A-Level Biology: Biological Molecules Lesson-by-Lesson Breakdown

Lesson 1: Introduction to biological molecules

Focus: What biological molecules are; why living things share a common chemistry; monomers vs polymers; condensation and hydrolysis.

Students should learn:

• the difference between a monomer and a polymer
• that condensation joins molecules and releases water
• that hydrolysis breaks molecules using water
• examples of biological monomers such as monosaccharides, amino acids, and nucleotides

Good outcome: Students can explain how large biological molecules are assembled and broken down.

Lesson 2: Carbohydrates I — monosaccharides and disaccharides

Focus: Structure of carbohydrates; glucose, fructose, galactose; formation of disaccharides.

Students should learn:

• the difference between monosaccharides and disaccharides
• examples such as maltose, sucrose, and lactose
• how glycosidic bonds form by condensation
• that glucose exists in different forms such as alpha-glucose and beta-glucose

Good outcome: Students can build and compare simple carbohydrate molecules.

Lesson 3: Carbohydrates II — polysaccharides and function

Focus: Starch, glycogen, cellulose, and structure-function relationships.

Students should learn:

• how polysaccharides are formed from many glucose units
• the differences between starch, glycogen, and cellulose
• how molecular structure relates to function in energy storage and cell walls
• that Edexcel also links carbohydrates to storing and providing energy

Good outcome: Students can compare storage and structural carbohydrates.

Lesson 4: Testing for carbohydrates

Focus: Food tests; qualitative and quantitative methods.

Students should learn:

• Benedict’s test for reducing sugars
• how non-reducing sugars are tested
• iodine/potassium iodide test for starch
• that chromatography and colorimetry may be used to identify sugars or estimate concentration

Suggested practical:

• test unknown samples for reducing sugar, non-reducing sugar, and starch
• prepare a dilution series and calibration curve for quantitative extension work

Good outcome: Students can choose the correct carbohydrate test and interpret results.

Lesson 5: Lipids

Focus: Triglycerides and phospholipids; saturated and unsaturated fatty acids; structure and function.

Students should learn:

• how triglycerides form from glycerol and three fatty acids
• how ester bonds are formed
• the difference between saturated and unsaturated fatty acids
• how phospholipids differ from triglycerides
• why lipid structure suits functions such as energy storage and membrane formation

Suggested practical: Emulsion test for lipids.

Good outcome: Students can explain how lipid structure relates to biological role.

Lesson 6: Proteins I — amino acids and protein structure

Focus: Amino acids; peptide bonds; levels of protein structure.

Students should learn:

• the general structure of an amino acid
• how peptide bonds form
• the difference between dipeptides, polypeptides, and proteins
• levels of protein structure: primary, secondary, tertiary, quaternary
• the roles of hydrogen bonds, ionic bonds, and disulfide bridges
• that Edexcel also emphasizes how primary structure affects 3D shape and properties of globular and fibrous proteins

Good outcome: Students can link protein shape to protein function.

Lesson 7: Proteins II — enzymes

Focus: Enzymes as biological catalysts; induced-fit model; factors affecting enzyme action.

Students should learn:

• that enzymes lower activation energy
• the induced-fit model
• enzyme specificity
• effects of temperature, pH, substrate concentration, enzyme concentration, and inhibitors
• that enzymes work in both intracellular and extracellular reactions

Suggested practical: Investigate the effect of one variable on the rate of an enzyme-controlled reaction.

Good outcome: Students can explain enzyme action and analyse enzyme experiment data.

Lesson 8: Nucleic acids

Focus: DNA and RNA structure; nucleotides; DNA replication.

Students should learn:

• that DNA and RNA are polymers of nucleotides
• the components of a nucleotide
• the differences between DNA and RNA
• complementary base pairing
• DNA as a double helix
• semi-conservative replication
• roles of DNA helicase and DNA polymerase

Good outcome: Students can describe how DNA stores and replicates genetic information.

Lesson 9: ATP, water, and inorganic ions

Focus: ATP as an energy carrier; biological importance of water; key inorganic ions.

Students should learn:

• that ATP is a nucleotide derivative
• how ATP is hydrolysed to ADP + Pi
• how ATP is resynthesised
• why water is important as a solvent, metabolite, temperature buffer, and cohesive substance
• roles of ions such as hydrogen, iron, sodium, and phosphate
• that Edexcel also highlights nitrate, calcium, and magnesium ions in plants

Good outcome: Students can explain why these small molecules and ions are essential for life.

Lesson 10: Review, application, and exam practice

Focus: Bringing the whole topic together; practical interpretation; exam-style comparisons and data analysis.

Students should practise:

• comparing carbohydrates, lipids, and proteins
• explaining structure-function relationships
• interpreting food test results
• analysing enzyme graphs
• answering synoptic questions linking molecules to membranes, respiration, transport, and genetics

Good outcome: Students can apply biological molecules knowledge rather than just recall definitions.