Which of the following statements about parasites are correct?
(A) The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors.
(B) The human liver fluke depends on two intermediate hosts, a snail and a mosquito, to complete its life cycle.
(C) Majority of the parasites harm the host; they may reduce the survival, growth and reproduction of the host.
(D) Parasites might render the host more vulnerable to predation by making it physically weak.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (C) and (D) only
(A) The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors. — True. Many parasites need intermediate hosts or vectors to reach their primary host.
(B) The human liver fluke depends on two intermediate hosts, a snail and a mosquito, to complete its life cycle. — False. The liver fluke, a trematode, needs a snail and a fish. The mosquito is the vector of the malarial parasite, not a host of the liver fluke.
(C) Majority of the parasites harm the host; they may reduce the survival, growth and reproduction of the host. — True. Parasites can also lower the population density of the host.
(D) Parasites might render the host more vulnerable to predation by making it physically weak. — True. A host weakened by parasites is easier prey for predators.
So A, C and D are correct.
NCERT Extract:
Population Interactions – “… The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of its primary host. The human liver fluke (a trematode parasite) depends on two intermediate hosts (a snail and a fish) to complete its life cycle. The malarial parasite needs a vector (mosquito) to spread to other hosts. Majority of the parasites harm the host; they may reduce the survival, growth and reproduction of the host and reduce its population density. They might render the host more vulnerable to predation by making it physically weak.”