Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

What is a primary function of algae in the environment?

1. They decompose organic matter

2. They produce much of the Earth's oxygen

3. They serve as parasites to other plants

4. They provide structural support to soil

The correct answer is: They produce much of the Earth's oxygen

Algae play a crucial role in the environment primarily by producing much of the Earth's oxygen through the process of photosynthesis. During photosynthesis, algae convert carbon dioxide and sunlight into energy, releasing oxygen as a byproduct. This is significant because algae, particularly phytoplankton in the oceans, contribute an estimated 50-80% of the world's oxygen supply. Their ability to harness sunlight and convert it into chemical energy makes them foundational to aquatic ecosystems and a vital component of the global carbon cycle. In contrast, while some organisms are involved in decomposition or providing structural support, they do not produce oxygen on the same scale as algae. Furthermore, algae are not parasites; they primarily engage in photosynthesis and are an essential part of many food webs, serving as a food source for various aquatic organisms. Thus, the primary function of algae in the environment is unequivocally tied to oxygen production, which is critical for the survival of most life forms on Earth.