What determines the length of food chains in an ecosystem? Why do food chains consist of no more than 3-5 links?

Any food chain begins with an organism that is capable of autotrophic nutrition. These are mainly plants. During photosynthesis, they create glucose, which is needed by other animals. Plants are eaten by herbivores. They, in turn, are eaten by predators that cannot feed on plants. Any chain ends with bacteria that recycle dead organisms. As we can see, chains are created due to the need to obtain glucose. The more organisms there are in the chain, the less glucose the organisms will receive.