Learning target: I can use measurements of gases, water, minerals and dry mass from a sealed growth chamber to argue where a plant's new matter came from and what its energy source was.
Read the scenario and study the ledger. Answer the warm-up questions first; they organize the evidence you will need. Then write your Claim, Evidence and Reasoning in the boxes. A strong response names specific numbers from the ledger and explains how the rule that matter is never created or destroyed connects those numbers to your claim.
You will need: This worksheet, Pencil, Scrap paper for the ledger, Calculator (optional)
A plant research lab grows basil in two identical sealed, clear chambers. The plants sit in trays of water mixed with minerals; there is no soil. Every gram that goes into or out of each chamber is recorded on a ledger, the way a bank records money. Chamber A gets bright lamps for 14 hours a day. Chamber B is kept dark. Both run for 30 days at the same temperature. Because weighing a living plant includes the water inside it, the lab measures dry mass: a matched set of plants was dried in an oven and weighed on day 0, and the chamber plants were dried and weighed on day 30. The numbers below are a teaching dataset, invented to be realistic and to add up cleanly.
| Item | Chamber A: lit 14 h per day | Chamber B: dark |
|---|---|---|
| Dry mass of plants, day 0 (g) | 40 | 40 |
| Dry mass of plants, day 30 (g) | 166 | 36 |
| Carbon dioxide added to keep the level steady (g) | 176 | 0 |
| Carbon dioxide removed because the level kept rising (g) | 0 | 6 |
| Oxygen removed because the level kept rising (g) | 128 | 0 |
| Oxygen added because the level kept falling (g) | 0 | 4 |
| Water taken from the tray by the plants (g) | 9400 | 310 |
| Water collected as condensation from the air (g) | 9328 | 312 |
| Minerals taken up from the tray solution (g) | 6 | 0.3 |
| Hours of light over 30 days | 420 | 0 |
On scrap paper draw two columns for Chamber A: 'In' and 'Out or kept.' Copy the carbon dioxide added, water kept and minerals into 'In' and the oxygen removed and the dry-mass gain into 'Out or kept.' Total each column. Then write one sentence beside each number saying what it proves (for example, '176 g of gas went in, so the air supplied matter'). Those sentences are your Evidence; the matching totals are the start of your Reasoning.
Chamber B's plants lost 4 g of dry mass while 4 g of oxygen was added and 6 g of carbon dioxide was removed, and the water rows show about 2 g of water appeared that the plants did not take from the tray. Set up the 'In' and 'Out' ledger for Chamber B, show that it balances, and then write the word equation for what the plants in the dark were doing with their stored sugar. Explain why this reaction is, in terms of matter, the reverse of photosynthesis.