Question

Which of these statements about starch digestion is false? a. It begins in the mouth. b. It occurs in the stomach. c. It requires the action of pancreatic amylase. d. It requires brush border enzymes for completion.

Short answer

The false statement about starch digestion is: "b. It occurs in the stomach."

Step-by-step solution

Analyze each statement

Let's analyze each statement about starch digestion one by one: a. Starch digestion begins in the mouth: This is true because the salivary glands secrete an enzyme called salivary amylase, which breaks down the starch molecules into maltose. b. Starch digestion occurs in the stomach: We need to consider this statement more carefully, as it is not clear whether it pertains to the entire process or just one specific step. c. Starch digestion requires the action of pancreatic amylase: This is true because, after being partially digested in the mouth, starch continues to be digested by pancreatic amylase in the small intestine. This enzyme converts the remaining starch into maltose. d. Starch digestion requires brush border enzymes for completion: This is true because maltose, the product of starch digestion, is further broken down by brush border enzymes in the small intestine. These enzymes, such as maltase, sucrase, and isomaltase, break down maltose into glucose, which is then absorbed by the body.

Identify the false statement

After analyzing each statement, we can conclude that statement b, "Starch digestion occurs in the stomach," is false. The stomach is involved in protein digestion through the action of gastric enzymes like pepsin. Starch digestion, however, is mainly a combination of actions performed by salivary amylase, pancreatic amylase, and brush border enzymes, which are in the mouth and small intestine.

Answer

The false statement about starch digestion is: "b. It occurs in the stomach."

Key concepts

Salivary Amylase

The process of starch digestion is quite fascinating and begins the very moment you take your first bite of a starchy food, like bread or potatoes. Salivary amylase is an enzyme that plays a crucial part in this initial phase of digestion. Produced by the salivary glands, this enzyme targets the complex carbohydrate structure of starch. It acts on the starch by breaking it down into smaller sugar units called maltose while the starch is still in your mouth.

Think of starch as a long chain of sugar molecules. Salivary amylase starts snipping that chain into smaller sections, making it easier for the body to fully break down and absorb later. This enzyme's activity is optimized at the pH found in your mouth, which is typically around neutral (pH 7). As the chewed food mixed with saliva, now called a bolus, travels down to the stomach, the acidic environment deactivates the salivary amylase, halting starch digestion momentarily.

Pancreatic Amylase

As the journey of digestion progresses, starch makes its way from the mouth through the stomach and into the small intestine. Here, pancreatic amylase takes center stage. Released by the pancreas into the small intestine, this enzyme picks up where salivary amylase left off in the mouth. Its role in starch digestion is pivotal.

Pancreatic amylase has a working pH range that aligns with the small intestine, which is typically around pH 7 to pH 8. In this environment, the enzyme efficiently breaks down the remaining starch into maltose. This action continues the process of simplifying the starch into manageable sugar units that the body can use. It is important to note that pancreatic amylase is robust, capable of tackling starches that weren't fully processed by salivary amylase, ensuring that the body maximizes nutrient absorption.

Brush Border Enzymes

Finally, the detailed breakdown of starch is finessed by an assembly of enzymes lining the surface of the small intestine, appropriately termed brush border enzymes. These enzymes reside on the microvilli, the tiny hair-like projections that give the intestinal lining a brush-like appearance. They feature prominently in the final act of starch digestion.

Specific Enzymes at Work

Maltase, sucrase, and isomaltase are prime examples of brush border enzymes. After pancreatic amylase breaks down starch into maltose, these brush border enzymes take the baton and split maltose into individual glucose molecules, the most basic form of sugar that the body can absorb into the bloodstream.

Strategic Location

The strategic placement of these enzymes right at the absorption site ensures that the newly freed glucose is promptly taken up by the body. This conversion by brush border enzymes represents the final step in the complex process of starch digestion, highlighting the importance of these enzymes in ensuring our bodies obtain the energy we need from the foods we consume.