Saprotrophs are organisms that obtain nutrients by decomposing dead organic matter. They play a crucial role in the ecosystem by breaking down dead plant and animal material, recycling nutrients back into the environment.

Among the given options, the class of organisms that belongs to saprotrophs is fungi.

Fungi as saprotrophs
Fungi are a diverse group of organisms that obtain nutrients through decomposition. They secrete enzymes that break down complex organic molecules into simpler forms, which can then be absorbed by the fungi for their own nutrition. Fungi can decompose a wide range of organic matter, including dead plants, animals, and even waste materials.

Explanation of other options:
a) Bryophytes: Bryophytes are a group of non-vascular plants that include mosses, liverworts, and hornworts. They do not belong to saprotrophs as they obtain nutrients through absorption from the environment and not by decomposing dead organic matter.

b) Algae: Algae are a diverse group of photosynthetic organisms that can be found in various aquatic environments. They are not saprotrophs as they obtain nutrients through photosynthesis, converting sunlight into energy.

c) Lichens: Lichens are unique organisms that result from a symbiotic relationship between a fungus and a photosynthetic partner (usually algae or cyanobacteria). While some fungi in lichens may have saprotrophic capabilities, lichens as a whole do not solely belong to saprotrophs.

In conclusion, fungi are the class of organisms that belong to saprotrophs. They play a vital role in nutrient cycling and decomposition in ecosystems.