Carbohydrates
Carbohydrates consist of carbon, hydrogen and oxygen, and the general formula of most is Cₙ(H₂O)ₘ. Monosaccharides (glucose C₆H₁₂O₆, fructose, galactose, the pentoses ribose and deoxyribose) are the simplest; disaccharides are built of two monosaccharides: sucrose = glucose + fructose, lactose = glucose + galactose, maltose = glucose + glucose. Polysaccharides are starch (reserve in plants), glycogen (reserve in animals and fungi; in liver and muscles) and cellulose (plant cell wall), all with glucose as the monomer. Chitin is a complex carbohydrate found in the insect exoskeleton and the fungal cell wall. Carbohydrates are a source of energy (about 17.6 kJ per gram when broken down) and a building material. Plant cells have much carbohydrate and animal cells little (about 1–5 %); cotton fibre is almost pure cellulose.
“Sugar family”. Draw a tree on the board: monosaccharides at the roots, disaccharides in the trunk, polysaccharides on the branches. Place the cards (glucose, sucrose, starch, cellulose, lactose, glycogen, fructose).