Which of the following is considered an induced chemical defense?

An induced chemical defense is a type of plant defense mechanism that is activated in response to herbivore attack or environmental stress. This means that these defenses are not constantly produced, but rather are synthesized when the plant detects a threat.

Thorns, which are a form of mechanical defense, can be considered a part of this response in certain contexts, as plants may produce more thorns or modify their growth in response to herbivore pressure. However, the more accurate definition of induced chemical defenses relates to the production of chemicals that deter herbivores or pathogens after an attack has occurred.

In contrast, stored toxins, leaf toughness, and resins can be seen as constitutive defenses, which means they are always present in the plant regardless of whether a threat is present. These attributes serve to deter herbivores at all times, rather than being specifically induced by an attack.

While thorns are an important form of defense and can sometimes increase in response to herbivore pressure, in the context of defining induced chemical defenses, they are better classified alongside other structural defenses, rather than the biochemical changes in response to stressors. Thus, understanding the nature of these defenses is crucial for properly identifying them in plant biology.