Can energy from heterotrophs move back to autotrophs through a food chain? Why?

The only lake in a small village was dried up and used as a construction ground for a hospital and community buildings. That year the number of patients suffering from malaria increased in the village. What could be the reason behind it? Explain with the help of a food chain.

What is ? in the following flow chart of the food chain?

State whether the following is biodegradable or non-biodegradable.

Sewage: _____.

State whether the following is biodegradable or non-biodegradable.

Slag: _____.

State whether the following is biodegradable or non-biodegradable.

Cattle dung: _____.