In an association of two animal species,one is a termite which feeds on wood and the other is a protozoan $Trichonympha$ present in the gut of the termite. What type of association do they establish?

Select the statement that best describes commensalism.

Which of the following statements regarding species interdependence are true?
$I.$ An association of two species where one is benefited and the other remains unaffected is called mutualism.
$II.$ An interspecific association where both partners derive benefit from each other is called commensalism.
$III.$ $A$ direct food relation between two species of animals in which one animal kills and feeds on another is referred to as predation.
$IV.$ $A$ relationship between two species of organisms where both partners are benefited from each other is called symbiosis.

Why do parasites exhibit parasitism?

If the '$+$' sign is used for a beneficial interaction,the '$-$' sign for a detrimental interaction,and the '$0$' sign for a neutral interaction,then which population interaction is represented by '$+$' and '$-$'?

Match the following population interactions with their respective signs and descriptions:

Interaction Type	Sign	Description
$(a)$ Parasitism	$(i) -, 0$	$(A)$ Both get benefitted
$(b)$ Amensalism	$(ii) -, -$	$(B)$ One gets harmed,other has no effect
$(c)$ Competition	$(iii) +, -$	$(C)$ Both get harmed
$(d)$ Mutualism	$(iv) +, +$	$(D)$ One is harmed and second is benefited