Biology:2012:CBSE:[All India]:Set-II

Pollen grains of Vallisneria have a mucilaginous outermost layer that prevents them from damaging.

(a) In case of incomplete dominance the F1 phenotype does not resemble either of the two parents and is in between the two.

(b) In case of complete dominance the F1 phenotype resembles only one of the two parents.

The entry of only one sperm is ensured by:

1.    Electrical change in egg’s membrane.

Coelacanth is considered as the missing link between fish and the amphibians. These were the first amphibians which lived on both land and water.

Vehicles fitted with catalytic converters should use unleaded petrol because lead in the petrol inactivates the metal catalyst present in the converter.

Acrosome is a cap-like structure present in the anterior part of sperm head. It contains the enzyme hyaluronidase, which hydrolyses the outer egg membrane and thus it facilitates penetration of the egg at the time of fertilisation.

(a) Apis indica is the most common species of bee suitable for apiculture. 
(b) Leghorn or Minorca are the improved breeds of chicken

Cyanobacteria such as Anabaena and Nostoc, fix atmospheric nitrogen. They serve as important bio-fertilisers especially in paddy fields.

Thermus aquaticus is the source organism that possesses Taq polymerase. Taq DNA polymerase is a processive, 5'→3' DNA polymerase, thermally stable enzyme which can withstand high temperature and has a temperature optimum of 70°C-74°C.

The source of cyclosporin-A is Trichoderma polysporum. It is an immunosuppressant drug that acts mainly on T-lymphocytes and is used extensively in the prevention and treatment of graft-host reactions in bone-marrow, kidney, heart, and liver transplants.