Which one of the following types of organisms occupy more than one trophic level in a pond ecosystem?

Which one of the following system constitutes the primary producers

In a biotic community, primary consumers are

Word detritus includes

Consider the following statements concerning food chains.

$I$. Removal of $80\; \%$ tigers from an area resulted in greatly increased growth of vegetation.

$II.$ Removal of most of the carnivores resulted in an increased population of deers.

$III.$ The length of food chains is generally limited to $3$ to $4$ trophic levels due to energy loss.

$IV.$ The length of food chains may vary from $2$ to $8$ trophic levels.

Which two of the above statements are correct?