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Biology LibreTexts

1.2: Science Experiments

So what exactly is an experiment?

At first you may picture a science laboratory with microscopes and chemicals and people in white lab coats. But do all experiments have to be done in a lab? And do all scientists have to wear lab coats?


Figure below shows a laboratory experiment involving plants. An experiment is a special type of scientific investigation that is performed under controlled conditions, usually in a laboratory. Some experiments can be very simple, but even the simplest can contribute important evidence that helps scientists better understand the natural world. An example experiment can be seen here or here As many different types of of experiments are possible, an experiment must be designed to produce data that can help confirm or reject the hypothesis.

Laboratory experiment studying plant growth

A laboratory experiment studying plant growth. What might this experiment involve?

Scientist looking through microscope

In this experiment, a scientist is conducting research (and taking notes) while looking through a microscope.

Medicine From the Ocean Floor

Scientists at the University of California, Santa Cruz are looking to perhaps the largest resource yet to be explored for its medical potential: the ocean. And they are taping this resource with some state-of-the-art technology. These scientists are using robots to sort through thousands of marine chemicals in search of cures for diseases like cholera, breast cancer, and malaria. These experiments are described in the following KQED links:


An experiment generally tests how one variable is affected by another. The affected variable is called the dependent variable. In the plant experiment shown above, the dependent variable is plant growth. The variable that affects the dependent variable is called the independent variable. In the plant experiment, the independent variable could be fertilizer—some plants will get fertilizer, others will not. The scientists change the amount of the independent variable (the fertilizer) to observe the effects on the dependent variable (plant growth). An experiment needs to be run simultaneously in which no fertilizer is given to the plant. This would be known as a control experiment. In any experiment, other factors that might affect the dependent variable must be controlled. In the plant experiment, what factors do you think should be controlled? (Hint: What other factors might affect plant growth?)

Sample Size and Repetition

The sample in an experiment or other investigation consists of the individuals or events that are studied, and the size of the sample (or sample size) directly affects the interpretation of the results. Typically, the sample is much smaller than all such individuals or events that exist in the world. Whether the results based on the sample are true in general cannot be known for certain. However, the larger the sample is, the more likely it is that the results are generally true.

Similarly, the more times that an experiment is repeated (which is known as repetition) and the same results obtained, the more likely the results are valid. This is why scientific experiments should always be repeated.

Bio-Inspiration: Nature as Muse

For hundreds of years, scientists have been using design ideas from structures in nature. Now, biologists and engineers at the University of California, Berkeley are working together to design a broad range of new products, such as life-saving milli-robots modeled on the way cockroaches run and adhesives based on the amazing design of a gecko's foot. This process starts with making observations of nature, which lead to asking questions and to the additional aspects of the scientific processBio-Inspiration: Nature as Muse can be observed at

Super Microscopes

Microscopes are arguably one of the most important tools of the biologist. They allow the visualization of smaller and smaller biological organisms and molecules. With greatly magnified powers, these instruments are becoming increasingly important in modern day research. See the following KQED videos for additional information on these remarkable tools.


  • An experiment is a special type of scientific investigation that is performed under controlled conditions, usually in a laboratory.
  • An experiment generally tests how one variable is affected by another.
  • The sample size in an experiment directly affects the interpretation of the results.
  • Repetition is the repeating of an experiment, validating the results.

Explore More

Use this resource to answer the questions that follow.

  1. Describe controlled experiments.
  2. Describe field experiments.
  3. What is a variable? Give an example.
  4. What are the independent and dependent variables?
  5. Why is it best to only have one independent variable in an experiment?


  1. What is an experiment?
  2. Compare the dependent variable to the independent variable.
  3. Identify the independent and dependent variables in the following experiment: A scientist grew bacteria on gel in her lab. She wanted to find out if the bacteria would grow faster on gel A or gel B. She placed a few bacteria on gel A and a few on gel B. After 24 hours, she observed how many bacteria were present on each type of gel.