- Statins competitively inhibit the enzyme b-hydroxy-b-
methyl glutaryl CoA reductase responsible for synthesis of
cholesterol and lower the blood-cholesterol level. - Polyblend is a fine powder of recycled modified plastic
waste. It is mixed with bitumen to lay roads as it increases
its water repellent properties.- Amount of DDT in fish eating birds will probably be 25
ppm. It is due to the accumulation of pesticide or toxicant
at successive trophic levels of the food chain by the process
of biomagnification. - Mechanism of obtaining parthenocarpic fruits is becoming
important these days because (i) seeds are irritants during
eating of the fruit, (ii) processing of fruits by food industry
requires the removal of seeds which is quite difficult, and
(iii) there is an increasing tendency to grow fruit bearing
plants inside green houses, but reliable insect pollinators
cannot be ensured in each and every case.- (a)
(b) RNA is less suitable as a genetic material than DNA because
(i) presence of 2’–OH group in its sugar makes it highly
reactive, labile, unstable and easily degradable. (ii) presence
of uracil makes it less stable and therefore, mutation rate is
faster in RNA.
- Secondary immune response occurs at the second and
subsequent exposures to the same antigen. Every new
encounter with the same antigen results in a rapid
proliferation of memory B-cells, this is called "booster
response". The antibody titer after subsequent encounters is
far greater than during a primary response and consists mainly
of IgG antibodies. Antibodies produced during a secondary
response have an even higher affinity for the antigen. Thus,
secondary immune response is more accelerated and intense
than the primary immune response.
OR
Mycorrhizal associations perform several functions for the
plants— (i) absorption of water (ii) solubilisation of organic
matter of the soil humus, release of inorganic nutrients,
absorption and their transfer to root (iii) direct absorption of
minerals from the soil over a large area and handing over the
same to the root (iv) secretion of antimicrobial substances
which protect the young roots from attack of pathogens.
- At high altitudes, human body compensates low oxygen
availability by increasing red blood cell production,decreasing the binding affinity of haemoglobin and by
increasing breathing rate.- (a) Exine of pollen grains is made of a highly resistant
fatty substance called sporopollenin. Sporopollenin is
not degraded by any enzyme. It is not affected by high
temperature, strong acid or strong alkali. Because of
the sporopollenin, pollen grains are well preserved as
microfossils.
(b) Corpus luteum secretes large amounts of progesterone
which is essential for maintenance of the endometrium.
Such an endometrium is necessary for implantation of
the fertilised ovum and other events of pregnancy. Corpus
luteum also secretes relaxin during later stages of pregnancy
and helps to soften ligaments, especially those that hold the
pubic symphysis together. - Miller (1953) circulated four gases: methane, ammonia,
hydrogen and water vapour in an air tight apparatus and
passed electrical discharges from electrodes at 800°C. The
mixture was then passed through a condenser. The gases
were circulated continuously in this way for one week and
the chemical composition of the liquid inside the apparatus
was analysed. He found a large number of simple organic
compounds including some amino acids such as alanine,
glycine and aspartic acid. He also found the substances
like urea, hydrogen cyanide, lactic acid and acetic acid. He
conducted this experiment to test the idea that organic
molecules could be synthesised in a reducing environment. - (a) Common cold is characterised by nasal congestion
and discharge, sore throat, hoarseness, cough, headache,
tiredness, etc., which usually last for 3-7 days. Droplets
resulting from cough or sneezes of an infected person are
either inhaled directly or transmitted through contaminated
objects.
(b) The use of drugs like anti-histamine, adrenalin and steroids
quickly reduces the symptoms of allergy. - (a) Part labelled as 'A' is primary spermatocyte. It undergoes
two successive divisions (maturation divisions). The first
maturation division is reductional or meiotic. Hence, the
primary spermatocyte divides into two haploid daughter
cells called secondary spermatocytes. Both secondary
spermatocytes undergo second maturation division to form
four haploid spermatids. The spermatids are then transformed
into spermatozoa by the process of spermiogenesis.
(b) Part labelled as 'A' represents primary spermatocyte and
the part labelled as 'B' represents spermatid. Primary
spermatocyte is diploid (2n = 46, in humans). It undergoes