A balanced diet contains carbohydrates for energy, lipids (fats) for stored energy and insulation, proteins for growth and repair, vitamins and minerals in small amounts for health, fibre to keep food moving through the gut, and water. Too little of a nutrient causes a deficiency disease; for example, too little vitamin C causes scurvy.
Digestion breaks large insoluble molecules into small soluble ones that can be absorbed. Enzymes speed this up: amylase breaks starch into sugars, protease breaks proteins into amino acids, and lipase breaks fats into fatty acids and glycerol. The small intestine is long and lined with villi, which give a huge surface area for absorbing food into the blood. Bacteria in the large intestine also help digestion.
Worked example
Why must starch be digested before it can be absorbed?
- Starch molecules are large and insoluble.
- They cannot pass through the gut wall into the blood.
Answer:Amylase breaks them into small sugar molecules that can.
Key words
- enzyme
- a protein that speeds up a reaction
- nutrient
- a substance in food the body needs
- villi
- tiny folds in the small intestine that absorb food
- deficiency
- not having enough of a nutrient
New questions every time.
NGSS-referenced: MS-LS1-3