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WACE ATAR Biology study materials
WACE ATAR Biology study resources

WACE ATAR Biology practice questions

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Question 1Science Inquiry Skills

A student wants to test whether light intensity affects the rate of photosynthesis in pond weed. Which variable should be manipulated in this investigation?

  1. Distance of the lamp from the plant Correct answer.
  2. Concentration of carbon dioxide in the water
  3. Temperature of the room
  4. Volume of water in the test tube

Explanation

The independent variable is the factor deliberately changed by the investigator, which here is the light intensity, adjusted by moving the lamp to different distances. All other factors must be held constant as controlled variables so the effect on the dependent variable can be attributed to light alone.

Question 2Science Inquiry Skills

In an experiment measuring the effect of pH on enzyme activity, the rate of reaction is recorded in millilitres of gas produced per minute. What type of variable is this measurement?

  1. Categorical variable
  2. Controlled variable
  3. Dependent variable Correct answer.
  4. Independent variable

Explanation

The dependent variable is the response that is measured and that depends on the manipulated factor. Here the investigator changes pH and measures gas production rate as the outcome, so the measurement is the dependent variable.

Question 3Science Inquiry Skills

A scientist repeats an experiment five times and obtains very similar results each time. Which quality of the data is best demonstrated?

  1. Reliability Correct answer.
  2. Objectivity
  3. Accuracy
  4. Validity

Explanation

Reliability refers to how consistent repeated measurements are when the procedure is repeated under the same conditions. Closely matching results across trials indicate that the method produces reproducible data, even though it does not by itself prove the data are correct.

Question 4Science Inquiry Skills

Which statement best describes the purpose of a control group in a biological experiment?

  1. It allows the independent variable to be changed more often
  2. It provides a baseline for comparison without the treatment being tested Correct answer.
  3. It ensures the dependent variable can be measured
  4. It increases the total number of samples collected

Explanation

A control group is treated identically to the experimental group except that it does not receive the treatment under investigation. Comparing the two groups allows the investigator to attribute any difference to the treatment rather than to other factors.

Question 5Science Inquiry Skills

A student records the number of bacteria colonies growing on agar plates kept at 20 degrees Celsius, 30 degrees Celsius and 40 degrees Celsius. Which type of graph is most appropriate for displaying these results?

  1. Pie chart showing the proportion of colonies at each temperature
  2. Line graph with temperature on the horizontal axis Correct answer.
  3. Bar chart with colony counts on the horizontal axis
  4. Scatter plot with no axis labels

Explanation

Temperature is a continuous numerical variable, so a line graph with temperature on the horizontal axis and colony number on the vertical axis best shows the trend. Line graphs are appropriate when the independent variable is continuous and ordered.

Question 6Science Inquiry Skills

Which of the following is the most appropriate unit for reporting the mass of a small biological specimen such as an insect?

  1. Milligrams Correct answer.
  2. Litres
  3. Kilometres
  4. Degrees Celsius

Explanation

Mass is measured in units such as grams and milligrams, and milligrams suit small specimens because they allow precise reporting. Litres measure volume, degrees Celsius measure temperature and kilometres measure length.

Question 7Science Inquiry Skills

A researcher claims that a new fertiliser increases plant height. To support this claim, the researcher should compare treated plants with which group?

  1. Plants given the same volume of water but no fertiliser Correct answer.
  2. Plants given twice the recommended fertiliser dose
  3. Plants measured at a different time of year
  4. Plants of a different species grown outdoors

Explanation

A valid comparison requires a control group that is treated identically except for the absence of the fertiliser. This isolates the fertiliser as the cause of any difference in height.

Question 8Science Inquiry Skills

When recording observations during a field survey, which practice best reduces observer bias?

  1. Using a standardised data sheet with predefined categories Correct answer.
  2. Recording only observations that support the hypothesis
  3. Estimating values from memory after the survey
  4. Allowing each observer to choose their own recording method

Explanation

A standardised data sheet with predefined categories ensures that all observers record the same information in the same way, reducing subjective judgement. This improves the consistency and comparability of the data collected.

Question 9Science Inquiry Skills

A student measures the length of five leaves and obtains 4.2 cm, 4.4 cm, 4.1 cm, 4.3 cm and 4.2 cm. What is the mean leaf length?

  1. 4.24 cm Correct answer.
  2. 4.20 cm
  3. 4.15 cm
  4. 4.30 cm

Explanation

The mean is calculated by adding all values and dividing by the number of measurements. The sum is 21.2 cm, and dividing by five gives 4.24 cm.

Question 10Science Inquiry Skills

In an investigation, the rate of an enzyme-controlled reaction is measured at five different substrate concentrations. Which statement describes the most appropriate way to improve the validity of the investigation?

  1. Ensure the substrate concentration is the only factor deliberately varied Correct answer.
  2. Record the results to two decimal places
  3. Repeat each concentration ten times
  4. Use a more precise measuring cylinder

Explanation

Validity depends on whether the experiment truly tests the intended relationship, which requires that only the independent variable is changed while all others are controlled. Repeating trials and improving precision affect reliability and accuracy rather than validity.

Question 11Science Inquiry Skills

A graph shows that as light intensity increases from 0 to 400 units, the rate of photosynthesis rises steeply and then levels off. What is the most likely explanation for the plateau?

  1. Light intensity has stopped affecting the plant entirely
  2. The plant has begun to respire faster than it photosynthesises
  3. Another factor such as carbon dioxide concentration has become limiting Correct answer.
  4. The temperature has fallen to zero degrees Celsius

Explanation

When the rate levels off despite increasing light, some other factor required for photosynthesis has become limiting. Carbon dioxide concentration or temperature commonly limits the rate once light is no longer the limiting factor.

Question 12Science Inquiry Skills

Which of the following is an example of a quantitative observation?

  1. The water looked slightly cloudy
  2. The fish appeared stressed during handling
  3. The heart rate of the fish was 84 beats per minute Correct answer.
  4. The fins were a pale orange colour

Explanation

Quantitative observations involve numerical measurements that can be counted or compared statistically. A heart rate recorded as a number is quantitative, whereas descriptions of appearance are qualitative.

Question 13Science Inquiry Skills

A scientist wants to determine whether a correlation between two variables is statistically significant. Which approach is most appropriate?

  1. Assume any visible trend on a graph is significant
  2. Apply a statistical test that accounts for sample size and variability Correct answer.
  3. Round the data so that the trend becomes clearer
  4. Repeat the experiment until the trend appears

Explanation

Statistical significance is assessed using a formal test that considers both the size of the effect and the variability and number of observations. Visual trends alone cannot establish whether an observed relationship is likely due to chance.

Question 14Science Inquiry Skills

In a study of plant growth, researchers measure the height of 50 seedlings grown in a greenhouse. Which measure best describes the spread of the data around the mean?

  1. Median
  2. Mean
  3. Mode
  4. Standard deviation Correct answer.

Explanation

Standard deviation quantifies how far individual measurements typically lie from the mean, so it describes the spread of the data. Mean, median and mode are measures of central tendency rather than of dispersion.

Question 15Science Inquiry Skills

A student investigates the effect of temperature on the rate of yeast respiration by counting gas bubbles produced per minute. The student notices that the bubble count is difficult to reproduce. Which improvement would most directly increase the reliability of the data?

  1. Using a larger test tube
  2. Changing the amount of sugar between trials
  3. Counting bubbles over a longer fixed time period and repeating each temperature Correct answer.
  4. Measuring the gas volume only once at each temperature

Explanation

Reliability improves when measurements are repeated and when each measurement is made over a sufficient period to reduce random counting error. Repeating each temperature and extending the counting time both reduce the influence of chance variation.

Question 16Science Inquiry Skills

A researcher reports that a drug reduced tumour size in mice. Which additional information is most important for judging whether the result is trustworthy?

  1. The number of mice in each group and whether the groups were randomly assigned Correct answer.
  2. The name of the laboratory where the work was done
  3. The colour of the cages used to house the mice
  4. The time of day when the results were published

Explanation

Trust in an experimental result depends on adequate sample size and on random assignment to treatment and control groups, which reduce bias and chance effects. These details allow readers to judge whether the observed difference is meaningful.

Question 17Science Inquiry Skills

Which statement correctly distinguishes a hypothesis from a prediction?

  1. A hypothesis describes observations, while a prediction explains the underlying mechanism
  2. A hypothesis is a testable explanation, while a prediction is an expected outcome if the hypothesis is true Correct answer.
  3. A hypothesis is a prediction that has been confirmed, while a prediction is always false
  4. A hypothesis is a proven fact, while a prediction is an untested guess

Explanation

A hypothesis offers a testable explanation for an observation, and a prediction states what should be observed if that explanation is correct. Predictions are derived from hypotheses and are checked against data.

Question 18Science Inquiry Skills

A table reports the mean number of stomata per square millimetre on the upper and lower surfaces of leaves from three plant species. Which conclusion is best supported if all species show far more stomata on the lower surface?

  1. Stomata are absent from the upper surface of all leaves
  2. Stomatal number is unrelated to leaf surface
  3. The lower surface always has twice as many stomata as the upper surface
  4. Stomata are distributed unevenly, with more on the lower leaf surface across these species Correct answer.

Explanation

The consistent pattern across species supports the general conclusion that stomata are more numerous on the lower surface. The data show a difference in distribution rather than an absolute absence or a fixed ratio.

Question 19Science Inquiry Skills

In a controlled experiment, which procedure best minimises the effect of confounding variables?

  1. Using a different measurement technique for each group
  2. Randomly assigning subjects to treatment and control groups Correct answer.
  3. Testing all subjects at different times of day
  4. Allowing subjects to choose their own group

Explanation

Random assignment distributes unknown and known sources of variation evenly between groups, reducing the chance that a confounding variable explains the result. Applying identical procedures to all groups further supports valid comparison.

Question 20Science Inquiry Skills

A student plots data on a graph and finds that the points form a straight line passing through the origin. What does this indicate about the relationship between the variables?

  1. The variables are directly proportional Correct answer.
  2. The dependent variable is independent of the other
  3. The variables are inversely proportional
  4. There is no relationship between the variables

Explanation

A straight line through the origin indicates that the dependent variable changes by a constant factor as the independent variable changes, which is a directly proportional relationship. An inverse relationship would produce a curve decreasing toward an asymptote.

Question 21Science Inquiry Skills

Two students measure the same solution using the same method and obtain 5.0 mol/L and 5.1 mol/L, while the accepted value is 6.0 mol/L. Which statement best describes their results?

  1. The results are precise but not accurate Correct answer.
  2. The results are neither precise nor accurate
  3. The results are accurate but not precise
  4. The results are both accurate and precise

Explanation

Precision refers to how closely repeated measurements agree with each other, while accuracy refers to how close they are to the accepted value. The two measurements agree closely but both lie well below the accepted value, so they are precise but inaccurate.

Question 22Science Inquiry Skills

An investigation reports a mean with a large standard deviation relative to the mean. What is the most appropriate interpretation?

  1. Individual measurements vary widely around the mean Correct answer.
  2. The measurements are all very close to the mean
  3. The mean has been calculated incorrectly
  4. The experiment measured the wrong variable

Explanation

A large standard deviation relative to the mean indicates that individual values are spread widely around the central value, reflecting high variability. It does not by itself indicate an error in calculation or a fault in the experimental design.

Question 23Science Inquiry Skills

A student designs an experiment to test whether a fertiliser affects the growth of duckweed. The student uses 20 containers, placing 10 in a sunny window with fertiliser and 10 in a shaded corner without fertiliser. Which criticism of this design is most significant?

  1. The number of containers is too small to allow any conclusion
  2. Duckweed is not a suitable organism for growth studies
  3. Light exposure differs between the groups, confounding the effect of the fertiliser Correct answer.
  4. The experiment lacks a measurable dependent variable

Explanation

Two variables differ between the groups, namely fertiliser treatment and light exposure, so any difference in growth cannot be attributed to the fertiliser alone. To be valid, the design must hold light conditions constant while varying only the fertiliser.

Question 24Science Inquiry Skills

A researcher finds a strong negative correlation between the amount of exercise people report and their resting heart rate. Which conclusion is most justified?

  1. Exercise definitely causes resting heart rate to fall
  2. Resting heart rate determines how much people exercise
  3. The correlation proves the hypothesis that exercise improves fitness
  4. There is an association, but a causal relationship cannot be concluded from correlation alone Correct answer.

Explanation

Correlation describes an association between variables but does not establish causation, because other factors may influence both variables. A causal claim would require a controlled experimental design rather than observational data.

Question 25Science Inquiry Skills

A scientist wants to estimate the population size of snails in a rock pool area and decides to use a quadrat sampling method. Which condition is essential for this method to give a representative estimate?

  1. Quadrats must be placed only where snails are most abundant
  2. Quadrats must be placed randomly within the area being sampled Correct answer.
  3. The same quadrat must be reused in the same position each time
  4. Only large snails should be counted in each quadrat

Explanation

Random placement of quadrats ensures that every part of the area has an equal chance of being sampled, which reduces bias and makes the estimate representative. Sampling only favourable locations or fixed positions would overestimate or misrepresent the population.

Question 26Science Inquiry Skills

A student wants to test whether a particular nutrient solution increases the rate of root growth in bean seedlings. Which of the following best describes the purpose of including a control group in this investigation?

  1. To ensure that all seedlings receive exactly the same volume of liquid each day
  2. To provide a baseline for comparison so the effect of the nutrient solution can be isolated Correct answer.
  3. To increase the total number of plants measured and improve the reliability of the results
  4. To allow the student to calculate the mean root length for the treatment group

Explanation

A control group is treated identically to the experimental group except that it does not receive the treatment being tested. Comparing the two groups lets the investigator attribute any difference in root growth to the nutrient solution rather than to other factors. Without this baseline, no valid conclusion about the treatment's effect can be drawn.

Question 27Science Inquiry Skills

Which of the following is the most appropriate way to reduce the effect of random measurement error in an investigation?

  1. Round each reading to the nearest whole number
  2. Use a single measurement taken by the most experienced person
  3. Discard any readings that differ noticeably from the others
  4. Repeat the measurement several times and calculate the average Correct answer.

Explanation

Random errors scatter above and below the true value, so averaging repeated measurements tends to cancel them out and gives an estimate closer to the true value. Systematic errors, by contrast, are not reduced by repetition. Averaging is therefore the standard method for improving precision.

Question 28Science Inquiry Skills

A scientist hypothesises that the rate of water uptake by plant shoots increases as the humidity of the surrounding air decreases. Which observation would support this hypothesis?

  1. Shoots in dry air take up more water per hour than shoots in humid air Correct answer.
  2. Water uptake is the same in both dry and humid air
  3. Shoots in humid air take up more water per hour than shoots in dry air
  4. Water uptake increases in both air conditions as temperature rises

Explanation

The hypothesis predicts that lower humidity leads to a higher rate of water uptake. A result showing greater uptake in dry air than in humid air directly matches that prediction. The other observations either contradict the prediction or describe a different variable.

Question 29Science Inquiry Skills

In an investigation, a student records the number of seeds that germinate in each of four petri dishes kept at different temperatures. Which variable is the dependent variable?

  1. The number of seeds placed in each dish
  2. The temperature of each petri dish
  3. The type of seed used in the investigation
  4. The number of seeds that germinate Correct answer.

Explanation

The dependent variable is the one that is measured or observed as an outcome of the investigation. Here germination counts are recorded to see how they respond to temperature. Temperature is the independent variable, while seed number and seed type are controlled variables.

Question 30Science Inquiry Skills

A student wants to determine the effect of light intensity on the rate of oxygen production by pondweed. Which method would best allow the rate to be calculated?

  1. Note the colour of the pondweed under each light intensity
  2. Count the bubbles released per minute at each light intensity Correct answer.
  3. Record the temperature of the water at the end of each trial
  4. Measure the total length of the pondweed before and after the experiment

Explanation

Rate is a change in a quantity over time, so counting oxygen bubbles per unit time provides a direct measure of the rate of oxygen production. The other methods either measure unrelated quantities or do not involve a time component that would allow a rate to be calculated.

Question 31Science Inquiry Skills

Which of the following best describes the purpose of peer review in the publication of scientific findings?

  1. The journal edits the paper to make it more readable for a general audience
  2. Government agencies approve the findings before they are released
  3. Independent experts evaluate the methods and conclusions before publication Correct answer.
  4. The authors check their own work for arithmetic mistakes before submitting

Explanation

Peer review involves independent specialists in the field examining a manuscript for soundness of methods, interpretation of data and clarity of reasoning. It acts as a quality-control step before findings enter the scientific literature. It does not guarantee correctness but filters out weak or flawed work.

Question 32Science Inquiry Skills

A student is unsure whether a set of measurements is precise. Which feature of the data would best indicate high precision?

  1. Repeated measurements are very close to one another Correct answer.
  2. A single measurement is taken with a very sensitive instrument
  3. The mean of the measurements matches the accepted value
  4. The measurements are recorded to many decimal places

Explanation

Precision refers to how closely repeated measurements agree with each other, regardless of whether they are close to the true value. Closeness to the accepted value describes accuracy rather than precision. Recording many decimal places does not by itself make data precise.

Question 33Science Inquiry Skills

A scientist wants to determine the effect of a new antibiotic on bacterial growth. Which of the following would be the most appropriate control?

  1. A bacterial culture grown at a different temperature
  2. A sterile agar plate with no bacteria added
  3. A bacterial culture treated with a higher concentration of the antibiotic
  4. A bacterial culture treated with the same volume of solvent but no antibiotic Correct answer.

Explanation

A valid control must be treated identically to the experimental culture except for the absence of the antibiotic. Using the same solvent without the antibiotic isolates the effect of the antibiotic itself. The other options change additional factors or omit the bacteria entirely.

Question 34Science Inquiry Skills

A student measures the mass of a specimen three times and obtains 5.2 g, 5.3 g and 5.2 g, while the true mass is 6.0 g. Which statement best describes these measurements?

  1. They are accurate but not precise
  2. They are precise but not accurate Correct answer.
  3. They are both accurate and precise
  4. They are neither accurate nor precise

Explanation

Precision is shown by how closely repeated readings agree, and these three values are very close together. Accuracy is shown by how close the readings are to the true value, and all three are well below 6.0 g. The data are therefore precise but inaccurate, indicating a systematic error.

Question 35Science Inquiry Skills

A researcher suspects that a set of results contains a systematic error. Which observation would best support this suspicion?

  1. All readings are shifted in the same direction from the true value Correct answer.
  2. The measurements were made by two different people
  3. The sample size is smaller than originally planned
  4. Readings are scattered randomly above and below the true value

Explanation

A systematic error affects every measurement in a consistent way, shifting all readings in the same direction by a similar amount. Random errors, by contrast, scatter in both directions. A consistent offset therefore points to a systematic problem such as faulty calibration.

Question 36Science Inquiry Skills

A student investigates whether temperature affects the rate of fermentation in yeast. The student sets up five flasks at 20, 25, 30, 35 and 40 degrees Celsius, keeping all other conditions identical. Which statement best identifies the independent variable?

  1. The concentration of the sugar solution
  2. The volume of gas produced per minute
  3. The temperature of the yeast mixture Correct answer.
  4. The time over which gas is collected

Explanation

The independent variable is the factor deliberately changed by the investigator across the treatment groups. Here temperature is varied across five flasks, so it is the independent variable. Gas volume per minute is the dependent variable, and sugar concentration and collection time are controlled.

Question 37Science Inquiry Skills

A student wants to estimate the population size of grasshoppers in a large paddock. Which method would be most appropriate?

  1. Mark a sample of captured grasshoppers, release them, then recapture and count marked individuals Correct answer.
  2. Estimate the population from the number of grasshoppers caught in a single sweep net
  3. Count all grasshoppers in a single square metre and multiply by the area of the paddock
  4. Record the number of grasshoppers seen during a one-hour walk through the paddock

Explanation

The mark-recapture method is suited to mobile animals that cannot be counted directly or sampled with quadrats. The proportion of marked individuals in a second sample allows the total population to be estimated. The other methods either assume uniform distribution or rely on a single uncontrolled sample.

Question 38Science Inquiry Skills

A scientist reports a mean value of 50 units with a 95% confidence interval of 46 to 54. Which interpretation is most appropriate?

  1. Exactly 95% of individual measurements fall between 46 and 54
  2. The experiment was repeated 95 times to obtain the mean
  3. The results are not statistically significant because the interval is wide
  4. The true population mean is likely to lie within this range Correct answer.

Explanation

A confidence interval estimates a range within which the true population parameter is likely to fall, with a stated level of confidence. It describes uncertainty in the estimate of the mean, not the spread of individual data points. A 95% interval therefore indicates likely values of the population mean.

Question 39Science Inquiry Skills

A student wants to compare the mean heights of plants grown under three different light colours. Which type of graph would be most appropriate for presenting the summarised results?

  1. A pie chart showing the proportion of plants in each light colour group
  2. A line graph plotting individual plant heights in the order they were measured
  3. A scatter plot of plant height against plant identification number
  4. A bar chart showing the mean height for each light colour with error bars Correct answer.

Explanation

Bar charts are used to compare summary values such as means across discrete categories. Adding error bars communicates the variability or uncertainty of each mean. Line graphs and scatter plots are better suited to continuous relationships between numeric variables.

Question 40Science Inquiry Skills

A student claims that a new fertiliser causes greater plant growth because plants given the fertiliser were taller. Which additional step would most strengthen the conclusion?

  1. Use a larger pot for each plant to allow more root space
  2. Measure the plants more frequently during the growing period
  3. Include a control group given the same treatment without the fertiliser Correct answer.
  4. Report the final heights to two decimal places

Explanation

To conclude that the fertiliser caused the difference, the investigator must rule out other explanations by comparing against an untreated control. A control group isolates the effect of the fertiliser from other variables. More frequent measurement or greater precision improves data quality but does not establish causation.

Question 41Science Inquiry Skills

A researcher finds that students who eat breakfast score higher on a test than students who do not. Which statement best describes the limitation of this finding?

  1. It is invalid because the sample was not randomly assigned to schools
  2. It proves that breakfast causes higher test scores
  3. It cannot be reported because test scores are qualitative data
  4. It shows an association but does not prove that breakfast causes higher scores Correct answer.

Explanation

Observational comparisons can reveal an association between two variables but cannot establish causation, because other factors may differ between the groups. Confounding variables such as sleep, income or study habits could influence both breakfast habits and test performance. Only controlled experiments with random assignment can support causal claims.

Question 42Science Inquiry Skills

A student wants to test the effect of pH on the activity of an enzyme. Which procedure would best control the temperature variable?

  1. Record the temperature at the start of each trial
  2. Allow the temperature to vary naturally during the trials
  3. Use a different enzyme concentration for each pH value
  4. Perform all trials in a water bath set to the same temperature Correct answer.

Explanation

A controlled variable must be kept constant across all treatment groups, and a water bath actively maintains a constant temperature. Merely recording temperature does not prevent it from changing and affecting enzyme activity. Varying enzyme concentration would introduce an additional confounding factor.

Question 43Science Inquiry Skills

A student plots the rate of an enzyme reaction against substrate concentration and obtains a curve that rises steeply then levels off. Which conclusion is best supported by this pattern?

  1. The reaction rate decreases steadily as substrate concentration increases
  2. There is no relationship between substrate concentration and reaction rate
  3. The reaction rate approaches a maximum as substrate concentration increases Correct answer.
  4. The reaction rate is highest at the lowest substrate concentration

Explanation

A curve that rises and then plateaus indicates that the rate increases with substrate concentration up to a limiting value. The plateau occurs when the enzyme active sites become saturated. This pattern supports a maximum rate rather than a continuing increase or decrease.

Question 44Science Inquiry Skills

A student needs to determine whether a difference between two treatment means is statistically significant. Which approach is most appropriate?

  1. Repeat the experiment until the means differ
  2. Compare the two means by eye and decide whether the difference looks large
  3. Perform a statistical test that accounts for sample size and variability Correct answer.
  4. Report only the larger mean as the result

Explanation

Statistical significance depends on the size of the difference relative to the variability of the data and the sample size. A formal statistical test quantifies the probability that the observed difference arose by chance. Visual inspection or selective reporting does not provide an objective basis for the decision.

Question 45Science Inquiry Skills

In a field study, a researcher records the number of a particular bird species observed in a forest and in a grassland on the same day. Which factor would most threaten the validity of the comparison?

  1. The two habitats were surveyed by different observers at different times of day Correct answer.
  2. The survey was repeated on three separate days
  3. The same counting method was used in both habitats
  4. The weather was recorded during each survey

Explanation

Validity requires that the only meaningful difference between the groups is the variable being compared. If observers or times of day differ, these factors could account for differences in bird counts rather than habitat type. Standardised methods and repeated surveys strengthen validity.

Question 46Science Inquiry Skills

A student designs an investigation with three replicate containers per treatment and finds that the results within each treatment vary widely. Which conclusion is most appropriate?

  1. The results are unreliable and more replicates may be needed to detect a treatment effect Correct answer.
  2. The experiment should be repeated with only one container per treatment
  3. The treatment has no effect because the replicates differ
  4. The variability proves that the treatment caused the differences between groups

Explanation

High variability within treatments reduces the reliability of the results and makes it harder to detect a real treatment effect. Increasing the number of replicates helps to produce a more stable estimate of the mean. Variability does not by itself show that the treatment has no effect.

Question 47Science Inquiry Skills

A researcher measures the rate of transpiration in a plant under still air and then under moving air, keeping light and temperature constant. The rate is higher in moving air. Which conclusion is best supported?

  1. Temperature has no effect on transpiration
  2. Still air causes stomata to close permanently
  3. Light intensity is the main factor controlling transpiration
  4. Moving air increases the rate of transpiration under these conditions Correct answer.

Explanation

Because light and temperature were held constant, the observed difference can reasonably be attributed to the movement of air. The result supports the conclusion that moving air increases transpiration under the tested conditions. Conclusions about other factors cannot be drawn because they were not varied.

Question 48Science Inquiry Skills

A scientist reports that a treatment produced a mean increase of 2 units with a 95% confidence interval of -1 to 5. Which interpretation is most appropriate?

  1. The observed increase is not statistically significant at the 95% level Correct answer.
  2. The treatment definitely increases the variable by 2 units
  3. The confidence interval proves the sample size was too small
  4. The treatment definitely has no effect on the measured variable

Explanation

A confidence interval that spans zero includes the possibility of no effect, so the observed increase is not statistically significant at the stated confidence level. This does not prove that the treatment has no effect, only that the data are consistent with no effect. The width of the interval reflects uncertainty rather than a definite conclusion about sample size.

Question 49Science Inquiry Skills

A student wants to reduce the risk of bias when selecting plants for a treatment and control group. Which procedure would be most effective?

  1. Assign the tallest plants to the treatment group to ensure they grow well
  2. Allow the student to choose which plants look healthiest for the treatment group
  3. Assign plants to groups randomly so each has an equal chance of either treatment Correct answer.
  4. Assign plants to groups based on the order in which they were purchased

Explanation

Random assignment gives every individual an equal chance of being placed in any group, which prevents systematic differences between groups before treatment begins. This minimises selection bias and strengthens the validity of the comparison. Deliberate or convenience-based assignment can create pre-existing differences.

Question 50Science Inquiry Skills

An ecologist samples a population using quadrats and obtains very different counts between quadrats placed in different parts of a habitat. What is the most appropriate response?

  1. Increase the number of quadrats and sample randomly across the habitat Correct answer.
  2. Use only the quadrats with the highest counts to represent the habitat
  3. Reduce the quadrat size until all counts are similar
  4. Conclude that the population cannot be estimated

Explanation

High variation between quadrats means a small sample may give an unreliable estimate of the mean density. Increasing the number of randomly placed quadrats improves the reliability of the estimate and better captures habitat heterogeneity. Selecting only certain quadrats would bias the result.