Lesson 2: Identifying & Controlling Independent, Dependent & Fixed Variables
Carrying out a practical biological investigation with direction into a biological context.
🎯 Ngā Whāinga Akoranga | Learning Intentions
The difference between independent, dependent, and controlled/fixed variables, and why uncontrolled variables invalidate biological conclusions.
Identify IV and DV with units, list 3+ controlled variables with explicit control methods, and justify why each controlled variable must remain constant.
🎥 Media Anchor & Pedagogical Scaffold
Fair Testing & Variable Control in Biology
Video Clip: GCSE Science Revision — Independent variable, dependent variable, and control variables (Freesciencelessons) (Runtime: 4m 48s).
🧠 1. Before Viewing (Activate & Predict)
If temperature fluctuates while testing enzyme pH rate, how do you know which factor caused the change in reaction speed?
👁️ 2. During Viewing (Watch With a Job)
- Three types: write the definitions of independent variable, dependent variable, and control variable. Give one example of each from a biology investigation (e.g. enzyme rate experiment).
- Control variables: why is it important to control variables that are not being tested? What happens to your results if you don't?
- Your investigation: identify the independent variable, dependent variable, and at least TWO control variables you would use in your biology investigation for NCEA Level 1 Biology (Internal).
🗣️ 3. After Viewing & Kaiako Move (Process & Apply)
Kaiako Move: Provide 'Variable Audit Cards' for students to identify flaws in un-controlled experiment scenarios.
Immediate Task: Complete Section 2 of your Investigation Log: Variables Identification & Control Strategy Table.
⚡ Whakaoho | Do Now: Investigation Recall (10 mins)
The experiment that proves nothing. A student tests enzyme activity at 20 °C and 40 °C. The 40 °C run used a fresh enzyme batch, a bigger test tube, and was done the next day.
Two minutes: their results show faster reaction at 40 °C. State why that result cannot be trusted, and name three things that changed besides temperature. Any one of them could be the real cause — that is what uncontrolled means.
📖 Activity 1: Investigation Planning & Practical Execution (25 mins)
Audit a method (12 min). Given a written method, identify the IV, the DV with units, and every variable left uncontrolled. For each uncontrolled one, say specifically how it could produce a false result — not 'it would affect it', but which direction and why.
Control your own (13 min). List at least five controlled variables for your own investigation. Beside each, write how you will hold it constant, with a number or a piece of equipment. 'Keep it the same' is not a control; 'same 250 mL beaker, 20 mL measured with a pipette' is.
📝 Activity 2: Level 1 Biology Investigation Log & Merit/Excellence Scaffolding (20 mins)
Report — Section 2. Submit: (1) the audited method with IV, DV and all uncontrolled variables named and their likely effect stated; (2) your own controlled-variable table with a concrete method for each; (3) one sentence on which uncontrolled variable would damage your results most, and why.
🏫 Kaiako Planning & Pedagogy Notes
NCEA Level 1 Alignment: Direct preparation for NCEA Level 1 Biology — Internal (Carry out a biological investigation with direction). Emphasise complete variable control, accurate data processing, and clear biological explanations for Merit/Excellence grades.