Tyrannosaurus rex was the largest of the dinosaurs.
(i) It was about 20-feet in height.
(ii) It had huge fearsome dagger-like teeth.

These are analogous organs, doing the same function.
Analogous organs are those organs, in different groups of organisms, which perform the same function, but are dissimilar in their basic structural plan and developmental origin. 

Migration may bring in more such alleles, that bestow upon the individuals of the population, such adaptations/traits, which are selected by nature.
similarly, emigration may lead to removal of such alleles that confer better adaptations.
Immigration can also bring in those alleles which confer those traits, which are not suitable to the given environment, i.e. they are not selected by nature.

Survival of the fittest means that those individuals which survive and reproduce successfully in their given environment or habitat, are called fit.
Such individuals produce more progeny (with more fit individuals), than the others who are less-adapted to survive and reproduce in that environment.

(a) Hearts of humans and monkeys.
(c) Thorns of Bougainvillea and tendrils of Cucurbits.
These are homologous structures as they have similar anatomical structures, but perform different functions.

Role of genetic variations in evolution:
1. Genetic variability is necessary for evolution. They are the raw materials of evolution.
2. Genetic variations in a population arise due to two different mechanisms. They are gene migration and genetic drift.

Types of variations:
1-Interspecific variations.
2-Interaspecific variations.

Role of sum in origin and evolution of life. Sun, The ultimate source of energy for the living world on this plant has played a significant role in the origin and evolution of life.
1. Influence of high energy radiations from sun: The simple elements such as carbon, oxygen, hydrogen and nitrogen combined to form complex molecules of organic compounds under the influence of high energy radiations from the sun.
2. Formation of chlorophyll: The earlier organism present at the earth were heterotrophs, as the chemical evolution proceede and omplex macromolecules joined with each other. The chlorophyll was formed and the organisms became autotrophs and started manufacturing their own organic food.
3. Solar energy: Solar energy is the only source of energy in the living world. Sun has played a vital role in the chemical evolution.

The given equation represents Hardy-Weinberg's (genetic) equilibrium.
The principle states that allele frequencies in a population are stable and remain constant from generation to generation.
(a) The sum total of all the allelic frequencies is one.
Individual frequencies are named p and q, which represent the frequency of allele A and a, respectively, in a population of diploid organisms.
The frequency of AA individuals is p², while that of aa is q² and Aa is 2pq; hence p²+2pq+q²=1.
(b) When the frequency measured differs from the expected values, the difference indicates the extent of evolutionary change.
The disturbance in genetic equilibrium, would then be interpreted as resulting in evolution.

Convergent evolution:
It is the evolutionary process in which anatomically different organs in different groups of organisms, evolve towards the same function.
Analogous organs are the result of convergent evolution, e.g. Sweet potato (root modification) and potato (stem modification) are analogous, as they both are tuberous with stored food materials.
Divergent evolution:
It is the evolutionary process in which the same structure develops in different directions in different groups of organisms as adaptations to different needs.
Homologous organs are the result of divergent evolution, e.g. human hands are homologous to the wings of a bird, as their basic structure (number and types of bones) is similar. 

(i) Antibiotics are the chemicals produced by bacteria which hinder growth of other microbes.
(ii) Indiscriminate and overuse of antibiotics are possible reasons for development of resistance in bacteria to antibiotics.
(iii) DNA fingerprinting is used to identify the antibiotic for which bacterium is resistant. This technique helps in selection of the right antibiotic for treatment.

(a) Culture: It is defined as an accumulation of knowledge and accomplishment of Knowledge and accomplishment. Following evidences suggest that Homo erectus had a culture.
1. The tools found amongst fossil remains of this species show that its members were capable of making tools and transmitting this knowledge to next generations.
2. He had achieved techniques for hunting and utilising wild game.
3. Ability of Homo erectus to accumulate and transmit culture is the fact that members were widely dispersed and apparently successful in living in a variety of environment.
(b) Culture of Neanderthal man represent advancement from Homo erectus as his tools were of wider variety and was capable of creating fire when needed.
His methods of burial suggest a much more sophisticated type of reasoning ability.
Thus the above facts show that along with organic evolution there occurred cultural evolution.
Nature selection operates in the following ways according to Darwin's theory:
(1) All planted and animals reproduce in geometrical pattern. The number of organisms produced are much more that can survive due to limited space and food.
(2)  Due to same basic requirement competition between organisms take place and those who are better adapted to environment survive while the rest die.
(3)  The individuals having useful variation overpower those without or having harmless variations and these variations are transmitted to further generations.

Natural Selection: In modern term natural selection is differential reproduction. Natural selection is main evolutionary process which causes the change of allele frequencies or in other words selection is the consistent differences in contribution of various genotypes to the next generation.
In in a population both small and largest individuals contribute relatively fewer offspring to the next generation then those closer to the averages do, stabilizing selection is operating.
If centre of population contributes more then equilibrium is maintained while if extremes of population work then two peaks in the distribution of a trait produced, while former is disruptive selection.

(a) Nature selects for fitness.
(i)  We must remember that fitness is based on the characteristics which are inherited.
(ii) So there must be a genetic basis for getting selected and to evolve; in other words, there are some organisms which are better adapted to survive in an otherwise hostile environment.
(iii) Adaptive ability is inherited and it has a genetic basis; hence fitness is the end result of the ability to adapt and get selected by nature.
(b) The rate of appearance of new forms is linked to the lifespan of the species.
(i) Microbes have the ability to divide and multiply to produce millions of individuals within hours.
(ii) A colony of bacteria (say A) growing on a given medium, has built-in variation in terms of ability to utilise a food component.
(iii) A change in the composition of the medium will allow only those individuals who can survive in the changed condition.
In due course of time, the variant population (say B) would outgrow the population A and appear as a new species; this would happen within a few days.
(iv) This is also true for microbes to develop antibiotic-resistant varieties.
(v) Use of pesticides like DDT against mosquitoes has resulted in mosquito populations with DDT-resistance within a few years.
(vi) For a change to occur in a fish or fowl would take million years, as their would take million years, as their lifespans are in years.