Food chains are limited in size in terms of energy flow due to the principles of energy transfer and the inefficiency of energy conversion in each trophic level. The concept of the 10% rule explains why energy decreases as it moves up the food chain. According to this rule, only approximately 10% of the energy from one trophic level is transferred to the next trophic level. The remaining 90% is lost as heat or used for metabolic processes.

The limited transfer of energy from one trophic level to the next is due to several factors:

Due to these energy losses and inefficiencies, food chains are limited in size. The transfer of energy becomes progressively reduced as it moves up the trophic levels. This limits the number of trophic levels that can be sustained in a food chain.

In a food web, which is a more complex network of interconnected food chains, the most energy is typically transferred at the primary producer level. Primary producers, such as plants or algae, capture and convert sunlight energy through photosynthesis into chemical energy in the form of organic compounds. This initial energy input into the food web provides the foundation and supports the subsequent transfer of energy to higher trophic levels. Consequently, the most energy transferred in a food web occurs at the primary producer level.

Dr Abdullah S. Seddiek thank you for your contribution to the discussion

The level of the food web that has the most energy is the producers, according to the 10% rule. Producers are organisms that make their own food, such as photosynthetic plants, algae and bacteria, or chemosynthetic bacteria. Thus, since producers make their own food, they can get 100% of the available energy. The first trophic level of the food chain has the most energy. This level contains the producers, which are all of the photosynthetic organisms. This includes plants and sometimes photosynthetic bacteria and protists. These organisms take energy from the sun and turn it into organic sugar. At the bottom of a food chain is always the primary producer. In terrestrial ecosystems most primary producers are plants, and in marine ecosystems, most primary producers are phytoplankton. Both produce most the nutrients and energy needed to support the rest of the food chain in their respective ecosystems. There is less available energy in the fourth trophic level because of the loss of energy through metabolism in each of the lower trophic levels. he greatest amount of energy available in the food chain is at the bottom of the food chain. Energy is transferred between trophic levels when one organism eats another and gets the energy-rich molecules from its prey's body. However, these transfers are inefficient, and this inefficiency limits the length of food chains. A food chain describes how energy and nutrients move through an ecosystem. At the basic level there are plants that produce the energy, then it moves up to higher-level organisms like herbivores. After that when carnivores eat the herbivores, energy is transferred from one to the other. The different feeding positions in a food chain or web are called trophic levels. Generally, there are no more than four trophic levels because energy and biomass decrease from lower to higher levels.