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State the opinion of Russian scientist Oparin and English scientist Haldane about the origin of first life.

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The opinion of Russian scientist Oparin and English scientist Haldane is as follows :
First life must have come from pre-existing non-living organic molecules (RNA, proteins etc.).
The structure of life must have been formed after chemical evolution, i.e. organic matter must have come into existence by the aggregation of inorganic molecules.
These substances must have been transformed into a colloidal system to produce life.
At that time the conditions on earth were very high temperature, volcanic storms, degenerate type of atmosphere which contained water, methane, ammonium etc.
The next step in molecular evolution was the creation of micro molecules.

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Explain Miller's experiment on origin of life with diagram.

OR
Explain Miller's experiment for origin of life with diagram.
OR
Draw well labelled diagram of S. L. Miller's experiment.
OR
Draw well labelled diagram showing laboratory conditions similar to conditions of earth. (MARCH 2023)

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In 1953, an American scientist named S. L. Miller created in the laboratory a condition similar to the Earth's primordial atmosphere.
He mixed CH4, H2, NH3 and water vapour in a closed flask at a temperature of 800oC and arranged the electrodes and gave electric shocks. Then the mixture was cooled in the condenser and made a liquid.
He Collected the liquid in a separate flask.
After two weeks of the procedure, the fluid was analyzed by chromatography.
He found that amino acids were formed in it. Besides hydroxy acids (scientific name of H2O), aliphatic acids were also present.
Similarly, other scientists have observed in this type of experiment that sugars, nitrogen bases, pigments and fats were produced.

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State three possibilities for evolution of living forms according to theory of special creation.

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Traditional religious literature informs us of a particular creation.
This theory has three connotations.

This theory has three connotations.

(1) According to the first possibility, all organisms seen today must have originated in this form.

(2) According to second possibility, the same biodiversity as it was at the time of origin will also, be in the future.

(3) A third possibility is that the earth is about 4000 years old.

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Explain the evolutionary theory of living form based on the observations of Charles Darwin.

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Ideas related to the evolution of living forms are based on the observations of Charles Darwin during his voyage around the world in the ocean liner H.M.S. Beagle.
Concluded that organisms on Earth not only resemble each other, they also resemble organisms from years ago.
Many of these organisms are extinct.
Some organisms have become extinct in different periods of the history of the earth, while new ones have also emerged.
Organisms are evolved gradually. Any population is stable due to variation in traits.
Factors such as some natural situations (air, food, physical elements etc.) enables better survival.
This situation tends to leave behind less able organisms, which do not fit in the changed invitations and die. or become extimet.
Population that have good fitness can survive on the earth (Survival of the fittest).
According to Darwin fitness means reproductive fitness.
Organisms that are better suited to the environment can produce more offspring than others to survive longer and nature selects them, which Darwin called natural selection.

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Explain divergent and convergent evolution with example.

OR
Explain Analogous organs with examples.
OR
Explain homologous and analogous structures with eample.(MARCH 2025)

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Divergent evolution :
Organisms which have the same structure (formation), but are adapted in different directions and according to their different needs shows divergent development.
This structure is called equivalent structure similar or Homologous organs.
Equivalence indicates common ancestors.
Example :
(1) Vertebrate Heart and Brain
(2) In plants, the thorn of Bougainvillea and Cucurbita represents homology.
(3) Whales, bats, leopards and humans have similarities in the bones of the forelimb.
Convergent evolution :
  • Organisms in which the internal structure is not the same, but are adapted to perform the same function, such development is called convergent evolution.
  • These structures are also called Analogous organs.

Example :

(1) The wing of a butterfly and a bird look the same and are used for flying. But they are not anatomically similar.

(2) Eye of Octopus and Mammals

(3) Flippers of penguins and dolphins

(4) Roots of sweet potatoes and tubers of potatoes.

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What are homologous organs? Explain with example.

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The organs of animals which have similar internal structure but different functions are called homologous organs.
For example whales, bats, leopards and humans (all mammals) have similarities in the internal structure of the forelimbs.
All of them have humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs.
In these animals, organs with the same structure performs different functions, as they are adapted in different directions. This is the evolution of divergence.
These structures are homologous organs.
Equivalence indicates common ancestors.
Other examples are the hearts and brains of vertebrates.
Thorn and tendrils of Bougainvillea and Cucurbita represents homology.

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Give difference between homologous and Analogous Organs. (June 2025)

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Homologous

Analogous

Organs

Organs

The organs of animals which have similar internal structure but performs different functions are called homologous organs.

The organs which are different in their internal structure.

The organs differ in their functions.

The organs appear same and their functions are similar.

Example : limbs of vertebrates such as man, cheetah, whale and Bat

Example : 1. wings of butterfly and birds.

2. flippers of penguins and dolphins.

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Explain the embryological basis of development.

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Ernst Haeckel gave the embryological basis of development, as the evidence of evolution.
Based on his observation some traits are common in all lineages during the embryonic stage, but absent in the adult organism.
For example, in the embryos of all vertebrates including humans, there is a row of vestigial folds behind the head, but it is only functional in fish, not in other adult vertebrates.
However, the proposed embryological basis of this development was rejected by Karl Ernst von Baer.
He noted that embryos sometimes, do not pass through the adult stages of other animals.

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Define the term : Species

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The group of organisms having maximum similar characteristics and can interbreed is called species.

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Write a note on fossil evidence. State the method by which age of fossils is calculated.

OR
Evidence that evolution of life has taken place on earth.

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Evidence of the emergence and development of life on earth are
(1) Fossils are the hard parts of life forms in rocks.
(2) Rocks, sediments and layers of the Earth's layers indicate the layering of organic elements over Earth's long history.
(3) Sedimentary rocks of different ages contain fossils of different life forms that must have died out during the formation of these particular rocks.
(4) Some of them show similarities with modern organisms. They represent extinct organisms.
(5) It means that life-forms change with time. And some life-forms do not change for certain planetary periods.
(6) All this is called fossil evidence.
(7) The age of fossils can be known by the method of radioactive-carbon dating.

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Describe an interesting observation supporting evolution by natural selection of melanised moths. OR Moth evolution is observed during industrialisation in England - Explain this statement. (JUNE 2025)

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An interesting observation supporting evolution by natural selection comes from England.
Impact of industrialisation:
In a collection of moths made in 1850s, i.e., before industrialisation set in, it was observed that there were more white-winged moths on trees than dark-winged or melanised moths.
However, in the collection carried out from the same area, but after industrialisation, i.e., in 1920, there were more dark-winged moths in the same area, i.e., the proportion was reversed.
The explanation given for this observation was that ‘predators will spot a moth against a contrasting background’.
During post-industrialization period, the tree trunks became dark due to industrial smoke and soots.
Under this condition the white-winged moth did not survive due to predators, dark-winged or melanised moth survived.
Before industrialisation set in, thick growth of almost white-coloured lichen covered the trees - in that background the white winged moth survived but the dark-coloured moth were picked out by predators.
Lichens are good pollution indicators.
They will not grow in areas that are polluted.
Moths that were able to camouflage themselves, i.e., hide in the background, survived.
The areas where industrialisation did not occur e.g., in rural areas, the count of melanic moths was low.
This showed that in a mixed population, those that can better-adapt, survive and increase in population size.

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What is adaptive radiation? Explain with examples. [NCERT Exercise Q.8](JULY 2023)

OR
Explain adaptive radiation.(JUNE 2024, March 2024, March/apRIL 2022)

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The process of development of different species starting from one point of a given geographical area to other geographical habitats is called adaptive radiation.
(1) Darwin finches
Darwin finches is an excellent example of this type of phenomenon.
Darwin saw several species of finches across the Galapagos Islands.
He speculated that all species had evolved on the island by themselves.
Along with other features of the original finches (seed eating), their beaks may have evolved for other forms that made them insectivorous and herbivorous finches.

(2) Australian marsupials

Another example is the Australian marsupial.
Most marsupials were different from each other.
They evolved from a common set of ancestors, but they all evolved on the Australian island continent.
When more than one adaptive radiation occurs in a geographical area (representing different habitats) it is called convergent evolution.
Mammals of Australian marsupials (E.g.:- the wolf and the Tasmanian wolf) show a similar evolution.

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State the Lamarck's observation on biological evolution.

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Lamarck's theory is "Theory of Inheritance of Acquired Traits".
Naturalist Lamarck said that, living forms evolved, they evolved organs, but they were transmitted through the use and disuse of those organs.
Development of organs is created and maintained in organisms under environmental pressure.
Lamarck gave the example of giraffe.
Giraffes adapted by lengthening their necks to reach edible leaves of tall trees.
This acquired trait of long neck was inherited in its subsequent generations.
Over the years the giraffe gradually acquired a long neck.
In this way, the characteristics acquired by the organism are inherited by its offspring.
The less used organs become non-functional or rudimentry.

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State the views of Thomas Malthus on natural selection.

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Natural resources are limited, their size is constant except for seasonal variations.
Members of a population, though outwardly similar, show differences in characteristics.
Most of the variations are hereditary.
If this is the reality and if every organism reproduces at the maximum rate then theoretically the population will grow like explosives and it is equally true that realistically the population size is limited.
This means that there is competition for resources.
Some were able to survive and thrive at the expense of others, while some could not be promoted.

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Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.

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When a colony of bacteria is grown in agar culture medium supplemented with tetracycline antibiotics, the tetracycline-sensitive colonies die.
Darwinian selection theory suggests that the environment selects organisms with useful variation over those which do not have useful variations.
It is mainly because, in a dynamic environment, these organisms are better adapted to survive.
A well-defined example for Darwin's theory is antibiotic resistance in bacteria.
When bacteria were grown on tetracycline containing agar medium, all the bacteria died. However, the ones having variations conferring tetracycline resistance survived. Later, these bacteria multiplied and increased their number.
As a result of this, tetracycline-resistant bacteria evolved and survived because of the environment that selected these over the others.

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The basic essence of Darwinism regarding evolution is natural selection. – Explain.

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The rate of emergence of new forms of organisms and the life cycle all are related to life span.
The rate at which new forms of organisms appear and is related to the life cycle or life span.
Rapidly dividing microorganisms have high multiplicity, reach millions within hours.

Example (1): A colony of bacteria growing in a given culture medium (say A) varies in terms of its ability to utilize food components.

If the composition of the medium is changed, only that fraction of the population (say B) that survives the changed condition will remain.
Over a certain period of time, a variant form of this population will outgrow the others and come into being as a new species.

Example (2) : But when this matter is applied to fish or chicken, it takes millions of years because their life span is in years.

It can be said that B's fitness is better than A's under the new conditions.
So called fitness is based on characteristics which are inherited.
Therefore there must be a genetic basis for selection and development.
In other words some organisms are better adapted to survive in a changing environment.
Adaptability is hereditary. It has genetic basis.
Fitness is the end result of the ability to adapt and to be selected by nature.
Two key evolutionary concepts developed by Darwin are natural selection and branching.
Darwin stated that variations are inherited and are well adapted to a particular habitat and resource.

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What do you understand about the theories of Hugo-de-Vries?

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Hugo-de-Vries's theory is called Mutation theory.
When the new traits i.e. new variation in traits suddenly comes into existence is called accidental variation (mutation).
Once a mutation is created, it becomes permanent immediately. It means that it continues to appear thereafter.
In the first decade of the 20th century, Hugo-de-Vries worked on evening primrose (Oenothera lamarckiana) plants.
Here it is presented the idea that mutation means a sudden big difference in the population.
He believed that mutation is the main cause of development.
According to him mutation is random and non-directional.
According to Darwin, variation is small and directional.
De-vries believed mutation caused speciation and hence saltation (single step large mutation is called saltation).

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Explain natural selection on different traits with diagram.

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Natural selection disturbs the Hardy-Weinberg equilibrium by changing the frequency of alleles in a population.
It can lead to three types of selection:
(a) Stabilizing selection : Here, more individuals acquire mean character value and variation is reduced.
(b) Directional selection : Individuals at one extreme are more favoured.
(c) Disruptive selection : Individuals at both extremes are more favoured.

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Explain the factors affecting the Hardy-Weinberg equilibrium.

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Five factors affecting the Hardy–Weinberg equilibrium are:
(1) Genetic Drift : The change in gene frequency by chance is called genetic drift.
(2) Mutation : It results in the formation of new alleles over a few generations; this may lead to speciation.
(3) Genetic Recombination : Reshuffling of gene combinations during crossing over results in genetic recombination and thus variation.
(4) Gene Flow (Gene migration) : Movement of genes from one population to another is called gene migration. If gene migration occurs repeatedly, it is called gene flow.
(5) Natural Selection :
(a) Stabilizing selection: Here, more individuals acquire the mean character value and variation is reduced.
(b) Directional selection: Individuals at one extreme are more favoured.
(c) Disruptive selection: Individuals at both extremes are more favoured.

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For the MN-blood group system, the frequencies of M and N alleles are 0.7 and 0.3, respectively. The expected frequency of MN-blood group bearing organisms is likely to be :

//X

(p + q)2 = p2 + 2pq + q2
Where ; M = p and N = q
So, (p + q)2 = p2 + 2pq + q2
= (0.7)2 + 2(0.7)(0.3) + (0.3)2
= 0.49 + 0.42 + 0.09
49% MM : 42% MN : 9% NN
Thus, in this equation the value of 2pq is 0.42 or 42%.

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The frequency of three gene variants in a certain type of population is as follows : Gene variants : BB Bb bb Frequency : 22% 62% 16% Find the frequency of B and b factors.

//X

As per Hardy weinberg equation :
p2 + 2pq + q2 = 1
Frequency of B : B = BB + Bb
= %
= (22 + 31)
= 53%
Frequency of b : b = bb + Bb
= %
= (16 + 31)%
= 47%
Hear, frequency of B = 53% and Frequency of b = 47%.

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Explain the Hardy-Weinberg equilibrium principle.

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In a given population one can find out the frequency of occurrence of alleles of a gene or a locus.
This frequency is supposed to remain fixed and even remain the same through generations.
Hardy-Weinberg principle stated it using algebraic equations.
This principle says that allele frequencies in a population are stable and is constant from generation to generation.
The gene pool (total genes and their alleles in a population) remains constant. This is called genetic equilibrium.
Sum total of all the allelic frequencies is 1. Individual frequencies, for example, can be named p, q etc.
In a diploid, p and q represent the frequency of allele A and allele a.
p2 + 2pq + q2 = 1. This is a binomial expansion of (p + q)2.
Where ; p2 - Frequency of individuals with genotype AA.

q2 - Frequency of individuals with genotype aa.

2pq - Frequency of individuals with genotype Aa.

When frequency measured, differs from expected values, the difference (direction) indicates the extent of evolutionary change.
Disturbance in genetic equilibrium, or Hardy-Weinberg equilibrium, i.e. change of frequency of alleles in a population would then be interpreted as resulting in evolution.

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Explain organisms are allowed to reproduce and leave greater number of progeny by natural selection.

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Pre-existing advantageous mutations when selected will result in observation of new phenotypes.
Over few generations, this would result in Speciation.
Natural selection is a process in which heritable variations enabling better survival are enabled to reproduce and leave greater number of progeny.
A critical analysis makes us believe that variation due to mutation or variation due to recombination during gametogenesis, or due to gene flow or genetic drift results in changed frequency of genes and alleles in future generation.

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Draw a diagram of the evolution of the plant forms through geological period.

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For answer see the Page no. 299 and point 6.8 Fig.(a) of summary.

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Give a brief account on plant evolution.

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About 2000 million years ago (mya) the first cellular forms of life appeared on earth.
The mechanism of how non-cellular aggregates of giant macromolecules could evolve into cells with membranous envelope is not known.
Some of these cells had the ability to release O2.
The reaction could have been similar to the light reaction in photosynthesis where water is split with the help of solar energy captured and channelized by appropriate light harvesting pigments.
Slowly single-celled organisms became multi-cellular life forms.
Sea weeds and few plants existed probably around 320 mya.
They were widespread on land when animals invaded land.
Giant ferns pteridophytes were present around
200 million years ago.

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Draw a diagram representing the evolutionary history of vertebrates through geological periods.

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For answer see the Page no. 300 and point 6.8 Fig.(b) of summary.

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Find the developmental stages of an animal by using various resources like school library or internet and discuss with your teacher.

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During the Eocene period, the horse evolved from Eohippus.
Eohippus → Mesohippus → Marychippus → Pliohippus → Iccus.
Changes during development :

(1) Gradual increase in height (28 cm to 150 cm)

(2) Gradual reduction in fingers (4 to 1)

(3) To use grass as food, tooth structure become complex (increased size of molar crowns)

(4) Increase in length of head and neck

(5) Increase in length of anterior and posterior appendages

(6) Brain and sensory organs developed

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Give a brief account of evolution of vertebrates.

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About 2000 million years ago the first cellular life was found on earth.
About 350 million years ago, jawless fishes emerged.
Some mammals live entirely in water. Whales, dolphins, seals and sea cows are some examples.

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Match Ten modern animals with their ancient fossils using internet resources. Name both.

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Modern Animals

Fossils

1.

Modern Human (Homo sapiens)

1.

Cro-magnon man (Homo sapiens)

2.

A horse

2.

Eohippus

3.

Bird

3.

Ornithomimus (Dinosaur)

4.

Amphibians

4.

Labyrinthodontia

5.

The camel

5.

Poebrotherium

6.

Elephant

6.

Moeritherium (Post eocene period)

7.

Whales

7.

Protocytes

8.

Arthropoda (crustacean and insects)

8.

Trilobites

9.

Reptiles

9.

Stegoce phalians (carboniferous period)

10.

Terrestrial animals

10.

Cosopterygian fishes

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Find out through the internet and popular science articles whether animals other than man have self-consciousness.

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Apart from humans, there are many other animals that possess self-consciousness.
(1) One such example is the Dolphin. They are believed to have a high level of intelligence. Also, they have a sense of self and can identify themselves amongst others. They whistle, tail-slap and exhibit body movements to communicate with each other.
(2) Some other animals that exhibit self-consciousness are parrots, crows, gorillas, orangutans, chimpanzees etc.

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Can we call human evolution as adaptive radiation?

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No, Human evolution can not be referred to as adaptive radiation because adaptive radiation is an evolutionary process which gives rise to new species from a single common ancestor at a rapid rate. There are radiation lines radiating in different directions.
Human development is a gradual process. It takes a long time.
Australopithecine has many ape-like features.
Modern humans have many well-developed traits.

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Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.

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Huxley suggested that humans evolved from apes, but fossil evidence suggests that humans and apes are descended from a common ancestor (evolved in parallel).
Chimpanzees are more evolved than humans.
Humans are the most advanced species. There were no two opinions.
Compared to the 14,000 genes of Chimpanzees and humans, Ape may have been under the pressure of natural selection.
Our large brains and high intelligence are a gift of natural selection.
Humans and Chimpanzees followed a different evolutionary path from a common ancestor 5 million years ago.
Humans and chimpanzees underwent changes so that the fittest were passed on to future generations by natural selection.
Their genes were carried over.
But according to a study in the US, humans have significantly fewer positive genes than Chimpanzees has.

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Describe origin and Evolution of Man.

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About 15 mya primates such as Dryopithecus and Ramapithecus existed.
They appeared to be similar to Gorillas and Chimpanzees in their appearance and walking.
Ramapithecus was more similar to man whereas Dryopithecus was more similar to apes.
Few fossils of bones that resemble human bones have been discovered in Ethiopia and Tanzania.
The skull of a child Chimpanzee is more similar to that of an adult human than that of an adult chimpanzee.
These human-like features further support the belief that 3-4 million years ago human-like primates roamed East Africa.
They were probably 4 feet tall or less, but could walk upright.

(i) Australopithecines :
Two mya Australopithecines existed. They most likely lived in East African grasslands.
They used stone weapons for hunting.
Essentially had a fruit-based diet. They also survived on plant-based diet and did not eat meat.
The first human-like organism was the hominid and was called Homo habilis.
Brain capacity was 650 – 800 cc.
(ii) Homo erectus :
Fossils discovered in Java in 1891 seemed to be of the next stage i.e. Homo erectus.
They evolved about 1.5 mya.
Had large brain with capacity around 900 cc.
Probably ate meat.
(iii) Neanderthal man :
Brain size was around 1400 cc.
Lived in east and central Asia between 1,00,000 - 40,000 years back.
They developed use of animal hides to protect their body.
Buried their dead.
(iv) Homo sapiens :
Arose in Africa.
Migrated across continents and developed distinct races.
During ice age 75,000 - 10,000 years ago modern Homo sapiens arose.
Prehistoric cave art developed about 18,000 years ago.
Prehistoric man-made paintings are found in one such cave on the Bhimbetka rock in Raisen district of Madhya Pradesh.
Agriculture came around 10,000 years back and human settlement started.

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Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference etc.)

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Ans. (A) Brain size and function :

(1)

Australopithecines

450 - 600 cc

(2)

Homo habilis

650 - 800 cc

(3)

Homo erectus

900 - 1200 cc

(4)

Neanderthal man

1400 cc

(5)

Cro - Magnons

1600 cc

(6)

Homo sapiens

1450 - 1650 cc
There is a growth in the grey matter of brain.
The number of sulci and gyri also increases in brain.
(B) Skeletal Structure :
The spine is the only found to have the same curve in the ape. The length of the arms is found to be longer than the legs.
Human spine is 'S' shaped, legs longer than arms.
(C) Food habits :
Dryopithecus and Ramapithecus herbivores, frugivorous.
Australopithecines - frugivorous, carnivores
Homo habilis - frugivorous
Homo erectus - carnivores
Homo neanderthals - omnivores
Homo sapiens - omnivores

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When mammals took over the earth write the character and continental drift of the mammals of that time?

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The first mammals were like shrews.
Their fossils are small sized.
Mammals were viviparous and protected their unborn young inside the mother's body.
Mammals were more intelligent in sensing and avoiding danger at least.
When reptiles came down mammals took over this earth.
There were in South America mammals resembling horse, hippopotamus, bear, rabbit, etc.
Due to continental drift, when South America joined North America, these animals were overridden by North American fauna.
Due to the same continental drift pouched mammals of Australia survived because of lack of competition from any other mammal.