Secondary 3 Combined Science Scientific Inquiry Quiz

Secondary 3 Combined Science Quiz - Scientific Inquiry

Answer Key

Section A: Multiple Choice Questions

1. C — Identifying the problem / research question
Marking note: The scientific method begins with observation and the formulation of a research question before any hypothesis is formed or data is collected. [1]

2. C — Mass of the pendulum bob
Marking note: The mass of the bob is a controlled variable. The length is the independent variable and the time for one swing is the dependent variable. [1]

3. B — A testable prediction that attempts to explain an observation
Marking note: A hypothesis must be testable and falsifiable. It is not a conclusion (A) or a description of apparatus (C). [1]

4. C — Independent variable
Marking note: The independent variable is the one deliberately changed by the experimenter. The dependent variable is measured; controlled variables are kept constant. [1]

5. B — To provide a baseline for comparison with the experimental setup
Marking note: A control setup allows the experimenter to compare results and determine whether the independent variable caused the observed effect. [1]

Section B: Short Answer and Structured Response

6. A fair test is an experiment in which only one variable (the independent variable) is changed at a time, while all other variables are kept constant. This ensures that any change in the dependent variable can be attributed to the independent variable alone.
Marking note: Award 1 mark for stating that only one variable is changed; award 1 mark for stating that all other variables are kept constant (or equivalent wording). [2]

7.
(a) Independent variable: Temperature (of the water) [1]
(b) Dependent variable: Rate of dissolving (of sugar) / time taken for sugar to dissolve [1]
(c) Any one of: mass/volume of water, mass of sugar, type of sugar, stirring or no stirring [1]
Marking note: Accept any reasonable controlled variable relevant to the experiment.

8. Repeating measurements is important because it:

• Helps to increase the reliability of the results
• Allows the experimenter to identify anomalies/outliers
• Enables the calculation of a mean/average, which is more representative of the true value
• Reduces the effect of random errors
  Marking note: Award 1 mark for each valid reason, up to a maximum of 2 marks. Accept equivalent phrasing. [2]

9.
(a) As light intensity increases, the number of bubbles per minute increases. The rate of increase is gradual at lower intensities and becomes steeper at moderate intensities, then the rate of increase slows down at higher intensities (between 50 and 60 units).
Marking note: Award 1 mark for stating the general trend (increase); award 1 mark for describing the change in rate / levelling off at higher intensities. [2]

(b) At higher light intensities, light is no longer the limiting factor. Another factor (such as carbon dioxide concentration or temperature or chlorophyll content) becomes the limiting factor, so increasing light intensity further does not significantly increase the rate of photosynthesis.
Marking note: Award 1 mark for identifying that another factor becomes limiting; award 1 mark for naming a valid limiting factor. [2]

10.

• Accuracy refers to how close a measured value is to the true or accepted value.
  Example: A student measures the boiling point of pure water as 100°C, which is the accepted value — this is accurate.

• Precision refers to how close repeated measurements are to each other (regardless of whether they are close to the true value).
  Example: A student measures the boiling point of water three times and gets 97.1°C, 97.2°C, and 97.1°C — these are precise (close together) but not accurate (not close to 100°C).

Marking note: Award 1 mark for a correct definition of accuracy, 1 mark for a correct definition of precision, and 1 mark for appropriate examples. Accept equivalent wording and valid examples. [3]

11.
(a) The hypothesis predicts that as the concentration of salt solution increases, the mass of the potato strip will decrease (due to water leaving the potato cells by osmosis). [1]

(b) Apparatus: Potato, cork borer, ruler, electronic balance, distilled water, salt solutions of different concentrations (e.g. 0%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%), beakers, paper towels.

Procedure:

1. Cut potato strips of equal size using a cork borer and ruler (e.g. 3 cm long).
2. Measure and record the initial mass of each potato strip using the electronic balance.
3. Place one potato strip into each beaker containing a different concentration of salt solution.
4. Leave the potato strips for a set period of time (e.g. 30 minutes).
5. Remove the potato strips, gently blot dry with paper towels, and measure the final mass.
6. Calculate the change in mass for each strip.
7. Repeat the experiment and calculate the mean change in mass for each concentration.

Marking note: Award 1 mark for listing appropriate apparatus, 1 mark for controlling variables (equal size strips, same time), 1 mark for measuring mass change, and 1 mark for repeating/reliability. Accept any valid and complete procedure. [4]

12. Any two of the following:

• It helps to identify errors or flaws in the experimental design, data analysis, or conclusions.
• It ensures the research is valid and reliable before it is accepted by the scientific community.
• It provides an objective evaluation by other experts in the field.
• It helps to prevent bias from influencing the results or interpretation.
• It ensures that the work meets ethical and scientific standards.

Marking note: Award 1 mark for each valid reason, up to 2 marks. [2]

13.
(a) Mean length = (15.1 + 15.2 + 15.1 + 15.3 + 15.2) ÷ 5 = 75.9 ÷ 5 = 15.18 cm
Marking note: Award 1 mark for correct working (sum ÷ 5); award 1 mark for correct answer (15.18 cm). Accept 15.2 cm if rounded to 1 decimal place, but award only 1 mark if no working is shown. [2]

(b) The precision of the ruler is 0.1 cm (or 1 mm).
Marking note: The smallest division on the ruler is 0.1 cm, so measurements are precise to the nearest 0.1 cm. [1]

14.

• A conclusion is a summary of the findings of an investigation, based directly on the data/results collected. It states what the data shows.
• An inference is an explanation of the results, going beyond the data to suggest why something happened, often based on scientific knowledge or reasoning.

Marking note: Award 1 mark for defining conclusion correctly; award 1 mark for defining inference correctly. Accept equivalent wording. [2]

15. Any two of the following:

• Comparative data showing that crops treated with the fertiliser produce a higher yield than crops without the fertiliser (control group).
• Repeated trials across different fields/seasons to show the results are reproducible and not due to chance.
• Statistical analysis showing that the difference in yield is statistically significant.
• Evidence that other variables (water, sunlight, soil type) were controlled so that the fertiliser is the only factor responsible for the difference.

Marking note: Award 1 mark for each valid piece of evidence, up to 2 marks. [2]

Section C: Data Interpretation and Extended Response

16.
(a) Graph requirements (3 marks):

• 1 mark: Correct labels on both axes — x-axis: "pH", y-axis: "Rate of Reaction (units/min)"
• 1 mark: Suitable scale on both axes (evenly spaced, using at least half the grid)
• 1 mark: All points correctly plotted and a smooth curve drawn through the points (line of best fit)
  Marking note: Deduct 1 mark if no smooth curve is drawn; deduct 1 mark if scale is inappropriate or axes are unlabelled. [3]

(b) The optimum pH is pH 7 (where the rate of reaction is highest at 30 units/min). [1]

(c) At pH values above 7, the enzyme becomes denatured (or its active site changes shape). The hydrogen bonds and other bonds that maintain the enzyme's three-dimensional structure are disrupted by the alkaline conditions. As a result, the substrate can no longer fit into the active site, and the rate of reaction decreases. At pH 12, the enzyme is completely denatured and the rate drops to 0.
Marking note: Award 1 mark for stating that the enzyme is denatured / active site changes shape; award 1 mark for explaining the effect on substrate binding or reaction rate. [2]

17.
(a) Independent variable: Colour of light [1]
(b) Dependent variable: Height of seedlings (after two weeks) / growth of seedlings [1]
(c) Using 10 seedlings instead of 1 increases the reliability of the results. It allows the student to calculate a mean, identify anomalies, and reduce the effect of random variation between individual seedlings. A single seedling might be unusually tall or short due to factors unrelated to the colour of light.
Marking note: Award 1 mark for mentioning reliability/reducing random error; award 1 mark for mentioning mean/anomalies. [2]
(d) Limitation: The experiment only tested three colours of light. It did not include a control group (e.g. white light or no light) for comparison.
Improvement: Include a control group of seedlings grown under white light (or natural light) to compare the effect of coloured light against normal conditions.
Marking note: Accept any valid limitation (e.g. only one variable of light colour tested, no control, small sample size, only height measured). Award 1 mark for identifying a valid limitation and 1 mark for a valid improvement. [2]

18.
(a) Major flaw: There is no control group. All 50 students studied while listening to music, so there is no comparison group that studied without music. Without a control, the researcher cannot determine whether the music had any effect on test performance.
Marking note: Award 1 mark for identifying the lack of a control group; award 1 mark for explaining why this is a problem. [2]

(b) Improvement: The researcher should divide the students into two groups:

• Experimental group: Studies with music (as before).
• Control group: Studies in silence (no music).

Both groups should study the same chapter for the same amount of time (30 minutes) under the same conditions (same room, same temperature, etc.). Both groups then take the same test. The researcher compares the mean test scores of the two groups to determine whether music had an effect.
Marking note: Award 1 mark for suggesting a control group (no music), 1 mark for keeping other conditions the same, and 1 mark for comparing results between groups. [3]

19.
(a) Any one of: Wear safety goggles (to protect eyes from acid splashes) / wear gloves / work in a well-ventilated area / handle hydrochloric acid carefully (it is corrosive). [1]

(b) The graph levelled off because the calcium carbonate was completely used up (the reactant was exhausted). Once all the calcium carbonate has reacted, no more carbon dioxide gas is produced, so the volume of gas stops increasing even though the reaction may still be occurring with excess acid.
Marking note: Award 1 mark for stating that a reactant is used up; award 1 mark for linking this to the cessation of gas production. [2]

(c) With a higher concentration of hydrochloric acid, the graph would show:

• A steeper initial gradient (the reaction starts faster because there are more acid particles per unit volume, leading to more frequent successful collisions).
• The graph would reach the same final volume of gas (assuming the same amount of calcium carbonate is used — the total volume of CO₂ depends on the amount of calcium carbonate, not the concentration of acid, as long as there is sufficient acid to react completely).
• The graph would level off sooner (the reaction finishes faster).

Marking note: Award 1 mark for steeper initial gradient, 1 mark for same final volume, and 1 mark for levelling off sooner. If the student incorrectly states a higher final volume, do not award that mark but award the other marks independently. [3]

20. Example answer (accept any valid scientific example):

Original theory: The geocentric model of the universe stated that the Earth was at the centre of the universe and that the Sun, Moon, planets, and stars all orbited around the Earth. This was widely accepted for centuries.

New evidence: Galileo Galilei used a telescope to observe the phases of Venus and the moons of Jupiter. The phases of Venus could only be explained if Venus orbited the Sun, not the Earth. The discovery of moons orbiting Jupiter showed that not everything orbited the Earth.

Revised theory: The heliocentric model, proposed earlier by Copernicus and supported by Galileo's observations, replaced the geocentric model. In this model, the Sun is at the centre and the Earth and other planets orbit around it.

Marking note: Award 1 mark for describing the original theory/model, 1 mark for describing the new evidence, 1 mark for explaining how the theory was revised/replaced, and 1 mark for clarity and coherence of the explanation. Accept any valid example (e.g. atomic model, plate tectonics, germ theory, evolution). Award marks independently for each component. [4]

Total: 40 marks