AP Biology Exam Prep: Research Questions + Null and Alternative Hypotheses

Summary

The video introduces AP Biology Science Practice 3: Questions and Methods, focusing on identifying testable questions and stating null and alternative hypotheses. These skills involve applying biology knowledge to scientific investigations.

Testable Questions and Hypotheses

Scientific investigations begin with questions about the natural world. A hypothesis is a testable explanation for observations, based on available data and inductive reasoning. It must be possible to test through an experiment or study, and it is narrower in scope than a theory.

The basic scientific process described in the video is:

1. Make an observation or ask a question.
2. Research the topic.
3. Form a hypothesis.
4. Test the hypothesis.
5. Analyze the data.
6. Report conclusions.

When given observations, data, or a model, students should be able to propose a question that could guide an investigation.

Example: CFTR and cystic fibrosis The video describes a mutation in the gene encoding CFTR chloride ion channels and its association with unusually thick, dehydrated mucus. A useful testable question would investigate how the mutation changes the structure of the CFTR protein, connecting protein structure to its function.

Null and Alternative Hypotheses

The independent variable is what is manipulated or tested, while the dependent variable is what is measured in response.

A null hypothesis predicts no significant relationship between the independent and dependent variables. An alternative hypothesis predicts that there is a relationship—that the independent variable affects the dependent variable.

For example, when testing whether water type affects plant growth:

• Independent variable: Type of water
• Dependent variable: Plant growth
• Null hypothesis: Water type does not affect plant growth.

When testing whether biofertilizer affects plant growth, the null hypothesis predicts that the fertilizer does not affect growth, while the alternative hypothesis predicts that it does.

Interpreting Evidence

The instructor presents the following rules for deciding which hypothesis is supported:

• Error bars: If error bars overlap, the video says there is no statistically significant difference, supporting acceptance of the null hypothesis. If they do not overlap, it says the evidence supports the alternative hypothesis.
• Chi-square test: Compare the calculated chi-square value with the critical value. If the calculated value is below the critical value, the video says to accept the null hypothesis. If it is above the critical value, the result is statistically significant and supports the alternative hypothesis.

For example, a calculated chi-square value of 4.3 is below the critical value of 5.991 for 2 degrees of freedom, so the video concludes that the null hypothesis is supported.

The video notes that statistical tests and error bars will be covered in more detail later.

Reading Experimental Results

A respirometer example compares oxygen consumption in a rat and a mouse at different environmental temperatures. Based on the graph, the supported hypothesis is that the mouse has a higher metabolic rate per gram of tissue than the rat, as it consumes more oxygen relative to its body mass.

Speakers and Sources Featured

Mr. Poser, an AP Biology teacher, is the sole speaker. The video also uses instructional examples involving CFTR and cystic fibrosis, plant growth, chi-square values, and oxygen consumption in a rat and a mouse.