Four Groups of Biological Molecules: Monomers, Chains and Identification Tests
Integrated ScienceChemical ReactionsAges 14–15Virtual lab
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Chemical Reactions
Choose a group of substances and watch monomers link together into a long chain: glucose molecules join to form starch, amino acids join into a protein chain via peptide bonds, glycerol combines with three fatty acids to form a fat, and ethylene polymerizes into polyethylene. On the right, a test tube shows identification tests: iodine solution turns starch blue-black, biuret reagent turns protein purple, and shaking fat with water leaves it floating as an undissolved layer. Raise the temperature above 70 °C to watch the protein chain unfold and coagulate – denaturation.
Lesson: Carbohydrates, Proteins, Lipids and Polymers
What it shows
Starch, proteins and many plastics are polymers: long chains built by joining small monomers. Glucose units link through glycosidic bonds to form starch, and amino acids link through peptide bonds to form proteins, each new bond releasing one water molecule. A fat is built differently, from one glycerol and three fatty acids joined by ester bonds. Ethylene forms polyethylene by addition polymerisation, with no by-product. Simple tests identify each group: iodine turns starch blue-black, biuret reagent turns protein purple, and fat floats as a separate layer on water.
How to use
Choose a Substance group and watch the chain build, adjusting the Number of monomers in the chain and the Chain-building speed. Then use Switch reagent to add iodine solution, biuret reagent or water to the test tube, and have students record each result in a table to build an identification key for all four groups. For protein, raise the Test tube temperature above 70 °C and compare with the unheated sample.
Parameters you can change
- Substance group Carbohydrate – starch (glucose monomer), Protein (amino acid monomer), Lipid – fat (glycerol + fatty acids), Polymer – polyethylene (ethylene monomer)
- Reagent added to the test tube No reagent added yet, Iodine solution, Biuret reagent (Cu(OH)₂ in NaOH), Distilled water, shaken well
- Test tube temperature 20–100 °C
- Number of monomers in the chain 4–20 monomers
- Chain-building speed 0.5–4 monomers/s
Questions to explore
- How could you tell apart samples of starch paste, egg white and cooking oil using the reagents in the simulation?
- What happens to the protein above 70 °C, and why does boiled egg white turn solid?
- What is the monomer of polyethylene, and how does forming it differ from forming starch?
