USA Biology Olympiad (USABO) Practice Exam

What role does primary productivity play in an ecosystem?

1. It determines species variety

2. It influences weather patterns

3. It affects energy flow to herbivores

4. It shapes soil composition

The correct answer is: It affects energy flow to herbivores

Primary productivity refers to the process by which photosynthetic organisms, primarily plants and phytoplankton, convert sunlight into chemical energy through photosynthesis. This process is fundamental to ecosystem functioning as it establishes the base of the food web. The organic materials produced by primary producers serve as the primary source of energy for herbivores and, subsequently, for higher trophic levels, including carnivores. The correct response highlights the critical role primary productivity plays in affecting energy flow to herbivores. When primary productivity is high, it means there is ample energy available for herbivores to consume, which can lead to increased herbivore populations and subsequently support more carnivores. This energy transfer is crucial for maintaining the structure and dynamics of the ecosystem. While factors like species variety, weather patterns, and soil composition are influenced by various ecological interactions, the direct link between primary productivity and the energy available to herbivores is essential for understanding how ecosystems function. Without sufficient primary productivity, an ecosystem can become imbalanced, leading to declines in herbivore and, ultimately, carnivore populations.