Final answer:
The passage of digested food into the bloodstream is called Absorption. This process primarily occurs in the small intestine and is crucial for nutrients to be transported and used throughout the body.
Step-by-step explanation:
Absorption in the Gastrointestinal Tract
The answer to the student's question is Option 2: Absorption. After food is digested, the resulting simple nutrient molecules enter the bloodstream through the process of absorption. This essential function occurs primarily in the small intestine, where nutrients are absorbed from the lumen of the alimentary canal through the mucosal cells. While certain substances, like water and some minerals and vitamins, are also absorbed in both the stomach and large intestine, about 95% of nutrients are taken up in the small intestine. Notably, lipids are absorbed into lacteals and enter the bloodstream via the lymphatic system. These nutrients are then transported throughout the body to be utilized by cells.
In contrast, digestion is the process of breaking down food into nutrients through mechanical and chemical means, while metabolism involves the chemical reactions that occur within a living organism to maintain life. The term 'molecular' refers to the smallest unit of a chemical compound that can take part in a chemical reaction but is not a process related to nutrient intake.