Engelmann's Pond

Quick start

1. Choose 1 TUBE or 3 TUBES at the top.
2. Choose an LED colour in the LAMP module and set its BRIGHTNESS.
3. Drag the lamp along the rail, or tap the distance display and type a value.
4. Turn the WATER BATH on and wait until the thermometer reads the set temperature.
5. Wait about 3 minutes (use ×10 or ×30 on the lab clock), then press START on the bubble counter.
6. The count appears in the Data tab. Work out the rate yourself.

New to the lab? Open the Guide tab and follow Action spectrum.

Using the controls

• Knobs: drag round, or use the scroll wheel over the knob.
• Displays: tap to type. Enter confirms, Esc cancels, and tapping anywhere else also confirms. The edit box is amber, so you can tell it apart from the display.
• ×1, ×10 and ×30 on the LAB CLOCK speed up time while you wait. Manual counting always runs at ×1.
• Rebuild the bench (below) runs the first-visit tour again.
• ⟩ at the top of the side panel hides it. Click any tab to bring it back.
• The lamp, bath, solution, sprigs and tube switch are locked while a counter runs.

The light

• The LED head has nine colours. Each colour gives a different number of photons at the same brightness, so set the light with the PAR meter, not the dial.
• No LED is monochromatic. The SPECTROMETER shows each LED’s band and reads its peak and FWHM. Use half the FWHM as the uncertainty Δλ in the wavelength.
• PAR is photon flux, 400–700 nm, in µmol m⁻² s⁻¹. It cannot see far red (730 nm). LUX is brightness to the human eye, so it reads green far higher than red or blue.
• The lamp is not a point source: close up, halving the distance does not quite quadruple the light.
• ROOM LIGHTS add a little white light. Turn them off for dim-light work.

Counting bubbles

• AUTO: an optical gate on each tube counts bubbles for the time you choose. With three tubes, all three are counted at once and logged as three counts. Two bubbles very close together pass as one, so the gate undercounts fast streams.
• MANUAL: press TAP (or the space bar) for every bubble, and use the stopwatch. With three tubes you count the selected tube only: nobody can tally three streams at once. Each manual count takes a real minute.
• After any change, the sprig takes a few minutes to settle. The log records how long it had.
• RECUT STEM gives a fresh cut. Bubble size changes, so the count changes too.

One tube or three

• 3 TUBES puts three tubes in a row across the beam, 2.5 cm apart, each with its own sprig and solution. The lamp, bath and NaHCO₃ setting are shared.
• Only the middle position is on the lamp’s axis. The outer tubes get a few percent less light, and much less when the lamp is close. Tap a tube (or its circle in the TOP VIEW) to select it: the meters read at the selected tube.
• ROTATE moves every tube one place, so each sprig spends time in each position.
• Repeated counts of one sprig are not independent replicates. In the Data tab, Each sprig’s mean is a trial treats each sprig as one replicate. This is the default with three tubes.

Temperature and CO₂

• The WATER BATH holds its set temperature once it gets there. With the bath off, the water sits near 21 °C, and a close, bright lamp warms it.
• NaHCO₃ supplies dissolved CO₂. The sprig uses it up, so a busy solution slowly runs down. FRESH SOLUTION refills it.
• Water above about 38 °C damages the sprig, and the damage stays.

Guides

• Each guide unlocks one item at a time. Attempt an item to unlock the next. Tasks tick themselves off when the bench and the log show the work is done.
• Answers are saved in this browser. Use Download my answers to keep a copy or hand it in.

Predict, then fire

The Predict tab describes two set-ups that differ in one factor. Choose what happens to the rate, then FIRE: the lab counts both with your current sprig. The worked solution is shown after every answer, even a correct one.

Data and SGL

• The count log keeps every count. Copy log as table pastes into Excel or Word. Clear log starts again at Count 1.
• The results table groups ticked counts by your independent variable and warns you when a control variable was not held constant. For wavelength it gives each LED’s Δλ (half its FWHM), which goes to SGL as that point’s x uncertainty.
• Open in SGL sends the table to SGL, the graphing tool, with ± 1 SD error bars. SGL's Statistics panel gives the t-test and one-way ANOVA.

Conventions

• Table headings follow IB style, e.g. R / bubbles min⁻¹ and T / °C ± 0.1.
• Standard deviations are sample SDs (n − 1). Worked solutions show the equation, the rearrangement, the substitution and the evaluation.

Why the data are not perfect

Like a real pond weed, every sprig is different, bubbles vary in size, the rate wanders from minute to minute, the solution runs down, the water drifts in temperature and the counter misses close pairs. Repeated counts scatter. That is not a mistake: it is why you take many counts and test your means statistically.

For teachers: a set-up link

Pre-lab worksheet: What do you need? Students list the equipment they expect to need, then highlight or cross out each item as the bench tour builds it. Print-ready, with a teacher key on its own page.

Make a link that fixes how the lab works for your class, then post it in Teams. Students who open it cannot change these settings.

Before choosing manual only: Manual counting takes real time: every count is a real minute of watching and tapping, and the lab clock cannot speed it up. A full action spectrum takes about 25 minutes of counting with one tube (5 wavelengths × 5 counts) and about 45 minutes with three tubes, one tube at a time (5 wavelengths × 3 sprigs × 3 counts), plus set-up and settling. Plan a double lesson, or split the work across lessons. Counts are saved in the browser, so students must continue on the same device and browser.

Engelmann’s Pond is for learning and practising investigation skills. Its data are simulated: they are not a substitute for an IA, and students should not submit them as IA data.

Devices

Use a computer, or a tablet in landscape. Phones are not supported. Your counts and answers are stored only in this browser on this device.