$A$ detritus food chain begins with which organism?

In the given food chain,suppose the amount of energy at the fourth trophic level is $5 \, kJ$,what will be the energy available at the producer level? (in $kJ$)
Grass $\rightarrow$ Grasshopper $\rightarrow$ Frog $\rightarrow$ Snake $\rightarrow$ Hawk

Which of the following limits the number of trophic levels in a food chain?

What is transferred through a food chain in an ecosystem?

Define a food web. State its significance for an ecosystem.

What are trophic levels? Give an example of a food chain and state the different trophic levels in it.