Board exam

State the impact of constant mechanical agitation and pumping of air in the aeration tank on the sewage during the biological treatment. OR

1. aCattle excreta is important source for producing a domestic fuel. Name the fuel and write its main components.
2. bWrite the biological process that is responsible for the production of this fuel.

1. aGive an example of viral biocontrol agent.
2. bWhy are they considered to be desirable when an ecologically sensitive area is being treated?

Bio-diversification of life started to occur almost 3 billion years ago. Since then new species have been evolving and then disappearing en masse from earth.

1. aHow many episodes of mass extinctions of species have already taken place and which one is in progress in the current era ?
2. bHow is current episode in progress different from the previous episodes and why ? Explain.

1. (i)
   State the role of a selectable marker in r-DNA technology.
2. (ii)
   Name one such selectable marker which is considered to be useful for E.coli.
3. (iii)
   Give one reason why is it considered to be a useful marker. OR What are plasmids ? How are they different from cloning vectors ? Give one example each for a viral and a bacterial cloning vector.