Final answer:
Plants, algae, and cyanobacteria use sunlight to perform photosynthesis, converting carbon dioxide and water into glucose and oxygen, thereby producing their own food and contributing to the food chain and atmospheric oxygen.
Step-by-step explanation:
Plants, algae, and cyanobacteria are all photoautotrophs, which means they are capable of synthesizing their own food using light as an energy source through a process called photosynthesis. During photosynthesis, these organisms use sunlight to convert water and carbon dioxide into glucose and oxygen. Glucose provides the energy they need to grow and thrive while oxygen is released as a byproduct. This amazing capability allows photoautotrophs to serve as the foundation of most ecosystems, providing essential organic compounds and oxygen to other forms of life that cannot produce their own food.
Specifically, cyanobacteria harness the sun's energy by oxidizing water to provide electrons, which is part of the energy generation process in photosynthesis. These photoautotrophs, including planktonic algae, can be found in large quantities in various aquatic environments, sometimes covering vast areas on the water's surface. Plants, algae, and cyanobacteria alike are critical for life on Earth because they form the base of the food chain and contribute significantly to the atmospheric oxygen.