Advanced Placement (AP) Biology Practice Exam

Which of the following is classified as a plant hormone?

1. Insulin

2. Abscisic acid

3. Adrenaline

4. Glucagon

The correct answer is: Abscisic acid

Abscisic acid is classified as a plant hormone because it plays a crucial role in regulating various physiological processes within plants. It is involved in response to environmental stress conditions, such as drought, by helping to close stomata to reduce water loss. Additionally, abscisic acid is important in seed dormancy and promoting the maturation of seeds, making it vital for plant growth and development. This hormone helps communicate the plant's conditions and needs, allowing for appropriate responses to environmental changes. Insulin and glucagon are hormones produced by the pancreas and are involved in regulating blood glucose levels in animals, making them significant in animal physiology but unrelated to plant hormone functions. Adrenaline is a hormone produced by the adrenal glands in response to stress and is part of the fight-or-flight response in animals, which again places it outside the scope of plant hormones.