Definition
Divergent evolution is a type of evolution where similar body structures have evolved to perform different functions based on the need of the organism.
Cause/driving force
Due to the presence of different environments, certain body parts of organisms have modified their functions so that they can adapt to these habitats. These body parts are called homologous organs as they have similar body structure but different functions.
Significance
Divergent evolution indicates that the organisms have a common ancestor but they develop different characteristics (due to the changing environment) giving rise to new species.
Examples
In animals :
The forelimbs of Whales, Bats, Cheetahs and Humans have a similar bone structure (contain humerus, radius, ulna, carpels, phalanges) but they perform different functions. In whales it is used for swimming, Bats use it for flying, Cheetahs for running and Humans for different functions.
The hearts in various vertebrates (fishes, amphibians, reptiles, birds, and mammals) have similar structure but vary in the number of chambers they have due to diverse habitats and energy requirements.
In plants :
The thorns of Bougainvillea and the tendrils of Cucurbita are modified branches i.e. they have the same basic structure and common ancestor but the functions are different. The thorns are used for protection and the tendrils are used as support to the plant.

(a) Cotton bollworm attacks cotton crops and causes lot of damage to the crop.
Bt cotton plant contains the gene coding for Bt toxin which is produced by Bacillus thuringiensis. The toxin is coded by a gene Cry IAc named cry. Bacillus Thuringiensis forms protein crystals during a particular phase of their growth.
These crystals contain a toxic insecticidal protein. The Bt toxin protein exists as inactive protoxin but once an insect ingests the inactive toxin, it is converted into an active form of toxin due to alkaline pH of gut which solubilise the crystals.
The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and eventually causes death of insect.
(b) Cry IAb codes for proteins that control corn borer.

Analogy and homology of structures indicate the evidences of evolution from comparative study of morphology and anatomy of form, structure, relative position of different organs and their functions. Analogy indicates that similar environmental conditions and habitat result in the selection of similar adaptive features in different groups of organisms towards the similar function.
This shows the evolution of similar functional structures from unrelated organs. This is the result of convergent evolution. 
Homology includes the organs having similar structure origin and development, developed to have different forms so as to perform different functions in different groups of organisations. This phenomenon of producing functionally different forms from structurally similar organs is the result of divergent evolution. It indicates towards the common ancestory.

(a)
(b) The virus is called retro virus because its genetic material is RNA that is transcribed to DNA using enzyme reverse transciptase.
(c) Yes, the infected cell can survive, while viruses are being replicated and released.

The process by which retrovirus gains entry into human host body or the mechanism by which AIDS virus causes immunodeficiency is as follows:

Bacillus thuringiens· :
(a) This bacterium produces a protein, which is toxic to he larvae of insects like bollworm, budworm, flies, bettles,etc.
 Bt-toxin gene has been cloned from the bacteria and been expressed in plants to provide resistance to insects without the need for chemical insecticides.
(b) The gene (cry) coding for the protein has been isolated using restriction enzymes.
They are cloned in the vectors and then introduced into a number of crop plants like cotton, tomato, corn, rice, etc.
There are a number of different forms of the gene, that code for insect-specific Cry proteins, e.g., crylAc and cryllAb control cotton bollworm.
crylAb controls corn borer.
The transgenic plants (called as Bt corn, Bt rice, Bt cotton, etc.) produce the protein in their cells and express the insect/pest resistance.

(a) The source plant of heroin isPapaver somniferum (opium poppy).
(i) Morphine is extracted from the latex of poppy plant and by acetylation of morphine, heroin is obtained.
(b) Heroin is a depressant and slows down the body functions.

Transmissible-Whooping cough, tuberculosis, measles, syphilis, influenza. All others are non-transmissible diseases.

(i) Large head, mobile neck, short trunk with broad chest, long limbs;
(ii) large, highly convoluted brain;
(iii) well developed facial muscles to express emotions; and
(iv) lack of tail.

Gene therapy would be a better option because it has the potential to completely cure the patient.

(i) If the population is huge, total number is not an easily adoptable measure as counting takes a very long time.
(ii) For some ecological investigations, there is no need to know the absolute population densities.

Symptoms of dengue fever:
(i) fever
(ii) headache
(iii) muscle and joints pain
(iv) characteristic skin rashes
(v) decrease in platelet count in severe cases.
The disease is transmitted by Aedes mosquito.

Hibernation-winter sleep to escape in time e.g., bears.
Aestivation-summer sleep to avoid heat and desiccation, e.g. snails/fish
Diapause-suspended development/activity, e.g. zooplanktons.
Spore formation-to tide over unfavourable conditions, e.g. fungi/bacteria/lower plants.
Dormancy-By reducing metabolic activity, e.g. seeds
(any three with corresponding examples)

The parasite that causes malignant malaria in humans is Plasmodium falciparum. The sporozoites of Plasmodium enter the human body, when a female Anopheles mosquito bites a healthy person.
Life cycle of Plasmodium in human : 
(i) When the mosquito bites a man, sporozoites present in the salivary glands of female Anopheles mosquito are injected into the blood of the man
(ii) From the human blood, sporozoites enter the liver cells and grow in size to become a rounded schizont called cryptozoite. The latter divides to form cryptomerozoites.
(iii) The crypto-merozoite enters the human RBCs, and meta-cryptozoites are formed. The metacryptozoites divide to form meta-cryptomerozoites
(iv) In RBC, meta-cryptomerozoite becomes a rounded disc-like young trophozoite, which undergoes mitotic division to form multinucleate organisms, which give rise to merozoites
(v) Some erythrocytic merozoites enter fresh RBCs and form rounded gametocytes. When female Anopheles mosquito sucks the blood of human, gametocytes enter the stomach of the mosquito

Mechanism of AIDS infection involves.
(i) After entering into the body of a person, the virus attacks the macrophages. Inside macrophages, the RNA genome of the virus replicates to form viral DNA with the help of enzyme reverse trancsriptase.
(ii) The viral DNA gets integrated into the host cell's DNA and use the raw material and infected cell machinery to produce virus particles.
(iii) The macrophages continue to produce virus particles and act, like a HIV factory
(iv) Simultaneously, virus enters the helper T-lymphocytes (T_H). Where also, it replicats and forms progeny viruses.
(v) Progeny viruses released in the blod, attack the other helper T-lymphocytes, resulting in progressive decrease in their number in infected person. With the lack of T-lymphocytes, B-lymphocytes do not produce antibodies to encounter the pathogens/ antigens.
(iv) Infected person becomes so immunodeficient that he/she is unable to protect himself/herself against any infection/pathogen such as Mycobacterium, viruses and even parasites like Toxoplasma.

Mass extinction: There have been some episodes of large groups of plants and animals, becoming extinct over a relatively short span of time. Such episodes are called mass extinction. The most recent mass extinction took place about sixty million yeras ago, when the age of dinosaurs came to an abrupt end.

With the industrial growth in 1920, the white-winged grey-coloured Biston betularia was rapidly replaced by a dark-coloured melanic Biston carbonaria as the later had more chances of survival and favoured by Natural selection. But after 1956, the coal was rapidly replaced by oil and electricity as energy source in the industries which reduced soot deposition. So the light coloured moth is again replacing the dark-coloured moth by reverse evolution.

(a) Isolation of nematode-specific gene.
(c) Production of sense and anti-sense RNA in the host.
(d) Formation of ds RNA (as the sense and anti-sense RNA are complementary to each other). if Silencing of specific mRNA of the nematode.
(g) Host expresses the interfering RNA.
(h) Parasite cannot survive and host (tobacco) plant is protected.

(b) Both assertion and reason are true but reason is not the correct explanation of assertion.

(a): Predation and parasitism are considered to be negative interactions, because in both of these interactions one species gains and the other suffers. Predation is the interaction between species involving killing and consumption of prey. The species which eats the other is called the predator, and the one consumed by other is termed as prey. Predation is commonly illustrated by the herbivore-carnivore interaction.
Parasitism is the interaction in which the species smaller in size (the parasite) lives in or on the larger species (the host) from which it obtains food and shelter. Parasites like leeches, tick, lice, mites feed on the body fluids of the hosts. Parasites, like the predators limit the population of the host species. Parasites are generally host- specific, and do not have choice or alternatives like predators. Parasites are smaller in size and have higher biotic/reproductive potential compared to the predators. Parasites have poor means of dispersal and require specialised structures to reach or invade the host. Predators, on the other hand, are quite mobile and capable of capturing the prey.

(a): Innate immunity is non-specific type of defence, that is accomplished by providing different types of barriers to the entry of the foreign agents into our body. Mucus coating of the epithelium lining in the respiratory, gastrointestinal and urogenital tracts traps microbes and prevents their entry in our body.

(i) The year 2000 shows the maximum difference (1100 kg/hect) between growth of Bt and non-Bt cotton crop.
(ii) This is because Bt cotton crop has provided much benefits not only in terms of quantity, but also in terms of quality. Thus, it has become the first choice for farmers growing cotton in their fields.
(iii) Yes, the transgenic variety of cotton crop is still in use. In fact, the genetically modified variety of cotton is preferred over conventional cotton because of benefits like
(a) Increased Pest Resistance : This results in enhancement of crop quality.
(b) Higher yield due to increased crop resistance,the crop yield is also enhanced.

(i) (d)
(ii) (b)
(iii) (b)
(iv) (d)
(v) (a)