In the digestive system of living organisms, option 4 is correct. Proteins are broken down into amino acids.

Option 1 is incorrect. Glucose is not broken down into glycerol in the digestive system. Glycerol is a component of fats, and fats are broken down into glycerol and fatty acids, not glucose.

Option 2 is also incorrect. Glucose is not converted into glycogen in the digestive system. Glycogen is a storage form of glucose in animals and is formed in the liver and muscles.

Option 3 is incorrect as well. Glucose is not broken down into carbon dioxide and water in the digestive system. This process, known as cellular respiration, takes place in cells to release energy, not in the digestive system itself.

Therefore, option 4 is the correct statement. In the digestive system, proteins from food are broken down by enzymes into amino acids, which are then absorbed into the bloodstream and used by the body for various functions.