AP Biology: Seed Dormancy, Scarification, and Germination Timing Practice Questions
Practice ecological and evolutionary reasoning with original AP Biology multiple-choice questions about how dormancy and scarification affect germination timing. These items distinguish a viable dormant seed from a dead seed, connect environmental cues to fitness trade-offs, and test the evidence needed for causal conclusions.
Free original practice questions for study purposes. Open Exam Prep is an independent study resource and is not affiliated with, endorsed by, or sponsored by the makers of AP Exams.
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Answer the questions below — you get instant feedback and a full explanation for each.
1. What is the main ecological benefit of seed dormancy in a seasonal habitat?
Explanation. Dormancy can prevent germination during a brief favorable signal followed by lethal conditions. It spreads germination through time, but it does not guarantee survival or remove resource requirements.
2. A viable seed has a water-impermeable coat and does not germinate in moist soil. Which treatment most directly tests whether physical dormancy is limiting germination?
Explanation. Controlled scarification tests whether coat impermeability prevents water uptake. A matched untreated group reveals whether abrasion changes germination while other conditions remain constant.
3. Researchers compare intact seeds with scarified seeds. Which additional measurement best shows that scarification increased permeability without simply killing embryos?
Explanation. Water uptake measures the proposed permeability mechanism, while a viability test detects damage to the embryo. Germination alone cannot distinguish failed imbibition from embryo death.
4. Seeds from a fire-prone habitat germinate after heat exposure in the laboratory. What is the most cautious conclusion?
Explanation. The experiment supports a causal effect of the tested heat treatment on germination. It does not establish that heat is the only cue or that germination after every natural fire leads to successful recruitment.
5. A desert plant produces some seeds that germinate after the first rain and others that remain dormant. How can this variation increase long-term fitness?
Explanation. Spreading germination across rainfall events is a form of risk spreading. Some seedlings may exploit an early rain, while dormant seeds preserve future opportunities if that event is followed by drought.
6. Which observation best distinguishes a dormant seed from a dead seed?
Explanation. Dormancy is a temporary block to germination in a living seed. Viability testing and a suitable dormancy-breaking treatment can separate viable dormant seeds from dead seeds.
7. A cold winter followed by warm spring conditions triggers germination in a plant population. Which experiment best tests whether the sequence of temperatures matters?
Explanation. Random assignment and multiple temperature sequences isolate the effect of order from the effects of cold or warmth alone. Germination and viability should be measured for each treatment.
8. Scarified seeds germinate sooner than intact seeds, but many seedlings die in a late frost. Which conclusion is best supported?
Explanation. Germination speed is not the same as reproductive success. Dormancy can be beneficial when it prevents emergence during a temporary warm period that is followed by lethal cold.
9. After seeds pass through a bird's gut, germination increases. Which finding would most strongly support scarification rather than fertilizer in the droppings as the mechanism?
Explanation. If standardized mechanical abrasion reproduces the response after residue is washed away, the result supports coat modification. Separate nutrient controls would further distinguish scarification from fertilization.
10. A population's seeds require weeks of moist chilling before they germinate. What timing advantage can this requirement provide in a temperate climate?
Explanation. A chilling requirement can act as a seasonal filter: seeds experience winter before responding to later warmth. This reduces the chance of vulnerable seedlings emerging just before freezing conditions.
11. Scientists suspect that increasingly warm winters reduce germination in a species with a chilling requirement. Which response variable best tests the proposed population consequence?
Explanation. Tracking dormancy release, germination, viability, and establishment across controlled winter regimes connects the temperature mechanism to a biologically meaningful recruitment outcome.
12. Two populations of the same species differ in dormancy depth, and the difference persists when their seeds are raised in a common environment. What can researchers conclude?
Explanation. A common environment reduces immediate environmental variation, but maternal provisioning or inherited effects may persist. Crosses or multi-generation common-garden studies are needed to separate these explanations.
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FAQ
What is the difference between seed dormancy and seed death?
A dormant seed is alive but does not germinate until particular internal or environmental conditions are met. A dead seed has lost viability and will not germinate after an appropriate dormancy-breaking treatment.
What does scarification do to a seed?
Scarification weakens or opens a resistant seed coat through abrasion, digestion, heat, or another process. In some species this permits water or gases to enter, but excessive treatment can damage the embryo.
Why does germination timing affect fitness?
A seedling must emerge when water, temperature, light, and competition permit survival and growth. Germinating too early or too late can reduce establishment even when germination itself succeeds.