📝 Controlled experiments in biology (7 MCQs)
📖 From Campbell Biology • 1. Evolution and the theme of Biology and Scientific Inquiry • 7 questions available
What is Controlled experiments in biology?
Definition:
Controlled experiments in biology are experimental setups where all variables except the one being tested (the independent variable) are held constant, and a control group is used for comparison, allowing researchers to isolate the effects of the independent variable on the dependent variable, and this approach is the gold standard for establishing causal relationships in biological research.
Working:
Controlled experiments work by manipulating the independent variable and observing the dependent variable while keeping other factors (e.g., temperature, humidity, genetics) the same for both experimental and control groups; the control group serves as a baseline, and any difference in the dependent variable between groups can be attributed to the independent variable, and this design minimizes confounding variables and allows for statistical analysis to test for significance, such as using t-tests or ANOVA.
Example:
A simple example is testing the effect of a new drug on blood pressure: the experimental group receives the drug, the control group receives a placebo, both groups are measured for blood pressure before and after, and all other factors (diet, activity) are controlled; if the drug group has a significantly lower blood pressure, the drug is effective, and this controlled design provides strong evidence for causality.
Reason:
Controlled experiments are essential in biology because they provide the most rigorous test of hypotheses, allow for cause-and-effect conclusions, and are the foundation of evidence-based medicine, ecology, and genetics, making them indispensable for scientific progress.
📝 All Controlled experiments in biology MCQs
Q1. A researcher wants to determine whether a new fertilizer increases plant growth. Which experimental design provides the strongest basis for attributing differences in growth to the fertilizer?
📖 Explanation: A controlled experiment changes the factor being tested while keeping other relevant conditions comparable. The untreated group provides a baseline, allowing researchers to determine whether differences in growth are associated with the fertilizer rather than unrelated conditions.
Q2. Two groups of genetically similar seedlings receive identical light, water, soil, and temperature. Group A receives a nutrient solution, while Group B receives only water. After four weeks, Group A is taller. What is the strongest interpretation?
📖 Explanation: Because the groups were kept under comparable conditions and differed primarily in the treatment, the observed growth difference supports an effect of the nutrient solution. However, a controlled experiment does not automatically prove that every possible cause has been eliminated.
Q3. A biologist tests whether background color affects the survival of model insects exposed to predators. Which modification would most improve the experiment's ability to isolate the effect of background color?
📖 Explanation: Random assignment and comparable experimental conditions reduce the influence of confounding variables. If predator exposure, enclosure conditions, and insect characteristics differ systematically between groups, survival differences could not be confidently attributed to background color.
Q4. A student claims, 'The experimental group grew more than the control group, so the treatment must have worked.' However, the experimental group also received twice as much water. What is the main flaw in this reasoning?
📖 Explanation: The reasoning confuses correlation with a controlled causal comparison. Because the treatment group received both the intended treatment and extra water, either factor, or their interaction, could explain the greater growth. The variables must be separated.
Q5. A graph shows mean survival after exposure to a condition. The control group has survival of 90%, while three treatment levels show 88%, 65%, and 40%, respectively. Which conclusion is best supported by the pattern?
📖 Explanation: The pattern shows progressively lower mean survival as treatment intensity increases, while the control provides a comparison baseline. This supports a dose-related relationship, but mean values alone do not establish that every individual responds identically.
Q6. A researcher compares two populations to test whether temperature affects enzyme activity. Population X is tested at and Population Y at , but X is measured in the morning and Y in the afternoon. Which redesign most directly improves causal inference?
📖 Explanation: Testing both temperatures with randomly assigned samples and consistent measurement conditions prevents population identity and time of measurement from becoming confounding factors. Repeated measurements also help distinguish a treatment pattern from random experimental variation.
Q7. A researcher obtains these results: Control survival = 80%; Treatment A = 78%; Treatment B = 52%. Treatment A was applied to one group, while Treatment B was applied to another group that also received less food. Which conclusion is most defensible?
📖 Explanation: Treatment B is associated with lower survival, but reduced food is a confounding variable that provides an alternative explanation. A stronger experiment would keep food availability constant while independently varying the treatment, allowing its specific effect to be evaluated.