Unit 02 · The Earthworm
This is your first internal dissection. After tools, safety, and ethics, you open a real specimen and read its body plan for yourself — the earthworm's segmentation, its external landmarks, and the organs laid out along its length. The work is technique and careful observation: shallow, controlled cuts along the correct line, looking before you disturb anything, then locating and naming structures and explaining what each one does. An instructor watches you work, and the specimen — opened cleanly, structures intact — is the proof.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Instrument handling & safe technique | Grips the scalpel, scissors, forceps, or probe awkwardly; cuts too hard or too deep; puts hands or specimen at risk. | Holds the instruments correctly with reminders and cuts more carefully, but still presses too hard or steadies the specimen poorly. | Holds each instrument the right way and makes shallow, controlled cuts, working safely for both the student and the specimen. |
| Careful exposure & observation | Cuts before looking and tears or destroys structures while opening the specimen. | Opens the specimen roughly along the correct line but disturbs organs before observing them. | Opens the specimen cleanly along the dorsal midline without damaging structures, and observes the layout before disturbing anything. |
| Locating & naming external structures | Cannot point to the clitellum, segments, or setae, or tell anterior from posterior. | Finds a few external landmarks with prompting but confuses dorsal and ventral or miscounts segments. | Locates and names the clitellum, segments, and setae on the specimen and orients it correctly by anterior/posterior and dorsal/ventral. |
| Locating & naming internal structures | Guesses at the organs or names the wrong ones once the specimen is open. | Finds the larger organs but cannot reliably distinguish crop from gizzard or trace the blood vessel and nerve cord. | Locates and names the dorsal blood vessel, aortic arches, crop, gizzard, intestine, seminal vesicles, nephridia, and ventral nerve cord on the specimen. |
| Explaining structure & function (and specimen care) | Cannot say what a structure does, and lets the specimen dry out or handles it carelessly. | Explains one or two structures' functions but not the rest, and keeps the specimen moist only when reminded. | Explains why key structures do their jobs — the gizzard grinding, the clitellum's role, how segmentation aids movement — while keeping the specimen moist, handling it respectfully, and cleaning up afterward. |
| 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 pale band is the clitellum — it’s segments 32 to 37, and it secretes the cocoon. The dark line down the dorsal side is the dorsal blood vessel; I traced it forward to the five pairs of aortic arches that pump the blood. Just behind them the crop stores food and the gizzard grinds it, which is why the gizzard wall feels muscular.”
“I think that tube is the stomach? I cut it before I really looked, so it’s kind of torn now. I’m not sure which end is the front.”
You demonstrate this unit by doing the dissection while an instructor watches — locating, exposing, and naming real structures and explaining their function on your own specimen, not a written test. A criterion counts as mastered only when you can perform the technique cleanly and identify and explain the structures on the actual specimen. 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.