Unit 02 · Plankton & Primary Production
Plankton are the drifters that run the ocean. This unit sorts them out — phytoplankton that photosynthesize and zooplankton that graze, the lifelong holoplankton and the larval meroplankton — then follows the energy they capture: how sunlight in the euphotic zone powers primary production, why nutrients and upwelling decide where blooms happen, and how this thin drifting layer feeds nearly every ocean food web and produces roughly half the oxygen you breathe. Mastery means you can read a drop of seawater as the base of the ocean’s economy.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Plankton types & classification | Uses “plankton” as one undifferentiated category. | Separates phytoplankton from zooplankton but confuses holoplankton with meroplankton. | Sorts plankton by role (photosynthesizing phytoplankton vs grazing zooplankton) and by life history (lifelong holoplankton vs larval meroplankton), and explains what each does in the water column. |
| Primary production & photosynthesis | Thinks the open ocean’s food comes from plants on the seafloor. | Knows phytoplankton photosynthesize but cannot tie it to the sunlit zone. | Explains primary production in the euphotic zone — sunlight fixed into food and oxygen — and why it stops below the reach of light. |
| Nutrients, upwelling & blooms | Assumes plankton grow evenly everywhere in the sea. | Names nutrients as a factor but not upwelling or seasonality. | Links nutrient limitation and upwelling to where and when blooms form, and predicts productive versus barren water. |
| Food-web base & the biological pump | Dismisses plankton as unimportant “scum” on the water. | Knows plankton feed other animals but misses the carbon and oxygen story. | Places plankton at the food-web base, explains the biological carbon pump, and credits phytoplankton with about half of Earth’s oxygen. |
| Lab technique (plankton-tow microscopy) | Skips the tow or cannot find organisms under the scope. | Collects a sample but struggles to count or identify what is in it. | Runs a clean plankton tow — samples, counts, and identifies phyto- and zooplankton under the microscope, recording what it finds. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“This tow is mostly diatoms — phytoplankton — with a few copepods grazing on them. They photosynthesize up here in the sunlit zone, which is why there’s nothing like this in the dark deep. Blooms this thick show up where upwelling brings nutrients to the surface, and plankton like these make about half the world’s oxygen.”
“It’s just green stuff floating. Plankton are tiny fish, right? And they live at the bottom of the ocean.”
You demonstrate this unit through a plankton tow and microscope session where you sample, count, and identify what you catch, then reason from it aloud — not a multiple-choice test. A criterion counts as mastered only when you can both work the microscope and explain the biology of primary production behind it. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.