sOLuTIOns- (i) Mammals are capable of forming urine, that is more
concentrated than blood plasma, thus maximising the
amount of water retained. The nephron of mammals
is able to do this because it possesses a loop of Henle.
The loop of Henle has a key role in water conservation,
as good amount of water is reabsorbed from the
glomerular filtrate over here. Based on lengths of
the loop of Henle, there are two types of nephrons:
(i) cortical nephrons: they have short loops of Henle
which only just extend into the medulla and function
most importantly when the water supply is normal
to excessive, (ii) juxtamedullary nephrons : they
have long loops of Henle that extend deep into the
medulla and function most importantly when water is
in short supply. The lengths of loops of Henle and of
the collecting ducts, and the general thickness of the
medulla region of the kidneys, increase progressively
in animals best adapted to the drier habitats.
(ii) Kidney tubule X belongs to mammal B, kidney tubule
Y belongs to mammal A and kidney tubule Z belongs
to mammal C. According to the graph, mammal C is
producing most concentrated urine which indicates
that it is adapted to arid habitats and possesses
kidney with juxtamedullary nephrons. Mammal A is
producing least concentrated urine which implies
that it thrives well in aquatic habitat so it possesses
kidney with cortical nephrons. Mammal B is producing
intermediate concentration of urine which indicates
that it is well adapted to terrestrial habitats, with
adequate water supply hence, possesses kidney
tubules intermediate between the two.
- (i) Type I survivorship curve belongs to humans, type II
belongs to Hydra and type III belongs to oyster.
(ii) Type I surviorship curves are characterised by high
age-specific survival probability in early and middle
life, followed by rapid decline in survival rate in later
life. They are typical for species that produce few
offspring but care for them well, e.g., humans.
In Type III curves, greatest mortality is experienced in
early life with relatively low rates of death for those
surviving. This type of curve is characteristic of species
that produce large number of offspring.
Oysters, produce vast number of offspring, only a
few of which, live to reproduce. However, once they
become established and grow into reproductive
individuals, their mortality rate is extremely low, so
they have type III survivorship curve.
Type II curves are an intermediate between types I
and III, where roughly constant mortality rate and
survival probability is experienced regardless of age,
e.g., Hydra.- (i) The given processes P and Q belong to ELISA
(enzyme-linked immunosorbent assay). P is indirect
ELISA and Q corresponds to sandwich ELISA. The assay
makes use of an enzyme that reacts with a colourless
substrate to produce a coloured product. The enzyme
is covalently linked to a specific antigen/antibody that
recognizes a target antibody/antigen. If the target
is present, the antibody-enzyme complex will bind
to it and, on addition of the substrate, the enzyme
will catalyse the reaction, generating the coloured
product. Thus, the presence of the coloured product
indicates the presence of the antigen or antibody.
(ii) The indirect ELISA is used to detect the presence of
antibody and is the basis of the test for HIV infection.
The HIV test detects the presence of antibodies that
recognize viral core protein antigens. Viral core proteins
are adsorbed to the bottom of a well. Antibodies
from the person being tested are then added to the
coated well. Only a person infected with HIV will have
antibodies that bind to the antigen. Finally, enzyme-
linked antibodies to human antibodies are allowed to
react in the well and unbound antibodies are removed
by washing. Substrate is then applied. An enzyme
reaction yielding a coloured product suggests that
the enzyme-linked antibodies were bound to human
antibodies, which in turn implies that the patient has
antibodies to the viral antigen. Moreover, this assay
is quantitative i.e., the rate of the colour-formation
reaction is proportional to the amount of antibody
originally present.
The sandwich ELISA is used to detect antigen rather
than antibody. Antibody to a particular antigen is
first adsorbed to the bottom of a well. Next, solution
containing the antigen (such as blood or urine, in
medical diagnostic tests) is added to the well and
binds to the antibody. Finally, a second, different
antibody to the antigen is added. In this case, the
rate of colour formation is directly proportional to the
amount of antigen present. Consequently, it permits