1. Food changes in consistency and form as it moves through the digestive system. In the mouth, chewing and saliva break food into a moist bolus, and enzymes begin breaking down carbohydrates through hydrolysis. The bolus travels down the esophagus to the stomach, where gastric juices and churning transform it into a semi-liquid mixture called chyme. In the small intestine, chyme mixes with bile and enzymes that further digest carbohydrates, proteins, and fats into their simplest forms, while the large intestine absorbs water and electrolytes, solidifying the remaining material into feces.
2. The breakdown of food, or digestion, transforms complex molecules into simpler forms that the body can absorb. Mechanical digestion, like chewing in the mouth and churning in the stomach, physically breaks food into smaller pieces, increasing surface area for enzymes. Chemical digestion uses enzymes and substances like amylase, pepsin, bile, and lipase to break down carbohydrates into simple sugars, proteins into amino acids, fats into fatty acids and glycerol, and nucleic acids into nucleotides. This breakdown allows nutrients to be absorbed in the small intestine: carbohydrates and proteins into the bloodstream, fats into the lymphatic system, and vitamins and minerals through specific transport processes. Water and electrolytes are absorbed mainly in the large intestine. These nutrients are then transported to cells for energy, growth, and repair, making digestion essential for health and function.