Plant hormonal regulation differs from animal hormonal regulation in that:

• A. plant hormones are composed solely of proteins, whereas animal hormones are not
• B. animal hormones never influence gene expression, while plant hormones always do
• C. plant hormones are transported exclusively through specialized glands
• D. plant hormones often act at very low concentrations and can have multiple, sometimes opposing, effects depending on context

Answer: (D)

Verified step by step guidance

1. Understand the concept of plant hormones: Plant hormones are chemical messengers that regulate various physiological processes in plants, such as growth, development, and responses to environmental stimuli. They are distinct from animal hormones in their mechanisms and effects.
2. Recognize the key characteristics of plant hormones: Unlike animal hormones, plant hormones often act at very low concentrations and can have multiple effects depending on the context. These effects can sometimes be opposing, depending on factors such as the type of tissue, developmental stage, or environmental conditions.
3. Clarify the incorrect options: Plant hormones are not composed solely of proteins; they include diverse chemical classes such as auxins, gibberellins, cytokinins, ethylene, and abscisic acid. Additionally, plant hormones are not transported exclusively through specialized glands, as plants lack glands; they are transported through vascular tissues or diffuse between cells. Animal hormones can influence gene expression, so the statement that animal hormones never influence gene expression is incorrect.
4. Compare plant and animal hormonal regulation: Animal hormones are typically produced by specialized glands and transported through the bloodstream to target tissues. In contrast, plant hormones are synthesized in various parts of the plant and can act locally or be transported through vascular tissues or cell-to-cell diffusion.
5. Conclude with the correct answer: The defining feature of plant hormonal regulation is that plant hormones often act at very low concentrations and can have multiple, sometimes opposing, effects depending on the context. This flexibility allows plants to adapt to changing environmental conditions and developmental needs.