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A decomposer breaks down dead organic material and absorbs products of that breakdown; many bacteria and fungi perform this role. Decomposers connect detritus from different trophic levels to material recycling, so placing all decomposers at one final step of every food chain is misleading. See Clark, Douglas and Choi, Biology 2e, 46.1: grazing and detrital food webs.

A eukaryote is an organism belonging to the lineage characterized by a membrane-bounded cell nucleus and extensive cellular compartmentalization. A nuclear envelope surrounds the nuclear genome; nuclear chromosomes are typically linear. Ribosomes perform biological translation outside the cell nucleus. See OpenStax Microbiology, 3.4: nuclear organization and protein synthesis. Specialized biological cells can lose their cell nucleus, as mature mammalian red blood cells do, while remaining parts of eukaryotic organisms; see OpenStax Biology 2e, 40.2: mature red blood cells.

Yeasts, plants and animals are all eukaryotes. Typical cells in these groups have mitochondria, but chloroplasts belong to photosynthetic plant and algae lineages, not to every eukaryote. A cell wall occurs in typical plant and fungus cells but is absent from animal cells. These are comparisons of representative cells, not a checklist every specialized cell must satisfy. See OpenStax Biology 2e, 4.3: nucleus, organelles and representative cells.

The interesting feature is controlled separation: cell membranes and organelle membranes let different cellular processes occupy distinct compartments while membrane transport connects them. The evolution of eukaryotes also involved partnership: mitochondria descend from a bacterial endosymbiosis. Modern phylogenetics supports an archaeal ancestry for the nuclear lineage, alongside this bacterial contribution; see two-domain system. Thus the history of a whole eukaryote cannot be read as the history of just one of its genes.

A fungal cell wall contains structural polysaccharides including chitin and glucans. Its composition and organization vary among fungi; the diagram illustrates a composite rather than a pure chitin shell. A fungus sharing a cell wall with a plant does not imply shared wall chemistry.^[ref]

A fungus is a eukaryote that obtains nutrients by absorption rather than photosynthesis. Fungi include unicellular yeasts and multicellular forms. Their cell walls differ from bacterial peptidoglycan walls; having a cell wall does not make a fungus a plant. See OpenStax Biology 2e, 24.1: fungal nutrition and organization.