Biology:2015:CBSE:[All India]:Set- II

Following are the two advantages of using unleaded petrol as fuel in automobiles:

• Unleaded petrol does not release lead compounds from exhaust fumes into the atmosphere and causes less pollution.
• As unleaded petrol does not emit harmful compounds, it helps in preventing health diseases like bronchitis, asthma and lung diseases.

After attacking the host cell, retrovirus enters into macrophages (as in case of HIV) where RNA genome of the virus replicates to form viral DNA using reverse transcriptase enzyme. This viral DNA gets incorporated into the host's cell DNA and directs the infected cells to produce more viruses. Hence, the infected host cell possesses viral DNA.

Adenosine deaminase (ADA) enzyme deficiency is caused due to the mutation in the gene encoding it and this gene is present on chromosome number 20.
ADA deficiency is inherited as an autosomal recessive trait.

Cistron is a section of gene that codes for a certain polypeptide or protein.

Drones of honey bees are haploid and possess 16 chromosomes.
Drones of honey bees donate 16 chromosomes (one pair) to the progeny; thus, mitosis is the cell division that is involved in the production of sperms by drones.

Mutualism is a relationship between the organisms of two species in which both organisms are benefited.

Examples of the organisms involved that are commercially exploited in agriculture are as follows:
(i) Commercial exploitation of Rhizobium in agriculture
Continuous growth of crops leads to the nutrient deficiency in soil. Farmers, then, grow leguminous crops containing Rhizobium in its roots to replenish the lost nutrients (especially nitrogen) in the soil.

(ii) Commercial exploitation of Mycorrhiza in agriculture
Mycorrhiza is an association of the soil fungus with the roots of higher plants. Farmers use Mycorrhiza commercially in agriculture as it improves the soil quality and reduces soil erosion by improving plant rooting capacity. The fungal hyphae spread into the root tissues and help the plants to optimally use the soil's water and minerals.
Thus, to increase the yield of plants and to replenish the soil nutrients, Mycorrhiza is commercially exploited in agriculture.

Four techniques where the principle of ex-situ conservation of biodiversity has been employed are as follows:

• Preservation of the gametes of threatened species (using cryopreservation techniques) in viable and fertile condition for long periods
• In-vitro fertilisation of eggs
• Propagation of plants using tissue culture technique
• Keeping the seeds of different genetic strains that are commercially important plants for long periods in seed banks

(a) The plants obtained by micropropagation are called somaclones because they are genetically identical to each other as well as to the parent plant.

(b) The advantages of micropropagation are as follows:
(i) It helps in the propagation of a large number of plants in a short span of time.
(ii) It helps in the production of healthier plants that are disease and pest resistant.

Supernatant from the primary treatment is passed into large aeration tanks during secondary treatment. In these tanks, the effluent is agitated mechanically and air is pumped into it. This causes vigorous growth of the bacteria that lead to the formation of floc, which consists of bacterial and fungal filaments in a mesh-like structure. While growing, these microbes consume the major part of organic matter in the effluent; it decreases the biological oxygen demand (BOD).

After a significant drop in BOD is observed, effluent is passed on to the settling tank.

(a) Analogous organs or structures are those that are similar in function but different in origin.
From the given options, following are the analogous structures:

• Eyes of octopus and mammals perform the same basic visual function but they differ in the origin of their retina.
• Tubers of sweet potato and potato perform the same function of food storage but they are modifications of root and stem, respectively.

(b) The kind of evolution represented by analogous organs or structures is convergent evolution as they have different origins but evolve similar traits with evolution to perform the same function.