1.2 (i) know the difference between monosaccharides, disaccharides and polysaccharides, including glycogen and starch (amylose and amylopectin) (ii) be able to relate the structures of monosaccharides, disaccharides and polysaccharides to their roles in providing and storing energy

Explain how the structure of polysaccharides makes them suitable for energy storage.

• Polysaccharides are large and insoluble, so they do not affect the water potential of cells.

• Their compact structure allows large amounts of energy to be stored in a small volume.

• Branching (e.g., in amylopectin and glycogen) provides many ends for enzymes to act on, allowing rapid hydrolysis to glucose for energy release.

State three functions of carbohydrates in living organisms.

Carbohydrates provide energy (e.g. glucose), store energy (e.g. starch and glycogen), and act as structural materials (e.g. cellulose in plant cell walls).

Define a monosaccharide and describe its function.

A monosaccharide is a simple sugar made of one unit. It is small and soluble, so it diffuses easily into cells and is used in cellular respiration.

State the general formula of a monosaccharide.

(CH₂O)ₙ, where n is typically 3 to 6.

Name the three types of monosaccharides by carbon number and state a function for each.

• Triose (3C) – Respiration intermediate.
• Pentose (5C) – Component of DNA/RNA.
• Hexose (6C) – Energy source (e.g., glucose).

Define a disaccharide and give three examples with their monomers.

A disaccharide is formed by two monosaccharides joined by a glycosidic bond in a condensation reaction. Examples:
• Maltose = glucose + glucose.
• Sucrose = glucose + fructose.
• Lactose = glucose + galactose.

Explain how disaccharides are broken down.

Disaccharides are hydrolysed into monosaccharides by breaking the glycosidic bond using water. This reaction is catalysed by enzymes.

Define a polysaccharide and state three examples.

A polysaccharide is a polymer made of many monosaccharides joined by glycosidic bonds. Examples: starch (amylose + amylopectin), glycogen, cellulose.

State the monomer used to build starch and glycogen.

α-glucose.

Describe the structure of amylose.

Amylose is an unbranched polymer of α-glucose with 1,4 glycosidic bonds. It coils into a helix, making it compact for storage.

Describe the structure of amylopectin.

Amylopectin is a branched polymer of α-glucose with both 1,4 and 1,6 glycosidic bonds. The branches allow faster enzyme access for hydrolysis.

Compare amylose and amylopectin.

• Amylose: Unbranched, 1,4 bonds, forms a compact helix.
• Amylopectin: Branched, 1,4 and 1,6 bonds, allows faster glucose release.

Describe the structure of glycogen.

Glycogen is a highly branched polymer of α-glucose with 1,4 and many 1,6 glycosidic bonds. It is more branched than amylopectin.

Explain how glycogen is suited to its function in animals.

• Highly branched → rapid glucose release.
• Compact → fits into small spaces.
• Insoluble → doesn’t affect water potential.

State where glycogen is stored in humans.

In liver and muscle cells.

Explain why starch and glycogen are good energy storage molecules.

• Compact for dense energy storage.
• Insoluble, so they don’t affect osmotic balance.
• Branching allows rapid hydrolysis into glucose.

Define condensation and hydrolysis reactions in carbohydrate metabolism.

• Condensation: Joins monomers by forming a glycosidic bond and removing water.
• Hydrolysis: Breaks glycosidic bonds by adding water.

Define a glycosidic bond.

A covalent bond formed between two sugar units during a condensation reaction.