Scientific Reasoning
A scientist notices that fish are disappearing from one section of a lake. Saying, "The water contains a substance that is killing the fish" goes beyond what was directly observed.
Identify the type of scientific thinking represented by the second statement.
Inference
Scientists change the amount of water given to plants and measure how tall the plants grow.
What is the independent variable?
Amount of water
A scientist records:
4, 6, 8, 10, 12
What is the mean?
8
A scientist measures the same object several times and gets nearly identical measurements.
What characteristic of the measurements does this demonstrate?
Precision
A scientific explanation is supported by a large amount of evidence and is used to explain how or why a natural phenomenon occurs.
What scientific concept describes this type of explanation?
Scientific theory
A researcher asks:
"How does the amount of sunlight a plant receives affect its growth?"
What makes this a scientifically useful question?
It is testable and involves measurable variables.
Scientists change the amount of water given to plants and measure how tall the plants grow. Scientists keep the type of plant, soil, container, and amount of sunlight the same.
What are these variables called?
Controlled variables
A data set contains the values:
5, 7, 7, 8, 10
What is the mode?
7
The actual temperature is 25°C.
A thermometer reads:
25.1°C, 24.9°C, 25.0°C
Are these measurements accurate, precise, or both?
Both accurate and precise.
A scientific statement describes a consistent pattern or relationship observed in nature.
What scientific concept describes this type of statement?
Scientific law
A student observes that plants near a window are taller than plants across the room.
The student concludes that sunlight caused the difference.
Give one reason the conclusion may be premature.
Other variables could explain the difference, such as water, temperature, soil, or other environmental conditions.
A scientist tests a new medicine.
What is the purpose of Group B?
It serves as the control/comparison group
A scientist wants to show how the temperature of a solution changes over a period of 10 minutes.
Which type of graph would best show the change over time?
Line Graph
Two scientists investigate the same phenomenon but obtain different results.
Name TWO things they should compare before deciding why their results differ.
Possible answers include procedures, sample size, variables, equipment, conditions, number of trials, or experimental error.
Scientists develop new technology that allows them to collect evidence that could not previously be obtained.
How could this affect scientific knowledge?
New evidence could strengthen, modify, refine, or challenge existing scientific explanations.
A student wants to investigate whether the amount of sunlight affects plant growth.
Which question is more scientifically useful?
A. Why are some plants healthier than others?
B. How does the number of hours of sunlight affect plant height?
B — it identifies measurable variables and can be tested through an investigation.
A student investigates whether fertilizer affects plant growth.
The student changes:
The student then measures plant height.
Why would it be difficult to determine whether fertilizer caused the difference in plant growth?
Multiple variables were changed. Because the student did not control the other conditions, the effect of fertilizer cannot be isolated.
What are two types of graphs a scientist could use to display qualitative data?
Bar Graph and Circle Graph
A scientist repeats an experiment several times and gets nearly identical results.
A student concludes: "The results are consistent, so the conclusion must be correct."
What important idea is missing from this reasoning?
Consistent results support reliability/precision, but they do not automatically prove the conclusion is correct. The measurements could consistently contain an error, or an uncontrolled variable could affect every trial. They need replication and peer review.
A model accurately predicts what will happen under normal conditions but does not accurately predict what happens under extreme conditions.
What should scientists conclude about the model?
The model has a limitation. Scientists should identify the conditions under which the model works and where it does not, rather than automatically declaring the model useless.
A scientist begins with an observation, researches what is already known, develops a possible explanation, conducts an investigation, analyzes the data, and communicates the results.
The investigation does not support the original hypothesis.
Explain why the investigation can still be scientifically useful and identify what the scientist should do next.
The results provide evidence even though the hypothesis was not supported. The scientist should analyze the results, consider experimental error or uncontrolled variables, communicate the findings, and use the evidence to revise the explanation or develop a new question.
Two students investigate the same question.
Student A:
Student B:
Explain TWO reasons Student B's investigation provides stronger evidence.
Student B has a larger sample size and repeated trials, which can provide more reliable evidence. Student B also controls important variables, making it easier to determine whether the independent variable caused the observed effect.
Scientist measures the heights of 20 plants. Most plants are between 18–23 cm, but one plant is 41 cm. What should the scientist do to analyze the data. What should the scientist investigate, and why should the scientist not simply remove it.
Use the median instead of the mean to find the middle point because the outlier will affect the mean. The scientist should determine whether it resulted from measurement or experimental error or represents a genuine unusual result. It should not automatically be removed simply because it changes the conclusion. The data should be honestly reported.
Two research teams investigate the same question.
Team A obtains the same result across many repeated trials.
Team B uses the same basic procedure independently and obtains a very different result.
Explain why the disagreement does not automatically mean one team is "bad at science." What should scientists investigate before deciding what the evidence means?
Scientists should compare procedures, sample size, variables, equipment, environmental conditions, number of trials, measurement methods, and possible experimental errors or uncontrolled variables. Independent replication is important because it tests whether results can be reproduced.
A company pays for research on its own product.
The researchers obtain results that do not support the company's advertising claims.
The company asks them to remove those results from the report.
What scientific principles are being threatened? Explain.
Objectivity and honest reporting of data. Scientists should report relevant results accurately rather than selecting only results that support a desired conclusion.