Respiration — OCR GCSE Biology
Test yourself on Respiration with OCR GCSE practice questions.
Start free
7 days Premium · Then free forever · No card, no charge
Respiration explained
Lipids, including fats and oils, are large macromolecules formed from the combination of glycerol and fatty acids.
Read the full explanation
Each triglyceride lipid molecule is synthesized by chemically bonding one molecule of glycerol to three fatty acid chains. Lipids do not form repeating chains of identical units, so they are macromolecules rather than true polymers. Synthesized lipids provide vital functions: concentrated long-term energy storage, thermal insulation, protection of vital organs, and formation of phospholipid cell membranes. Lipase enzymes hydrolyze lipids back into glycerol and fatty acids for respiration.
Your focus
- Describe the chemical composition of lipids as one glycerol bonded to three fatty acids.
- Explain the physiological importance of synthesized lipids in organisms.
- Describe the enzymatic breakdown of lipids by lipase into fatty acids and glycerol.
Respiration exam tips
Marking Points
- stating that a lipid molecule is synthesized from one molecule of glycerol and three fatty acids
- identifying roles of synthesized lipids: energy storage, thermal insulation, and cell membranes
- explaining that lipase enzymes break down lipids into fatty acids and glycerol for cellular respiration
Examiner Tips
- 💡Always state the exact molecular ratio: one molecule of glycerol joined to three fatty acid molecules.
- 💡Mention that breakdown products of lipids can be oxidized in cellular respiration to supply ATP.
Common Mistakes
- calling lipids polymers, forgetting they are macromolecules made from two different constituent molecules (1 glycerol + 3 fatty acids)
- stating lipids consist of equal numbers of glycerol and fatty acid molecules rather than a 1:3 ratio