Final answer:
Photosynthetic organisms are important to most ecosystems because they produce oxygen and organic molecules.
a) Produce oxygen and organic molecules
Step-by-step explanation:
Photosynthetic organisms, such as plants, are important to most ecosystems because they produce oxygen and organic molecules. They capture carbon dioxide from the atmosphere and convert it into sugars, which can be used by other organisms as a source of energy and to build organic compounds. Additionally, photosynthetic organisms release oxygen into the atmosphere, which is essential for cellular respiration and helps maintain the balance of gases in the atmosphere.