This is a working draft for Leslie's review. The dependency edges below are a first pass — the diagram and the prerequisite table are the parts to check hardest, since they drive hold-vs-advance decisions.
The course map shows the eight units as a spine — the physical ocean first, human impact last. But the real prerequisite structure isn't a straight line: it's a directed graph. Marine biology is cumulative — plankton needs the ocean, fish need both the algae that feeds them and the invertebrate body plans they build on, ecosystems need the organisms that fill them. A weak concept early doesn't just lower one grade, it cascades into everything downstream that needs it. This page is the map a guide uses to find the concept that's actually blocking a stuck student.
An arrow means “must be mastered first.” Units 05, 06, and 08 each pull from two upstream units — those are the cascade points where one soft prerequisite quietly breaks several later units.
Prerequisite gating
A unit unlocks when its prerequisites are mastered — demonstrated, not merely seen. "Covered in class" is not the gate; a cleared rubric is. The difference matters most at the cascade points, where a soft prerequisite quietly breaks two or three later units.
| Unit | Must have mastered first |
|---|---|
| 01 The Ocean Environment | — (entry point) |
| 02 Plankton & Primary Production | 01 (light, nutrients & zones set where plankton live) |
| 03 Marine Plants, Algae & Kelp | 02 (surface photosynthesis & primary production come first) |
| 04 Marine Invertebrates | 02 (many inverts are planktonic or filter the plankton base) |
| 05 Fish & Sharks | 03 (algae & kelp habitat) + 04 (invertebrate body plans precede vertebrate anatomy) |
| 06 Reptiles, Birds & Mammals | 03 (productive kelp/algae food webs) + 05 (vertebrate anatomy — tetrapods build on fish) |
| 07 Ocean Ecosystems | 05 (fish — the dominant vertebrate consumers that structure communities) |
| 08 Humans & the Ocean | 06 (marine tetrapods — whaling & conservation) + 07 (ecosystems — impact acts on whole systems) |
Gap-cascade diagnosis
When a student stalls late, the visible symptom is rarely the real problem — the broken concept is usually upstream. Trace the arrows backward. Common cascades:
| Late symptom | Upstream concept to check first |
|---|---|
| Human-impact arguments stay vague (Unit 08) | Ocean ecosystems from Unit 07 — you can't judge overfishing or protection without knowing how the food web is wired. |
| Food-web & energy-flow reasoning collapses (Unit 07) | Fish from Unit 05 — the dominant vertebrate consumers that structure most communities. |
| Diving & thermoregulation adaptations don't make sense (Unit 06) | Fish anatomy from Unit 05 — tetrapod body plans are modified vertebrate anatomy. |
| Fish anatomy & buoyancy confuse the student (Unit 05) | Invertebrate body plans from Unit 04 — structure-function reasoning starts with the simpler phyla. |
Using the graph to plan a re-attempt
The graph turns a "not yet" into a targeted re-attempt instead of a whole-unit re-teach. When a student fails a downstream demonstration:
- Trace backward to the upstream node the symptom points to.
- Re-attempt the upstream concept first — close the gap at its source, not where it surfaced.
- Then re-run the downstream demonstration. Often it passes without any re-teaching of the downstream unit at all, because the cascade is resolved.
This is also where the integration guide matters: some marine biology concepts lean on a reading or data skill from another spoke — reading a temperature–salinity profile, keying out a specimen with a dichotomous key — not on an upstream biology unit. When the upstream marine biology node looks solid but the student still stalls, check the cross-disciplinary dependency before re-teaching the biology.