In algae and fungi, the zygote formed as a result of sexual reproduction, develops a thick wall that protects the zygote from desiccation and mechanical injuries; hence the zygote is able to remain dormant during the unfavourable conditions and germinate at the return of favourable conditions. Since sexual reproduction brings in variation(s), at least some variants will be able to survive, in case of an adverse change in the environmental conditions. Because of the survival advantages (mentioned above), sexual reproduction is favoured under such conditions.

Vegetative reproduction is also a type of asexual reproduction; it is because it involves a single parent and there is no formation or fusion of gametes. The term clone is applicable to the individuals formed by vegetative reproduction, because they are genetically and morphologically identical among themselves and to the parent.

Since single-celled organisms reproduce by cell division (into two new individuals), there is no natural death for them.

a. Three cuts.
b. Four strands.
c. Sticky ends, since they have complementary bases, they can rejoin fragments with complementary sticky ends to form rDNA (gene from vector and the gene to be cloned is inserted)
d. DNA ligase

BOD value - 30mg/L - Secondary effluent from STP
BOD value - 8mg/L – River Water
BOD value - 500mg/L – Sewage Water
(Fact – The greater the BOD of water, the more is its pollution potential.)

AIDS is a fluid transmitted disease and is considered as an STD because the probability of fluid transmission is maximum during sexual intercourse.

(i) HCI of stomach belongs to the physiological barrier.
(ii) Macrophages come under cellular barrier.

(a) EI Nino. It is an abnormal warming of surface ocean waters in the eastern tropical Pacific. It is called the Southern Oscillation. The Southern Oscillation is the see-saw pattern of reversing surface air pressure between the eastern and western tropical Pacific; When the surface pressure is high in the eastern tropical Pacific it is low in the western tropical Pacific, and vice-versa. Because the ocean warming and pressure reversals are, for the most part, simultaneous, scientists call this phenomenon the EI Nino/Southern Oscillation or ENSO for short.

Unfortunately not all EI Nino's are the same nor does the atmosphere always react in the same way from one EI Nino to another. This is why NASA's Earth scientists continue to take part in international efforts to understand EI Nino events. Hopefully one day scientists will be able to provide sufficient warning so that we can be better prepared to deal with the damages and changes that EI Nino causes in the weather.

(i) Hot spots of biodiversity. The concept of 'Hot-spots' was developed by Norman Myres (1988) to designate specific areas for in-situ conservation. The conservation the hot spots are the richest and most threatened reservoirs of plants and animal life on earth.
The criteria for determining hot spots are:
1. Number of endemic species.
2. Degree of threat which is measured in terms of habitat loss.
There are 25 hot spots in the world out of which two are in India. They are Western Ghats and eastern Himalayas.
Hot spot of Eastern Himalayas are active centres of evolution and rich in diversity of flowering angiosperms. Western Ghats have semi evergreen forests. Western Ghats include two main centres of biodiversity i.e. Agastyamalai hills and Silent valley.
(ii) Ex-situ conservation. It means maintenance of off site collections either in gardens by farmers, botanical garden for storing seeds, genes, pollen, tissue culture etc.
The rare plants have been found to flourish in large numbers under the care and protection of gardeners and nature lovers.
The farmers have been maintaining genetic diversity (enormous varieties) of crop plants since ancient times by saving seeds or other components for the next plantings.
Collection of samples of cultivated and wild varieties of plants and storing them in botanical gardens is another method of conservation of germplasm.
In seeds, the living meterial remains in metabolically suspened state. When the seeds are to be stores for longer periods, it is necessary to avoid conditions which favour respiration and enzymatic actions.
(iii) India's effort in biodiversity conservation. India has greatly contributed to conservation of biodiversity owing to its great utility and need for conservation. The following measures have been taken for this purpose:
1. Setting up bodies like Indian Board for Wildlife, Bombay Natural History  etc.
2. observation of first week of October as national wildlife week.
3. Introduction of Wildlife Protection Act in 1972.
4. Setting up of sanctuaries, national parks and biosphere reserves.

1. Alexander Fleming, while working on Staphylococci bacteria, observed a mould growing in one of the unwashed culture plates, around the mould the bacterium could not grow.
2. He found that it was due to a chemical produced by the mould Penicillium notatum and named the chemical as Penicillin.
3. Its full potential as an antibiotic was established later by Ernst Chain and Howard Florey.

This is because plasmid is a circular DNA molecule. When cut with enzyme, it becomes linear, but does not get fragmented.
Whereas, a linear DNA molecule gets cut into two fragments. Hence, a single DNA band is observed for plasmid while, two DNA bands are observed for linear DNA in agarose gel.

Since plants cannot move away from their predators (herbivores) and harsh environmental conditions, many of them have become extinct. But animals can move away from the harmful/unfavourable environments or their predators and evolution of favourable characters has thus taken place in them.

(a) Contact inhibition is the property shown by normal cells,by the virtue of which contact with other cells inhibits their uncontrolled proliferation and growth.
(b) All normal cells have cellular oncogenes (c-onc) or proto-oncogenes;when activated under certain conditions,such genes could lead to oncogenic transformation of cells,i.e.they become cancerous.

1. The biodiversity we see today is the story of evolution, i.e. evolution is considered as a process, that has resulted in various life forms.
2. If we talk about the life on earth, evolution is considered as a consequence of the process, called natural selection.
3. It is difficult to decide, whether evolution and natural selection are processes or results of some unknown processes.

1. convergent evolution is the evolutionary process, where anatomically different structures in different groups of organisms evolve towards the same function, in similar habitats.
2. Such structures in different groups of organisms which perform similar function, but are anatomically different, are called analogous organs.
3. The wings of a butterfly and those of bird are anatomically different, but perform the same function (flying); hence they are said to be analogous organs.

1. Active immunity is produced by injecting the microbes deliberately during immunisation.
2. Antibodies are produced by the B-cells of our body in response to the antigens;they neutralise the pathogenic agents during actual infection.
3. The vaccines also generate memory B-cells and T-cells,which recognise the same pathogen on subsequent exposure and destroy them by a massive production of antibodies.

1.The gene for haemophilia is present in the X-chromosome.
2.The son receives the X-chromosome from his mother; so a carrier-mother passeson the disease to 50% of her sons.
3. When the mother is normal, the sons .have no chance of getting the disease, even if the father is haemophilic, because father passes on the Y-chromosome to his sons.

The other possible types of dominance are:
(i) Incomplete dominace.
e.g. Flower colour in snapdragon.
(ii) Codominance.
e.g. Blood group AB.

1. The characters are controlled by 'Factors' which are stably passed down without any change from the parents to the offspring, through the gametes.
2. The allels do not show any blending.

1. In haploid organisms, meiosis occurs during development of zygote.
2. It is the only diploid stage (formed by the fusion of two haploid gametes) in the life-cycle that can undergo meiosis.

1. Emasculation is necessary to prevent the self-pollen grains falling on the stigma.
2. Emasculation is not needed when the female parent chosen bears unisexual,  i.e. female flowers.

1. In haploid organisms, showing haplontic life cycle, gamete formation involves only mitosis; the diploid zygote formed by the fusion of two haploid gametes, undergoes meiosis (zygotic meiosis).
2. In diploid organisms, showing diplontic or haplodiplontic life cycle, gamete formation involues meiosis (gametic meiosis) and haploid gametes are formedl; the diploid zygote undergoes mitosis to form diploid individuals.

1. Since geitonogamy involves two different flowers of the same plant, it is genetically similar to autogamy; both autogamy and geitonogamy do not result in genetic variation in the progeny.
2. Geitonogamy and cross-pollination involve different flowers and a pollinating agent.

On the basis of colour production in the presence of chromogenic substrate, the recombinants and non-recombinants can be differentiated. In this, a recombinant DNA is inserted within coding sequence of an enzyme \(\beta\)-galactosidase, which results in inactivation of enzyme.
In plate A. the bacterial colonies having inserted plasmid, shows no colouration. While in plate B. insertion of plasmid does not occur, therefore it shows blue colour.