered to be the precell, which got later transformed into first living cell. The coacervate can reproduce by budding.

5. Evolution of complex biochemical reactions: Primitive organism utilize chemi¬cal substances present in the environment as food hence, they are:

• Heterotrophic, chemosynthetic organisms appeared due to mutation and natural selection in heterotrophs.
• Blue-green algae evolved from chemosynthetic organisms by mutation and natural selection.
• The liberation of free oxygen into the atmosphere produced by the blue-green algae due to the process of photosynthesis.

It finally changed the reducing atmosphere into an oxidizing one and therefore, all possibilities of further chemical evolution were finished.
Free-living eukaryotes originated in the ocean from blue-green algae.

6. The origin of well-developed organisms: From the simple eukaryotes which were like unicellular organisms of today various forms of life evolved during the passage of time.

Question 3.
Write the process of formation of organic molecules in seawater on earth with the help of Miller and Urey’s experiment
Answer:
The work of A.I. Oparin (1938-1965), HLUrey, and Stanley Miller (1959) provided evidence in the favour of biochemical origin of life. They had prepared the atmos¬phere like that of primitive earth and as described by Oparin, they made the synthesis of organic compounds by the following methods:

(i) Four elements H, C, O (not free O₂), and N react .with each other to form H₂O, CH₄, NH₃, CO_2, and HCN on the primitive earth.

(ii) From these four elements following organic molecules were formed in seawater of earth:
(a)

(b) CH₄, H₂O, NH₃ → Amino acids.
(c) CH₄, HCN, H₂O, NH₃ → Nitrogenous bases.

(iii) Macro-molecules of organic compounds were synthesized by these above pre¬pared organic compounds.

• Sugar + Sugar → Polysaccharides (Carbohydrate).
• Fatty acids + Glycerol → Fats.
• Amino acid + Amino acid → Protein.
• Nitrogenous base + Sugar → Nucleoside.
• Nucleoside + Phosphoric acid → Nucleotide.
• Nucleotide + nucleotide → Nucleic acid.
• Nitrogenous base (Adenine) + Sugar + Phosphate →Adenosine phosphate.

(iv) The above organic compounds and salts together constituted the first living being.

Question 4.
Name connecting link of reptiles and birds. Also, write their characters.
Answer:
Archaeopteryx is the connecting link between birds and reptiles. Archaeopteryx was a bird. It is regarded as the connecting link between reptiles and birds, which suggests the path of evolution of the latter from the former. It is found as fossils. They are found during the Jurassic period for 140 million years. Archaeopteryx exhibits both reptiles and birds like characters.

1. Reptiles like characters:

• Bones were similar to that of reptiles in which air sacs were absent.
• Tail-bearing vertebra.
• It had teeth in jaws, scales were present on the body.
• Metacarpals were free.
• The pelvic girdle recombines with the pelvic girdle of reptiles.

2. Birds like characters:

• Presence of feathers on the body.
• Forelimbs were modified in wings.
• Skull large and monocondylar.
• Jaws were modified into a beak.
• Hallux was backward and pointed.

Question 4.
(i) The study of fossils support evolution of organism. Discuss?
(ii) Describe convergent evolution with an example each from animals and plants.
Answer:
(i) By the careful analyses of the distribution of fossils in the different strata of rocks gives the time of the history of the earth the study showed that life form varied over time, some were simple and those in the superfluid layers resembled modern organism. Some fossils indicate connecting links i.e. they share features of two groups of organisms indicating the evolution of one group into the other.

(ii) Convergent evolution refers to the evolutionary process of selection of similar adaptive features in different groups of organisms in a similar habitat towards the same function.

• It is the similar habilat that has resulted in selection of similar structures.
• Analogous structures that are not anatomically similar but perform the same functions result from convergent evolution. Examples: Wings of butterfly and wings of birds.

Question 6.
Organic Evolution is a continued process, explain it in favour of it giving any three evidences.
Answer:

Evolution is a complex phenomenon accounting for the present-day diversity among organisms. But it has clearly maintained the basic unity among them since it occurred over a period of millions of years, no one would have seen/recorded evolution and hence scientists have provided various evidence to prove evolution.

Some of the evidence of organic evolution are described below :

I. Evidences from Embryology :

• Important activities that occur various animals are:
• For survival, all animals get energy and various substances from the environment.
• In all organisms, energy is produced from ATP.
• In all organisms, the duplication of DNA is similar.
• In all organisms, protein synthesis is the same and it is produced from ribosomes.
• In all organisms respiration and steps of respiration is the same.
• All organisms multiplicate and reproduce, due to which they have basic similarities.
• All organisms conduct hereditary characters on similar principles.

II. Evidence from Anatomy: The anatomy of living organisms will be explained with different examples:

• Homologous organs: Organs which are similar in structure and origin but different in function and appearance is known as homologous organs.
• Analogous organs: Organs which are different in origin and structure but performing similar functions are known as analogous organs.
• Vestigial organs: Organs that are reduced and have become functionless in an organism, but were functional in their ancestors are called vestigial organs.

III. Evidences from vestigial organs: Organs of the body which are non-functional but they are functional in some other organisms are called vestigial organs:

Morphological evidence of evolution is provided by the presence of vestigial organs of body which are often undesired, degenerated and non-functional. These might have been large and functional in some other animals or in ancestors of those which now possess it in rudimentary forms. e.g„ vermiform appendix in man, muscles of external ear (pinna) in man, nictitating membrane or plica, semilunaris in human eye, wisdom teeth (third pair of molars) tail bone (coccyx) in man, wings of ostrich, hindlimbs in snakes, etc.

Question 7.
What do you mean by organic evolution? How do fossils exhibit evidence to prove organic evolution?
Answer:
Descent with modification in an organism is known as organic evolution.

Evidence of organic evolution from fossils record: Fossils are treated as significant evidence of organic evolution. Fossils are the remains or impressions of ancient organisms preserved in the layers of rock and soil. Fossils only do not prove the theory of organic evolution, yet it evidently prove that gradually complexity increased in body organization. The complexity in the body of organization can be noticed as we study the upper layers. Thus, it can be concluded from above observations :

• The crust of the earth and the organisms living on it underwent change in the course of time.
• The organisms with simple structural organization originated earlier than the complex ones.
• Some of the organisms lived on the earth for short time and became extinct. This was a result of drastic changes in the climate on the earth.

Hence, forth fossils produce bonafide record of such plants and animals which had shown their existence once upon a time and now are extinct or not present exactly in the same form, thus, producing strong evidence in favour of organic evolution.

MP Board Class 12th Biology Solutions