Final answer:
Galactose found in the bloodstream indicates the consumption of lactose, because lactose comprises glucose and galactose and breaks down to release galactose during digestion.
Step-by-step explanation:
If one finds galactose in a blood sample taken from a patient's portal vein, it suggests that the patient has likely consumed lactose, as galactose is one of the two monosaccharides that make up lactose. Lactose is commonly known as milk sugar and is found in dairy products. The other component of lactose is glucose. Therefore, upon the consumption of lactose, the enzyme lactase hydrolyzes lactose into glucose and galactose. The galactose then enters the bloodstream, where it can be detected.
Given the options provided, the correct answer is (4) Lactose. This is because only lactose, when digested, releases galactose into the blood. While sucrose, another disaccharide, is hydrolyzed to produce glucose and fructose, and does not yield galactose as one of its components. Similarly, the consumption of glucose or fructose alone would not directly introduce galactose into the bloodstream.