What do you need?
Plan your investigation before you open the lab. Then, as you build the bench, highlight each piece of equipment you need and cross out each one you don't.
1 · Your goal
Tick the investigation you are doing.
- Action spectrum: which colours of light drive photosynthesis?
- Light intensity: how does the amount of light affect the rate?
- Limiting factors: does CO₂ matter more in bright light or dim light?
- My own question: ______________________________________________
My research question, in one sentence:
| Variable | What it is in my investigation | How I will measure it or keep it constant |
|---|---|---|
| Independent | ||
| Dependent | ||
| Controlled 1 | ||
| Controlled 2 | ||
| Controlled 3 | ||
| Controlled 4 |
2 · Before you open the lab: what will you need?
Do this before you look at the bench. Think about a real lab: what would you need to set up, measure, control and record for your goal? List equipment and materials, and say why.
| # | Item I think I need | Why I need it |
|---|---|---|
| 1 | ||
| 2 | ||
| 3 | ||
| 4 | ||
| 5 | ||
| 6 | ||
| 7 | ||
| 8 | ||
| 9 | ||
| 10 |
How many sprigs of Elodea will you use, and why that number?
3 · Build the bench: highlight or cross out
Now open Engelmann's Pond and follow the bench tour. As each piece of equipment appears, find it below. Highlight the row if you need it for your goal. Cross out the row if you don't. Tick “On my list?” if it was already on your list in section 2.
| Equipment (in tour order) | What it does | On my list? | Why I need it, or why not |
|---|---|---|---|
| Glass tank, test tube and Elodea sprig | Holds the sprig in water; O₂ leaves the cut end as bubbles | ||
| LED lamp: 9 colours, brightness, distance rail | Sets the colour and amount of light | ||
| Spectrometer | Shows the lamp's spectrum; reads peak wavelength and FWHM | ||
| NaHCO₃ solution and Fresh solution | Supplies dissolved CO₂; the sprig uses it up | ||
| Sprig selector, Recut stem, New sprigs | Chooses among 9 different sprigs; makes a new cut | ||
| Three tubes and ROTATE (3 TUBES mode) | Tests three sprigs at once; moves them between positions | ||
| Water bath and thermometer | Holds the water at a set temperature; reads it to ± 0.1 °C | ||
| PAR meter | Counts photons from 400 to 700 nm, in µmol m⁻² s⁻¹ | ||
| Lux meter | Measures brightness as the human eye sees it | ||
| Automatic bubble counter (optical gate) | Counts bubbles for a set time | ||
| Manual tally and stopwatch | You count each bubble and time it yourself | ||
| Lab clock: ×1, ×10, ×30 | Speeds up waiting while the sprig settles | ||
| Room lights switch | Adds or removes a little white light from the room |
Which items on your section 2 list are not on the bench? What would a real lab use for them?
4 · Plan your time
Every count of bubbles lasts as long as you set it to, usually 60 s.
If your teacher has set manual counting, each count is a real minute of watching and tapping. The lab clock cannot speed it up.
| Number of conditions (e.g. wavelengths) | Sprigs | Counts per sprig per condition | Minutes per count | Total minutes of counting |
|---|---|---|---|---|
Total = conditions × sprigs × counts × minutes per count. Add time for setting up and for the sprig to settle (about 3 minutes after each change).
Counting by hand, a full action spectrum is about 25 minutes of counting with one tube and about 45 minutes with three tubes, one tube at a time. Your counts are saved in the browser, so finish on the same device and browser you started on.
5 · What did your list miss?
Answer after you have built the bench, before you start counting.
- Which highlighted items were not on your section 2 list? Why do you need them?
- Did you cross out anything you had listed? Why don't you need it after all?
- The bench has both a PAR meter and a lux meter. Which one will you use to set the light, and why?
- Look at your sprig count from section 2. Is that enough independent replicates? Explain.
- One change you will now make to your plan:
Engelmann's Pond is for practising investigation skills. Its data are simulated and must not be used as IA data.
Teacher key
Hand out sections 1 and 2 before students open the lab, so their list is a genuine prediction. The bench tour then works as the check. The key matches the app's three guides.
| Equipment | Action spectrum | Light intensity | Limiting factors |
|---|---|---|---|
| Tank, tube and sprig | Need | Need | Need |
| LED lamp | Need: colour is the independent variable | Need: white LED; distance or brightness is the independent variable | Need: white LED at low and high light |
| Spectrometer | Need: Δλ = FWHM / 2 for each LED | Not needed | Not needed |
| NaHCO₃ and Fresh solution | Control at 1.00 %; refresh now and then | Control at 1.00 % | Need: 0.10 % and 1.00 % are the independent variable |
| Sprig selector | Need: same sprigs throughout | Need: same sprigs throughout | Need: same sprigs throughout |
| Recut stem, New sprigs | Not needed: changes bubble size mid-experiment | Not needed | Not needed |
| Three tubes and ROTATE | Recommended: three sprigs as replicates; rotate | Recommended | Recommended |
| Water bath and thermometer | Control at 25.0 °C | Control: a close lamp warms the water without it | Control at 25.0 °C |
| PAR meter | Need: equal photon flux, 100 µmol m⁻² s⁻¹ | Need: measures the independent variable | Need: sets low (≤ 60) and high (≥ 300) light |
| Lux meter | Not needed: the trap (eye-weighted) | Not needed | Not needed |
| Automatic counter | Need (unless set to manual) | Need (unless manual) | Need (unless manual) |
| Manual tally and stopwatch | Need if manual; else a check on the gate | Same | Same |
| Lab clock | Need: wait about 3 min after each change | Need | Need |
| Room lights | Switch off (control) | Switch off | Switch off |
Things students often miss
- Setting the light with the PAR meter, not the lux meter or the brightness dial.
- Waiting for the sprig to settle after every change.
- Switching the room lights off.
- Refreshing the NaHCO₃ during a long run.
- More than one sprig: repeated counts of one sprig are not independent replicates.
- The LED is not monochromatic: Δλ comes from the spectrometer.
Before choosing manual counting, plan the time. Each count is a real minute. A full action spectrum is about 25 minutes of counting with one tube and about 45 minutes with three, plus set-up. Plan a double lesson or split it across lessons; counts stay on the same device and browser.
Engelmann's Pond is for learning and practice. Its data are simulated and are not a substitute for an IA. Created by Christopher B. Slough.