Learning target: I can use data from three jars to make a claim about which resource limits a population, support it with specific numbers, and explain the reasoning that connects resource supply to carrying capacity.
Read the scenario and study the dataset. Answer the warm-up questions first; they will organize your evidence. Then write your Claim, Evidence and Reasoning in the boxes. A strong response quotes specific counts and days from the table, compares the jars, and explains why the numbers came out the way they did using the ideas of limiting resource and carrying capacity.
You will need: This worksheet, Pencil, Scrap paper for evidence sentences
Daphnia, often called water fleas, are tiny crustaceans about the size of a sesame seed that live in ponds and eat single-celled algae. A class set up three identical one-liter jars of filtered pond water, put ten Daphnia in each, and placed them side by side under the same lamp at the same temperature. The only difference was feeding. Jar A received 1 milliliter of green algae culture every day. Jar B received 3 milliliters every day. Jar C received 3 milliliters every day through Day 12 and then nothing. Every three days the class counted the Daphnia in each jar and measured the dissolved oxygen, which stayed above 7 milligrams per liter in every jar for the whole experiment (Daphnia are fine above about 3).
| Day | Jar A (1 mL algae/day) | Jar B (3 mL algae/day) | Jar C (3 mL/day, then none after Day 12) |
|---|---|---|---|
| 0 | 10 | 10 | 10 |
| 3 | 16 | 18 | 18 |
| 6 | 24 | 32 | 33 |
| 9 | 32 | 55 | 54 |
| 12 | 38 | 85 | 86 |
| 15 | 41 | 110 | 92 |
| 18 | 42 | 122 | 70 |
| 21 | 41 | 126 | 44 |
| 24 | 42 | 125 | 25 |
A piece of evidence is a sentence with at least one number and a comparison. Try these frames: 'By Day ___, Jar A had only ___ Daphnia while Jar B had ___.' 'Jar C peaked at ___ on Day ___ and fell to ___ by Day ___, after feeding stopped on Day 12.' 'Oxygen stayed above ___ mg/L in all jars, so ___.' Write three such sentences on scrap paper before filling in the Evidence box, then use the Reasoning box to say what each sentence proves.
Design a fourth jar that would test whether Jar B's population could have grown even larger with more food, or whether some other resource (space, oxygen or waste build-up) would take over as the limiting resource at higher numbers. State the feeding rate, what you would measure besides the count, and sketch the two different curves you would expect depending on which answer is correct. Then write a sentence explaining why the limiting resource can change as a population grows.