Human Digestion and Enzyme Activity Essentials

Human Digestion and Nutrient Absorption

1) Where does most chemical digestion of starch begin?
Mouth

2) Which product of digestion is absorbed into the bloodstream?
Glucose

3) Which process moves glucose into the blood when its concentration is lower in the blood than in the intestine?
Diffusion

4) Which structure increases the surface area for absorption?
Villi

Enzymes, Substrates, and Products

Organ Functions and Adaptations

A) i) Organ where proteins begin to be digested:
Stomach

ii) Bile is produced in the:
Liver

B) State the function of bile in digestion:
Bile neutralizes the acid from the stomach.

Small Intestine Adaptations

C) Explain two ways in which the small intestine is well adapted to its function:

• The wall of the small intestine is very long, which increases the surface area for absorption.
• It contains villi, which create a larger surface area so that more food can be absorbed efficiently.

Food Tests and Dietary Requirements

A) Identify the food test for:

1. Starch: Iodine solution
2. Reducing sugars: Benedict’s solution

B) State the positive result for each test:

• Starch → Blue-black color
• Reducing sugars → Orange-red color

The Importance of Fibre

C) Explain why fibre is important in the diet:

• It prevents constipation.
• Muscles in the digestive system contract against it to move food through the system.

Mechanical vs. Chemical Digestion

D) Explain the difference between mechanical and chemical digestion. Name one place in the body where each takes place.

• Mechanical digestion: Physically breaks food into smaller pieces (e.g., chewing in the mouth) to help it pass through the system.
• Chemical digestion: The breakdown of nutrients into smaller molecules using enzymes (e.g., in the stomach or small intestine).

Enzyme Activity Experiment Results

Experimental Variables

• Dependent variable: Time for starch to disappear
• Control variable: pH

Conclusion from Results

When the temperature is low, starch takes more time to disappear. At 40°C, the starch disappears the quickest. When the temperature increases or decreases away from the optimum 40°C, it takes longer for the starch to disappear.

Cellular Processes and Energy

9. a) Ion
c) A
d) Helps with cell respiration

Calculating Energy in Food

10. a) Which food contains the most energy?
The peanut, because it caused the largest temperature increase in water (25°C), meaning the most energy was transferred.

b) Energy Calculation:
E = m × temperature change × specific heat capacity
Volume: 50 cm³ → 1 cm³ = 1 g; therefore, mass (m) = 50g.
Energy = 50 × 25 × 4.2
Energy = 5250 J