These seven questions use all four lessons in the set. Write each answer on paper before you open the explanation.
The lessons are in interpreting enzymes and experimental rates. Note your slips in the mistake log and paper-error review.
Questions
1. An enzyme forms 9 cm³ of product in the first minute and 15 cm³ in total after 2 minutes, then no more. Calculate the initial rate and state why no more product forms.
Answer
Initial rate = 9 cm³ per minute. The second minute gives 15 − 9 = 6 cm³, so the rate has fallen.
No more product forms because the substrate has been used up. The enzyme is still active.
2. Two enzymes each convert 30 cm³ worth of substrate fully. Enzyme A takes 3 minutes and enzyme B takes 6 minutes. Compare them.
Answer
Both produce the same total (30 cm³), because the total depends on the substrate. Enzyme A is faster: its average rate is 30 ÷ 3 = 10 cm³ per minute, against 30 ÷ 6 = 5 cm³ per minute for enzyme B.
3. Trial 1 uses 25 °C and 1% substrate (rate 4). Trial 2 uses 25 °C and 3% substrate (rate 10). Trial 3 uses 45 °C and 3% substrate (rate 18).
Name the fair pair for the effect of temperature and state the change.
Answer
Trials 2 and 3. Both use 3% substrate and only temperature differs. The rate rises from 10 to 18, an increase of 8 units.
4. Explain why trials 1 and 3 in question 3 are not a fair pair.
Answer
Both temperature (25 °C and 45 °C) and substrate concentration (1% and 3%) differ. The change in rate from 4 to 18 cannot be linked to one factor.
5. Three repeats at one condition give 12, 13 and 25 cm³. Identify the anomalous value, give a possible cause, and calculate the mean without it.
Answer
The value 25 cm³ is anomalous because it is far from 12 and 13. A possible cause is a longer collection time or extra enzyme added to that tube.
Mean without it = (12 + 13) ÷ 2 = 12.5 cm³.
6. A student deletes the anomalous value from question 5 without comment. State what is missing from the student’s method.
Answer
The student gives no evidence or reason for removing the value. A better response identifies it, names a likely cause, and reports the mean with and without it, or repeats the trial.
7. Mean rates of an enzyme at 10 °C, 30 °C and 50 °C are 2, 11 and 1 units. Write a qualified conclusion.
Answer
“The rate was highest at 30 °C (11 units) and lower at 10 °C (2 units) and 50 °C (1 unit).
Few collisions at 10 °C and denaturation at 50 °C are consistent with these values.
Only three temperatures were tested, so the optimum could lie between 10 °C and 50 °C.”
If you got these wrong
- Questions 1 and 2: read separating initial rate from total product formed.
- Questions 3 and 4: read choosing a fair comparison.
- Questions 5 and 6: read explaining an anomalous point.
- Question 7: read writing a qualified conclusion.
To practise against the clock, use the timed original practice session builder. If you want a teacher to read your answers and sharpen the wording, see online one-to-one Biology tuition or the one-hour trial class (from RM50).