Plants convert the sun's energy into their leaves, roots, stems, flowers and fruit through photosynthesis. Organisms eat the plants, and through the process of respiration use the stored energy to conduct their everyday activities. Additionally, some energy is lost as heat. In all, the organism uses about 90 percent of the stored plant's energy. After several steps in the food chain, no energy is left to recycle.

Plants convert sunlight to stored energy through photosynthesis. They combine sunlight with carbon dioxide and water to make glucose and oxygen. The plant releases the oxygen to the atmosphere, while the glucose is stored in the plant tissue. The molecular bonds formed between the carbon atoms in the glucose store the energy.

Organisms eat the plants. Their bodies break the carbon bonds in the glucose to produce energy. Animals combine oxygen with glucose to form carbon dioxide, water and energy. The energy is used for daily activities, and some of the energy is lost to the atmosphere as heat.

Energy transfer in the ecosystem is complex. Plants make the energy, herbivores eat the plants and carnivores eat the herbivores. Eventually an animal dies, and microbes return its physical matter to the soil and atmosphere for plants to use again. However, by this point, the physical material may have passed through several organisms, possibly as many as nine or more. All of the energy from the original plant has been used or converted to heat, and nothing is left to recycle.