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 — molecules first, ecosystems last. But the real prerequisite structure isn't a straight line: it's a directed graph. Some units depend on two earlier ones; 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 06, 07, 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 Chemistry of Life | — (entry point) |
| 02 Cell Structure & Function | — (entry point) |
| 03 Cellular Energetics | 01 (macromolecules, enzymes) + 02 (membranes, transport) |
| 04 Cell Communication & Cycle | 02 (signaling depends on membrane structure) |
| 05 Heredity | 04 (meiosis depends on the cell cycle) |
| 06 Gene Expression | 01 (DNA chemistry) + 05 (inheritance) |
| 07 Natural Selection | 05 (allele frequency) + 06 (variation source) |
| 08 Ecology | 03 (energy flow) + 07 (population adaptation) |
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 |
|---|---|
| Can't reason about gene regulation (Unit 06) | DNA chemistry from Unit 01 — not the regulation itself. |
| Chi-square crosses fall apart (Unit 05) | Meiosis from Unit 04 — the probability follows the chromosomes. |
| Energy-flow questions in Ecology stall (Unit 08) | Photosynthesis/respiration from Unit 03. |
| Selection logic doesn't land (Unit 07) | Where variation comes from — Unit 06 gene expression. |
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 biology concepts depend on a chemistry or applied-math idea from another spoke. When the upstream biology node looks solid but the student still stalls, check the cross-disciplinary dependency before re-teaching the biology.