Lipases break down lipids (fats) to glycerol and fatty acids.

The idea

Lipases are enzymes that catalyse the hydrolysis of lipids into glycerol and fatty acids. Lipids are large, insoluble molecules made of glycerol joined to fatty acids by ester bonds. Hydrolysis uses water to split these bonds, producing glycerol and fatty acids, which are small enough to be absorbed across the small intestine wall. Lipase is produced in the pancreas and small intestine, and bile from the liver emulsifies lipids into small droplets to increase the surface area for lipase action.

What earns the marks

• Lipases are enzymes that catalyse the breakdown of lipids into glycerol and fatty acids.
• Lipids are made of glycerol joined to fatty acids by ester bonds.
• Digestion is hydrolysis: water is used to split ester bonds.
• Lipase is produced in the pancreas and small intestine.
• Bile emulsifies lipids, increasing surface area so lipase acts faster.
• Glycerol and fatty acids are small and soluble enough to be absorbed across the small intestine wall.

Common mistakes and how to put them right

• Saying lipases break lipids into amino acids.

  Put it right: Lipases produce glycerol and fatty acids.

• Confusing emulsification with digestion.

  Put it right: Bile emulsifies lipids physically, while lipase hydrolyses them chemically.

• Writing that lipids are broken down into glucose.

  Put it right: Lipids are broken down into glycerol and fatty acids.

Exam tips

• Name both products: glycerol and fatty acids.
• Link bile to emulsification and increased surface area for lipase.
• Use the term hydrolysis and state that water is used to break ester bonds.