--- title: "The Digestive System and Testing Food for Nutrients" description: "Digestion is a sequence of organs each doing one job to a food molecule too big to absorb, with enzymes and bile doing the chemistry. Simple colour tests let a learner check which nutrient classes are" canonical: https://lightmysky.com/learn/science/the-digestive-system-and-testing-food-for-nutrients-mt__mBJCQEqPS source: https://lightmysky.com/learn/science/the-digestive-system-and-testing-food-for-nutrients-mt__mBJCQEqPS.md retrieved: 2026-09-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # The Digestive System and Testing Food for Nutrients Digestion is a sequence of organs each doing one job to a food molecule too big to absorb, with enzymes and bile doing the chemistry. Simple colour tests let a learner check which nutrient classes are actually present in a sample. Subject: Science · Area: Organisms & Life Processes · Ages 14 to 15 Page: https://lightmysky.com/learn/science/the-digestive-system-and-testing-food-for-nutrients-mt__mBJCQEqPS ## Ready when they can - Follow a named food molecule through the gut and say which organ and which enzyme acts on it - Explain what bile does and why it is not an enzyme - Carry out and interpret tests for starch, sugar, protein and fat, including a negative result ## Lesson: Following food through the gut Digestion breaks big food molecules into small ones your blood can absorb. In the mouth, chewing breaks food up while saliva starts the chemical work. Food slides down the esophagus to the stomach, where acid and churning make a soupy mix. In the small intestine most digestion finishes and nutrients pass into the blood, and the large intestine reclaims water from what is left. Each enzyme works on one nutrient in one place. Salivary amylase starts on starch in the mouth. Pepsin starts on protein in the stomach. Pancreatic juices and small-intestine enzymes finish starch, protein, and fat in the small intestine. Bile is made by the liver and stored in the gallbladder, then released into the small intestine. It breaks large fat globules into tiny droplets, which gives enzymes far more surface to work on. Bile is not an enzyme, because it never snips molecules apart; it works like dish soap on grease. **Example.** To test a food, check each nutrient class and always run a negative control, like water, that holds no nutrient. If the sample changes and the control does not, the nutrient is present. If the sample looks just like the control, the result is negative and the nutrient is absent. **Recap.** Track the organ, name the enzyme, and trust a test only against its control. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Enzyme Action and the Active Site](https://lightmysky.com/learn/science/enzyme-action-and-the-active-site-mt__ozLTPNN0H) - [Digestion & Enzymes](https://lightmysky.com/learn/science/digestion-and-enzymes-mt_0NlbulkB5P) - [Calculating Dietary Energy](https://lightmysky.com/learn/science/calculating-dietary-energy-mt_83KkBCtVyR) - [Gut Bacteria & Digestion](https://lightmysky.com/learn/science/gut-bacteria-and-digestion-mt_fCvmdI6xGO) ## Opens up - [Non-Communicable Disease and What Counts as a Risk Factor](https://lightmysky.com/learn/science/non-communicable-disease-and-what-counts-as-a-risk-factor-mt_IciZ1CJn6h) - [Digestion and Absorption in the Mammalian Gut](https://lightmysky.com/learn/science/digestion-and-absorption-in-the-mammalian-gut-mt_xZ2-3ZClDa)