Experimental Design
9th Grade Biology · Self-Paced Learning Module
Video Lessons
3 Videos🎬 Upload Your Own Videos Optional
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Video
Nature of Science — Amoeba Sisters
Scientific method, variables (IV, DV, controlled), hypothesis, control group, and graphing data
▶ Open on YouTube ↗CER (Claim, Evidence, Reasoning) — Amoeba Sisters
How to write a scientific explanation using the Claim, Evidence, and Reasoning framework
▶ Open on YouTube ↗General Lab Safety — Amoeba Sisters
Proper lab attire, PPE, disposal of materials, heating precautions, and essential safety rules
▶ Open on YouTube ↗Lesson Slides
10 SlidesConcept Explorer
Interactive ReferenceVariables
The factors in an experiment that can change. Identifying them correctly is the foundation of a valid scientific study.
What You Change
The ONE factor a scientist deliberately changes to test its effect. Also called the manipulated variable. It goes on the X-axis of a graph.
Example: Amount of fertilizer given to plants
What You Measure
The factor that is observed and measured — it "depends" on the IV. Also called the responding variable. It goes on the Y-axis.
Example: Height of plants after 2 weeks
What You Keep the Same
All other factors held constant throughout the experiment so they don't affect results. Without controls, you can't know which variable caused the outcome.
Examples: Amount of water, light intensity, pot size, type of soil
IDAT — I Do A Test
I = Independent (what I change)
D = Dependent (what I measure)
A = All other things kept the same
T = Test (one variable at a time)
Only change ONE variable at a time or results are invalid!
Example: "If the amount of fertilizer given to plants is increased, then their height will increase, because fertilizer provides nutrients that fuel plant growth."
Control Group
The "standard" group that receives no treatment — the baseline for comparing experimental results.
What is a Control Group?
The group that is NOT exposed to the independent variable. It provides a baseline to compare against the experimental group(s) and shows what results look like without any manipulation.
vs. Experimental Group
The experimental group receives the independent variable treatment. Everything else is kept identical to the control group. The difference in outcomes is attributed to the IV.
Plant Fertilizer Study
Control group: Plants given 0g of fertilizer (water only)
Experimental groups: Plants given 5g, 10g, 15g of fertilizer
Comparing each group to the control tells us whether fertilizer actually caused a difference.
Validity & Reliability
Valid: The experiment actually tests what it claims to test (proper controls)
Reliable: Results are consistent when repeated (multiple trials)
Without a control, you cannot claim causation — only correlation.
Graphing & Data Visualization
Graphs are visual tools for communicating data patterns clearly. Choosing the right graph type matters.
Continuous Data Over Time
Best for showing trends over time or when both variables are continuous numbers.
Example: Plant height measured daily over 4 weeks
X-axis = Time (IV) · Y-axis = Height (DV)
Comparing Categories
Best for comparing discrete categories or groups. Each bar represents one group or category.
Example: Average height of plants given 0g, 5g, 10g fertilizer
X-axis = Fertilizer amount · Y-axis = Height
Correlation Between Variables
Best for showing the relationship (correlation) between two continuous variables. A trend line (line of best fit) shows direction of relationship.
Example: Study hours vs. test score
Every Graph Must Have:
- Title (descriptive: "Effect of X on Y")
- Axes labeled with units
- Intervals that are equal and consistent
- Legend (if more than one data set)
- Scale that fills the graph space
Example: "The Effect of Fertilizer Concentration on Plant Height After 14 Days"
Measurements & SI Units
Accurate, precise measurements in standard units are essential for reproducible science.
Two Different Things
Accuracy: How close a measurement is to the true value
Precision: How consistent/repeatable measurements are
Ideal: both accurate AND precise. You can be precise but wrong (systematic error).
Standard Units in Science
- Length: meter (m), cm, mm, km
- Mass: gram (g), kg, mg
- Volume: liter (L), mL, cm³
- Temperature: Celsius (°C) or Kelvin (K)
- Time: seconds (s), minutes, hours
Using the Right Tool
- Ruler/meter stick — length
- Triple-beam/digital balance — mass
- Graduated cylinder — liquid volume
- Thermometer — temperature
- Stopwatch — time
- pH meter/strips — acidity
Meniscus Rule
Water in a graduated cylinder forms a curved surface called a meniscus. Always read the volume at the bottom of the meniscus at eye level. Parallax error occurs when you read from above or below.
Claim · Evidence · Reasoning (CER)
The three-part framework scientists use to communicate conclusions drawn from data.
Your Answer to the Question
A concise statement that answers the experimental question. Does NOT include data or explanation — just the direct answer.
Example: "Increasing fertilizer concentration increases plant height."
Specific Data That Supports It
Specific, quantitative data from the experiment. Must include numbers and units. Reference the data table or graph directly.
Example: "Plants given 10g of fertilizer grew 24 cm, while control plants (0g) grew only 11 cm."
Why the Evidence Supports the Claim
Connects the evidence to the claim using scientific principles. This is the "because" — explaining the mechanism behind the data.
Example: "Fertilizer provides nitrogen and other minerals required for protein synthesis and cell growth in plants."
What to Avoid
- ❌ Claim includes data ("because the numbers showed…")
- ❌ Evidence is vague ("the plant grew more")
- ❌ Reasoning restates the evidence instead of explaining it
- ❌ No scientific vocabulary in reasoning
- ✅ All three parts clearly separated and connected
Claim: Increasing light intensity increases the rate of photosynthesis.
Evidence: At 100% light intensity, the plant produced 0.62 mol/hr of glucose, compared to only 0.18 mol/hr at 25% intensity.
Reasoning: Light energy is required to power the light-dependent reactions in chloroplasts. More light provides more energy to split water molecules and generate ATP and NADPH, increasing the rate at which the Calvin Cycle can produce glucose.
🦺 Lab Safety
Safety is not optional. Every person in the lab is responsible for their own safety AND the safety of others.
👓 Personal Protective Equipment (PPE)
- Safety goggles must be worn whenever using chemicals, heat, or glassware
- Lab coat or apron protects clothing from spills
- Gloves required when handling hazardous chemicals or biological materials
- Closed-toe shoes only — no sandals or open-toed footwear in lab
- Tie back long hair and secure loose clothing before starting
⚗️ Chemical Safety
- Never smell chemicals directly — waft fumes toward you with your hand
- Never taste any substance in the lab (even if it looks like food)
- Read the label TWICE before using any chemical
- Add acid to water — NEVER water to acid (exothermic reaction)
- Dispose of chemicals only in designated waste containers
- Know the location and use of the eyewash station
🔥 Heat & Fire Safety
- Never heat a sealed container — pressure can cause explosion
- Point the opening of heated test tubes away from people
- Use heat-resistant gloves or tongs when handling hot objects
- Keep flammable materials away from open flames
- Know the location and operation of the fire extinguisher
- If clothing catches fire: Stop, Drop, and Roll
🔪 Glassware & Sharp Instruments
- Inspect glassware for cracks or chips before use — discard damaged items
- Never use chipped or broken glassware
- Carry glassware upright and with two hands
- Cut away from yourself when using scalpels or dissection tools
- Broken glass goes in a designated sharps container — NOT regular trash
🧫 Biological Safety
- Treat all biological specimens and cultures as potentially hazardous
- Wash hands thoroughly with soap before AND after lab activities
- Never remove biological samples from the laboratory
- Dispose of biological waste in biohazard bags or designated containers
- Report any cuts, punctures, or spills involving biological material immediately
📋 General Lab Rules
- No food or drink in the laboratory — ever
- Never run, push, or engage in horseplay in the lab
- Do not perform unauthorized experiments
- Clean up your workspace completely before leaving
- Wash hands before leaving the lab even if you wore gloves
- Alert teacher immediately if you feel unwell during lab
Key Vocabulary
Tap to flipKnowledge Check
10 QuestionsAssignment
6 Parts · 50 Points TotalExperimental Design — Unit Assignment
Complete all six parts using what you learned from the videos, slides, and concept explorer. Type answers directly in the boxes. Use the Print button to submit or follow your teacher's instructions.
Key Concepts Reference
Variables
IV = what you change · DV = what you measure · Controlled = kept the same
Control Group
Baseline with no treatment · Compare experimental groups against it
Graphing
IV on X-axis · DV on Y-axis · Title, labels, units, scale (TAILS)
Measurements
SI units · Accuracy vs. precision · Right tool for each measurement
CER
Claim (answer) + Evidence (specific data) + Reasoning (scientific explanation)
Lab Safety
PPE always · Waft chemicals · Goggles on · Know emergency equipment
Multiple Choice — Core Concepts
10 pts ▼Select the best answer for each question (2 pts each).
Identify Variables — Scenario Analysis
9 pts ▼Matching — Terms & Definitions
8 pts ▼Match each term to its correct definition.
Term
Definition
A. A testable prediction written in "if…then…because" format
B. The group that receives no experimental treatment (baseline)
C. The variable that is measured; responds to the IV
D. Consistency of repeated measurements
E. A framework: Claim + Evidence + Reasoning
F. The curved surface of a liquid in a graduated cylinder
G. A trend line on a scatter plot showing the data's general direction
H. A fake treatment given to a control group in human studies
Graph Construction & Analysis
8 pts ▼| Temperature (°C) | Reaction Rate (products/min) |
|---|---|
| 10 | 4 |
| 20 | 12 |
| 30 | 22 |
| 37 | 28 |
| 45 | 16 |
| 55 | 3 |
Write a CER — Scientific Explanation
10 pts ▼▶ View Scoring Rubric
| Component | Full Credit | Partial Credit | No Credit |
|---|---|---|---|
| Claim (2 pts) | Direct, concise answer; no data included | Answers but is vague or partially includes data | Missing, restates question, or includes data |
| Evidence (4 pts) | Specific, quantitative data with numbers and units from all key data points | Uses data but lacks numbers/units or is incomplete | Vague ("the numbers showed…") or no data cited |
| Reasoning (4 pts) | Explains mechanism using scientific vocab; clearly connects evidence to claim | Provides some explanation but lacks detail or vocabulary | Restates evidence or provides no scientific explanation |