IB MYP Integrated Sciences e-Assessment : Enzymes and homeostasis Exam Style Practice Questions - New Syllabus
Question a (2 marks)
Humans use enzymes within the digestive system to break up their food to obtain the necessary nutrients. State two functions of enzymes.
▶️Answer/Explanation
Function 1: Enzymes act as biological catalysts, speeding up chemical reactions in the digestive system without being consumed in the process.
Function 2: Enzymes break down large food molecules (like proteins, carbohydrates, and fats) into smaller, absorbable molecules (like amino acids, sugars, and fatty acids).
Question b (3 marks)
Enzymes work at a specific pH known as the optimum pH. The graphs below show the optimum pH for different enzymes found in the human body.
Graphs:
- Pepsin: Optimum pH around 2
- Amylase: Optimum pH around 7
- Trypsin: Optimum pH around 8
In the human digestive system, digested food is neutralized when it reaches the small intestine.
Use the graphs to determine which enzyme you would expect to see in the small intestine. Justify your answer using scientific reasoning.
▶️Answer/Explanation
Enzyme Expected in the Small Intestine:
– Trypsin
Justification:
– The small intestine has a slightly alkaline pH (around 7-8), which is the optimum pH for trypsin (pH ~8).
– Pepsin, which works best at a highly acidic pH (pH ~2), is active in the stomach but not in the small intestine.
– Amylase, which works best at a neutral pH (pH ~7), is active in the mouth and small intestine, but trypsin is more specific to the small intestine’s slightly alkaline environment.
– Therefore, trypsin is the enzyme most likely to be active in the small intestine due to its optimum pH matching the pH of the small intestine.
Question c (3 marks)
In the small intestine, hydrochloric acid is neutralized with sodium hydrogen carbonate (\( \text{NaHCO}_3 \)). The word equation for this reaction is: hydrochloric acid + sodium hydrogen carbonate → sodium chloride + water + carbon dioxide
Write down a balanced chemical equation for this reaction.
▶️Answer/Explanation
Balanced Chemical Equation:
\[ \text{HCl} + \text{NaHCO}_3 \rightarrow \text{NaCl} + \text{H}_2\text{O} + \text{CO}_2 \]
Explanation:
The reaction between hydrochloric acid (HCl) and sodium hydrogen carbonate (NaHCO₃) produces sodium chloride (NaCl), water (H₂O), and carbon dioxide (CO₂). The equation is already balanced as written.