Carbohydrate

Definition

A biomolecule composed of carbon, hydrogen, and oxygen in approximately 1:2:1 ratio, serving as a primary energy source and structural component in living organisms. In arthropods, carbohydrates function metabolically as stored energy (glycogen, trehalose), as dietary fuel, and as precursors for chitin synthesis—the nitrogenous polysaccharide that forms the exoskeleton. Carbohydrates range from simple sugars (monosaccharides like glucose and fructose in nectar) to complex polymers (polysaccharides like cellulose, which termites and other detritivores digest via symbiotic microorganisms).

Etymology

From carbo- (carbon) + hydrate (combined with water), reflecting the empirical formula (CH₂O)ₙ suggesting hydrated carbon.

Example

Honey bees convert floral nectar—rich in sucrose and other simple carbohydrates—into honey through enzymatic processing and dehydration, storing it as an energy-dense food reserve for colony survival during winter or dearth periods. The disaccharide trehalose serves as the primary circulating blood sugar in most insects, analogous to glucose in vertebrates.

Synonyms

• saccharide
• glycide

Related Terms

• Chitin
• Trehalose
• Glycogen
• metabolism
• respiration
• nectar
• Hemolymph
• digestion
• polysaccharide
• monosaccharide

Usage Notes

In entomological contexts, distinguishes between metabolic carbohydrates (energy storage and transport) and structural carbohydrates (chitin in cuticle, peritrophic matrix). Trehalose concentration in hemolymph is a common physiological indicator of insect stress or nutritional status. Not all carbohydrates are digestible by arthropods; many rely on gut symbionts to break down cellulose, hemicellulose, or pectin. The term 'carbohydrate' is broader than 'sugar'—the latter typically refers to mono- and disaccharides, while the former includes complex polysaccharides.