Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Mechanical digestion is the physical breakdown of food into smaller pieces without changing its chemical nature. This occurs via chewing in the mouth, churning in the stomach, and emulsification by bile. Its primary goal is to increase the surface area for enzyme action.
Chemical digestion is the breakdown of large, insoluble molecules into small, soluble molecules that can be absorbed into the bloodstream, facilitated by enzymes.
Hydrochloric acid () in the gastric juice provides an acidic environment (approximately ) which kills bacteria and provides the optimum for the enzyme pepsin to function.
Bile is produced in the liver and stored in the gallbladder. It is alkaline, which helps neutralize the acidic chyme coming from the stomach to reach an optimum of to for pancreatic enzymes.
Emulsification is a form of mechanical digestion where bile salts break down large fat globules into smaller droplets, increasing the surface area for the enzyme lipase.
The absorption of nutrients occurs primarily in the small intestine (ileum), which is highly adapted with villi and microvilli to increase the surface area for diffusion and active transport.
📐Formulae
💡Examples
Problem 1:
Explain the effect of on the activity of pepsin found in the stomach.
Solution:
Pepsin works optimally at approximately . If the increases significantly (becomes more alkaline), the enzyme denatures.
Explanation:
Pepsin is an enzyme adapted to the acidic environment created by . High concentration maintains the enzyme's active site shape. At higher , the ionic bonds in the protein structure are disrupted, changing the shape of the active site so it can no longer bind to the substrate.
Problem 2:
A person has their gallbladder removed. Why are they advised to reduce their intake of high-fat foods?
Solution:
The lack of stored bile reduces the efficiency of lipid emulsification.
Explanation:
Without a gallbladder, there is no reservoir to release concentrated bile into the duodenum when fat enters. This leads to slower mechanical digestion (emulsification), meaning lipase has less surface area to act upon, resulting in undigested fats passing through the gut.
Problem 3:
During an experiment, lipase was added to a solution of lipids. The was measured over minutes. Predict the change in .
Solution:
The will decrease (become more acidic) over time.
Explanation:
Lipase catalyzes the hydrolysis of lipids into glycerol and fatty acids. The release of fatty acids increases the concentration of ions in the solution, thereby lowering the .