Unit 03 · Photosynthesis & Plant Energy
Photosynthesis is where a plant builds itself out of air and light. This unit works through the two stages inside the chloroplast — the light reactions on the thylakoid membranes that capture energy, and the Calvin cycle in the stroma that fixes carbon into sugar — the pigments that harvest different wavelengths, and the C3, C4, and CAM strategies plants use in different climates. It also follows the sugar back through cellular respiration and confronts the big surprise: most of a plant's dry mass comes from CO₂ in the air, not from the soil. Mastery means you can trace energy and carbon through the whole system and explain where a plant's substance actually comes from.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Light reactions & the Calvin cycle | Treats photosynthesis as one vague step that “makes food.” | Names the two stages but cannot say what each produces or consumes. | Traces light energy to ATP and NADPH in the light reactions and their use to fix CO₂ into sugar in the Calvin cycle. |
| Chloroplast structure & pigments | Cannot locate where photosynthesis happens in the cell. | Names the chloroplast but not the thylakoids, stroma, or why leaves are green. | Maps the light reactions to the thylakoids and the Calvin cycle to the stroma, and explains how chlorophyll and accessory pigments absorb different wavelengths. |
| C3, C4 & CAM pathways | Assumes every plant fixes carbon the same way. | Names the pathways but cannot link them to climate or leaf structure. | Compares C3, C4, and CAM, and explains how each manages the trade-off between fixing carbon and losing water. |
| Respiration & the source of plant mass | Believes a plant's mass comes mainly from the soil. | Knows CO₂ is used but still credits the soil for most of the gain. | Explains that most dry mass comes from atmospheric CO₂, and traces sugar through cellular respiration to release its energy. |
| Lab technique (floating-disk assay & pigment chromatography) | Cannot get the disks to sink or run a readable chromatogram. | Runs the assay but mishandles the timing, light, or pigment separation. | Measures photosynthetic rate with the floating-disk assay and separates leaf pigments by chromatography, reading both results correctly. |
| 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. |
“The disks floated back up faster under the bright light because photosynthesis was making oxygen inside them. And the plant’s mass mostly comes from CO₂ it pulls out of the air in the Calvin cycle — van Helmont’s willow gained kilograms while the soil barely lost any.”
“Plants eat sunlight and grow out of the dirt. There’s a light part and a dark part, maybe? The disks did something in the cups.”
You demonstrate this unit through the floating-disk assay and leaf-pigment chromatography, explaining the energy and carbon behind every reading aloud — not a multiple-choice test. A criterion counts as mastered only when your data shows the process working and you can justify the plant biology 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.