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

The given figure is of Blastocyst and the part labelled “A” is 'Trophoblast (the outer layer)'.

Interferons are anti-viral proteins (released by virus infected cells) that protect our non-infected cells from further viral infection.

Commensalism is the interaction between a whale and the barnacles growing on its back.

In a dihybrid cross, when the two genes are located on the same chromosome then the proportion of parental gene combinations be much higher than non-parental types, it was experimentally shown by Morgan and his group in process of linkage and recombination.

Parthenocarpic fruits are either seedless or contain non-viable seeds as in banana fruits. Hence, banana is considered a good example of parthenocarpy.

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

Wing of a cockroach and wing of a bird are analogous organs as their origin is not the same but they perform similar functions. From the above example one can infer the evolutionary relationship between organisms.

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

Macrophages act as HIV factory in humans when infected by HIV.
The events that occur in the infected cells are:
a) After entering into human body, HIV enters into macrophages (human cell)
b) In macrophage, RNA genome of virus replicates into viral DNA by the process of reverse transcription
c) Viral DNA is incorporated into host cell DNA
d) Viral DNA directs infected cell to produce viral particles.
e) After assembling of viral particles the virus ruptures the infected cell. 
f)   Simultaneously, new HIV particles infect helper T-lymphocytes by replicating and producing viral progeny.
g) Viral progeny released in blood attacks other helper T-cells and this repeated process leads to progressive decrease in the number of helper T-lymphocytes

The two types of immune responses in humans are:

i) Humoral immune response- It is a primary immune response mediated by B-lymphocytes. B-lymphocytes originate and mature in bone marrow and later migrate to lymphoid tissue throughout the body. Production of antibodies by B-lymphocytes is stimulated by helper T cells and suppressed by suppressor T cells. Some B cells are changed into plasma cells, which produce antibodies but some get transformed into memory cells which recognise the same antigen when introduced subsequently. The antibodies are found in blood hence such type of response is also called antibody mediated immunity (AMI).