Explore topic-wise InterviewSolutions in .

(i) Human arm and fore leg of cow are homologous organs because they are built upon the same fundamental plan (pentadactyl pattern) but they perform different functions as grasping in man and locomotion in cow.

(ii) Bat’s wing and grass hopper’s wing are analogous organs because they perform the same function bat differ in their origin and structure. Wings of bats are modified fore limbs where as grasshoppers wings are modified outgrowth of the body wall.

Ramapithicus -> Australopithicines -> Homoerectus -> Neanderthalman -> Homosapiens

Dryopithecus —> australopithecus —> Homo erectus —> neanderthal man —> Homo sapiens

(S.L. Miller created condition similar to prehistoric earth with reducing environment, high energy ladiations, high temperature etc. in the laboratory). He created electric discharge in a closed flask, containing CH₄, H₂, NH₃ and water vapour, at 800^o C, observed formation of amino acid (organic molecules), thus supporting that life originated from pre-existing non-living organic molecule.

Name of the scientist is S.L. Miller. 

Purpose of 'a' is to supply electric discharge as a is a substitute of thundering. 

Conclusion : Life originates from pre-existing life. It proved the chemical evolution of life.

Detailed Answer :

Chemicals found in the samples drawn from 'c' sugar, proteins and amino acids.

It provided experimental evidences for the theory of chemical evolution of life. It proved that life originates from pre-existing life.

Some objections raised against Darwinism were Darwin failed to explain the mechanism of variation.

1. Darwinism explains the survival of the fittest but not the arrival of the fittest. 

2. He focused on small fluctuating variations that are mostly non-heritable. 

3. He did not distinguish between somatic and germinal variations.

4. He could not explain the occurrence of vestigial organs, over specialization of some organs like large tusks in extinct mammoths and over sized antlers in the extinct Irish deer, etc.

(i) and (ii): Analogous (iii) and (iv): Homologous.

Natural selection can be explained clearly through industrial melanism. Industrial melanism is a classical case of Natural selection exhibited by the peppered moth, Bistort betularia. These were available in two colours, white and black. Before industrialization peppered moth both white and black coloured were common in England. Pre-industrialization witnessed white colpured background of the wall of the buildings hence the white coloured moths escaped from their predators. Post industrialization, the tree trunks became dark due to smoke and soot let out from the industries.

The black moths camouflaged on the dark bark of the trees and the white moths were easily identified by their predators. Hence the dark coloured moth population was selected and their number increased when compared to the white moths. Nature offered positive selection pressure to the black coloured moths. The above proof shows that in a population, organisms that can adapt will survive and produce more progenies resulting in increase in population through natural selection.

i. Stabilising selection (centipetal selection): This type of selection operates in a stable environment as shown in fig. The organisms with average phenotypes survive whereas the extreme individuals from both the ends are eliminated. There is no speciation but the phenotypic stability is maintained within the population over generation. 

For example, measurements of sparrows that survived the storm clustered around the mean, and the sparrows that failed to survive the storm clustered around the extremes of the variation showing stabilizing selection.

ii. Directional Selection: The environment” which undergoes gradual change is subjected to directional selection, as shown in fig. This type of selection removes the individuals from one end towards the other end of phenotypic distribution. 

For example, size differences between male and female sparrows. Both male and female look alike externally but differ in body weight. Females show directional selection in relation to body weight.

iii. Disruptive selection: (centrifugal selection) When homogenous environment changes into heterogenous environment this type of selection is operational as shown in fig. The organisms of both the extreme phenotypes are selected, whereas individuals with average phenotype are eliminated. This results in splitting of the population into sub population/species. This is a rare form of selection but leads to formation of two or more different species. It is also (called adaptive radiation. 

(E.g:) Darwin’s finches beak size in relation to seed size inhabiting Galapagos islands. Group selection and sexual selection are other types of selection. The two major group selections are Altrusim and Kin selection.

It is an ancestor of amphibians.

Homo habilis did not eat meat. They were vegetarian. 

Homo erectus ate meat. They were meat eater.

1. Selected mating 

2. Flow of genes (either by immigration or emmigration) 

3. Occurance of mutation 

4. Definite population size