Q: Given a scientific passage and an answer, generate a question for the given answer.
Passage: Duckweed: Jonathan Jordan; Cattails: User:JoJan/Wikimedia Commons. Duckweed and cattails are respectively the primary producers in standing and running freshwater biomes . Duckweed: CC BY 2.0; Cattails: CC BY 3.0. Answer: primary producer
A:
Duckweed and cattails serve what role in the food chain in freshwater biomes?