Question 5
Why do saprophytes belong to the heterotrophic group?
The right answer is the one marked above.
Because they obtain nutrition from dead organisms or decaying organic matter. That food was produced by some other organism.
Producing your own food is autotrophic nutrition — saprophytes do not do it. Whether an organism is unicellular or multicellular has no bearing on its mode of nutrition; most fungi are multicellular and saprophytic.