Planning Investigations Flashcards

A student plans to investigate how different types of soil amendments (compost, peat moss, sand) affect the growth rate of tomato plants. The experiment will use identical pots, the same variety of tomato seedling, and equal amounts of water and sunlight. Midway through the experiment, a city-wide power outage causes the indoor grow lights to fail for 48 hours. What is the most scientifically sound next step?

Answer: Continue the experiment, but make a detailed note of the power outage in the procedure and discuss its potential impact in the conclusion.

While restarting is an option, it is not always practical or necessary. The most scientifically sound and professional approach is to meticulously document the unplanned event (the confounding variable) and its potential effects. This acknowledges the imperfection in the design, allows the investigation to be completed, and requires the researcher to critically analyze how the event may have influenced the results in their final discussion. This reflects real-world scientific practice where unforeseen events occur.

A researcher is planning an observational study to determine if there is a correlation between the proximity of a student's home to a major highway and their reported allergy symptoms. Since it is not possible to randomly assign students to live in different locations, what is the best strategy to minimize bias in the investigation's plan?

Answer: Employ statistical controls by collecting data on and adjusting for potential confounding variables like family income, home age, and presence of pets.

In observational studies where randomization is not possible, controlling for confounding variables is the most critical strategy to reduce bias. Variables like family income (which can affect healthcare access and home environment), home age (materials used), and pets are all factors that could influence allergy symptoms independently of highway proximity. By measuring these and using statistical methods to account for their effects, the researcher can more accurately isolate the potential correlation being studied.

Which of the following research questions is best suited for a comparative investigation rather than a descriptive or experimental one?

Answer: Do the shell thicknesses of desert tortoises differ between populations in the Mojave and Sonoran deserts?

A comparative investigation involves collecting data on different groups or under different conditions to make a comparison, without manipulating an independent variable. This question directly compares a specific trait (shell thickness) between two distinct, naturally occurring populations (Mojave vs. Sonoran tortoises). A descriptive study would detail one population, and an experimental study would involve manipulating a variable (like diet) to see its effect on shell thickness.

A student designs an experiment to test the effect of different pH levels on the activity of the enzyme catalase. The plan involves setting up test tubes with catalase solution at pH 4, 7, and 9. However, the student uses a different brand of buffer solution for each pH level. This introduction of different buffer brands is best described as what type of error in planning?

Answer: The introduction of a confounding variable.

A confounding variable is a factor other than the independent variable (pH) that might affect the dependent variable (catalase activity) and is linked to the independent variable. Since each pH level is paired with a different buffer brand, any observed differences in enzyme activity could be due to the pH, the specific chemical composition of the buffer, or an interaction between the two. This makes it impossible to isolate the effect of the pH alone.

When planning an investigation, a researcher must decide on the precision of the data to be collected. Which of the following scenarios demonstrates the most appropriate consideration of data precision?

Answer: Choosing a stopwatch that measures to the hundredth of a second to time the germination of radish seeds over two weeks.

The choice of measurement tool and its precision must match the scale and expected rate of change of the phenomenon being investigated. Radish seeds can germinate at slightly different times, so measuring in hours or even minutes might group too many together. A stopwatch with 0.01s precision, while potentially excessive, allows for the most accurate ranking and analysis of germination times. The other options are mismatched: a glacier's movement is vast, so millimeters are too precise; an athlete's heart rate changes rapidly, so beats per hour is not precise enough; and a kitchen scale is not sensitive enough for microgram measurements.

A team is planning to investigate the effectiveness of a new insulating material. Their plan involves creating two identical model houses, one with the new insulation and one with standard insulation (the control). They will place a heat lamp in each and measure the internal temperature every 10 minutes for 2 hours. Which modification to the plan would most significantly increase the reliability of the potential findings?

Answer: Conducting multiple trials of the entire experiment.

Reliability in scientific investigations refers to the consistency and repeatability of results. While the other options might add interesting data points or increase the magnitude of the effect, conducting multiple trials is the most direct way to ensure the observed results are not due to chance, measurement error, or some other anomaly in a single run. Repeating the experiment helps confirm that the findings are consistent and dependable.