Read the given passage and answer the following questions:
Bacteria like Streptococcus pneumoniae and Haemophilus influenzae are responsible for the disease pneumonia in humans which infects the alveoli (air filled sacs) of the lungs. As a result of the infection, the alveoli get filled with fluid leading to severe problems in respiration. The symptoms of pneumonia include fever, chills, cough and headache. In severe cases, the lips and finger nails may turn gray to bluish in colour. A healthy person acquires the infection by inhaling the droplets/aerosols released by an infected person or even by sharing glasses and utensils with an infected person. Dysentery, plague, diphtheria, etc., are some of the other bacterial diseases in man. Many viruses also cause diseases in human beings. Rhino viruses represent one such group of viruses which cause one of the most infectious human ailments – the common cold. They infect the nose and respiratory passage but not the lungs. The 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 such as pens, books, cups, doorknobs, computer keyboard or mouse, etc., and cause infection in a healthy person.
The passage describes diseases that spread from person to person. For vector-borne diseases such as malaria, an important control measure is to introduce, in ponds, a fish that feeds on mosquito larvae. This fish is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Gambusia
Malaria and filariasis spread through insect vectors, so the most important control measure is to control or eliminate the vectors and their breeding places. Mosquitoes lay eggs in still water, and their larvae grow there. Gambusia is a fish that feeds on mosquito larvae. When it is introduced into ponds, it eats the larvae before they become adults, so fewer mosquitoes are left to spread the disease. Other measures in the same list are avoiding stagnant water, cleaning coolers, using mosquito nets and spraying insecticides in ditches and swamps. The other fishes are known from other chapters: the Nile perch and the cichlid fishes of Lake Victoria (an invasive species and its victims), and the clown fish that lives among the tentacles of a sea anemone (commensalism).
NCERT Extract:
Common Diseases in Humans – “… For diseases such as malaria and filariasis that are transmitted through insect vectors, the most important measure is to control or eliminate the vectors and their breeding places. This can be achieved by avoiding stagnation of water in and around residential areas, regular cleaning of household coolers, use of mosquito nets, introducing fishes like Gambusia in ponds that feed on mosquito larvae, spraying of insecticides in ditches, drainage areas and swamps, etc.”