Question

One who gets food at the cost of other is-
A. Parasite
B. Commensal
C. Saprophyte
D. Insectivore

Answer 1

Nutrition is a process of intake of nutrients (like carbohydrates, fats, proteins, minerals, vitamins and water) by an organism as well as the utilization of these nutrients by the organism. Modes of nutrition means methods of procuring food or obtaining food by an organism.
There are mainly two types of modes of nutrition- Autotrophic and Heterotrophic. The organisms which make their own food are called autotrophs and the organisms which depend on autotrophs for their food or survival are called heterotrophs.

Complete answer:
Now, to solve this question we have to look at all the options given.
Parasite- The parasitic nutrition is performed by the parasites. In this nutrition an organism derives its food from the body of another living organism (called its host) without killing it. Example- fungi, bacteria, plants and animals.
Commensal- Commensalism is a type of symbiotic nutrition in which only one organism benefits while the other organism neither benefits nor harms. Example- remora (a type of suckerfish).
Saprophyte- Saprophytes are the organisms which show saprotrophic nutrition in which an organism obtains its food from decaying organic matter of dead plants, dead animals and rotten bread, etc. Example- fungi and many bacteria.
Insectivore- The plants have special structural features which help them to trap insects and they digest them by secreting digestive juices commonly known as heterotrophic plants. Example- venus flytrap, pitcher plant.

So, the correct answer is option A (parasite) because a parasite receives its food from the host but gives no benefit to the host in return.

Note-
Parasitic mode of nutrition is observed in several bacteria, a few plants like Cucuta (amarbel) and some animals like Plasmodium and roundworms. The microorganism Plasmodium causes malaria disease. Roundworms cause disease in man and domestic animals. This microorganism lives inside the body. Other examples of parasites are lice, leeches, tapeworms and ticks