Regardless of the many different tools and methods used in research, all scientific investigations are based on observation and experimentation, key elements of the scientific method. The scientific method is one of the most powerful tools of modern science.
Often, science textbooks describe "the scientific method," as if there is a single, simple flow chart that all scientists follow. This is an oversimplification. Although such flow charts incorporate much of what scientists do, you should not conclude that scientists necessarily progress through the steps of the process in one prescribed, linear order. That said, we will introduce you to this traditional flow chart, which consists of five main steps: making observations; asking questions; forming hypotheses; making predictions based on the hypotheses; and testing the predictions by making additional observations or conducting experiments. We will highlight this version of the scientific method using the study of coral bleaching as an example.
The scientific study of coral reefs is becoming increasingly important. Coral reefs support the largest diversity of life in the oceans. They provide fisheries and storm protection for about a billion people, and are a magnificent source of natural beauty. But coral reefs are endangered. Over the past 20 years, about half of the world's reef-building corals have been destroyed by rising water temperature and other factors.
High temperatures disrupt a fascinating aspect of coral biology. Corals are animals, yet if you look inside the cells of most corals, you will find algae growing there symbiotically. These algae are dinoflagellates. Dinoflagellates use the energy of sunlight to produce carbohydrates, which they deliver to the coral cells, and the coral cells, in turn, provide a home and inorganic nutrients for the dinoflagellates. Under environmental stress, such as high water temperature, the symbiotic interaction suffers and the corals eject the algae—a process called bleaching. Without their chief source of nutrients, the corals eventually die, unless they can re-establish a symbiosis under better environmental conditions.
Researchers want to understand the effects of heat on corals. Rachel Bay and other members of Steve Palumbi's laboratory at Stanford University's Hopkins Marine Station are performing experiments on corals in small back-reef pools in American Samoa.
One of these experiments will highlight a scientist's most powerful tool—the scientific method. Observations are the starting point. Here we will show you a flow chart of the scientific method that incorporates much of what scientists do. However, it will be an oversimplification, as there is no one prescribed, linear order. There are many ways to do science.
While studying these corals, the researchers observed that during low tides some pools reached higher temperatures than others. In fact, corals were thriving in pools that reached temperatures known to kill other corals outright. Could the corals have genetic adaptations to survive heat stress, or have they physiologically acclimated to the heat?
Such questions represent a second key step of the scientific method. In answer to a question, an investigator forms a tentative proposition, called a hypothesis. The researchers started with this hypothesis: Heat stress results in coral bleaching, but corals from warm pools are less subject to bleaching under heat stress than are corals from cool pools.
Based on this hypothesis, the researchers made a prediction, which is the next stage in the scientific method. They predicted that the cool-pool corals would bleach at higher rates under experimental conditions than the warm-pool corals would.
In the scientific method, a prediction is tested by a well-designed experiment. The most informative experiments are those that have the ability to show that the prediction is wrong, the potential to falsify the hypothesis.
This experimental setup is a controlled experiment. Controlled experiments manipulate one factor of interest while holding other variables constant in order to test the influence of the manipulated variable.
In this controlled experiment, branches of tabletop corals from both warm pools and cool pools were transplanted into laboratory aquaria and maintained at a safe temperature. So the controlled variable was whether the experimental corals came from the cool-pool or the warm-pool environment.
Two branches from each individual coral were taken so that they could be tested in two separate aquaria. These corals were then subjected to two different temperature conditions. Some of the corals—the experimental groups—were subjected to heat stress, which consisted of temperatures that mimicked the daily temperature cycle in the warm pools of the reef. The control groups were corals not exposed to the heat stress protocol. Then the researchers measured the extent of bleaching, based on the amount of chlorophyll still present in the sample.
Chlorophyll is the photosynthetic pigment of the symbionts. The amount of chlorophyll in a heat-stressed sample is compared in a ratio to the amount of chlorophyll in its duplicate held at standard temperature conditions. A value of one means that there is no difference in chlorophyll and, therefore, no difference in bleaching between the two conditions. A value of less than one means that the heat-stressed corals bleached more than those held at standard temperatures.
The results are graphed here with the cool-pool and warm-pool corals on the x-axis. On the y-axis is their bleaching response, the chlorophyll ratios. Note that corals originating from both warm and cool pools showed bleaching in respose to heat stress. On average, the cool-pool corals retained only half their chlorophyll, while the corals originating from the warm pools retained 85% of their chlorophyll under heat stress. So both of the groups showed bleaching, but the corals from the warm pools of the reef maintained their chlorophyll better than the corals from the cool pools. These bars represent averages of 17 samples from the cool pool and 8 from the warm pool.
How can you assess these data? Statistical tests help to evaluate the significance of the results.
In science, a null hypothesis provides a baseline for comparison. A null hypothesis is the premise that observed differences result from random variation, rather than a specific response to the experimental conditions. So the null hypothesis is that the difference we see between 85% and 50% is due to chance.
A statistical test generates a numerical probability that the null hypothesis is correct. A probability is given as a p-value between 0 and 1. Traditionally, if the p-value is low—less than 0.05 (or 5%)—this means that the probability that the null hypothesis is correct is only 5% or less, and so the null hypothesis is rejected. With the data in the coral experiment, the p-value is calculated to be less than 0.00001 (0.001%). With this really low p-value, the null hypothesis is rejected and, in contrast, the original hypothesis is supported. That is, the corals from the warm pools do bleach less in response to heat stress in the laboratory than the corals from the cool pools.
With this response defined in the laboratory, now the researchers can ask new questions. For instance, if cool-pool corals are transplanted into warm pools for many months, will they acclimatize and then bleach less under heat stress in the laboratory? The researchers did perform these experiments and found that corals did acquire more heat resistance. These experiments are important, because more knowledge of the mechanisms of heat stress and heat resistance in corals could lead to new strategies to decrease their losses as their environments change.
The scientific method is one of the most powerful tools of modern science. In the scientific method, two kinds of logic are employed. The formation of a hypothesis requires inductive logic. Using inductive logic, specific observations or facts are used to develop a new hypothesis that is compatible with those observations or facts. In other words, inductive logic moves from specific facts to a more general statement. More than one hypothesis may be compatible with the facts, which is why a hypothesis must now be tested.
The next step in the scientific method is to apply a different form of logic—deductive logic—to make predictions based on a hypothesis. Deductive logic starts with a statement believed to be true (or, a hypothesis that is to be tested) and then goes on to predict what facts would also have to be true to be compatible with that statement.
Once predictions are made from a hypothesis, experiments can be designed to test those predictions. The most informative experiments are those that have the ability to show that the prediction is wrong. If the prediction is wrong, the hypothesis must be questioned, modified, or rejected.
The traditional textbook description of the scientific method includes a linear series of five steps. However, this traditional description doesn't describe how science is often conducted in real life. Scientific investigations take many forms and are performed by individuals or teams with their own personalities, creativity, knowledge, and experiences. For more information on how scientists conduct science in the real world, click the link below.
Understanding how science really works