How nutrients are digested and used by the body
Food contains nutrients, each with a special job. Carbohydrates and fats give energy, proteins help build and repair the body, vitamins and minerals protect against disease, roughage helps food move through the intestines, and water carries substances around the body. Simple tests detect nutrients: iodine turns starch blue-black, copper sulphate and caustic soda turn protein violet, and fat leaves an oily patch on paper.
Digestion breaks food into simple, soluble substances. It begins in the mouth, where teeth grind food and saliva starts digesting starch. Food then passes through the oesophagus to the stomach, where acid and digestive juices act on proteins. In the small intestine, bile from the liver and juices from the pancreas complete digestion, and villi absorb nutrients into the blood. The large intestine absorbs water. A shortage of nutrients causes deficiency diseases: lack of vitamin A causes night blindness, vitamin D causes rickets, iron causes anaemia and iodine causes goitre.
Why it matters
Understanding nutrients helps you plan balanced meals, read food labels and avoid conditions like anaemia, common among young people. Government programmes such as mid-day meals aim to prevent malnutrition. Knowing how digestion works explains why chewing well and eating fibre-rich food prevent stomach problems. This leads into life processes in Class 10.
Key terms
- Nutrient
- A substance in food that the body needs for energy, growth or protection.
- Roughage
- The fibre in food that cannot be digested but helps move food through the gut.
- Digestion
- The breakdown of complex food into simple substances the body can absorb.
- Deficiency disease
- An illness caused by a lack of a particular nutrient in the diet.