A single path of energy flow through trophic levels in an ecosystem is known as a food chain. It represents the transfer of energy and nutrients as one organism consumes another in a linear sequence. However, it's essential to note that ecosystems are complex, and multiple interconnected food chains form a food web, which more accurately represents the intricate interactions between various organisms in an ecosystem.

Let's take an example of a simple food chain:

Grass (Producer) -> Grasshopper (Primary Consumer) -> Frog (Secondary Consumer) -> Snake (Tertiary Consumer) -> Hawk (Quaternary Consumer)

Now, let's address why approximately 90% of energy is lost between trophic levels, with only about 10% being transferred to the next level:

As energy is transferred from one trophic level to the next, these cumulative losses add up, resulting in a significant reduction of available energy. This pattern is consistent in most ecosystems and forms the basis for the 10% rule, which states that approximately 10% of the energy is transferred from one trophic level to the next in a food chain or food web. The rest of the energy is dissipated as heat or used by the organisms at that level for their own needs, ultimately contributing to the functioning and dynamics of the ecosystem.

Dr Gaurav H Tandon thank you for your contribution to the discussion

Primary producers use energy from the sun to produce their own food in the form of glucose, and then primary producers are eaten by primary consumers that are in turn eaten by secondary consumers, and so on, so that energy flows from one trophic level, or level of the food chain, to the next. Each food chain is one possible path that energy and nutrients may take as they move through the ecosystem. All of the interconnected and overlapping food chains in an ecosystem make up a food web. Organisms in food webs are grouped into categories called trophic levels. The flow of energy in an ecosystem is always unidirectional. It is said to be unidirectional because some energy is lost in form of heat when moving from one trophic level to the next for the maintenance of the homeostasis of an organism. The flow of energy in an ecosystem follows the 10% rule, meaning only 10% of the energy is transferred to the successive trophic level and the rest is lost in the atmosphere. The energy is produced by the autotrophs, as they have photosynthetic pigments to harness the sunlight into chemical energy via photosynthesis. Energy flow in an ecosystem is consistently unidirectional or one way, i.e., solar radiations – producers – herbivores – carnivores. It cannot pass in the reverse direction. There is a decrease in the content and flow of energy with the rise in trophic levels. Everytime an organism consumes something, 90% of the energy is lost as heat during respiration, in digestion, etc. Only 10% is involved in building the body tissue. This 10% is passed to the next trophic level and so on. The amount of energy at each trophic level decreases as it moves through an ecosystem. As little as 10 percent of the energy at any trophic level is transferred to the next level; the rest is lost largely through metabolic processes as heat. At each step up the food chain, only 10 percent of the energy is passed on to the next level, while approximately 90 percent of the energy is lost as heat.