Nutrient cycles are cyclical in nature. Examples of nutrient cycles are carbon cycle, nitrogen cycle and water cycle. Large amount of carbon is stored in carbon sinks such as oceans and forests.
Feeding relationships in food chains can be classified as producers and consumers. The position of consumers in the food chain would determine if the consumer is a primary consumer, secondary consumer or tertiary consumer.
Energy flow through food chains and food webs is non-cyclical. Ultimate source of energy that flows through food chains and food webs is from the sun. Energy in the form of heat is lost during respiration, egestion and urination. Energy trapped in uneaten body parts such as bones, cartilage and teeth is also not recycled to the ecosystem. Energy transfer between trophic levels in food chain is estimated at 10% and this figure is not fixed as the efficiency of energy transfer is dependent on the composition of body mass of the prey and the metabolism rate of the consumer.
Status of the ecosystem at a specified area at a fixed time point is represented by pyramid of numbers and biomass respectively while status of ecosystem at a specified area over a time interval is represented by a pyramid of energy. Shape of pyramid of numbers and biomass can be upright or inverted while pyramid of energy is always upright.