Grazing food chain:
Initiated by living plants (producers), which are then eaten by herbivores (primary consumers).
Illustration: Grass $\to$ Grasshopper $\to$ Frog $\to$ Snake.
Detritus food chain:
Commences with dead organic matter (detritus), consumed by decomposers (detritivores) such as fungi and bacteria.
Illustration: Dead leaves $\to$ Earthworm $\to$ Bird.