Many insects get nutrients for growth and development from plant leaves. Plant leaves consist of cells mostly devoted to photosynthesis, but some dedicated to structure, transport or defense. Plant cell contents are surrounded by a cell wall. The cell wall contains cellulose and other factors that are refractory to digestion by the majority of insect herbivores. Cell wall components cannot be assimilated by most insects and are discarded in the frass.
The cell contents are more readily assimilated. Insect biologists are interested in how insects are able to release the cell contents from the cell wall. Cell contents are more thoroughly released from small leaf pieces than large ones. Under the right conditions some but not all of the cell contents can leak. Experiments with grasshoppers fed whole leaves have shown that a substantial fraction of the cell contents, including carbohydrates and proteins, are eliminated in the frass: they are not assimilated. If the grasshoppers are fed powdered leaves instead of whole leaves, all of the protein and carbohydrate in the cell content is assimilated.
Chewing the food is important for optimal nutrient release. Grasshoppers use mandibles cut leaves into pieces small enough to enter the digestive system. Grasshoppers use a muscular section of gut with sharp sclerotized cuticle (the proventriculus) like a blender to create even finer particles. There is a tradeoff between speed of consumption and assimilation. Grasshoppers can consume more leaf material if they eat faster and digest larger particles. The fraction of the nutrient content assimilated is reduced. The fastest nutrient assimilation requires the grasshopper to balance the rate of consumption against the efficiency of assimilation of volume consumed.