Carbohydrates and lipids
Cambridge A-Level Biology (9700) · Unit 2: Biological molecules · 16 flashcards
Carbohydrates and lipids is topic 2.2 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 2 — Biological molecules , alongside Testing for biological molecules, Proteins and Water. In one line: A monomer is a small repeating unit. A polymer is a large molecule made of many monomers joined together. A macromolecule is a very large molecule, often a polymer, with a high molecular weight (.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 16 flashcards — 8 definitions and 8 key concepts — covering the precise wording mark schemes reward. Use the 8 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
The terms 'monomer', 'polymer', and 'macromolecule'
A monomer is a small repeating unit. A polymer is a large molecule made of many monomers joined together. A macromolecule is a very large molecule, often a polymer, with a high molecular weight (
What the Cambridge 9700 syllabus says
Official 2025-2027 spec · AS LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- describe the breakage of a glycosidic bond in polysaccharides and disaccharides by hydrolysis, with reference to the non-reducing sugar test
- describe the molecular structure of the polysaccharides starch (amylose and amylopectin) and glycogen and relate their structures to their functions in living organisms
- describe the molecular structure of the polysaccharide cellulose and outline how the arrangement of cellulose molecules contributes to the function of plant cell walls
- state that triglycerides are non-polar hydrophobic molecules and describe the molecular structure of triglycerides with reference to fatty acids (saturated and unsaturated), glycerol and the formation of ester bonds
- relate the molecular structure of triglycerides to their functions in living organisms
- describe the molecular structure of phospholipids with reference to their hydrophilic (polar) phosphate heads and hydrophobic (non-polar) fatty acid tails
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Carbohydrates and lipids
- › Remember: three polypeptide chains form one collagen molecule (triple helix). Molecules then arrange into fibrils, and fibrils into fibres.
- › Distinguish between the direct Benedict’s test and the non-reducing sugar test which requires prior acid hydrolysis and neutralization.
- › Amylose is unbranched with 1,4-glycosidic bonds only; amylopectin is branched and contains both 1,4 and 1,6-glycosidic bonds.
- › Recall that hydrolysis reactions use water to split molecules, whereas condensation reactions release water.
- › Understand that the non-reducing sugar test hydrolyzes disaccharides into monosaccharides, increasing the total concentration of reducing sugars detected.
Draw the ring structure of α-glucose.
The α-glucose ring has the -OH group on carbon 1 pointing DOWN. Note the positions of other -OH groups and the CH₂OH group.
Define the terms 'monomer', 'polymer', and 'macromolecule'.
A monomer is a small repeating unit. A polymer is a large molecule made of many monomers joined together. A macromolecule is a very large molecule, often a polymer, with a high molecular weight (
What are monosaccharides, disaccharides and polysaccharides? Provide an example of each.
Monosaccharides are simple sugars (
What type of bond joins smaller molecules to form polymers, and how is this bond formed?
Covalent bonds join smaller molecules (monomers) to form polymers. These bonds are formed through condensation reactions, where a water molecule is removed.
Which of the following are reducing sugars: glucose, fructose, maltose, sucrose?
Glucose, fructose, and maltose are reducing sugars. Sucrose is a non-reducing sugar.
Describe the formation of a glycosidic bond.
A glycosidic bond forms between two monosaccharides by a condensation reaction. An -OH group is removed from each monosaccharide, releasing a water molecule and linking the sugars together through an oxygen atom.
Give an example of the formation of a glycosidic bond with reference to sucrose.
Sucrose is formed from glucose and fructose. A glycosidic bond forms between carbon 1 of glucose and carbon 2 of fructose, with the removal of a water molecule.
Give an example of the formation of a glycosidic bond with reference to polysaccharides.
Starch is formed from many α-glucose molecules. Glycosidic bonds form between carbon 1 and carbon 4 of adjacent α-glucose molecules, linking them into a long chain with the release of water molecules.
Describe the process of hydrolysis in the context of breaking down polysaccharides and disaccharides.
Hydrolysis is the breaking of a glycosidic bond by the addition of water. A water molecule (H₂O) is added, with -H attaching to one monosaccharide and -OH to the other, separating them. This process is key in digestion and is tested for with a non-reducing sugar test (
Describe the molecular structure of starch, including amylose and amylopectin, and relate their structures to their function in energy storage.
Starch is a polysaccharide composed of glucose monomers. Amylose is a long, unbranched chain of α-glucose linked by α-1,4-glycosidic bonds, forming a helical structure. Amylopectin is branched, with α-1,4-glycosidic bonds and α-1,6-glycosidic bonds at the branch points. The compact structure allows for efficient storage of glucose.
Describe the molecular structure of glycogen and relate its structure to its function in energy storage.
Glycogen is a highly branched polysaccharide of α-glucose, similar to amylopectin but with more frequent α-1,6-glycosidic branches. This branching allows for rapid hydrolysis and release of glucose when needed, important for maintaining blood sugar levels.
Describe the molecular structure of cellulose and explain how its arrangement contributes to the function of plant cell walls.
Cellulose is a linear, unbranched polysaccharide of β-glucose linked by β-1,4-glycosidic bonds. Many cellulose chains run parallel and are cross-linked by hydrogen bonds, forming strong microfibrils. These microfibrils provide tensile strength and rigidity to plant cell walls.
Explain why triglycerides are described as non-polar and hydrophobic.
Triglycerides are non-polar due to the even distribution of electrons in their hydrocarbon chains of fatty acids. This lack of polarity makes them hydrophobic, meaning they are insoluble in water because they cannot form hydrogen bonds with water molecules.
Describe the molecular structure of a triglyceride, including its components and the type of bond formed.
Triglycerides consist of a glycerol molecule bonded to three fatty acids. The bonds are ester bonds, formed by the reaction of the glycerol's hydroxyl (-OH) groups with the carboxyl (-COOH) groups of the fatty acids, releasing three water molecules.
Relate the structure of triglycerides to their function as energy stores and insulation.
The long hydrocarbon chains of fatty acids in triglycerides are rich in chemical energy. Their non-polar nature allows them to be stored without dissolving in the aqueous cytoplasm, and their low density provides insulation.
Describe the molecular structure of phospholipids, highlighting the hydrophilic and hydrophobic regions.
Phospholipids consist of a glycerol molecule linked to two fatty acids and a phosphate group. The phosphate group is polar and hydrophilic (water-loving), forming the 'head,' while the fatty acid tails are non-polar and hydrophobic (water-repelling).
More topics in Unit 2 — Biological molecules
Carbohydrates and lipids sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Carbohydrates and lipids deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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