1.3.3 Distinguish between monosaccharides, disaccharides and polysaccharides (glycogen and starch – amylose and amylopectin) and relate their structures to their roles in providing and storing energy (β-glucose and cellulose are not required in this topic).

monosaccharides are basic molecular units, simple sugars.

e.g. glucose, which has a reactive group so it is good for respiratory substrate.

disaccharides, made up of two monosaccharides joined by glycosidic bonds in a condensation reaction.

e.g. sucrose, which has reactive groups joined to each other so it is unreactive, so good for transport function in plants.

polysaccharides: many monosaccharides joined by glycosidic bonds in a condensation reaction.

e.g. 

amylose: found in starch, energy storage molecule in plants, made up of alpha glucose molecules bonded by 1,4-glycosidic bonds in straight chains that form spirals/helix, a compact structure so can fit lots of glucose in small space, insoluble so no osmotic effect, held by glycosidic bonds so easily hydrolysed.

amylopectin: found in starch, energy storage molecule in plants, branched chains of alpha glucose molecules at 1,6-glycosidic bonds, lots of terminal ends so digested more rapidly than amylose, insoluble so no osmotic effect, a compact structure so can fit lots of glucose in small space, insoluble so no osmotic effect, held by glycosidic bonds and branched so hydrolyzed more rapidly.

glycogen: energy storage molecule in animals, bacteria and fungi, branched chains of alpha glucose molecules, can be hydrolyzed more rapidly than amylopectin as it has more branched chains at 1,6-glycosidic bonds, compact, insoluble; no osmotic effect.