Which of the following describes the process of starch digestion?
A. Starch to lactose to galactose
B. Starch to maltose to glucose
C. Starch to glycogen to glucose
D. Starch to sucrose to fructose
The correct answer and explanation is:
The correct answer is B. Starch to maltose to glucose.
Explanation:
Starch digestion involves a series of steps that break down the complex carbohydrate starch into simpler sugars that the body can use for energy. Here’s a detailed breakdown of the process:
- Starch to Maltose:
- The process begins in the mouth, where starch (a polysaccharide made up of glucose molecules) is broken down by the enzyme salivary amylase. This enzyme starts the process of hydrolyzing the starch into smaller sugar units, primarily maltose (a disaccharide made up of two glucose molecules). The breakdown continues until the starch is mostly converted into maltose. The action of salivary amylase continues as long as food remains in the mouth and is chewed, but it is halted when the food reaches the acidic environment of the stomach.
- Maltose to Glucose:
- In the small intestine, pancreatic amylase continues the digestion of starch, breaking it down further into maltose and other disaccharides. Maltase, an enzyme present in the lining of the small intestine, then acts on maltose to break it down into two glucose molecules. Glucose is a monosaccharide that can be absorbed directly into the bloodstream through the walls of the small intestine.
- Absorption and Use:
- Once glucose enters the bloodstream, it is transported to various cells throughout the body. Glucose is a primary source of energy for cells, and it can be used immediately or stored as glycogen in the liver and muscles for future energy needs.
The other options are incorrect because they describe processes involving different sugars:
- Option A (Starch to lactose to galactose): Lactose is a disaccharide made from glucose and galactose, but this is not part of starch digestion.
- Option C (Starch to glycogen to glucose): Glycogen is a storage form of glucose, not a product of starch digestion.
- Option D (Starch to sucrose to fructose): Sucrose is a disaccharide made from glucose and fructose, but it is not involved in starch digestion.
In summary, starch is first broken down into maltose and then converted into glucose, which is the key process for digesting starch in the body.