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CIE iGCSE Co-Ordinated Science B5 Enzymes Exam Style Questions Paper 1

CIE iGCSE Co-Ordinated Science Paper 1 - All Chapters

Question

Some species of bacteria live in alkaline hot springs at temperatures of 80 °C.

Which conditions will best suit the enzymes of these bacteria?

▶️ Answer/Explanation
Enzymes from these bacteria have adapted to function optimally in their natural environment which is at 80 °C and alkaline (high pH). Among the options, 70 °C is closest to 80 °C, and pH 9 represents alkaline conditions. Therefore, these conditions will best suit their enzymes for maximum activity.
✅ Answer: (D)

Question

Which type of molecules are enzymes?

A. carbohydrates
B. fats
C. hormones
D. proteins

▶️ Answer/Explanation
Enzymes are biological catalysts that speed up metabolic reactions. They are made up of proteins.
Carbohydrates and fats are not enzymes, and hormones are chemical messengers, not catalysts.
✅ Answer: (D)

Question

Which statements about enzymes are correct?

  1. Enzymes are biological catalysts.
  2. Enzymes are made of fat.
  3. Enzymes are made of protein.

A. 1 and 2
B. 1 and 3
C. 1 only
D. 3 only

▶️ Answer/Explanation
Enzymes are biological catalysts that speed up chemical reactions in living organisms without being used up themselves. They are made of protein, not fat. Therefore statement 1 is correct and statement 2 is incorrect. Statement 3 is also correct because enzymes are proteins. So the correct combination is statements 1 and 3.
✅ Answer: (B)

Question

The graphs show the possible effects of temperature on enzyme activity. Which graph is correct for a human enzyme?

▶️ Answer/Explanation

Human enzymes have an optimum temperature of around \(37^\circ\text{C}\) (body temperature). As temperature increases from \(0^\circ\text{C}\) to the optimum, enzyme activity increases because particles have more kinetic energy, leading to more frequent successful collisions between enzyme and substrate. Above the optimum temperature, the enzyme’s active site changes shape (denaturation) and enzyme activity decreases rapidly. Graph A correctly shows this bell-shaped pattern — activity rises to a peak at the optimum temperature and then falls.

Graph B shows decreasing activity from the start (incorrect), Graph C shows a plateau after the optimum (incorrect), and Graph D shows continuously increasing activity (incorrect).

✅ Answer: (A)

Question

Which statements are correct for all enzymes?

  1. They are proteins.
  2. They are not affected by temperature.
  3. They increase the rate of chemical reactions.
  4. They work best at a high pH.

A. 1, 2 and 4
B. 1, 3 and 4
C. 1 and 3 only
D. 2 and 4 only

▶️ Answer/Explanation
All enzymes are proteins (1) and they increase the rate of reactions by lowering activation energy (3).
They are affected by temperature (not 2) and each enzyme has an optimum pH, which is not always high (not 4). Thus only 1 and 3 are correct.
✅ Answer: (C)
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