Generally,the food chain has how many trophic levels?

Identify the stage of hydrarch succession shown in the figure.

Which of the following types of organisms occupies more than one trophic level in an aquatic ecosystem?

Select the incorrect statement from the following.

How many statements are correct?
$(a)$ Some animals like cockroaches,crows,etc.,are omnivores.
$(b)$ Detritus food chain $(DFC)$ begins with dead organic matter.
$(c)$ Each trophic level has a certain mass of living material at a particular time called as standing crop.
$(d)$ Species composition and stratification are two main structural features of an ecosystem.

Identify the group of herbivores from the following that are included as primary consumers in an ecosystem.