These eight questions use new experiments, so you practise the skills rather than memorise answers. Write each response before opening the explanation.
The lessons are in biological investigation. Log slips in the mistake log and paper-error review.
Questions
1. A student wants to investigate how the pH of a solution affects the activity of catalase in liver. Write a testable hypothesis. (2 marks)
Answer
“As the pH of the solution moves from 3 to 7, the volume of oxygen released per minute increases.” It names pH, the volume of oxygen and a direction. A statement that catalase activity is highest at an optimum pH is also acceptable if both variables are named.
2. Identify the manipulated and responding variables in: “The length of shoots of bean seedlings is measured after 10 days in 0%, 25%, 50% and 100% shade.” (2 marks)
Answer
Manipulated: the percentage of shade. Responding: the length of the shoots after 10 days.
3. State three fixed variables for question 2. (3 marks)
Answer
Any three: the type of seed, the number of seeds, the volume of water, the type and amount of soil, the temperature, the duration of 10 days.
4. Explain why a student should repeat each set-up at least three times. (2 marks)
Answer
A single result may be caused by a random error, so repeats let the student calculate an average. This makes the result more reliable.
5. Draw the headings for a results table that records the time taken for a 5 cm strip of onion skin to plasmolyse in 10%, 20% and 30% sucrose solution, with 3 trials. (3 marks)
Answer
Sucrose concentration (%) | Time taken (s): Trial 1 | Trial 2 | Trial 3 | Average time (s). The manipulated variable is first, and units appear only in the headings.
6. The times for 20% sucrose are 120 s, 132 s and 126 s. Calculate the average. (2 marks)
Answer
(120 + 132 + 126) ÷ 3 = 378 ÷ 3 = 126 s.
7. State three rules for drawing a biological specimen. (3 marks)
Answer
Use a sharp pencil with a single clear outline, do not shade, draw straight label lines that do not cross, and give the drawing a title.
8. A student sets up a dish of seeds at 25 °C with water and another at 25 °C without water. Name this second dish and state its purpose. (2 marks)
Answer
It is the control set-up for water. It shows that germination needs water, because the seeds without water can be compared with those that have it.
If you got these wrong
- Question 1: revisit writing a testable hypothesis.
- Questions 2 to 4 and 8: open identifying variables and controls.
- Questions 5 to 7: open planning tables and biological drawings.
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