USA Biology Olympiad (USABO) Practice Exam

Which statements correctly represent the characteristics of primary production?

1. Carried out only by green plants

2. Determines total energy flow through an ecosystem

3. Only carried out by photoautotrophs

4. All of the above

The correct answer is: Determines total energy flow through an ecosystem

Primary production refers to the process by which organisms create organic compounds from atmospheric or aquatic carbon dioxide, primarily through photosynthesis. This process is essential for the flow of energy in ecosystems, as it represents the initial stage of energy capture that supports all other life forms within that ecosystem. The statement that primary production determines total energy flow through an ecosystem is fundamentally accurate. Primary producers, such as plants, algae, and some bacteria, convert light energy into chemical energy. This energy is then transferred through the food chain as herbivores consume these producers, followed by carnivores consuming herbivores. Thus, the rate of primary production directly influences the amount of energy available for all other trophic levels. While it is true that green plants are significant contributors to primary production, there are other groups, such as algae and certain bacteria, that also perform primary production. Therefore, attributing this process solely to green plants is not entirely accurate. Similarly, while photoautotrophs—which include green plants, algae, and some bacteria—perform the bulk of primary production, there are also chemosynthetic organisms that carry out primary production in specific environments (e.g., deep sea hydrothermal vents) without sunlight. Thus, primary production is not limited to just photo