Label Busters

Label Busters: food tests for glucose and starch

This free game is part of our Pearson Edexcel iGCSE Biology (4BI1) course for exams in EXAM YEARS 2026-2029.

How do you test for glucose? The Benedict's test

Glucose is a reducing sugar, and the test for reducing sugars uses Benedict's reagent, a blue solution containing copper ions.

1. If the food is solid, crush it with a little distilled water so the sugars dissolve.
2. Put about 2 cm³ of the food solution in a test tube.
3. Add an equal volume (about 2 cm³) of Benedict's reagent.
4. Heat the tube in a hot water bath (around 80 °C) for about 5 minutes.
5. Look at the colour.

If there is no reducing sugar, the solution stays blue. If there is, it changes colour and a precipitate forms. The more glucose there is, the further it goes along the scale: blue → green → yellow → orange → brick red. Because the colour only gives a rough idea of how much sugar there is, the test is called semi-quantitative.

How do you test for starch? The iodine test

• Put a little of the food on a spotting tile (or in a test tube). Solid food can be tested directly.
• Add a few drops of iodine solution.
• No heating is needed: the colour changes straight away.

Iodine solution is orange-brown (yellow-brown). If starch is present, it turns blue-black. If there is no starch, it stays orange-brown.

How to play Label Busters

You join the Label Busters, a food-testing squad led by ZEST the lemon and DROP the lab robot. Food companies print claims on their packets, and your job is to check them with science.

• Each of the 8 cases is a food with a claim, such as a sports drink that says it has zero sugar or crackers that say they are starch-free.
• Pick the right test, then run it in a 3D lab one step at a time: goggles, crushing, adding the sample and reagent, and heating in the water bath. Wrong steps cost points, and DROP explains what went wrong.
• Read the colour of your result, then decide whether the label is true or whether to bust it with a giant rubber stamp.
• After two training cases, the colour chart is taken away in Expert mode, so you have to remember the colours.
• Finish with Colour Rush: put Benedict's results in order of glucose before the timer runs out.

Controls, safety and a sugar that doesn't react

Always run a control by testing distilled water too. Benedict's should stay blue and iodine should stay orange-brown. If they change colour, your equipment or reagents are contaminated.

Wear eye protection, because hot Benedict's reagent can spit, and heat the tube in a water bath rather than straight in a flame. Iodine stains skin and clothes. Never taste anything in a lab.

Not every sugar gives a positive Benedict's test. Table sugar is sucrose, a non-reducing sugar, so Benedict's stays blue with it.

Exam tips

• Name the reagent: Benedict's for glucose (reducing sugars) and iodine solution for starch. Don't mix them up with Biuret (protein) or the ethanol emulsion test (fats).
• Say that the Benedict's test must be heated in a water bath. Without heat it stays blue.
• Give both colours: Benedict's goes from blue to brick red; iodine goes from orange-brown to blue-black.
• Learn the order of the Benedict's colours: blue, green, yellow, orange, brick red.
• Starch is made of many glucose molecules joined together, but starch itself does not give a positive Benedict's test.