Final answer:
Saprotrophs are decomposers that feed on dead organic matter by externally digesting it.
Step-by-step explanation:
Saprotrophs are decomposers that feed on dead organic matter by secreting digestive enzymes and digesting it externally, rather than by ingesting the matter and digesting it internally.
Saprotrophs include fungi and single-celled protozoa.
Fungi, like those in Figure 24.5.4, are the only organisms that can decompose wood.