A mutually beneficial relationship between two different organisms for nutrition is called as
A. Symbiotic nutrition
B. Parasitic nutrition
C. Saprobiotic nutrition
D. Detritivores

Hint: Mutualism is a relationship in biology where there is mutual benefit to any two living organisms that are dependent on one another. This relationship provides positive effects on the survival of interacting populations.

Complete answer:
Option (A) is correct. Symbiotic nutrition takes place in two different organisms that are interacting with one another interdependently i.e., none of the organisms is harmed and there is a positive (beneficial) effect to both the organisms in terms of food, shelter, reproduction, etc. One common example of a symbiotic relationship in terms of gaining nutrition exists in lichens where fungi and algae form a symbiotic relationship with one another to obtain nourishment. So, a mutually beneficial relationship between two different organisms for nutrition is called symbiotic nutrition.
Option (B) is incorrect. Parasitic nutrition is a type of relationship that exists between the parasite and the host. It is a kind of heterotrophic nutrition in which parasites live on the surface of the body or inside the body of the host and directly gain nutrients from the body of the host. Hence, the parasites harm the host, thereby, not forming a mutually beneficial relationship.
Option (C) is incorrect. Saprobiotic nutrition takes place when the organism or saprophytic microbes obtain their nutrients from the dead and decaying matter of plants and animals. Hence, there is no benefit to the other organism and only the microbes are benefitted in this case. Therefore, it is not the type of mutually beneficial relationship.
Option (D) is incorrect. Detritivores include certain invertebrates, vertebrates, and plants that feed on the detritus (decomposing parts of animals and plants as well as feces) to obtain the nutrients.

Hence, the correct option is (A).

Note: The meaning of the word symbiotic is “living together” and hence the symbiotic nutrition implies that relationship between two different organisms that live together to obtain nutrients from one another without harming any of the population. Thus, it is a mutually beneficial relationship between two different organisms for nutrition.