When we ingest large molecules such as lipids, carbohydrates, and proteins, they must undergo catabolic reactions whereby enzymes split these large molecules into smaller molecules. This series of reactions is called Secretion Absorption Mechanical digestion Chemical digestion.
The Correct Answer and Explanation is:
Correct Answer: Chemical digestion
Explanation
When we consume food, it contains large, complex molecules such as lipids (fats), carbohydrates (sugars), and proteins. These macromolecules are too large to be directly absorbed into the bloodstream through the walls of the digestive tract. Therefore, they must first be broken down into their smaller, absorbable units. This process is known as chemical digestion.
Chemical digestion refers specifically to the enzymatic breakdown of food molecules. Unlike mechanical digestion—which involves physical processes like chewing and churning to break food into smaller pieces—chemical digestion involves catabolic reactions catalyzed by digestive enzymes. These enzymes are secreted by various glands and organs in the digestive system, including the salivary glands, stomach, pancreas, and small intestine.
For example:
- Carbohydrates are broken down into simple sugars (monosaccharides) by enzymes like amylase and maltase.
- Proteins are broken down into amino acids by enzymes such as pepsin, trypsin, and peptidase.
- Lipids are broken down into fatty acids and glycerol with the help of lipase enzymes and bile, which emulsifies fats for easier enzyme action.
These reactions occur in a step-by-step manner as food moves through the digestive tract—from the mouth to the stomach and then to the small intestine, where most chemical digestion and nutrient absorption occurs.
Once macromolecules are broken down into their basic units, these smaller molecules can be absorbed through the intestinal lining into the blood or lymph, supplying the body with essential nutrients for energy, growth, and repair.
In summary, chemical digestion is crucial because it transforms large, non-absorbable molecules into smaller units that the body can utilize. Without it, the nutrients in food would be biologically inaccessible despite mechanical processing or secretion.
