In a standard food pyramid, organisms are divided into trophic levels based on their means of gaining nutrients. As one moves upwards through trophic levels, the number of organisms that can be sustained decreases. This is because energy is lost between each level. Typically, about 90% of the energy in one trophic level is lost during transfer to the next highest level; this leaves on about 10% of the energy to be used by the consumer. Because of this disparity, it is very difficult to maintain large populations at higher trophic levels. This explains why lower level organisms can easily flourish (such as ants), while higher level organisms can easily become endangered (such as tigers).

The sun is the source of all energy in an ecosystem. Without the energy from the sun, the plants cannot grow and the animals would not have food to eat. Plants are considered producers, meaning that they are able to convert sunlight into chemical energy. Animals are considered consumers, in that they consume plants or other animals to absorb energy. If you trace back far enough in a food chain, you will always arrive at a producer and, subsequently, the sun.

Living things need water to grow, but it does not directly contribute energy. 

The great white shark is at the top of the food pyramid in its ocean ecosystem. Since it is at the top, it receives the least amount of energy from its food because the amount of energy decreases as one moves up the pyramid.

Green algae contains the pigment chlorophyll, which is responsible for photosynthesis. This makes green algae a producer, and the lowest level of the pyramid. As a result, the green algae will represent the largest amount of energy in the ecosystem. The anchovy eats the algae, the tuna eats the anchovy, the seal eats the tuna, and the shark eats the seal. After each level, approximately 90% of the energy of the pervious level is lost. After four transitions (to get to the level of the shark), only 0.01% of the original producer energy has been transferred to the shark!

Autotrophs are the base part of any food pyramid/web/chain. They take inorganic substances and turn them into organic substances that are later consumed and used by heterotrophs for energy. Most autotrophs absorb carbon dioxide from the atmosphere and minerals/nutrients from the soil in order to feed, reproduce, and grow, drawing their resources from the surrounding inorganic environment.

The sun, while crucial to many autotrophs, provides energy for the processes—however, it does not provide carbon, nutrients, or minerals. Human activity may contribute to the autotrophs' activity, but it is not the main source of the necessary resources.

Autotrophs make their own food, then using cellular metabolism, this food is converted to energy. Examples are plants converting sunlight, carbon dioxide and water into glucose and oxygen (photosynthesis). Then, the plants breakdown glucose, converting this food molecule into the energy molecule ATP via glycolysis, Krebs cycle and electron transport under aerobic conditions, and via fermentation under anaerobic conditions. Heterotrophs, like humans, must ingest organic material (food) in order to meet their energy demands.

The energy in a food pyramid decreases as it is tranferred up the pyramid. The bottom of the pyramid, the producers, start with the most energy. When they are eaten by primary consumers, only about ten percent of the energy is transferred to the next level; the rest is lost. The next level of secondary consumers also only keeps about ten percent of the energy from the level below that—only one percent of the original producer-level energy. This loss of energy continues up to the highest level of the pyramid. The lost energy is released as heat into the atmosphere. 

The sun is the main source of energy in all ecosystems. Plants harvest all their energy through photosynthesis, then other organisms eat the plants (and other producers) to gain energy. Without the sun this process would never happen. 

The majority of energy in a food chain is lost as respiratory heat. Whenever an organism takes food, breaks it down, and converts it to energy, heat is a byproduct that contains the energy lost. About 66% of the energy in a food chain is lost due to respiratory heat. No energy is lost to decomposers, rather, it is transferred to them. The decomposers respire, and create heat as well. 

Efficient foraging, also known as economical foraging, is the process by which organisms attempt to maximize their energy return for energy expended. In other words, if a lion was hunting she would want to find food that would give her more energy from eating it than she would spend hunting it.

A heterotroph consumes other organisms to obtain energy. Photoautotrophs use sunlight to make glucose in the process of photosynthesis. In photosynthesis, organisms combine carbon dioxide with water to produce sugar molecules. Chemoautotrophs use chemicals to build molecules and obtain energy.