The scientific method (materials-based)

Overview

To start the semester we will consider how scientists conduct their research, measure and quantify the natural world, and communicate their findings. We will learn foundational quantitative skills and concepts that will appear throughout the semester. We'll also consider how data is obtained using several common lab instruments.

Background

Measurement: Accuracy & Precision (4:52)

Measurement systems: TedED: Why the metric system matters (5:07) & BBC Earth Lab: A fun guide to Imperial measurements (2:50)

U.S. Metrication: Decades TV: U.S. metrication (2:24) & U.S. Metric Board 1981 PSA (0:59) & U.S. Office of Education 1978 cartoon commercial (1:00)

Unit conversions: The story behind the Fahrenheit (5:23)

Notation: Scientific notation (4:14) & Significant figures (5:03)

Article for concept application: Measurement of long-term climate trends (hurricanes) with evolving technology

Objectives

Upon completing this lab, students will be able to:

Identify the steps in the scientific method
Use standardized measuring systems to collect quantitative data
Express and convert numbers across units and notation
Distinguish accuracy vs. precision and explain why each matters
Accurately measure length and mass using standard lab equipment
Access, analyze, and apply scholarly literature

Introduction

What image comes to mind when you read the word scientist? For many people, it’s a laboratory scientist with a lab coat, protective eyewear, and latex gloves. This image is frequently portrayed in textbooks, advertisements, and TV shows. This is a very specific type of scientist, one who studies microscopic objects like cells, enzymes, and DNA. However, there are many other types of scientists working in a variety of settings, using a variety of technologies, studying objects ranging from molecules to the entire planet. This semester, you’ll learn how the field of ecology blends many scientific disciplines, as well as their tools and technologies, to study all living organisms on our planet.

The term scientist wasn't actually coined until 1834 when it was created to describe one brilliant woman, Mary Somerville, who broke the mold held at the time by “men of science”. Whereas her predecessors had largely focused their attention within one discipline, Mary Somerville was a self-taught mathematician who harmonized the fields of astronomy, geology, and biology into a single, interdisciplinary, and visionary form. Read the linked article to begin learning more about her life and her legacy.

Ecologists today integrate many scientific disciplines, tools, and technologies to study the diversity of life on this planet. Whether it’s microbes under Antarctic ice or common cranes (birds) migrating over Mt. Everest, ecologists are driven by two key motivations:

Describing the abundance and distribution of organisms on the planet; and
Understanding the relationships among organisms and their environments.

In this class, you’ll explore some of the most common ways ecologists measure and quantify these aspects of the natural world.

The scientific method

To conduct their research, scientists employ the scientific method. In many introductory textbooks, the scientific method is presented as a simple recipe for scientific investigations. It usually entails some version of the following steps, in order:

Make an observation
Formulate a question
Conduct background research
Develop a hypothesis
Design an experiment
Collect and analyze data
Communicate findings

While a helpful starting point, this linear, step-by-step representation is oversimplified. In the model, below, science is more accurately represented as an iterative process of of exploration and discovery, testing ideas, community analysis and feedback, and benefits and outcomes.

To see the how this model works in practice, watch the video below from the California Academy of Sciences:

Gathering data

A critical part of science is gathering data, which frequently requires measurement. Measurement is also critical to various other human enterprises, including trade, taxation, and construction. Although various measurement systems exist, commonalities exist. Most nested systems, meaning smaller standards (units) are used to measure smaller items. For example, we use inches to measure height and miles to measure distances among cities. They are also standardized, meaning at some level (ranging from local to global) people agree on what a measure means. These traits are critical to making measurements useful.

In this lab we'll discuss why the metric system is widely used globally as a measurement system. We'll also describe how one can convert among various units (both with-in the metric system and between systems) and introduce accuracy and precision, terms that are critical to categorizing the bias and reproducibility of data. You'll learn how to use scientific notation to write really large (or small) numbers. Finally, we'll practice measuring by introducing common lab tools that we'll use throughout the semester.

The Metric System

The metric system, also known as the International System of Units, is an internationally known and widely used measurement system. Base units in the metric system are grams (mass, abbreviated g), meters (length, abbreviated m), and liters (volume, abbreviated l or L). The system is easy to use as common prefixes added to these units indicate the scale of measurement . These prefixes are all based on the number of 10, so one can move between one metric unit by moving the decimal point and changing the associated prefix. Common prefixes include kilo (1000), milli (1/1000); others are noted below. For example, 745 centimeters is 7.45 meters or 7450 millimeters.

Length Mass Volume

1 km = 1000 meter (m) 1 kg = 1000 grams (g) 1 liter (L) = 1000 mL

1 m = 100 cm 1 g = 1000 mg 1 mL = 1000 μL

1 m = 1000 mm 1 mg = 1000 μg 1 μL = 1000 nL

1 mm = 1000 μm 1 μg = 1000 ng

1 μm = 1000 nm

American Standards

Although most countries use the metric system, the United States still practices the older Imperial system. Below is a list of conversion factors that will help in shifting between two forms of measuring.

Converting to and from American units and metric units seems tedious, but is a useful quantitative skill to practice.

Length Mass Volume

1 inch = 2.54 cm 1 lb = 16 oz 1 oz = 29.57 mL 1 pint = 2 cups

1 yd = 3 ft 1 gram = 0.035 oz 1 cup = 8 oz 1 quart = 2 pints

Conversions

There are many different ways and methods that can help you convert from one unit to another. Here we demonstrated one method known as dimensional analysis that may help keep things organized. First, identify the things you know: the number and unit you are given, as well as the unit you want to convert to. Next, identify the things you need to know to help you solve the problems. This may involve one or more conversions that are listed above. Then, you have to organize these conversions for calculations. Start with creating a diagram like the one shown below (note that the vertical lines may be more or less depending on the number of conversions you are using)

We will work through this method with an example question: convert 2.18 hours to seconds.

In the far left upper box, write down the number and unit you were given.

Without knowing how many seconds are in an hour off the top of your head, the conversion from hours to seconds is through minutes because

1 hour = 60 minutes

1 minute = 60 seconds

We will fill out the boxes in the second column with the conversion from hour to minutes. We want to cancel out hours to get minutes; since hours is in the top box, we will write hours in the bottom box of the second row and minutes in the top box. Make sure the numbers of the conversions follow the corresponding units.
To determine which unit belongs in which box, remember this: when you divide a unit by itself, that unit cancels out.

If the question was asking to convert to minutes, the placement of all the necessary conversion factors is complete. This is because the unit, hour, would be cancelled out, leaving minutes as the only unit left.
Moving from minutes to seconds, we add the second conversion in the boxes of the third column following the same approahc of the previous step. We want to cancel out minutes to get seconds, therefore we will put minutes in the bottom box and seconds in the top.

Now we are ready to complete the calculation: multiply all the numbers in the top boxes and divide by all the numbers in the bottom boxes. Make sure to cancel out the matching units, leaving any units not cancelled out (which should also be the unit you are trying to convert to). Write your answer in the far right upper box.
- Note that for all the individual columns (60 min/1 hour; 60 seconds/1 minute) the top and bottom components are equivalent—you are simply multiplying your original amount by 1!

Accuracy and Precision

Two adjectives are commonly used to describe a measurement: accuracy and precision.

Accuracy refers how close the measurement is to the standard or known value.

Precision refers to how close two measurements are to each other.

Accuracy and precision are independent of each other: a measurement can be accurate, precise, both, or neither. In the figure to the left,

A is accurate and precise
B is precise but not accurate
C is accurate but not precise
D is neither accurate nor precise

(Wikimedia commons, CC BY-SA 3.0, https://creativecommons.org/licenses/by-sa/3.0/)

Scientific Notation

Numbers written in scientific notation are written in the form:

m × 10n .

m is a real number that typically only has one digit before the decimal point, and the exponent n is an integer. Since the notation is based on multiplying by a power of 10, we can move the decimal point to the right (if n is positive) or left (if n is negative). This is useful as scientists often deal with very large or small numbers, resulting in many extra zeros that serve as placeholders. Scientific notation also relates to the use of significant figures, or the idea that mathematical operations can't add resolution to a measurement beyond those dictated by the precision of the device that was used to make the measurement.

Instructions for converting to scientific notation:

If you have a number between 0 and 1, form the coefficient by “moving” the decimal to the right until one non-zero digit is to the left of the decimal.
- For example, moving the decimal to the right of 0.0039267581 by 3 counts would place the decimal between 3 and 9. The coefficient used in scientific notation would thus be 3.93 (three significant figures, with the last digit rounded up since the following number is greater than 4).
If you have a number much greater than 1, form the coefficient by “moving” the decimal to the left until one non-zero digit is to the left of the decimal.
- For example, the coefficient used in writing 46,200,000 in scientific notation is 4.62 with the decimal point.
The value for the exponent (n) is determined by how many places you moved the decimal and which direction. When you move the decimal point to the right, the exponent is negative; when you move the decimal point to the right, the exponent is positive
- In the first example, the final value can be written in scientific notation as 3.93 × 10-3.
- In the second example, the final value can be written in scientific notation as 4.62 × 107.

Instructions for converting from scientific notation:

If a number written in scientific notation has a negative exponent, it means that the real number is between 0 and 1. The number of the exponent will help determine the number of zeroes you will have to add in front of the first number in the coefficient before placing a decimal point. Assuming the coefficient only has one number to the left of the digit, you will add a total number of zeroes that is equal to the (exponent - 1) to the front of the number and place the decimal point to left of all these zeroes.
- For example, 8.15 *10-5 is 0.0000815 in real numbers. Four zeroes were added because it would take five counts of the decimal moving to the right to get in between 8 and 1.
If a number is written in scientific notation using a positive exponent, it means that the real number is much greater than 1. The number of the exponent will help determine the number of zeroes you will have to add after the last digit before placing a decimal point. Generally, you will add (exponent – the number of digits after the decimal in the coefficient) zeros.
- For example, 7.02 *106 is 7,020,000 in real numbers. The decimal was moved two places and four zeros were added after the 2.

Science communication

Once scientists have collected their data and analyzed their results, they need to communicate their findings with other scientists and the general public. This occurs through conference presentations, social media, news outlets, and more. One key outlet through which new discoveries are shared with the scientific community is through scholarly literature. "Scholarly literature" encompasses articles, books, and other media produced by professional researchers who are experts in their field. While different disciplines have different conventions and styles, in general scholarly literature is produced for a specialized audience and is subject to rigorous editorial standards (including, in the best case, peer review).

Original findings are reported in scientific research articles, which typically follow a standardized structure:

Abstract: A concise , one paragraph summary of the article's key points
Introduction: Relevant background information necessary to understand why and how the authors conducted their research
Methods: Detailed description of how the scientists carried out their study, including the equipment, protocols, and techniques used to collect and analyze data.
Results: Report of the raw findings from the study, typically with tables, graphs, and other figures.
Discussion: Interpretation of the results in the context of previous research, explanation of any limitations, proposed future directions, and conclusions.

At their best, scholarly sources are more reliable and of higher quality than news stories, blog posts, or other online articles because they are subject to peer review by an independent group of experts. The table below shows some hints you can use to distinguish scholarly journal articles from other types of sources.

01. The Scientific Method

Methods

Part 1: The scientific method in action

Read the following USGS profile of ecologist Jim Estes and his research on sea otters. As you read, pay attention not only to what Estes discovered, but also to how his questions and research changed over time.

WERC, 2022. Emeritus and distinguished alumni profile: Jim Estes explains how sea otters run the world. USGS. https://www.usgs.gov/centers/werc/news/emeritus-and-distinguished-alumni-profile-jim-estes-explains-how-sea-otters-run

What was the initial scientific question that Estes set out to answer as a PhD student?

After a conversation with ecologist Bob Paine, how did Estes’ research question change?

Match each event from Estes’ investigation to the step from the conventional scientific method (note: not all steps will be used)

____ Researchers measure and compare the abundance of otters, urchins, and kelp among different islands

____ Estes notices there are many urchins and little kelp at an island without otters

____ Estes and his co-author publish their findings in the journal Science

____ Estes proposes that the presence of otters reduces urchin populations, allowing more kelp to grow

A. Make an observation

B. Formulate a question

C. Conduct background research

D. Develop a hypothesis

E. Design an experiment

F. Collect and analyze data

G. Communicate findings

Which statement best describes the relationship between Estes's research over the course of his career and the conventional scientific method?

A. Estes did not use the conventional scientific method because his work entailed observational studies, not controlled laboratory experiments

B. Estes’ research followed the conventional scientific method because each step was performed exactly once and in the prescribed order.

C. Many parts of Estes’ research can be described using conventional steps, but the actual process involved new observations, changing questions, collaboration, and repeated investigation.

D. Estes’s research shows that the conventional scientific method is not useful for guiding scientific investigations because he did not follow a linear path

Open the How Science Works interactive flowchart. Select the “detailed” framework and click through the intro to review the four essential components to the nature and process of science. Then use the interactive flow chart to map 6-8 steps taken by Jim Estes in his otter investigations as described in the article. Annotate each step with a short description, taken directly from the article or in your own words. Your map should include events from at least three of the four major components of the scientific process. Note that there is not one correct path, and some steps may be repeated multiple times.

When you’re satisfied with your diagram, export it as a PowerPoint.

Part 2: Data collection and measurement

When making observations, Estes could describe an island as having “lots of urchins” or “lots of kelp,” but scientists need standardized ways to record observations so that data can be compared among researchers, places, and times. Quantitative measurements also allow scientists to describe patterns more accurately and precisely than words like “lots” or “few.”

6. Examine the figures below from Jim Estes & John Palmisano’ 1974 Science article.

Fig. 1 Vegetation coverage and sea urchin density plotted against depth. The data for Amchitka Island and Shemya Island represent averages from four and three study areas, respectively. Vegetation cover at Shemya Island is coincident with the ordinate

Fig 2. Sea urchin size class distributions and associated biomass contributions. (a) Data collected from Amchitka Island (high-density sea otter populations). (b) Data collected from Shemya Island (sea otters absent). The dotted line represents the largest sea urchin size class observed at Amchitka Island.

For each quantity measured by Estes and his colleagues, indicate unit used to report it in the figures.

Water depth _______________

Vegetation cover _______________

Sea urchin density _______________

Sea urchin diameter _______________

Sea urchin biomass _______________

7. Estes and Palmisano estimated that foraging sea otters consumed 35,000 kg animal biomass per km2 per year. Write this number using proper scientific notation.

8. Convert 35,000 kg/km2 per year to g/m2 per year

9. A sea urchin has a known diameter of 32.0 mm. Two researchers measure it four times each and get the following values:

Researcher A: 31.1 mm, 32.8 mm, 31.7 mm, 32.5 mm
Researcher B: 34.0 mm, 34.1 mm, 34.0 mm, 34.1 mm

Which of the following statements best describe the difference? Select all that apply.

A. Researcher A is more accurate

B. Researcher B is more accurate

C. Researcher A is more precise

D. Researcher B is more precise

E. The researchers are equally precise

F. The researchers are equally accurate

10. Researcher B discovers that their calipers were miscalibrated and are consistently off by 2 mm. Which action(s) could be taken to address this problem?

Now, you will practice taking your own measurements using standard laboratory equipment.

Length measurements of everyday objects are usually conducted using rulers, tape measures, or calipers. Some length measurement devices have only one unit, while others have more than one. Use a meter stick and your knowledge of unit conversions to provide the following measurements:

11. What is the length of the lab table in meters?

12. What is the width of the table in centimeters?

13. What is the height of the table in kilometers? Write your answer using proper scientific notation.

Mass is a measure of the amount of matter in an object and is commonly measured in grams or kilograms. Weight is the force exerted on an object by gravity, so an object's weight can change depending on the strength of gravity (e.g. on Earth vs. the moon) while its mass remains the same. In this activity, we will use an electronic balance to measure mass in grams.

Practice operating the electronic scale in this lab by exercising the following steps.

Connect the scale to a power outlet in the lab. Turn on the scale by pressing down on the ON/OFF button (it may take a couple of seconds before the text appears on the screen).
Allow the scale to “adjust” itself before using (the screen may show a countdown before the scale is ready).
The default unit of the scale is set to grams (the letter “g” on the screen), make sure this is correct. If the unit is not in grams, you can change it by pressing the “CAL” or “MODE” button until the “g” appears.
Without any objects or force on the scale, the screen should read 0.0g. If it does not, press on the “ZERO” or “TARE” button once.

Now you are ready to take your measurements. Make sure to place the objects on the center of the scale for a precise measurement.:

14. What is the mass of the empty weighing tray in grams?

15. Press the TARE button, then add 4 beads to the weighing tray. What is the mass of the beads in grams?

16. What did pressing “tare” accomplish?

17. Remove the tray and beads from the balance. What happens to the reading, and why?

Electronic (digital) weighing scale (laboratory balance)

Image by Stan Zurek [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0, from Wikimedia Commons

Part 3: Communicating science through scholarly literature

Scientists rely on previously published research to understand what is already known, develop new questions, and interpret their results. They also publish their own research so that other scientists can evaluate and build upon it. In this section, you will compare different ways scientific information is communicated and practice locating and interpreting scholarly literature.

18. Which of the two sources presented to you in this exercise is an original scientific research article?

19. Which features of the source provide evidence it is a scientific research article?

20. What is the relationship between the two sources? Is one "better" than the other? Why or why not?

Estes continued investigating sea otters after the 1974 study. Use Google Scholar or the Newman Library to locate the following paper: “Sea Otter Predation and Community Organization in the Western Aleutian Islands, Alaska”

21. In what year was the article published?

22. What is the name of the journal in which the article was published?

23. Write out the full citation for the article in APA format.

24. Match each of the following sentences from the paper with its corresponding section

____ Sea urchin densities and size-class distributions were estimated by arbitrarily placing a 0.25-m2 quadrat on the ocean floor and removing all sea urchins within the quadrat for counts and measurements in the field laboratory

____ Predation is an important interaction in many marine communities

____ At 18 to 23 m, Shemya sea urchins were even less abundant, and no peaks in the size class distribution were apparent (Fig. 4)

____ This conclusion is similar to that reached by Vadas (1968), who found that Laminaria was dominant over Agarum in undisturbed areas of the San Juan archipelago

A. Introduction

B. Methods

C. Results

D. Discussion

25. Return to the How Science Works map you created in Question 5. Identify one specific event on your map where scholarly literature either influenced Estes's research or allowed his research to influence other scientists. In 1–2 sentences, explain the connection.

AI use disclosure: ChatGPT (OpenAI) was used to assist with brainstorming, question development, and revision of this activity. All content was reviewed and edited by the course instructor, and factual information was verified against the cited sources.

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