Which food part has lowest assimilation efficiency?
Wood yields low assimilation efficiency because most of its mass consists of cellulose embedded in hemicellulose and lignin. Vertebrate digestive enzymes cannot cleave cellulose, and lignin physically shields polysaccharides while resisting hydrolysis. Even consumers with symbiotic microbes recover energy slowly and incompletely, losing much material in feces. Seeds and fruits generally contain concentrated starches, oils, or sugars, while leaves, though fibrous and defended, usually contain more accessible cellular contents than secondary xylem. Carbon and mineral nutrients follow different a
Ref: Fundamentals of Ecology, Odum & Barrett, 5th Ed., Ch. 3