Question

The test tubes were left at room temperature for a week to see if algae would grow. Which variable is being investigated? A. the volume of water used B. the temperature of the test tube's contents C. the amount of chlorine present D. the amount of algae present

Short answer

D. the amount of algae present

Step-by-step solution

Identify the Main Focus of the Experiment

The first step is to understand the purpose of the experiment, which involves leaving test tubes at room temperature to observe a particular outcome.

Determine the Subject of Observation

Next, ascertain what is being observed or measured as a result of the week-long period, which is whether algae (a type of aquatic organism) will grow.

Identify the Investigated Variable

Algae growth, as the primary observation over the week, indicates the investigation's focus is on the outcome related to the presence or absence of algae.

Select the Correct Variable Option

Choosing from the options given, the amount of algae present reflects the result being measured; therefore, this is the variable being investigated.

Key concepts

Experiment Design

Experiment design is the foundation of scientific research. It starts with identifying a question that needs an answer. For example, in our exercise, the question aims to discover if algae will grow over time. The next step is to develop a plan, or procedure, to gather data. This includes setting up conditions, like leaving test tubes at room temperature for a week, and controlling other factors to ensure they don't affect the outcome. A well-designed experiment will include a control, or baseline, to compare results. It should also be repeatable, allowing others to verify findings. Key elements to consider when designing an experiment include:

• Clear hypothesis: What do you expect to find?
• Replicable methods: Can others recreate your study?
• Controlled variables: What factors will you keep constant?
• Independent variables: What are you changing in the setup?
• Dependent variables: What are you observing or measuring?

By carefully planning each stage, experimenters can ensure that their research provides valid and reliable results.

Hypothesis Testing

Hypothesis testing serves as a critical step in the scientific method. In this process, scientists make an educated guess, or hypothesis, about what they expect to find. For our experiment, a possible hypothesis might be that algae will grow in test tubes left at room temperature due to suitable conditions for their propagation. The hypothesis needs to be specific and testable, meaning you can measure whether your prediction is correct. Here’s how the process works:

• Formulate a hypothesis: Predict the study's outcome.
• Execute the experiment: Gather data through observation.
• Analyze results: Decide whether the results support the hypothesis.
• Draw conclusions: Determine the hypothesis's validity.

The beauty of hypothesis testing is it can lead to new questions and hypotheses, forming a cycle of inquiry that expands our understanding of the world. If your hypothesis is supported, that's great! If not, that leads to more questions and experiments. It's all part of the learning process.

Variable Identification

Identifying variables is crucial to any scientific experiment. In our example, the main variable explored is the amount of algae present after a week. Variables come in different types:

• **Independent variable**: This is what you change on purpose to observe effects. In our exercise, it is the condition of leaving test tubes at room temperature.
• **Dependent variable**: This is what you measure; the results of your change. Here, it’s whether algae grow or not.
• **Controlled variables**: These are all other factors kept consistent to ensure a fair test, like the volume of water and amount of chlorine present.

Understanding these variables helps in interpreting the results and ensuring the experiment is valid. By clearly defining which variables to manipulate and which to measure, researchers can draw meaningful conclusions from their experiments. Remember, a well-conducted experiment is as much about knowing what variables to keep constant as it is about measuring changes.