Which of these is most associated with villi?

Answer Explanation

b) phosphate ions

- Correct: Phosphate ions are responsible for activating salivary amylase. Saliva contains salivary amylase (also known as alpha-amylase or ptyalin), which is an enzyme that catalyzes the hydrolysis of starch into maltose and other smaller carbohydrates. However, salivary amylase is only activated in the presence of certain ions, particularly phosphate ions. These ions help to stabilize the enzyme's structure and facilitate its enzymatic activity. Therefore, phosphate ions play a crucial role in the function of salivary amylase.

a) Mucus

- Incorrect: Mucus in saliva serves primarily as a lubricant and protective barrier for the oral mucosa and facilitates swallowing. It does not directly activate salivary amylase

c) Chloride ions

- Incorrect: Chloride ions are electrolytes present in saliva, but they do not directly activate salivary amylase. Instead, they help maintain the osmotic balance and pH of saliva.

d) Urea

- Incorrect: Urea is a waste product found in urine and is not directly involved in the activation of salivary amylase.

Answer Explanation

D. oral cavity

- Correct: Chemical digestion of carbohydrates begins in the oral cavity. Salivary glands in the mouth secrete saliva, which contains an enzyme called amylase. Amylase breaks down complex carbohydrates (such as starch) into simpler sugars (such as maltose) through hydrolysis. This process initiates the digestion of carbohydrates before the food bolus reaches the stomach or small intestine.

A. esophagus

- Incorrect: The esophagus is primarily involved in the propulsion of food from the mouth to the stomach through peristaltic contractions. It does not play a significant role in the chemical digestion of carbohydrates.

B. stomach

- Incorrect: While the stomach plays a role in the digestion of proteins through the action of gastric juices containing pepsin and hydrochloric acid, it does not contribute significantly to the digestion of carbohydrates. In fact, the acidic environment of the stomach may temporarily inhibit the activity of salivary amylase.

C. duodenum

- Incorrect: The duodenum is the first part of the small intestine where the majority of chemical digestion occurs. While the duodenum receives pancreatic enzymes and bile that aid in the digestion of carbohydrates, proteins, and fats, the initial chemical digestion of carbohydrates primarily occurs in the oral cavity with the action of salivary amylase.

Answer Explanation

b) propulsion

- Correct: Propulsion is the movement of food along the length of the alimentary canal, from the mouth to the anus. This process occurs throughout most of the alimentary canal and includes both swallowing (deglutition) and peristalsis. Swallowing moves food from the mouth to the esophagus, while peristalsis involves rhythmic contractions and relaxations of smooth muscles in the walls of the digestive organs, pushing food forward through the esophagus, stomach, and intestines.

a) Ingestion: Ingestion refers to the intake of food into the mouth, which occurs at the beginning of the alimentary canal.

c) Segmentation: Segmentation involves the mixing and churning of food within certain regions of the digestive tract, particularly the small intestine. It does not occur throughout most of the alimentary canal but rather in specific areas where mechanical digestion and absorption are optimized.

d) Absorption: Absorption is the process by which nutrients and water are taken up from the digestive tract into the bloodstream or lymphatic system. While absorption occurs primarily in the small intestine, it also occurs in other parts of the alimentary canal, particularly in the large intestine, but it is not a continuous process throughout most of the alimentary canal like propulsion.