Explore topic-wise InterviewSolutions in Current Affairs.

Carbon atoms in diamond are bonded in a strong tetrahedron pattern making it hard and clear whereas carbon atoms in graphite are bonded in weak covalent bonds making it soft and black. Coal is a combustible sedimentary rock occurring in rock strata in layers or veins called coal beds. Because of pressure and elevated temperature the carbon becomes hard and chunky. 

The sweat evaporates because of increase in surface area and getting the temperature from atmosphere. This is resulting in decrease in temperature of skin and finally our body, which gives relief to us in hot days. Sweating is a natural mechanism to keep cool the surface of our body in hot days. This is the cause that with increase in temperature our body sweats a lot especially in hot summer days.

According to James Clerk Maxwell’s electromagnetic theory, a charged body in circular motion continuously emits energy as radiations. Electrons which revolve around the nucleus are negatively charged. Hence while electrons revolve around the nucleus, they should emit electromagnetic radiations lose energy and come closer to the nucleus Finally the negatively charged electrons should collapse into the nucleus.

But this does not happen in an atom. It Rutherford’s model failed to explain this.

Transfer of genes between population that differ genetically from one another is called gene flow.

(B) Acetic acid turns red litmus blue but it does not affect blue litmus.

Correct answer is (b) Oenothera lamarkiana

i. Gene flow is also called as gene migration.

ii. When a section of population migrates to another population, gene pool of both the populations change, as some alleles are lost from first population, while they are added to second population.

iii. When animals migrate from an area to another, they contribute their genes to the gene pool of that area and hence a change in gene frequency.

Correct option is (d) Mutations are non-random and directional

The structural, morphological change in chromosome due to rearrangement, is called chromosomal aberrations.

1. Stabilizing selection is the type of natural selection which balances the population, hence it is also known as balancing selection. 

2. In such population more individuals acquire a mean character value. 

3. Such selection tends to favour the intermediate forms and eliminate both the phenotypic extremes. 

E.g. More number of infants with intermediate weight survive better as compared to overweight or underweight infants. 

4. Stabilizing selection reduces variations. 

5. It tends to maintain phenotypic stability within population, and does not bring about drastic evolutionary changes. 

6. A population showing stabilizing selection is well-adapted to its environment

Genetic variations : The change in gene and gene frequencies is known as genetic variation. Genetic variations are caused by following factors:

(i) Mutations : Sudden permanent heritable change is called mutation. Mutation can occur in the gene, in the chromosome structure and in chromosome number. Mutation that occurs within the single gene is called point mutation or gene mutation. This leads to the change in the phenotype of the organism, causing variations.

(ii) Genetic recombination : In sexually reproducing organisms, during gamete formation, exchange of genetic material occurs between non-sister chromatids of homologous chromosomes. This is called crossing over. It produces new genetic combinations which result in variation. Fertilization between opposite mating gametes leads to various recombinations resulting into the phenotypic variations. These result in change in the frequencies of alleles.

(iii) Gene flow : Gene flow is movement of genes into or out of a population. Gene movement may be in the form of migration of organism, or gametes (dispersal of pollens) or segments of DNA (transformation). Gene flow also alters gene frequency causing evolutionary changes.

(iv) Genetic drift : Any random fluctuation (alteration) in allele frequency, occurring in the natural population by pure chance, is called genetic drift. For example, when the size of a population is severely reduced due to natural disasters like earthquakes, floods, fires, etc. elimination of particular alleles from a population becomes possible. Smaller populations have greater chances for genetic drift. It results in the change in the gene frequency. Genetic drift is also an important factor for evolutionary change.

(v) Chromosomal aberrations : The structural, morphological change in chromosome due to rearrangement of genes is called chromosomal aberrations. Due to changes in the gene arrangement or gene sequence variations are caused.

Correct answer is (c) Ichthyostega

1. Isolation means separation of the population of a particular species into smaller units. The organisms belonging to these subunits are prevented from interbreeding due to some barrier. These barriers are called isolating mechanisms.

2. They prevent the genetic exchange and gene flow. 

3. Due to isolating mechanisms in nature the divergence among organisms takes place gradually leading to speciation. The isolating mechanisms are of two types namely, geographical isolation and reproductive isolation.

I. Geographical Isolation : The barrier in the form of physical distance or geographical barrier is called geographical isolation. The original population gets divided into two or more groups by geographical barriers such as river, ocean, mountain, glacier, etc. Organisms cannot cross the barriers on their own and hence interbreeding is prevented between isolated groups.

The separated groups experience different environmental factors and they acquire new traits by mutations. The separated populations develop distinct gene pool and they do not interbreed. Each subgroup then evolves differently which results into formation of new species. E.g. Darwin’s Finches, African elephant, Loxodonta and Indian elephant, Elephas.

II. Reproductive Isolation : Two populations may be occupying the same area, they may not be separated by geographical barrier, but then also they are reproductively isolated. Such reproductive isolation occurs due to change in genetic material, gene pool and structure of genital organs. Such differences prevent interbreeding between population. Such isolation later leads to speciation.

III. Different types of reproductive isolations : Reproductive isolation is of two types, viz. prezygotic and post-zygotic isolating mechanisms.

1. Pre-zygotic or pre-mating isolating mechanisms do not allow individuals to mate with each other at all. 

2. By various mechanisms the two groups remain isolated. 

3. In post-zygotic or post-mating isolating mechanisms, the two individuals can mate but the result of mating is not favourable. 

4. Thus the populations remain isolated without the actual genetic exchange.

Correct answer is (b) divergent

1. The structural similarities between the homologous organs indicate that they have a common ancestry. 

2. Different homologous organs indicate divergent evolution or adaptive radiation. 

3. Homologous organs help in tracing the phylogenetic relationships. 

4. Homologous organs are those organs which are structurally similar but functionally dissimilar.

E.g. 

(i) Forelimbs of frog, lizard, bird, bat, whale and man are homologous to each other. All the limbs are morphologically similar in construction such as similar limb bones but are dissimilar in function. Frog limbs are meant for hopping, lizard limbs help in crawling, birds and bats fly with the . help of forelimbs while whale uses it for swimming and man for handling the objects.

(ii) Vertebrate heart and brain. & In plants, thorns of Bougainvillea and tendrils of Cucurbita represent homology.

Homologous organs are those organs, which are structurally similar but perform different functions.

 Correct Option is (A) vestigeal

Kettlewell reported that Biston betularia or peppered moth displayed industrial melanism.

Correct answer is (d) convergent evolution

1. Analogous organs are similar in function but dissimilar in structural details. 

2. They do not help to trace the relationship in the evolution but help to understand the convergent evolution. 

3. Structural modifications in the organs are due to similar habitat.

E.g.

(i) Wing of an insect and wing of a bird, both are useful in flight so they are functionally similar but are structurally different. Insect wing is formed by exoskeleton expansion while bird wing is the modified forelimb. 

(ii) Eye of the Molluscan octopus and of eye of mammals. They differ in their retinal position, structure of lens and origin of different eye parts, but both perform function of vision. 

(iii) The flippers of penguins (birds) and dolphins (mammals).

(iv) Sweet potato which is a root modification and potato which is a stem modification, both perform similar function of storing starchy food.

Thorns of Bougainvillea and tendrils of Cucurbita.

Correct option is (b) Flippers of dolphins and penguin

Propyl chloride

Isolation: Separation of a single population into several sub-units is called Isolation.

Interbreeding does not occur between isolated groups. Each group may develop a set of new traits that lead to evolutionary changes and towards formation of new species.

The isolating mechanisms are of two types:

i. Geographical isolation:

a. It occurs when an original population is separated into two or more groups by geographical barriers such as river, mountain, ocean, island formation, forests, etc.

b. The separated groups are exposed to different kinds of environmental factors. Hence, each group acquires variations by developing mutations, recombination, etc.

c. These variations are processed by natural selection. This leads to progressive genetic divergence. The separated populations develop distinct gene pool and they do not interbreed. Thus, the species are formed by geographical isolation.

d. The classic example of geographical isolation is that of Darwin’s finches.

e. Example: Darwin’s finches living on Galapagos islands differ not only among themselves but also from mainland finches in size, colour, beak and food habits.

ii. Reproductive isolation:

a. Reproductive isolation is brought about by the change in genetic material, gene pool and structure of genital organs.

b. It prevents interbreeding between populations whether they are geographically isolated or living close together.

(a) Pentanoic acid (b) But-1-yne (c) Heptanal (d) Pentanol

Carboxylic acid (-COOH) can be detected by using sodium hydrogen carbonate (NaHCO₃) test. Treating a carboxylic acid with NaHCO₃ causes effervescence due to the liberation of carbon dioxide (CO₂). 

The reaction is as follows: 

R-COOH + NaHCO₃→ R-COONa + CO₂ + H₂O

Sweet potato and potato.

1. (iii) Propanol

2. (iv) All of the above

3. (i) TRUE

4. (iii) Both (i) and (ii)

5. (ii) Concentrated sulphuric acid

1. Habitat or ecological isolating mechanism 

2. Seasonal or temporal isolating mechanism 

3. Ethological isolating mechanism

4. Mechanical isolating mechanism

Pre-mating or pre-zygotic isolating mechanisms:

i. Habitat isolation: In this isolation, members of a population living in the same region occupy different habitat. Thus, potential mates do not meet.

ii. Seasonal isolation: In this isolation, members of a population attain sexual maturity at different times, thus preventing interbreeding. Light coloured moth Dark coloured moth Dark coloured moth Light coloured moth Before industrial revolution After industrial revolution 10 Std. XII Sci.: Perfect Biology ‐ II

iii. Ethological isolation: In this isolation, members of two populations have different mating behaviours. This prevents interbreeding.

iv. Mechanical isolation: In this isolation, the members of two populations have difference in the structure of reproductive organs. So, interbreeding is not possible.

The answer is (d)

(1) Pre-zygotic or pre-mating isolating mechanisms do not allow individuals to mate with each other at all.

(2) By various mechanisms the two groups remain isolated. These mechanisms are of following types: 

(i) Habitat isolation : Habitat isolation is the phenomenon in which members of a population living in the same region occupy different habitats. Hence the potential mates do not interbreed among themselves.

(ii) Seasonal isolation : In seasonal isolation, members of a population share the same region but attaining sexual maturity at the different times of the year. They thus remain isolated reproductively preventing interbreeding among themselves. 

(iii) Ethological isolation : Ethological isolation is seen when members of two populations have different mating behaviours. This prevents interbreeding.

(iv) Mechanical isolation : Mechanical isolation is seen when the members of two populations have differences in the structure of reproductive organs. Due to such differences interbreeding is not possible.

The answer is (c) sodium ethoxide and hydrogen

2Na + 2CH₃CH₂OH → 2CH₃CH₂ONa + H

A) absolute alcohol

Na + CH₃CH₂OH → CH₃CH₂ONa + H₂

D) All of these

1. He may observe that the resulting mixture is a sweet odoured substance. 

2. The substance is ethyl acetate, an ester.

Correct option is  B) Hydrogen

Correct option is  B) Ethene

1. Water in rivers, reservoirs and lakes may contain many impurities. 

2. Under safe drinking water supply scheme, the water is purified through physical and chemical treatment which includes. 

a) Coagulation : 

Adding chemicals to bind with impurities in water forming heavy particles. 

b) Sedimentation : 

Making these heavy particles to settle at the bottom. 

c) Filtration: 

Passing the upper water through filters to remove remaining undissolved particles. 

d) Disinfection : 

Adding chlorine or bleaching powder to kill disease causing micro organisms.

The correct answer is C) Aeration.

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