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AP Biology · Unit 1 · Free Response

The FRQ: Six Questions, Six Shapes

Half the exam is six handwritten questions, and every one of them is built from the same short list of parts. Learn the shapes and the verbs and the free response stops being a writing test. It becomes a checklist.

What the free response section looks like

Six questions in 90 minutes, worth half your score. Two long questions at 9 points each, four short questions at 4 points each. You write by hand in a booklet. A formula sheet is provided. Every point is one task. A 4 point question is four things to say, not four paragraphs. Nobody earns a fifth point for writing more.

The six question numbers are six fixed types, and the parts inside each one follow a ladder that barely changes from year to year. Part (a) is nearly always a content question you could answer without reading the experiment. The last part is nearly always "justify" or "support," and that is where the average score falls apart. On recent exams, short questions averaged under 2.5 out of 4 and long questions averaged under 5 out of 9. The describe points get earned. The justify points do not.

This page gives you the six ladders, a translation table for the task verbs, the eight archetypes that make up almost every part, the graphing checklist, and two practice FRQs on Unit 1 content that you score yourself one point at a time.

Zoom out

The Six Ladders

This is the structure the College Board publishes. Memorize the shape of each one and you will know what part (d) is going to ask before you read part (a).

Question	Type	The ladder, part by part
1 9 pts	Interpret and evaluate experimental results	(a) Describe a concept behind the experiment. (b) Identify design elements: the control, the independent and dependent variables, and justify why they were chosen. (c) Analyze the data: describe a trend, compare groups. (d) Predict the effect of a change and justify it.
2 9 pts	Same, with graphing	(a) Describe a concept. (b) Construct a graph from a table, usually with error bars. This is 4 of the 9 points. (c) Analyze the data, often using the error bars to say what is significant. (d) Predict and justify.
3 4 pts	Scientific investigation	(a) Describe a concept. (b) Identify a control or a procedure, or state the null hypothesis. (c) Predict the result. (d) Justify the prediction.
4 4 pts	Conceptual analysis	(a) Describe. (b) Explain a mechanism. (c) Predict the effect of a disruption. (d) Justify.
5 4 pts	Analyze a model or visual	(a) Describe one part of the model. (b) Explain a relationship between two parts. (c) Trace, mark, or identify something on the model. (d) Explain what the model shows about a bigger idea.
6 4 pts	Analyze data	(a) Describe the data (a value, a trend). (b) Describe a second feature of the data (often the variation, not the mean). (c) Use the data to support or refute a hypothesis. (d) Explain how the result connects to a biological principle.

The move Before you read the stimulus, read every part's verb and write the ladder in the margin: D, I, P, J. Now you know what each part costs and what shape of sentence earns it. Then read the experiment hunting for the things the ladder needs: the control, the variable, the trend.

Zoom in

The Verb Is the Rubric

Same move as the multiple choice: find the verb first. On the FRQ the verb is not a hint. It is the literal scoring criterion. Readers are trained on these definitions, and the Chief Reader reports list "confusion between identify and describe" and "restating the stimulus instead of using biology" as point losses every single year.

The verb says	The point requires	What loses it
Identify	Name it. One phrase. "The control is the tube with substrate and no enzyme."	Writing three sentences. Naming a held constant condition when asked for the control group.
Describe	Give characteristics of the thing. What it is, what it does. No "why" required.	Vagueness ("ribosomes make amino acids"). Describing the wrong step of a process.
Explain	Give the mechanism that connects A to B. Cause, then effect, with the biology in between.	Restating that A and B are related without the step in between. Restating the stimulus.
Predict	State a specific outcome with a direction. "The rate will decrease." "The cell will gain mass."	"It will be affected." "More" or "fewer" when a specific value is possible (zero copies, not "fewer").
Justify	Give the reasoning that supports a claim or prediction you already made. Evidence, then mechanism.	A second prediction instead of a reason. Reasoning with no reference to the data or the scenario.
Support a claim	Point to specific data ("group 2 produced 18.6 mg/g vs 4.1") and say why the data mean what you say they mean.	Evidence with no reasoning. Reasoning with no numbers. Using the wrong figure when the question names one.
Calculate	Show the setup, the arithmetic, the unit, and the sign. Box it.	No units. Wrong sign on ψ_S. Celsius instead of kelvin. Dividing nucleotides by 2 to get amino acids.
Construct a graph	Four separate points: labeled axes with units, a scale that fits the data, correct plotting, error bars or a key. See the checklist below.	Missing units. A y axis that cuts off the top bar. Asymmetric error bars.
State the null hypothesis	"There is no difference" or "X has no effect on Y."	Writing the experimental hypothesis ("X will increase Y").
Determine / Evaluate	Reach a conclusion and say what in the data got you there.	A conclusion with no data behind it.

The single most important habit

Underline the verb in every part before you write. Then write one sentence per point that does exactly what the verb says. If the part is worth 1 point and asks you to "identify," your answer is a phrase. If it asks you to "justify," your answer is two sentences: the evidence, then the why. Match the length to the verb, not to how much you know.

The thought process

The FRQ Chain: From Reading the Question to Writing the Point

Same idea as the causal chains on the strategy pages. On a multiple choice question you run the chain from the clue to the concept to the answer. On an FRQ you run it from the verb to the tool to the sentence. If you cannot say each link out loud, you are not ready to write.

Read the parts first, not the stimulus. Underline the verb in (a), (b), (c), (d). Write the ladder in the margin: D, I, P, J. Note the points. Now you know what each part costs.therefore
Pick the tool for each part. Describe means archetype 1. Identify a control means archetype 2. Construct means the graph checklist. Predict and justify means archetypes 6 and 7, two sentences, direction then mechanism. You have decided the shape of every answer before reading a word of the experiment.therefore
Now read the stimulus, hunting. You are looking for exactly what the ladder needs: the control group, the variable they changed, the thing they measured, the trend in the table, the constraint the passage volunteers ("permeable to water but not sucrose"). Sort as you go: amber for what this question invented, blue for what you already knew.therefore
Conjure the class content. Ask which of the 15 concepts this is secretly about. A membrane spanning region made of nonpolar amino acids is hydrophobic interactions (Unit 1, Concept 5) and R groups (Concept 11). A mutation that swaps in a charged amino acid is tertiary structure (Concept 12) and shape determines function (Concept 13). Say the concept's one line definition to yourself. That line is going to be the mechanism in your justify.therefore
Build the causal chain for the scenario. Change → first effect → next effect → outcome. Charged R group in the nonpolar region → unfavorable interactions with the fatty acid tails → that region misfolds or fails to sit in the membrane → channel shape changes → water no longer passes → transport drops. The predict point is the last link. The justify point is the links in between.therefore
Write one sentence per point. The sentence does what the verb says. Direction word if it is a predict. A number from the table if it is a support. The mechanism from step 4 if it is an explain or justify. Then stop.therefore
Check, then leave. Does each sentence match its verb? Is there a direction word where one belongs? A unit on every number? Did you use the figure the question named? Yes to all, move to the next part. Do not add a sentence "just in case." It cannot earn a point and it can cost you time.

Where the chain breaks for most students Between step 3 and step 4. They read the stimulus, feel like they understand it, and start writing about the stimulus. The reader calls that "restating the prompt" and gives zero. Step 4 is the one that turns the scenario into biology. If you skip it, every justify point is gone.

The chain, run on Practice A below

Link	What you actually think
1. Verbs	(a) Describe, 1. (b) Explain, 1. (c) Predict, 1. (d) Justify, 1. Four sentences total, two of them with a mechanism.
2. Tools	(a) giveaway describe. (b) explain a mechanism. (c) predict the disruption, needs a direction. (d) justify, evidence then mechanism.
3. Hunt	Amber: aquaporin is a channel, the membrane spanning region is mostly nonpolar, a mutation puts a glutamic acid there. Blue: R groups, tertiary structure, hydrophobic interior of the bilayer.
4. Concepts	Nonpolar region in a nonpolar environment is hydrophobic interactions (U1 C5). Swapping one R group is primary structure, and its effect on the fold is tertiary (U1 C11, C12). Shape determines function (U1 C13).
5. Chain	Charged R group in the nonpolar region → repelled by fatty acid tails → region misfolds or pulls out of the membrane → channel shape changes → water cannot pass → transport falls.
6. Sentences	(a) Interactions between R groups: hydrogen bonds, ionic bonds, hydrophobic interactions, disulfide bridges. (b) Nonpolar R groups are stable among the nonpolar tails; polar or charged ones are not. (c) Transport decreases. (d) Charged R group, unstable in the core, misfold, shape, function.
7. Check	Direction in (c)? Yes, "decreases." Mechanism in (b) and (d)? Yes. Done. Four points, about six sentences.

The patterns

Eight Archetypes That Make Up Almost Every Part

Across the released exams, the parts repeat. Here are the eight shapes with a Unit 1 example of each, a model answer that earns the point, and the specific way students lose it.

1. The giveaway describe

Part (a) of almost every question A one point content question on a basic idea, often straight from Unit 1, attached to an experiment that does not matter yet.
Example: "Describe the role of water in the hydrolysis of ATP."
Earns it: "Water is a reactant. It is split, and its parts are added across the covalent bond between the terminal phosphates, breaking the bond and releasing energy."
Loses it: Naming a hydrogen bond. Describing dehydration synthesis. Saying "water helps the reaction" with no role stated. The 2024 readers flagged "hydrogen or phosphodiester bonds instead of covalent bonds" as a common miss on exactly this part.

2. Name the control, then say why

Two points that travel together Example: Soybeans grown in nitrogen free sand with four treatments: nothing added, nitrogen fixing bacteria, ammonium fertilizer, phosphate fertilizer. "Identify the control group and justify its use."
Earns it: "The control is the group with nothing added. It shows how much leaf protein the plants make with no nitrogen source, so any increase in the other groups can be attributed to the treatment."
Loses it: Naming a controlled variable ("all plants got the same light") instead of the control group. Justifying with "baseline" or "to compare" without saying what the control isolates.

3. Variables and the null hypothesis

One phrase each Example: "Identify the independent and dependent variables in the soybean experiment. State the null hypothesis."
Earns it: "IV: the nutrient treatment added to the sand. DV: leaf protein in mg per g. Null hypothesis: the nutrient treatment has no effect on leaf protein."
Loses it: Writing the experimental hypothesis for the null ("bacteria will increase protein"). Swapping IV and DV. Listing the thing measured as the IV.

4. Build the graph

Four points, four separate checks On Question 2 the graph is worth as much as the rest of the question combined. Readers score four things independently: axes labeled with units, a scale that fits all the data, correct plotting, and error bars drawn correctly or a key where needed. You can get 3 of 4 with a perfect graph that forgot "°C."
Loses it: No units. A y axis that tops out below the tallest bar. Error bars that are uneven above and below the mean. Bar graph for a continuous variable or a line graph for categories.

5. Describe the data, then use the error bars

Trend first, significance second Example: "Describe the effect of the treatments on leaf protein. Determine whether the bacteria and ammonium groups differ significantly."
Earns it: "Groups given a usable nitrogen source (bacteria, 18.6 mg/g; ammonium, 19.2 mg/g) made about four times the protein of groups without one (4.1 and 4.4 mg/g). The ±2 SE bars for the bacteria and ammonium groups overlap, so the difference between them is not statistically significant."
Loses it: Saying ammonium "worked better" because 19.2 is bigger than 18.6. Ignoring the error bars the stem told you about. Describing one group without comparing.

6. Predict the disruption

A mutation, a pH change, a heat shock, a missing nutrient Example: "A mutation replaces a nonpolar amino acid in a protein's hydrophobic core with a charged one. Predict the effect on the protein's function."
Earns it: "The protein's function will decrease or be lost."
Loses it: "The protein will be affected." No direction. Predicting the mechanism ("the R groups will repel") instead of the outcome; that is the justify point, not this one.

7. Justify or support, in two sentences

Evidence, then mechanism The template: "The data show ___ . This happens because ___ ." The first blank is a number or an observation from the scenario. The second blank is biology from your notes.
Example: "Justify your prediction about the mutation."
Earns it: "A charged R group in the hydrophobic core cannot form the hydrophobic interactions that hold the tertiary structure, so the protein folds differently. Because the shape of a protein determines its function, the altered fold changes or destroys the active site or binding site."
Loses it: Restating the scenario. "It will denature" with no link to the interactions or to function. A second prediction instead of a reason.

8. Calculate, and read the model

Show work, keep the unit, read the drawing Calculation example: "The standard deviation of leaf protein in the bacteria group is 1.4 mg/g with n = 8. Calculate the standard error of the mean." Earns it: "SE = SD ÷ √n = 1.4 ÷ √8 = 1.4 ÷ 2.83 = 0.49 mg/g." Loses it: dividing by n instead of √n, no unit, rounding before the last step.
Model example: A drawing of an amino acid. Earns it: identifying the amino group, the carboxyl group, and the R group, and stating that the R group is the only part that varies. Loses it: calling the whole molecule polar without looking at the R group. Treating a drawing of two monomers joined by a covalent bond as "hydrogen bonded."

Worth four points on Question 2

The Graph Checklist

What a four point graph looks like

Check these four, in this order, before you move on

Axes labeled with units. Independent variable on x. Dependent on y. "Mean change in mass (g)" not "mass." "Temperature (°C)" not "temp."
Scale fits the data. Look at the biggest number in the table, add its error bar, and make sure the axis goes past it. Even intervals.
Plot correctly. Bar graph for categories or treatment groups. Line graph for a continuous variable like time or concentration. Points where the table says.
Error bars or key. If the table gives SE or SD, draw bars the same distance above and below each mean. If the stem says ±2 SE, double it. More than one series, add a key.

The trap Students draw a beautiful graph and lose two points for "protein" with no unit and a y axis that stops at 19 when the top error bar reaches 20. The graph points are the easiest points on the exam to get all of, and the easiest to drop one of.

What to watch for

Six Ways to Lose a Point You Knew

✗Answering the wrong verb. Explaining when asked to identify. Predicting a mechanism when asked to predict an outcome. Describing the stimulus when asked to justify.

✗Restating the stimulus. "Buffelgrass increased after the fire because the fire created more space for buffelgrass." That is the scenario, repeated. The point wanted competition, resource availability, and a reason.

✗No direction. "The rate changes." "The cell is affected." Every predict point needs an arrow: up, down, in, out, faster, slower.

✗Evidence without reasoning, or reasoning without evidence. A support point is two halves. Cite the number, then say why it means what you claim.

✗Significance by eyeball. A taller bar is not a significant difference. Overlapping error bars means you cannot claim one. Say "the error bars do not overlap" out loud.

✗Imprecise words. "Hydrogen bond" for the bond hydrolysis breaks. "Adaptation" for every evolutionary process. "Opposite polarities attract." "Baseline." Readers are trained to see these as not knowing.

✓The point: one sentence that does exactly what the verb says, with a direction word where one belongs, a number where one is available, and the mechanism named.

Practice FRQ A · Short · Conceptual analysis · 4 points

One Charged Amino Acid in the Membrane

Run the chain first: verbs, tools, hunt, concepts, chain, then sentences. Write your answer to each part in the box. Then reveal the rubric for that part and check the box only if your answer actually does what the rubric says. Be a hard grader. The exam will be.

Aquaporin is a channel protein embedded in the plasma membrane that allows water to cross rapidly. The portion of the protein that spans the hydrophobic interior of the membrane is composed mostly of amino acids with nonpolar R groups. A mutation replaces one of these nonpolar amino acids with glutamic acid, which has a negatively charged R group at cellular pH.

(a) Describe the interactions that stabilize the tertiary structure of a protein. 1 point

1 point: Interactions between R groups, such as hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges (any two named, attributed to R groups, earns it).

Not enough: "Peptide bonds hold it together." Those are primary structure. Trap: listing bonds without saying they are between R groups. The verb was describe, the target was tertiary.

(b) Explain why the membrane spanning region of the protein consists mostly of amino acids with nonpolar R groups. 1 point

1 point: The interior of the bilayer is made of nonpolar fatty acid tails, so nonpolar R groups interact favorably with it (hydrophobic interactions) and keep the protein anchored, while polar or charged R groups would be unstable there.

Not enough: "Because the membrane is hydrophobic." That names the environment but not the interaction. The point needs nonpolar with nonpolar as the mechanism.

(c) Predict the effect of the mutation on the transport of water through the aquaporin. 1 point

1 point: Water transport will decrease (or the channel will stop working).

Not enough: "The protein will be affected." No direction, no point. Also not the point: a paragraph on misfolding. That is part (d). Save it.

(d) Justify your prediction. 1 point

1 point: A charged R group in the nonpolar region is destabilizing: it cannot form hydrophobic interactions with the tails, so that region misfolds or fails to stay in the membrane. The altered tertiary structure changes the shape of the channel, and because structure determines function, water no longer passes through normally.

Not enough: "The charged amino acid will make it not work." The readers want the chain: unfavorable interaction, changed fold, changed shape, lost function.

Your score on A0 / 4

Practice FRQ B · Long · Experimental results with graphing · 9 points

Where Does the Nitrogen Come From?

This one has a graph in it. Draw it on paper, then grade it against the four checks. The rest of the parts work like Practice A.

Soybean seedlings were grown for four weeks in sterile sand containing no nitrogen compounds. All plants received normal air (about 78 percent N₂), water, and light. Four groups of eight plants each received a different treatment. At the end of four weeks, leaf protein was measured. Mean leaf protein and standard error (SE) are shown in Table 1.

Table 1. Leaf protein after four weeks

Group	Treatment	Mean leaf protein (mg/g)	SE (mg/g)	n
1	Nothing added	4.1	0.2	8
2	Nitrogen fixing bacteria added	18.6	0.5	8
3	Ammonium (NH₄⁺) fertilizer added	19.2	0.4	8
4	Phosphate (PO₄³⁻) fertilizer added	4.4	0.25	8

(a) Describe why nitrogen is required for a plant to synthesize proteins. 1 point

1 point: Proteins are polymers of amino acids, and every amino acid contains nitrogen in its amino group, so without a nitrogen source amino acids (and therefore proteins) cannot be made.

Not enough: "Plants need nitrogen to grow." The point is the amino group. Name the part of the molecule that holds the nitrogen.

(b) Construct an appropriately labeled graph of the data in Table 1, including error bars of ±2 SE. 4 points

Draw it on paper. Then check each of the four graph points against your drawing.

1 point, axes: x axis labeled with the treatment groups and y axis labeled "Mean leaf protein (mg/g)," with the unit. 1 point, scale: y axis reaches at least 20.0 mg/g (the ammonium mean plus 2 SE) with even intervals. 1 point, plotting: four bars at 4.1, 18.6, 19.2, 4.4, each over the correct treatment. 1 point, error bars: drawn ±2 SE, which is ±0.4, ±1.0, ±0.8, ±0.5, the same distance above and below each mean.

Model graph

Error bars are ±2 SE. Bar graph because the treatments are categories, not a continuous variable.

(c) (i) Identify the control group. (ii) Using the error bars, determine whether groups 2 and 3 differ significantly in leaf protein, and explain your reasoning. 2 points

1 point (i): Group 1, nothing added. 1 point (ii): The ±2 SE bars for group 2 (17.6 to 19.6) and group 3 (18.4 to 20.0) overlap, so the difference is not statistically significant.

Not enough for (i): "Keeping light and water the same." That is a controlled variable, not the control group. Not enough for (ii): "Ammonium produced more." A bigger mean is not significance. Do the overlap test and say the result.

(d) A fifth group is given both nitrogen fixing bacteria and phosphate fertilizer. (i) Predict the mean leaf protein of this group relative to group 2. (ii) Justify your prediction. 2 points

1 point (i): About the same as group 2 (roughly 18 to 19 mg/g); no significant increase. 1 point (ii): The data show nitrogen was the limiting nutrient for protein synthesis (groups with a nitrogen source made far more protein) and phosphate was not (group 4 matched the control). Once the bacteria supply usable nitrogen, adding phosphate does not add protein, because phosphorus is used for nucleic acids and ATP, not for amino acids.

Not enough for (ii): "Phosphate does not help." Point to the data (group 4 vs group 1) and give the biology (phosphorus is not in amino acids).

Your score on B0 / 9

The golden rule

One point, one sentence, one verb. Underline the verb, write the sentence that does what it says, include the direction and the number if there is one, name the mechanism, and stop. Then go to the next part.

Back to the content

Every part (a) on this page came straight from the 15 concepts. If one of them was fuzzy, that is where to go.

Unit 1 strategy Unit 1 practice quiz