From food to fuel and new cells
Core + labelled SupplementB7.1–B7.3Two 45-minute sessions + optional consolidationResponses save in this browser when storage is available. Download a copy before changing device. Nothing is submitted to MSH or a teacher.
Suggested pacing: Session 1: starter 5 min, learn/watch 25 min, activities 15 min. Session 2: retrieval 5 min, quiz 10 min, exam practice 25 min, exit ticket 5 min. Pause or split further to suit your class.
Glucose can be used in respiration, but a diet also supplies materials for growth and repair and substances needed for normal body function. Protein supplies amino acids; vitamins and mineral ions have specific roles.
A balanced diet supplies enough energy and the right proportions of nutrients for a person’s needs. It includes carbohydrates, fats and oils, proteins, vitamins, mineral ions, fibre and water. “Balanced” does not mean equal masses of each food group. Requirements vary with activity, growth and other individual circumstances.
| Component | Examples of sources | Role / deficiency link |
|---|---|---|
| Carbohydrates | Rice, bread, potato, pasta | Fuel for respiration. |
| Fats and oils | Vegetable oils, nuts, oily fish | Energy store; insulation; components of cell membranes. |
| Protein | Beans, lentils, fish, eggs, meat | Growth and repair; making enzymes and other proteins. |
| Vitamin C | Citrus fruit, peppers, fresh vegetables | Healthy connective tissue; prolonged deficiency causes scurvy. |
| Vitamin D | Oily fish, eggs, fortified foods; also made in skin in sunlight | Supports calcium absorption and healthy bones; deficiency can cause rickets. |
| Calcium ions | Dairy products, calcium-fortified alternatives | Healthy bones and teeth. |
| Iron ions | Meat, beans, leafy green vegetables | Needed for haemoglobin; deficiency can cause anaemia. |
| Fibre | Whole grains, vegetables, fruit | Adds bulk to food and helps movement through the gut. |
| Water | Drinks and water-rich foods | Solvent and transport medium; needed for chemical reactions. |
Exam precision: scurvy → vitamin C deficiency; rickets → vitamin D deficiency. Fibre is useful even though human enzymes do not digest it.
The alimentary canal is a continuous tube. Food does not pass through the liver or pancreas: these organs supply substances to the canal.
| Organ | Main role |
|---|---|
| Mouth and salivary glands | Ingestion; chewing increases food surface area; saliva lubricates food and contains amylase. |
| Oesophagus | Moves food by coordinated muscular contractions (peristalsis). |
| Stomach | Muscular walls churn food; gastric juice contains acid and a protease. |
| Duodenum | First part of small intestine; receives bile and pancreatic juice. |
| Ileum | Later part of small intestine; absorbs digested nutrients. |
| Colon | Absorbs water from remaining gut contents. Water is also absorbed in the small intestine. |
| Rectum and anus | Rectum stores faeces; anus controls their release during egestion. |
| Liver and gall bladder | Liver produces bile; gall bladder stores and releases it. |
| Pancreas | Secretes digestive enzymes into the duodenum. |
| Process | What happens | Example |
|---|---|---|
| Ingestion | Taking food and drink into the body | Eating a piece of bread. |
| Digestion | Breaking down food | Starch molecules broken into smaller sugars. |
| Absorption | Digested nutrients cross from the gut into the blood | Glucose moves across the small-intestine lining. |
| Assimilation | Cells take up and use nutrients | Amino acids used to build a muscle protein. |
| Egestion | Undigested material leaves as faeces | Removal through the anus. |
Physical digestion makes smaller pieces without changing the food molecules. Chewing and stomach churning expose a larger surface area to digestive enzymes. Chemical digestion breaks large, insoluble food molecules into small, soluble molecules that can be absorbed.
Think of a large starch molecule as a connected chain. Cutting a piece of bread into crumbs does not break the chemical bonds in that chain; enzyme action does.
| Enzyme | Substrate → products | Secreted by / acts in |
|---|---|---|
| Amylase | Starch → simple reducing sugars, including maltose | Salivary glands and pancreas / mouth and small intestine. |
| Proteases | Proteins → amino acids (overall digestion) | Stomach, pancreas and small intestine / stomach and small intestine. |
| Lipase | Fats and oils → fatty acids + glycerol | Pancreas and small intestine / mainly small intestine. |
Stomach protease works in acidic conditions. Hydrochloric acid provides a suitable low pH and kills many harmful microorganisms in food.
Bile is an alkaline mixture, not an enzyme. In the duodenum it neutralises the acidic food mixture from the stomach, helping provide a suitable pH for intestinal enzymes. It also emulsifies fats: large droplets split into smaller droplets, increasing surface area for lipase. Emulsification itself does not make fatty acids.
Digestion creates molecules small enough to cross the intestinal lining. The intestine has a large absorptive surface; villi increase that area, a thin lining gives a short diffusion distance, and blood carries absorbed glucose and amino acids away. These details apply your earlier work on exchange surfaces; detailed villus anatomy is enrichment here.
Cognito · Open on YouTube. Internet access is required. If your school blocks the player, use the written lesson below.
A student’s sample lunch contains white rice and a sugary drink. Which addition would best broaden its nutrient range? This is a classroom comparison, not a personalised diet plan.
Suggested marking: one mark per valid point, up to 3.
One mark per correct answer. Select all eight answers, then check. You may change answers and check again for practice.
Not yet checked
Original Cambridge-style practice, not copied past-paper questions. Write first, then reveal mark points and self-assess. Written answers are not automatically graded; self-scores are not official grades.
Suggested marking: one mark per valid point, up to 2.
Suggested marking: one mark per valid point, up to 4.
Suggested marking: one mark per valid point, up to 2.
Suggested marking: one mark per valid point, up to 4.
Illustrative classroom data: equal starch mixtures at 37 °C and the same pH were tested with iodine every 30 s. “Time” is when a sample first remained yellow-brown. No result below is a live experiment.
| Tube | Contents | Time / s |
|---|---|---|
| A | Starch + active amylase | 120 |
| B | Starch + boiled, cooled amylase | Still blue-black after 600 |
| C | Starch + water | Still blue-black after 600 |
Suggested marking: one mark per valid point, up to 3.
Suggested marking: one mark per valid point, up to 3.
Suggested marking: one mark per valid point, up to 2.
Safety if teacher-led: eye protection for iodine; use a controlled water bath; do not taste materials. Teacher prepares boiled enzyme safely and cools it before use.
This lesson follows Cambridge 0654 syllabus for exams in 2025–2027, B7.1–B7.3. The verified sequence after B6 is B7 Human nutrition, B8 Transport in plants, B9 Transport in animals. Check the examination-year syllabus for other cohorts.
Official topic order and video pages checked on 14 September 2026 (Bermuda). Embedded videos are hosted by YouTube and require internet access; playback depends on regional and school settings. All written learning, diagrams and activities work without a network connection.
Independent MSH teaching resource; not endorsed by Cambridge International. Scientific diagrams are original schematics, not to scale. Supplement labels identify Extended work; application boxes may include supporting explanation beyond the specified minimum.
Responses remain on the current browser/device when local storage is permitted. Use the download button for a readable text record. No backend, login, tracking or gradebook submission is included.
Continue the series: B7 Human nutrition · B8 Transport in plants · B9 Transport in animals