Grades 3–5 · Organisms
How does food become nutrients the body can use?
A bite of bread cannot pass whole into your blood. Before your body can use it, large food molecules must become smaller substances. Breaking food down is digestion. Moving useful substances across the digestive tract's lining is absorption. These are different steps in the same journey.
Chewing breaks the mouthful into smaller pieces and mixes it with saliva. Saliva begins breaking down some starch, a substance in bread. After swallowing, squeezing waves of muscle move food along the esophagus, the tube leading to the stomach. The stomach churns the food with digestive juices, mixing it and continuing the breakdown.
In the small intestine, enzymes help finish much of the chemical work. Enzymes speed particular chemical changes. Starch, for example, is broken into simple sugars small enough to cross the intestinal lining. The bread itself never travels through a blood vessel as a tiny bread crumb: substances made from it cross the lining instead.
Mouth, Esophagus, Stomach and the intestines mark food's route through the tract. Nutrient transfer leaves that route toward Circulation to the body, showing a different movement across the lining.
In the diagramFood route and nutrient transferMouthEsophagusStomachSmall intestineLargeintestineCirculationto the bodyNutrient transferBreak down → absorb → transport
Blood carries many absorbed nutrients onward. Many fats first enter another network of small vessels carrying a fluid called lymph, then reach the blood. Material left in the digestive tract continues to the large intestine, where more water is absorbed and stool forms. The useful parts of the meal can now help supply energy and materials for growth and repair: a sandwich becomes useful through changes too small to see.
About this explanation
Starting knowledge: Sequence organ roles and distinguish movement from absorption.
Sources
- NIH National Institute of Diabetes and Digestive and Kidney Diseases — Your Digestive System & How It Works