Final answer:
The enzyme lacking in individuals who experience gastrointestinal upset after consuming dairy products is lactase. Lactose intolerance is due to the absence of lactase, which is necessary for digesting the lactose in milk.
Step-by-step explanation:
People who lack the enzyme lactase often experience GI upset after consuming milk and other dairy products. The correct answer to the question is A) lactase.
Lactose intolerance is a condition where individuals cannot digest the lactose found in milk, generally because of lack of the enzyme lactase. This causes symptoms such as bloating, cramps, nausea, and vomiting after the intake of dairy products. To manage this condition, individuals might choose lactose-free milk or supplements containing the lactase enzyme to improve digestion.
Without sufficient lactase, the lactose remains undigested and is fermented by bacteria in the colon, leading to discomfort. While other enzymes such as sucrase and maltase break down other sugars, it is the absence of lactase that causes lactose intolerance, resulting in gastrointestinal upset with the consumption of milk and other dairy goods.