Build a food web out of blocks, then measure what actually moves along it: clip a probe onto a link to read what it carries, or put a chamber round an organism to see everything crossing its boundary, heat included.

Data format

Each press of Collect Data is one capture, and every instrument on the board contributes to it. A probe adds a single row: the quantity it reads, the value, the unit, and the two organisms its link joins. A chamber adds one row per term in its budget, each marked in, kept or out, with heat’s destination reading “leaves the system”.

Plot Value against Trophic level for one quantity to see the tenfold step. Group a chamber’s rows by Direction to check that what went in equals what was kept plus what left. Filter To for “leaves the system” and the answer to what energy does that matter does not is a single value.

Model details

• The splits are round numbers. Of what a consumer takes in: a tenth to its own body, three tenths to waste, and the rest respired. Real values vary by species, diet and temperature; these are chosen so the tenfold step is legible.
• Producers respire, and it is shown. A plant captures 20,000 kJ and spends half of it staying alive, so 10,000 kJ goes on to whatever eats it. The model runs on gross production rather than quietly subtracting respiration, because a chamber makes the difference inspectable.
• Nitrogen has no respiration path, which is the point of including it. Breathing does not release nitrogen, so its budget has no term that leaves — the contrast that makes energy’s one-way trip visible.
• Nothing grows, breeds or dies. The numbers are the steady flows once everything has settled, so links can be compared with each other. Waiting will not multiply the rabbits.
• Animals do not drink. Breathing and waste are modelled, but there is no water input, so the only way matter reaches an animal is through its food.
• Waste goes to a decomposer, never straight to the soil. There is still food in it, and reservoirs here hold matter that has finished travelling.
• Heat on screen is compressed. Its intensity is scaled against the largest emitter and square-rooted; raw proportion would draw a second-level carnivore at under one percent opacity. The real steepness is in the exported numbers.
• The instruments are non-invasive, which real ones are not. Real respirometry alters an animal’s behaviour and its metabolic rate, which is why the technique needs acclimation periods and controls.

Standards

• HS-LS2-4 — Use mathematical representations to support claims for the cycling of matter and flow of energy among organisms in an ecosystem. The assessment boundary is proportional reasoning, so the instruments report values to compare rather than rates to track.
• HS-LS2-5 (secondary) — Model the role of photosynthesis and cellular respiration in cycling carbon among the biosphere, atmosphere, hydrosphere and geosphere. All four are on the board.

Design intent

• No readout panel, deliberately. Every number comes from an instrument the student placed, so deciding where to measure is part of the work — which is HS-LS2-4’s first evidence statement almost word for word.
• The chamber is a control volume — draw a boundary, account for everything crossing it. It reports in, kept and left rather than just in and out, because growth is not an output: the tissue is still there for whatever eats it next. Evidence 3c asks for exactly that separation.
• One quantity at a time, because a budget whose terms are in different units is not a budget. Switching a rabbit’s chamber from Carbon to Energy gives two budgets that both balance, one of which has a term that leaves for good.
• The tenfold drop is derived, not stated. Respiration and waste are modelled and the leftover is what moves on, so two probes one level apart show the rule rather than assert it.

Discussion prompts

• Probe one link, then the next one up the chain. About a tenth gets through. Where did the other nine tenths go, and can you account for all of it?
• Put a chamber on one animal and switch it between Energy and Carbon. Both balance. What is different about the two, and why does that difference matter?
• Why can a pyramid of biomass and a pyramid of energy have the same shape?
• Predict a longer chain’s top carnivore before measuring it. What does that imply about how many top predators an ecosystem can support?

How do I explore?

1. Tap a dashed + space to drop in the block that belongs there, or drag any block off the shelf.
2. Join two blocks by dragging from a circle on one block’s edge to the other block. The KEY along the bottom names what each line carries.
3. Drag a probe onto a link to read what it carries. There is one for each quantity, and you can put more than one on the same link to compare them side by side.
4. Drag the Chamber onto a living thing to see everything crossing its boundary, heat included. Tap Energy, Carbon, Biomass or Nitrogen on its bar to change what it measures.
5. Watch for a red wall. It means matter has reached that block and cannot get any further. Join that block on to something and the wall goes away.
6. Press Collect Data to send your readings to the data tools. Change the model and collect again.

What should I do/notice?

• Compare one link with the next one up the chain. About a tenth of the energy makes it to the next level. Where did the other nine tenths go?
• Put a chamber round one animal, then switch it from Carbon to Energy. Both balance — but one of energy’s terms leaves the board and never comes back, and carbon has no term like it. That difference is the whole idea.
• Watch the faint warm arcs. That is the energy respiration releases, leaving as heat. Only a chamber can measure it.
• Take the decomposers away and watch matter pile up with nowhere to go. Then ask why the energy does not pile up in the same way.
• Use the key at the bottom. Tap Air and every other line fades back, so you can follow just that one all the way round.

What about the data?

Every probe and chamber on the board sends what it reads to the data tools when you press Collect Data. Each row says what was measured, its value and unit, and where it was going. Plot the value against the trophic level to see the drop from one level to the next, and look for the rows whose destination is “leaves the system” — only energy ever has one.