Final answer:
The question "Spines, hairs, tough seed coats, and sticky gums and resins are all examples of plant____ defenses against herbivory." is addressed with 'mechanical defenses', which are physical structures that protect plants from being eaten by herbivores. Option c) Mechanical is the correct answer.
Step-by-step explanation:
Spines, hairs, tough seed coats, and sticky gums and resins are all examples of mechanical defenses that plants use to protect themselves against herbivory. Unlike chemical defenses, which involve the production of toxic substances that can deter or harm herbivores, mechanical defenses physically prevent or dissuade animals from eating the plants.
Examples include the thorns of the honey locust tree (Gleditsia triacanthos) and the spines that can be modified leaves. These defenses work by causing physical discomfort or damage to herbivores, effectively reducing plant damage from feeding.
Mechanical and chemical defenses are the two main types of protection plants have against herbivores. The foxglove plant, for instance, utilizes a chemical defense by producing toxic compounds like digitalis which can be harmful when ingested. Some organisms like the North American millipede (Narceus americanus) use both types, employing mechanical defense by curling into a ball while simultaneously producing a noxious substance to fend off predators.