Lesson Q1 L1 – Learning to Test Ideas: Controlled Experiments

Lesson Overview

Quarter 1 · Unit A: Life’s Chemistry and Cells in the Garden · Week 1 · AP Biology (Grades 10–12) · Lesson length: 50 minutes

Essential Question: How can we tell whether a change we make actually causes an environmental result?

Lesson Focus: Suppose Phoenix planted street trees in one neighborhood and the next summer that neighborhood was 2 °C cooler. Did the trees do it?

Why It Matters: Every AP Biology lab and FRQ 3 (Scientific Investigation) asks students to identify the independent and dependent variables, the controls, and a testable question (skills 3.A–3.C). This lesson starts the year-long garden investigation.

Teacher Note: Keep the urban-tree scenario open and unresolved during Engage; the productive uncertainty is the point. In Phoenix, shade from street trees changes the temperature and water loss that plants and people experience, a living example of environmental effects on phenotype (Topic 5.5).

Source: Adapted from Seeds of Science, Lesson 1 “Learning to Test Ideas” and Chapter 2. The urban-tree scenario, dog-vitamin thought experiment, DRY MIX tip, and sports-drink assessment are the author’s; the Phoenix framing and AP items are new.

Standards & Learning Targets

Standards Alignment

AP Biology CED (Fall 2025) — Topics & Learning Objectives: Topic 5.5 Environmental Effects on Phenotype (Unit 5: Heredity) — 5.5.A: Explain how the same genotype can result in multiple phenotypes under different environmental conditions.

AP Biology Science Practices / Skills: 3.A (Questions and Methods) — Identify or pose a testable question based on an observation, data, or a model; 3.B (Questions and Methods) — State the null hypothesis or predict the results of an experiment; 3.C (Questions and Methods) — Identify experimental procedures that align with the question, including identifying dependent and independent variables and identifying and justifying appropriate controls

AP Biology Big Ideas: Big Idea 4 — Systems Interactions (SYI); Big Idea 3 — Information Storage and Transmission (IST)

Student Learning Targets

Learning Targets — students will be able to

Distinguish an experiment from an observation or demonstration

Identify the independent, dependent, and controlled variables and the control group in an environmental study

Explain why a control group and an adequate sample size make evidence trustworthy

Key Vocabulary

experiment · observation · independent variable · dependent variable · controlled variable · control group · treatment group · sample size · fair test

Materials & Teacher Prep

Safety: Carry microscopes with two hands; never aim a mirror at the sun; let lamp housings cool. Phoenix heat: normal daily highs are about 105 °F in August, 100 °F in September and 89 °F in October (NOAA 1991–2020). Schedule field work early, use shade and short blocks, require water for everyone, follow school HeatRisk guidance, and stop at the first sign of heat illness. Sun-heated tools, pavement and metal can burn skin. Sources: NSTA, Safety in the Science Classroom (2013); CDC, Heat and Your Health; CDC, Sun Safety; NOAA NCEI 1991–2020 Phoenix normals. See the Safety & Fact-Check Log.

Lesson Flow & Timing

Phase 1 · Engage — The Hook

Teacher Talk

Tell students the scenario below is hypothetical, then ask them to picture it happening here in Phoenix.

PCM: Curiosity. “A city plants trees along streets in one neighborhood to reduce heat. The next summer that neighborhood averages 2 °C cooler than the summer before. The city announces a citywide planting program. Before it spends millions, should we accept the conclusion? What is missing?” Give two minutes of silent notebook writing, take a few responses, and do not resolve it yet. Then run the rigged ball drop (drop the pickleball from higher, then slip a notebook under the tennis ball) and let students name what is unfair. Before teams start, introduce the term experiment so students can use it accurately; Explain gives the formal definition.

Ask Students

“What would you need to see before you believed the trees caused the cooling?” “What did I do that made the ball test unfair?” “Is looking at a leaf under a microscope an experiment? Why or why not?”

PCM Differentiation

Thinker Students: List every factor other than trees that could explain a 2 °C drop (a cooler summer, monsoon timing, new paving). Which would a good study have to hold constant?

Harmonizer Students: Phoenix residents in neighborhoods with few trees often live with the most heat. Why would those families want the city to know for sure that trees work before choosing where to plant?

Phase 2 · Explore — Kagan Cooperative Activity

Cooperative Structure

Kagan structure: Think-Pair-Share. Every student commits to a written design before hearing a partner, so the quieter voices do the thinking too (See the Teaching Reference for the structure’s steps.) Post independent variable, dependent variable, controlled variable, control group, and sample size on the board now; students will need them during the work, and Explain formalizes them.

Step-by-Step

• Step 1 — Think alone (3 min): Pose the author’s thought experiment: “A veterinarian wants to know whether a daily vitamin improves the health of dogs. Design an experiment that would give trustworthy evidence.” Each student writes the independent variable, dependent variable, control group, and two controlled variables.

• Step 2 — Pair (4 min): Partners compare designs and agree on one improvement each partner’s design needs.

• Step 3 — Share (6 min): Call on four pairs. Record their independent variables, dependent variables, and controls in a three-column chart.

• Step 4 — Sample-size debrief (4 min): Ask “How many dogs, and why?” Establish that larger samples increase confidence but cost time and money, a trade-off that returns when teams decide how many radishes to plant.

Teacher Moves During Explore

Listen for designs without a comparison group and ask, “Compared with what?”

Push for one independent variable: “If you change the vitamin and the food, what caused the change?”

Note that a medical control group gets a placebo, but a garden control group simply gets no treatment and everything else the same

Phase 3 · Explain — Direct Instruction

Mini-lesson — Experiments, Controls, and Variables. Teacher move: Return to the urban-tree scenario and pull vocabulary out of the student designs; students record the points in their notebooks.

Experiment: a procedure in which a researcher deliberately changes one variable to see its effect on another; without manipulation it is an observation

Independent vs. dependent variable: the independent variable is what we change (street trees present or absent); the dependent variable is what we measure (air or surface temperature); memory tip DRY MIX: Dependent–Responding–Y-axis, Manipulated–Independent–X-axis

Control group: a comparable neighborhood that did not get trees, measured over the same summer with the same instruments; it shows what would have happened anyway

Controlled variables: building density, pavement type, elevation, measurement time of day, and instrument type are kept the same

Why it matters in Phoenix: impervious surfaces such as roads and parking lots change how water and heat move, so city decisions need evidence from fair comparisons

Key Message: An experiment changes one thing on purpose and compares the result to a control group that is identical in every other way. Without the control, we cannot claim cause and effect.

Check for Understanding — Ask Students

“What is the independent variable in the urban-tree study?” “Why could the city’s before-and-after comparison mislead them?” “What makes a sample size “big enough”?”

Phase 4 · Elaborate — Student Product & Differentiation

Student Product

Students restate the garden challenge in their notebooks (“With a partner, you will design and run a controlled experiment in two growing cells: one treatment, one control”) and list one variable they are curious about testing, with a sentence explaining why it interests them.

Differentiation

Support (scaffolded entry): Provide a fill-in frame: “If I change ___, I will measure ___, my control group will be ___, and I will keep ___ the same.” Model it once with the urban-tree study.

AP Extension: Redesign the city study as a true experiment with replication: how many neighborhoods, how would you assign trees randomly, and what would you measure at what times of day? Identify one ethical or political constraint on random assignment.

Multilingual Learners: Post a four-column word wall (change / measure / compare / keep the same) with icons; allow notebook answers in the home language with key terms labeled in English.

Phase 5 · Evaluate — Closure, Exit Ticket & Assessment

Exit Ticket

1. What is the difference between an experiment and an observation?

1. Why is a control group essential?

1. A sports drink company surveyed 50 athletes who drink its product and 80% said they felt stronger. Identify two problems with this study and describe a better design.

Answer Key / Look-Fors: (1) An experiment deliberately changes a variable; an observation records what happens without manipulation. (2) It provides a baseline that shows what would happen without the treatment, so a difference can be attributed to the treatment. (3) Problems: no control group, self-report bias, no random assignment, athletes already chose the drink. Better: randomly assign athletes to the drink or a look-alike placebo, measure a performance variable (sprint time), keep training constant, and use a large sample.

AP Exam Practice

(MCQ) A student places three tomato seedlings in a shaded bed and three in a sunny bed and measures their heights after four weeks. Which change would most improve the validity of the conclusion? (A) Measuring the plants every day instead of once (B) Increasing the number of seedlings in each bed and assigning them randomly (C) Using a different plant species in each bed (D) Adding fertilizer to the shaded bed only

Answer & Rationale: (B). Replication and random assignment reduce the effect of individual variation. (A) adds data but not validity; (C) and (D) introduce a second independent variable.

Expanding Circles

How does this connect to… Self — What is a claim in an ad you saw this week that needs a control group? • Classroom — How will our class keep every garden test a fair test? • School — What school decision (a new schedule, a shade structure) could be tested with a control group? • Community — Why would the City of Phoenix want controlled evidence before planting trees? • World — How do control-group trials improve food security worldwide?

Formative Assessment

Formative Assessment (to sort students, use the restated garden challenge in each notebook, the exit-ticket critique of the sports-drink survey, and the AP item)

Meets (3): Correctly identifies IV, DV, control group, and at least two problems in the sports-drink study and proposes a randomized, controlled redesign.

Approaching (2): Identifies the variables but the redesign lacks a comparable control group or a reasonable sample size.

Not Yet (1): Cannot separate IV from DV; reteach with the ball-drop demo and the DRY MIX chart before Lesson 1.2.

Extend & Looking Ahead

Extension: Students find a product or policy claim online and post the question “Where is the control group?” with a one-sentence critique. Teacher reference: the Chapter 2 sidebar “Is It Really an Experiment?” from Seeds of Science.

Looking Ahead: Lesson 1.2 looks at water, the molecule every garden experiment depends on.