606: Widespread resistance of malarial parasite to drugs like chloroquine has prompted attempts to develop a malarial vaccine to combat malaria. Why is it difficult to develop an effective malaria vaccine ?
(a) Malaria is caused by several species of Plasmodium
(b) Man does not develop, immunity to malaria during natural infection
(c) Vaccines can be developed only against bacteria
(d) Man is only an intermediate host and not the definitive host
Explanation:
For most infectious diseases for which effective vaccines are available, a single infection confers long standing protective immunity. A person who had measles does not develop measles again. This type of sterile protective immunity does not exist for malaria. So man lacks naturally acquired protective immunity against the plasmodium or other malarial parasites. Plasmodium has its own ingenious way of avoiding hosts' immune response and that is why it has been very difficult.
607: For developing inbred lines in farm animals, following factors are taken into consideration :
1. The crossbreds should be of outstanding type.
2. They should not carry any detrimental genes.
3. Progeney tested animals.
4. Herd size should be large.
Of the statements given above, which one of the following combinations of factors is most essential ?
(a) 1 and 3
(b) 2 and 3
(c) 1 and 4
(d) 2 and 4
608: A pesticide which is a chlorinated hydrocarbon is sprayed on a food crop. The food chain is: Food crop - Rat - Snake - Hawk. In this food chain, the highest concentration of the pesticide would accumulate in which one of the following?
(a) Hawk
(b) Food crop
(c) Snake
(d) Rat
Explanation:
Biomagnification, also known as bioamplification or biological magnification, is the increase in concentration of a substance, such as the pesticide DDT, that occurs in food chain. For example, though mercury is only present in small amounts in seawater, it is absorbed by algae (generally as methylmercury). It is efficiently absorbed, but only very slowly excreated by organisms (Croteau et al., 2005). Bioaccumulation and bioconcentration result in buildup in the adipose tissue of successive trophic levels: zooplankton, small nekton, larger fish etc. Anything which easts these fish also consumes the higher level of mercury the fish have accumulated. This process explains why predatory fish such as swordfish and sharks or birds like osprey and eagles have higher concentrations of mercury in their tissue.
609: Which one of the following is the correct sequence of the given substances in the decreasing order of their densities ?
(a) Steel > Mercury > Gold
(b) Gold > Mercury > Steel
(c) Steel > Gold > Mercury
(d) Gold > Steel > Mercury
Explanation:
The correct sequence in the decreasing order of densities : Gold > Mercury > Steel
610: Blight - the disease of potato can be cured by:
(a) Diathane
(b) Bordeaux mixture
(c) Dionine T-4
(d) Agrimycin and Ceresan