Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The Human Digestive System is a group of organs working together to break down food into small, soluble molecules that can be absorbed into the bloodstream.
The process consists of five main stages: Ingestion (taking food in), Digestion (breaking food down), Absorption (moving molecules into the blood), Assimilation (using molecules in cells), and Egestion (removing undigested waste).
Mechanical digestion is the physical breakdown of food (e.g., teeth chewing or stomach churning) to increase the surface area for enzymes.
Chemical digestion involves biological catalysts called enzymes. Specific enzymes include Amylase (for carbohydrates), Protease (for proteins), and Lipase (for fats/lipids).
The stomach secretes Hydrochloric Acid (), which provides an acidic environment (approximately ) to kill pathogens and provide the optimum for the enzyme pepsin.
The Small Intestine (specifically the ileum) is adapted for absorption with finger-like projections called villi. Villi increase the surface area and contain a lacteal for absorbing fatty acids and glycerol.
Bile is produced in the liver and stored in the gallbladder. It neutralizes the acidic mixture (chyme) entering the small intestine and emulsifies fats, breaking large fat globules into smaller droplets to increase the surface area for Lipase action.
📐Formulae
💡Examples
Problem 1:
A student is investigating the effect of on the enzyme pepsin. If the is increased from to , what happens to the rate of protein digestion?
Solution:
The rate of protein digestion will decrease to zero as the enzyme denatures.
Explanation:
Pepsin is a protease found in the stomach that has an optimum of approximately . At (an alkaline environment), the active site of the enzyme changes shape (denatures), meaning it can no longer bind to the protein substrate.
Problem 2:
Explain how the structure of a villus aids in the absorption of glucose.
Solution:
The villus has a one-cell thick wall and a rich network of blood capillaries.
Explanation:
The thin wall (epithelium) creates a short diffusion distance for glucose. The blood capillaries maintain a steep concentration gradient by constantly carrying absorbed glucose away to the rest of the body.
Problem 3:
Why is the emulsification of fats by bile considered mechanical digestion rather than chemical digestion?
Solution:
Because no chemical bonds are broken to create new substances.
Explanation:
Bile breaks large fat globules into smaller droplets. While this increases the surface area for the enzyme lipase to work, the chemical structure of the lipid remains the same until lipase acts upon it.