A student graphs the effect of salt concentration on seed germination. Which graph setup correctly follows Science Practice 4?

Place salt concentration on the x-axis and percentage germinated on the y-axis, labeling both variables and units. — B is correct because the independent variable, salt concentration, belongs on the x-axis, while the measured dependent variable, percentage germinated, belongs on the y-axis. Both axes should include variables and units. A reverses the axes, C omits the measured response and units, and D does not represent the experiment's independent and dependent variables.

A graph shows that increasing salt concentration causes the percentage of germinated seeds to decrease. Which statement is the best description of the relationship before proposing an explanation?

As salt concentration increases, the percentage of germinated seeds decreases. — B is correct because it states the observable pattern without adding an unsupported mechanism or statistical conclusion. A and C propose explanations that are not established by the stated graph alone, and D makes a statistical claim without statistical analysis.

Two treatment means have overlapping error bars. Which conclusion is supported by the article?

Overlap alone does not automatically prove that the treatments are identical. — D is correct because overlapping error bars do not automatically establish that two treatments are identical. Their interpretation also depends on what the error bars represent, such as standard deviation, standard error, or a confidence interval. A is too strong, B reverses the implication and lacks statistical testing, and C incorrectly assumes the error-bar definition.

For an inheritance experiment, the observed category counts are compared with expected counts. Which procedure is most appropriate for calculating the chi-square statistic?

χ² = Σ[(o − e)²/e] — C is correct because the article defines chi-square as χ² = Σ[(o − e)²/e], comparing observed values o with expected values e. A, B, and D do not use the stated chi-square formula. Even after calculating χ², the conclusion must be based on degrees of freedom and the appropriate critical value.

Which response is a complete scientific argument about an enzyme treatment?

The treatment reduced enzyme activity because the treated group had a lower mean reaction rate, and the altered temperature likely changed the enzyme's shape, reducing effective substrate binding. — B is correct because it includes a claim, evidence, and biological reasoning. The claim is that enzyme activity decreased; the evidence is the lower mean reaction rate; and the reasoning links the result to altered enzyme shape and reduced substrate binding. A and D mainly repeat evidence, while C is an unsupported claim without specific evidence or a biological link.

Which activity best represents the purpose of inquiry-based laboratory work in this course?

Posing questions, identifying variables, collecting data, analyzing patterns, and connecting evidence to biological principles — B is correct because inquiry-based laboratory work makes biological reasoning visible through questions, variables, data collection, pattern analysis, and evidence-based connections to biological principles. A omits investigation and reasoning, C contradicts the article's statement that laboratory work is part of content, and D reverses the proper investigation sequence.

From the free course AP Biology on Lykke

AP Practice 1

Key concepts: AP course principles: clarity, transparency, academic challenge, and student autonomy · AP opposition to indoctrination and emphasis on evaluating multiple perspectives · Evidence-based argumentation and respectful evaluation of others’ arguments · AP Biology course framework and Big Ideas · Evolution as the process driving the diversity and unity of life · Scientific practices: concept explanation, visual representations, questions and methods, data description, statistical tests and data analysis, and argumentation · Chi-square hypothesis testing · Using primary sources so students can evaluate evidence and experiences themselves · Formative assessment through unit Progress Checks · AP course organization, including class sections, join codes, and exam ordering

AP Practice 1

A population can become harder to kill without changing what an individual organism “tries” to do: if heritable variation already exists and an antibiotic eliminates susceptible bacteria, resistant variants leave more descendants. Evolution is a change in the genetic makeup of a population over time, and that process helps explain both the astonishing diversity of life and the shared biological features—the unity—of life.

In this original, unofficial practice task, you will interpret experimental results, construct a visual representation, evaluate competing explanations, and make an evidence-based argument. The biological situation connects directly to the AP Biology course framework:

Big Idea 1: Evolution — natural selection changes allele frequencies and produces adaptation.
Big Idea 2: Energetics — antibiotics impose a survival-related environmental pressure, although the central evidence here concerns inheritance and selection.
Big Idea 3: Information Storage and Transmission — genetic information is transmitted from parents to offspring, allowing resistance to persist.
Big Idea 4: Systems Interactions — organisms interact with their environment, including chemical conditions created by antibiotic exposure.

The task spirals through all six AP Biology science practices: 1. Concept Explanation, 2. Visual Representations, 3. Questions and Methods, 4. Representing and Describing Data, 5. Statistical Tests and Data Analysis, and 6. Argumentation. A strong response does not merely name evolution; it uses data to show a mechanism.

Investigation: antibiotic exposure and allele frequency

Researchers began with genetically variable bacterial populations containing a resistance allele, $R$, and a susceptible allele, $S$. Each culture received the same antibiotic concentration for four generations. A parallel control culture was grown without antibiotic. The table reports the frequency of $R$ among sampled bacteria.

Generation	Control: frequency of $R$	Antibiotic: frequency of $R$
$0$	$0.20$	$0.20$
$1$	$0.21$	$0.31$
$2$	$0.22$	$0.47$
$3$	$0.22$	$0.65$
$4$	$0.23$	$0.79$

These values are a practice dataset, not a quotation from a released AP question. They represent the kind of primary experimental evidence students must interpret directly: identify what was measured, compare treatment and control, and separate an observation from an explanation.

Question 1 — Describe the data. Describe the pattern in the antibiotic-treated culture and compare it with the control. Include numerical evidence.

Worked reasoning: The frequency of $R$ increased from $0.20$ to $0.79$ in the antibiotic treatment, an increase of $0.59$. In the control, it changed only from $0.20$ to $0.23$, an increase of $0.03$. The treated culture therefore shows a much larger increase in resistance-allele frequency across the four generations.

The rewarded reasoning is precise: state the direction of change, give values from the table, and make a treatment-versus-control comparison. Saying “resistance increased” without identifying the population, time interval, or evidence is incomplete Science Practice 4: Representing and Describing Data.

Build the evolutionary representation

Question 2 — Construct a visual representation. Create either a line graph of allele frequency against generation or a population model showing how selection changes the relative abundance of $R$ and $S$. Put generation on the horizontal axis, allele frequency on the vertical axis, use a scale from $0$ to $1$, and include separate, labeled lines for control and antibiotic treatment.

A correct graph reveals more than a list of numbers: the antibiotic line rises steeply while the control line remains nearly flat. In a model, show that antibiotic exposure reduces the relative reproductive success of susceptible bacteria, so descendants increasingly inherit $R$. The antibiotic does not need to create the resistance allele; selection changes the proportion of existing variants.

This required product assesses Science Practice 2: Visual Representations and Big Idea 1: Evolution. You may choose a graph, flow diagram, or annotated population model, but your representation must preserve the causal sequence: heritable variation $\rightarrow$ differential survival or reproduction $\rightarrow$ changed allele frequency.

Evaluate two interpretations

Two students make the following claims:

Claim A: “The antibiotic caused individual bacteria to mutate into resistant bacteria, and those same bacteria became stronger.”
Claim B: “The population already contained heritable variation. Antibiotic exposure favored bacteria carrying $R$, so those bacteria contributed disproportionately to later generations.”

Question 3 — Compare and critique. Which claim is better supported by the dataset? Use evidence from the treatment and control, identify one limitation, and respond to the weaker claim respectfully.

Worked reasoning: Claim B is better supported because the resistance frequency rose sharply under antibiotic exposure but changed little in the control. That pattern is consistent with selection favoring resistant bacteria. Claim A incorrectly treats evolution as a change in an individual during its lifetime; the measured change occurred in the genetic composition of a population across generations. The dataset alone does not prove whether resistance arose by mutation before the experiment or through another inherited mechanism, so the researchers would need additional evidence about initial variation and inheritance.

A respectful scientific response evaluates the argument, not the person: “Claim A does not fit the population-level pattern as well because it describes individual strengthening, whereas the data show a generational shift in allele frequency.” This is Science Practice 6: Argumentation—a claim supported by evidence and biological reasoning, with uncertainty stated honestly.

Statistical analysis and methods

Question 4 — Plan a test. Propose one method that would distinguish whether the observed increase in $R$ is reproducible rather than a chance result. Identify the independent variable, dependent variable, control, and replication.

A strong design would use several independently started control cultures and several independently started antibiotic-treated cultures. The independent variable is antibiotic exposure; the dependent variable is the frequency of $R$ after a specified number of generations; the no-antibiotic culture is the control; and independent cultures provide replication. Researchers could calculate means and variation among replicate frequencies, then apply an appropriate statistical test.

If the experiment tests expected genetic proportions, a chi-square hypothesis test may be appropriate. The listed biology learning objective includes performing chi-square hypothesis testing, using

$$\chi^2=\sum\frac{(o-e)^2}{e},$$

where $o$ is an observed result and $e$ is an expected result. The test does not prove that evolution occurred; it helps evaluate whether differences between observed and expected results are larger than would be likely from chance under the chosen null hypothesis.

Evolution, diversity, and unity

The same logic scales beyond bacteria. Heritable variation supplies differences, natural selection changes their frequencies when environments favor some variants, and common ancestry explains why different organisms retain shared biological features. Repeated divergence produces diversity; inherited molecular systems—such as DNA-based information storage and shared cellular chemistry—reveal unity.

Antibiotic resistance is therefore not an exception to evolution but a compact example of it. The population becomes more resistant because selection alters inherited variation over generations, not because the population makes a conscious decision or because every individual transforms in the same way.

Autonomy and evidence check

Choose your representation and your argument format: a graph with a written explanation, a causal diagram with an oral explanation, or a population model with an evidence table. Then complete an independent evidence check: mark each sentence in your response as observation, inference, or limitation, and revise any inference that is presented as though it were directly measured.

For timing, spend about $8$ minutes interpreting the dataset, $6$ minutes constructing the visual, and $6$ minutes writing the argument and method. Review errors by asking: Did I define evolution correctly? Did I compare treatment with control? Did my visual show allele-frequency change? Did I distinguish evidence from interpretation? Did I evaluate the argument rather than the person?

Progress Checks extend this kind of practice with formative multiple-choice and free-response questions. In AP Classroom, a teacher or AP coordinator creates the class section, and students join with a teacher-provided join code; the purpose is feedback about reasoning, not agreement with a particular viewpoint. AP exam points reward clear, evidence-based biology, while students retain responsibility for evaluating evidence and forming conclusions.