Final answer:
Carbon dioxide provides carbon atoms that are used to synthesize sugars during photosynthesis in autotrophs, which is essential for plant growth and survival of dependent organisms.
Step-by-step explanation:
During photosynthesis, carbon dioxide provides a source of carbon that is incorporated into sugar molecules. Autotrophs such as plants and algae, which have chloroplasts, or cyanobacteria, which utilize folded membrane structures, use chlorophyll to absorb light and convert it into chemical energy. The process begins with the absorption of light by chlorophyll and involves a series of reactions where water is oxidized, releasing oxygen, and carbon dioxide is reduced to form carbohydrates like glucose. This transformative process ultimately creates sugars that plants use for energy and growth, which are vital for the survival of all other organisms depending on plants for food and oxygen.