Pouring Energy Up the Pyramid: A Water Model of Trophic Levels

Investigation question: If producers capture 1,000 units of energy, how many trophic levels can that energy support, where does the rest go, and how does the answer change if the share passed up is larger or smaller than one tenth?

Your role today

• Pourer: Transfers water from each level to the next using the correct measuring tool, and pours the remainder into the heat and decomposer jugs as the accountant directs.
• Measurer: Reads every cylinder and syringe at eye level, calls the volume aloud, and confirms it before the pourer continues.
• Recorder: Fills the energy-accounting table row by row and plots the two graphs.
• Accountant and checker: Computes what each level should receive before it is poured, keeps the running totals for the heat and decomposer jugs, and runs the final sum check.

Safety

• Water on the floor is a slip hazard; keep all pouring over the tray and wipe spills at once.
• Food coloring stains skin, clothing and paper; roll up sleeves and keep the recording sheet away from the tray.
• The water is not for drinking; cups and syringes used here go back in the kit, not to mouths.
• Keep phones and calculators off the tray. No hazards beyond water and dye.

Procedure

1. Before pouring, the accountant fills in the 'should receive' column of the round 1 table for levels 2 to 5 using the ten-percent rule (divide by 10 each step), and the group writes a prediction for q1: how many levels will receive at least 1 mL?
2. Level 1 to level 2: measure 100 mL from the producer bottle with the 100 mL cylinder and pour it into the Level 2 cup. Record 100 mL received at level 2. Pour the remaining 900 mL from the bottle into the two jugs, about 600 mL into Heat and 300 mL into Decomposers, using the jug marks as a rough guide. Record the split.
3. Level 2 to level 3: measure 10 mL from the Level 2 cup with the 10 mL cylinder and pour it into the Level 3 cup. Pour the remaining 90 mL into the jugs in the same two-to-one split (about 60 and 30 mL, measured with the 100 mL cylinder). Record.
4. Level 3 to level 4: draw 1 mL from the Level 3 cup with the syringe and squeeze it into the Level 4 cup. Pour the remaining 9 mL into the jugs (about 6 and 3 mL, using the 10 mL cylinder). Record.
5. Level 4 to level 5: draw up the 1 mL from the Level 4 cup and expel 0.1 mL, about two drops, into the Level 5 cup; put the remaining 0.9 mL into the jugs. Record. Try to pass a tenth of the two drops to a sixth level and write what happens in q2.
6. Sum check: pour the Heat jug into the measuring jug and record the volume; do the same for the Decomposers jug; add what is still in the five level cups (level 1 is empty, levels 2 to 5 hold what they received minus what they passed on, which is the 'kept' column). Write the total in q3 and compare it with 1,000 mL.
7. Graph the volume received at each level on the first graph (0 to 1,000 mL). Then graph levels 2 to 5 again on the second graph (0 to 100 mL). Keep both; the analysis asks about them.
8. Round 2: collect the water from the jugs and cups back into the producer bottle, top it up to 1,000 mL, and rerun the transfers using your group's assigned fraction (5, 20 or 30 percent). Compute each 'should receive' value first, measure as before, and stop when the next level would get less than 1 mL. Record the number of levels supported.
9. Report your fraction and the number of levels supported on the class chart. Copy the class results into the round 2 summary table, then answer the analysis questions individually.

Record your observations

Lab 2 recording sheet: Pouring energy up the pyramid

In this model 1 mL of colored water stands for 1 unit of energy. The producer bottle holds the 1,000 units the plants captured from sunlight this year. At each level only part of the energy is passed up as food; the rest leaves as heat or goes to decomposers in wastes, remains and uneaten parts. A level exists in our model only if it receives at least 1 mL.

Analysis questions