# As You Read

• Explain the steps taken in scientific methods.
• Compare and contrast scientific variables and constants.
• Explain how a control is used during an experiment.
• Vocabulary: scientific methods, observation, inference, hypothesis, independent variable, dependent variable, constant, and control.

# Scientific Methods

Several steps were taken to learn about the pottery found at York Middle School. When the pottery was found, a decision was made to stop construction at the site. One adult guessed that the pottery was old. An expert was called to verify the guess made about the pottery. Based on prior knowledge and further testing, it was concluded that the pottery was from a prehistoric culture.

Think about the last time you had a problem that took several steps or actions to solve. Step-by-step procedures of scientific problem solving are called scientific methods. Solving any problem scientifically involves several steps. The steps used can vary from situation to situation and aren’t always done in the same order. But for now, take a look at each step in turn.

# Recognize the Problem

Ben thought about all the science he had learned over the past few months. He was eager to find out more about the world around him. As he looked around his bedroom, he wondered what he could explore. It was then that Ben noticed that the plant on his windowsill was droopy. He quickly watered the wilting plant. Later in the day, Ben observed that the droopy plant had perked up. He concluded that he should water the plant on a regular basis. Every day after school, he watered the plant in his room.

After a few weeks, Ben noticed that the leaves on his plant had turned yellow and brown. He knew from science class that plants need water, so why was this plant not doing well. He talked to his teacher about the plant. She suggested that Ben use what he learned in science class to solve his problem. She pointed out that this problem might make a good project for the upcoming science fair.

Ben already has completed the first step in using a scientific approach to solving a problem - he recognizes a problem. A scientific problem is simply a question you don’t know the answer to. To solve his problem, Ben must do research about his plant. Using sources of information, Ben identified his plant as a fig. In his Science Journal, he drew a picture of the plant and listed some facts about it.

## Observe

In order for Ben to be able to answer the question about why his plant was not thriving, he needed to plan and carry out an experiment. First, he made and recorded careful observations about his plant. Observations can be bits of information you gather with your senses. Most scientific observations are made with your eyes and ears. You also can observe with your senses of touch, taste, and smell. Ben observed that many of the leaves had fallen off his plant. The stem, in places, was peeling. Ben also noticed that some white, powdery, smelly stuff was covering the soil in the pot. He stuck his finger into the soil. It was wet.

## Infer

Observations like Ben’s often lead to inferences. An inference is a conclusion about an observation. Ben inferred that perhaps he was watering his plant too often. Can you make any other inferences about why Ben’s plant wasn’t thriving?

# Form a Hypothesis

After a problem is identified, a scientist might make a hypothesis. A hypothesis is a statement that can be tested. Hypotheses are based on observations, research, and prior knowledge of a problem. Sometimes more than one hypothesis can be developed.

Example 1 compares and contrasts hypotheses with two other scientific statements - scientific theories and scientific laws. Ben decided to use his inference about watering too often as his hypothesis. His hypothesis was the following: Fig plants grow best when they are watered only once a week.

• Example 1
• Hypothesis: A hypothesis is a statement that is tested with experiments. Hypotheses supported by repeated tests are used to form theories.
• Theory: A theory is an explanation supported by results of many experiments. Theories attempt to explain why something happens.

# Test Your Hypothesis

To test his hypothesis, Ben will carry out an experiment using three plants. An experimental investigation is a series of carefully planned steps used to test a hypothesis. In any experiment, it’s important to carefully consider what resources you will use and how you can take steps to prevent wasting those resources. It’s also important to keep everything the same except for the item or variable you are testing so that you’ll know which variable caused the results. The one factor that you change in an experiment is called the independent variable.

In Ben’s proposed experiment, the independent variable is the number of times he waters each plant in a week. He then will observe how well each plant grows based on the amount of water it receives. The growth of the plants is the dependent variable in Ben’s experiment. A dependent variable is the factor, or outcome, that will be measured in an experiment.

## Plan the Experiment

In order to test only one variable at a time, scientists often use constants. Constants are factors in an experiment that stay the same. In his experiment, Ben will use the same species and size of plants, which will be potted with the same kinds and amounts of soil. His teacher pointed out that Ben also must put his plants into identical containers. Another constant in Ben’s experiment will be the amount of light each plant will get.

Experimental investigations also have a control. A control is a standard used for comparison. Ben knows that all plants, even cacti, need water. His control will be that one of the plants receives no water during the experiment.

## Do the Experiment

Ben gathered all the materials he would need to test his hypothesis. Before he started, Ben knew from Ms. Garcia’s labs that he must write down a plan to follow. In his Science Journal, he wrote that he would use three fig plants. Plant A would not be watered. This would be his control. A second fig plant, Plant B, would get watered every day. The third fig plant, Plant C, would get watered only once each week. His experiment would last one month.

Ben then made a table in which to record his observations. He listed each plant and the number of times it was to get watered. Ben made room in the table for his measurements. He also made a plan to record his observations, which would include the height of each plant, the color of its leaves, and the number of leaves it dropped, if any.

# Analyze Your Data

Data are collected during any scientific study. Some data are numeric values such as the length of an object or the temperature of a liquid. Other data you collect may include observations that use adjectives and phrases such as “faster”, “smaller”, “not as well as”, and “greener”. An experimenter must record and study the data collected before he or she can draw conclusions about an experiment.

By the end of the month, Ben observed that the leaves still left on the plant that received no water were brown and shriveled. It had lost most of its leaves. The plant that was watered every day had a few leaves left on its branches, but these leaves didn’t look too healthy. A white, smelly substance covered the soil. Ben noticed that the plant that was watered once each week had grown the tallest. Many healthy green-and-white leaves hung from its branches.

# Draw Conclusions and Communicate

After studying his data, Ben was ready to draw some conclusions. A conclusion is a statement based on what was observed. Ben concluded that not watering a plant causes the leaves to dry out and die. Watering a plant too much also causes the leaves to die. Watering the plant once a week seems to be the best schedule, of those tested, for a fig plant.

Ben told his teacher about his results. She reminded him that in order to make sure his conclusions were valid, he should repeat his experiment. Ben agreed and did the same experiment again. Based on the results of his second experiment, Ben was able to conclude confidently that watering a fig plant once a week made it grow well in the conditions he used. His hypothesis was supported. An important step in the scientific process is to communicate the results of an investigation. Ben entered his project in his school’s science fair. He seemed to have won the science fair with his project and his teacher congratulated him and he thanked her for her help.