Biology Experiments

Biological Testing Definition

To understand how biological experiments are done, we first need to understand what biology is and how the scientific method allows biological testing and experiments to occur.

Knowledge in science is often organized in the form of testable predictions and explanations called hypotheses. Testing a hypothesis is one of the most critical steps in the scientific method. The scientific method allows for a procedural or systematic way of obtaining knowledge.

The general steps of the scientific method are:

1. Make observations (e.g., my lamp won't light up).

2. Ask questions (e.g., why won't my lamp light up?)

3. Background research, if needed (e.g., lamps often don't light up if the bulb is burned out).

4. Formulate a hypothesis by making predictions (e.g., if the light bulb is broken, then replacing it with a new one will make the lamp light up).

5. Test with experiments (e.g., I change out the broken light bulb with a new one).

6. Analyze data or results (e.g., my lamp now lights up!)

7. Report results (e.g., my hypothesis was supported because the lamp lit up, which means that the original light bulb was indeed burned out).

If the hypothesis had not been supported, we would have still reported the results and then tried to formulate a new hypothesis again. In this case, the new hypothesis could have been that the light bulb might be fine, but the electrical outlet is broken.

A hypothesis doesn't always have to be correct; instead, it serves as an "educated guess," and researchers have to devise experiments to see if it's accurate or not. Scientists usually formulate hypotheses by making predictions. An easy way to do this is by using "if-then" statements, such as the one shown in the scientific method step 4.

A scientific theory is a scientific explanation that is shown to have significant evidence for its validity through continuous testing using the scientific method. Keep in mind, though, that scientific theories can still be disproven!

Biological Testing in the Laboratory

By following this systematic framework, scientists can perform biological tests in the real world. Biological tests can be performed either in laboratories or in natural settings.

For instance, in nature, scientists can perform biological tests on the water to see if it is potable, polluted for aquatic life and humans, etc.

There are around 80,000-100.000 chemicals registered for commercial use, according to the EPA (U.S. Environmental Protection Agency). Currently, we don't understand all of their combined effects.

Researchers can collect water samples and perform pH tests, which tell us how acidic or basic water is. A pH lower than seven signifies that the water is acidic compared to a pH above 7, which indicates that the water is basic (Figure 1).

Figure 1: pH scale illustrated. Daniela Lin, Study Smarter Originals.

Biological Experiments Definition

Now that we understand how scientists systematically ask questions and apply biological tests, let's go over biological experiments.

Scientists, including biologists, conduct tests and experiments to prove or disprove a hypothesis. But how exactly do scientists set up their experiments? Well, the answer is that they devise controlled experiments.

The Definition of a Controlled Experiment in Biology

When researchers design experiments, they need to know what questions they are trying to answer. In controlled experiments, we aim to test how one variable affects another. This means we need to know the independent variable (usually denoted as X) and the dependent variable (usually marked as Y).

The independent variable (X) is the variable we are changing or manipulating to see its effects on the dependent variable. Therefore, the dependent variable (Y) is the actual variable that's being tested.

We also need a control group where no variable is changed or manipulated. This group is used to ensure that the experiment's results are due to the independent variable being manipulated and not due to extraneous variables.

The Definition of an Experimental Group in Biology

So, what might be an example of a controlled experiment?

Suppose scientists want to find out if sunlight affects plant growth. They would need to keep the plant type, soil type and amount, amount of water, and pot type constant. This is because these variables are known as our control variables. If using seeds, the seed amounts would have to be kept the same, as our independent variable is sunlight.

The only thing that would change between the control and the experimental group would be the independent variable (the amount of sunlight), in this case, as shown in Figure 2.

The control group has no independent variable, while the experimental group does. Plant growth is our dependent variable in this case, as it is what we are observing.

If, after a few weeks, the experimental group's flowers have grown and the control group's flowers have withered, then we know that sunlight affects plant growth! And our hypothesis has been proven correct.

A control group is always necessary, but we can have multiple experimental groups in more complicated experiments. For example, for the same experiment, we could have the control group again with no sunlight, experimental group 1 with artificial sunlight, and experimental group 2 with actual sunlight.

Figure 2: Controlled experiment in biology illustrated. Daniela Lin, Study Smarter Originals.

Types of Experiments in Biology

After understanding how scientists pose questions and answer them through experiments, we can now go over some common types of biological experiments conducted in the real world.

Experimental

These are controlled experiments that are usually conducted in laboratory settings. In clinical studies, experimental studies are studies in which participants are randomly assigned to either a control or experimental/treatment group. This is the most common type of biological experiment most of us deal with.

Quasi-experimental

Quasi-experiments are also controlled, but unlike experimental studies, participants aren't randomly assigned to the control or experimental/treatment group. This is because randomly assigning participants is usually complicated or not feasible in these cases.

Both experimental and quasi-experimental involve the changing and manipulating of independent variables.

Non-experimental

Non-experimental studies are also called observational studies. They do not involve the manipulation of independent variables. Instead, they focus on observing a participant or subject in a natural or laboratory setting.

Biological Experiment Examples

Experimentation is what drives science at its core. This is because experiments allow us to gather data, analyze results, and come up with conclusions. Researchers communicate and collaborate their findings through peer-reviewed articles. Through this process, many biologists, chemists, etc., have expanded their research and built upon it to create advancements in science.

For example, Frederick Griffith's 1928 experiment was the first discovery of Bacteria's "transforming principle." This led to the discovery that DNA or deoxyribonucleic acid is "the carrier of Genetic Information" and not other things such as RNA by Alfred Hershey and Martha Chase in 1952.

Other vital discoveries that occurred through experimentation include:

• Robert Hooke discovered Cells, the smallest units of life, using a microscope.

• Edward Jenner made the world's first vaccine (specifically for smallpox).

• Gregor Mendel's experiments with pea Plants led him to establish fundamental laws of Heredity.

• Louis Pasteur's experiments used swan-neck flasks to disprove the theory of spontaneous generation or the theory that living things could arise from non-living material.

• Alexander Fleming discovered penicillin by observing one growing on his petri-dish. Penicillin is an antibiotic that has saved many lives since then.

• Linus Pauling finds out what causes sickle cell anemia (change in the shape of the human protein hemoglobin).

• Roger W. Sperry showed that the two sides of the human brain could be independent.

• Most recently, Jennifer A. Doudna and Emmanuelle Charpentier discovered CRISPR-Cas9, allowing scientists to edit almost any organism's genetic code.