Unit 05 · Plant Growth & Hormones
Plants don’t just grow — they sense and respond. This unit covers the five classes of plant hormones — auxins, gibberellins, cytokinins, ethylene, and abscisic acid — and what each one does; the tropisms that steer growth toward light (phototropism), with gravity (gravitropism), and against a touched surface (thigmotropism); how apical dominance keeps a shoot’s tip in charge; and how photoperiodism and phytochrome let a plant read the length of the night to time flowering and germination. Mastery means you can predict how a plant will bend, branch, or bloom — and name the hormone or signal behind the move.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Plant hormones & their effects | Cannot name the plant hormones or thinks plants have none. | Names a hormone or two but confuses their effects. | Identifies auxins, gibberellins, cytokinins, ethylene, and abscisic acid and explains what each does — from stem elongation to fruit ripening to dormancy. |
| Tropisms (photo-, gravi-, thigmo-) | Thinks plants cannot move or respond to their surroundings. | Names a tropism but cannot explain what drives the bend. | Predicts and explains phototropism, gravitropism, and thigmotropism, linking each directional growth to the redistribution of auxin. |
| Apical dominance | Cannot explain why a pruned plant grows bushier. | Describes apical dominance but not the hormone behind it. | Explains how auxin from the shoot tip suppresses the side buds and predicts what happens when the tip is removed. |
| Photoperiodism & germination control | Thinks day length has no effect on flowering. | Mentions photoperiod but cannot connect it to phytochrome or germination. | Explains how phytochrome lets a plant measure night length to time flowering and germination, and predicts a short- vs. long-day response. |
| Lab technique (tropism & germination setup) | Sets up seedlings with no controlled light or gravity variable. | Runs the experiment but records growth loosely or skips the control. | Designs a clean phototropism or gravitropism trial with a proper control, measures curvature or growth over time, and links the result to a hormone. |
| 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. |
“I laid the seedlings on their side and the shoots curved back upward — that’s gravitropism, auxin building up on the lower side and pushing it to grow longer. When I pinched off the tip, the side buds finally took off, because I removed the auxin that was holding them back.”
“Plants just grow up toward the sun because they like light. Hormones are an animal thing — I don’t think plants really move.”
You demonstrate this unit through tropism and germination experiments — phototropism boxes, gravitropism trials, and timed germination setups — reasoning from what your seedlings did aloud, not a multiple-choice test. A criterion counts as mastered only when you can both run the setup and 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.