Final answer:
Photosynthetic organisms are central to sustaining life on Earth. Eukaryotic organisms perform photosynthesis in chloroplasts, while animals and fungi rely on other organisms to obtain their energy. Plants, algae, and cyanobacteria are autotrophs that use light to manufacture their own food.
Step-by-step explanation:
Actually, almost all organisms obtain their energy from photosynthetic organisms. For example, if a bird eats a caterpillar, then the bird gets the energy that the caterpillar gets from the plants it eats. So the bird indirectly gets energy that began with the glucose formed through photosynthesis. Therefore, the process of photosynthesis is central to sustaining life on Earth.
In eukaryotic organisms, photosynthesis occurs in chloroplasts. Only cells with chloroplasts - plant cells and algal (protist) cells - can perform photosynthesis. Animal cells and fungal cells do not have chloroplasts and, therefore, cannot photosynthesize. That is why these organisms, as well as the non-photosynthetic protists, rely on other organisms to obtain their energy. These organisms are heterotrophs.
Plants, algae, and a group of bacteria called cyanobacteria are the only organisms capable of performing photosynthesis. Because they use light to manufacture their own food, they are called autotrophs. Other organisms, such as animals, fungi, and most other bacteria, are termed heterotrophs because they must rely on the sugars produced by photosynthetic organisms for their energy needs.