Final answer:
Plants maintain a consistent size and shape primarily due to rigid cell walls and osmotic pressure regulation. They have developed adaptations like a waxy cuticle to manage their internal environments and respond to external changes through feedback mechanisms.
Step-by-step explanation:
Plants maintain a fairly constant size and shape due to several key features in their structure and physiology. One primary reason is the rigid cell walls that provide plants with structural support, helping them to protect against external changes such as temperature variations. In addition to support, these cell walls are essential in preventing the cells from bursting or shrinking due to osmotic pressure.
Furthermore, plants have evolved various adaptations including a waxy cuticle and strengthened stems and vascular systems as part of their negative and positive feedback mechanisms that allow them to maintain their internal environment and respond appropriately to external environmental changes.