USA Biology Olympiad (USABO) Practice Exam

Which statement accurately describes plant growth?

1. All plants exhibit secondary growth

2. Some plants lack secondary growth

3. Plants only grow for one season

4. Growth is solely determined by environmental factors

The correct answer is: Some plants lack secondary growth

The statement that some plants lack secondary growth is accurate because growth patterns in plants can vary significantly depending on the species. Secondary growth refers to the increase in thickness or girth of stems and roots that occurs primarily in woody plants, such as trees and shrubs, through the activity of the vascular cambium and cork cambium. However, many plants, especially herbaceous plants (like many annuals and perennials), do not undergo secondary growth. These plants primarily exhibit primary growth, which allows for elongation and development of leaves and stems without a significant increase in thickness. This is crucial to understanding plant biology as it highlights the diversity of growth forms among plants. For example, herbaceous plants remain relatively thin and grow primarily in height each season, rather than thickening like woody plants. Recognizing this variability helps in studying different plant responses to their environments and understanding their adaptations and life cycles.