In ecology, energy flow refers to the flow of energy through a food chain. In an ecosystem, we attempt to establish the feeding relationships between organisms living together. Each organism belongs to a ‘trophic level’ which refers to the position occupied by an organism in the food chain. Energy is passed on from every trophic level to the next and each time about 90%90% of the energy is lost with some being lost as heat into the environment and some being incompletely digested food. So primary consumers get about 10%10% of the energy produced by autotrophs while secondary consumers get 1%1% and tertiary consumers get 0,1%0,1%. A general energy flow scenario is as follows:

Autotrophs: solar energy is fixed by autotrophs (also called producers, such as green plants) into energy in the form of carbohydrates. This is done by photosynthesis.
Primary consumers: part of the food made available by plants is consumed by primary consumers known as herbivores. The energy gained is converted to body heat or used to grow, reproduce, etc. Energy loss also occurs in the expulsion of undigested food by egestion.
Secondary consumers: carnivores and omnivores consume the primary consumers, and use the energy obtained to grow, move, respire etc.
Tertiary consumers: may be the major predators of an ecosystem, and feed on the primary and secondary consumers with some energy passed on and some lost as with other levels of the food chain.
Decomposers: A final link in any food chain are the decomposers which break down the organic matter of the tertiary consumers and release the nutrients into the soil. They also break down plants, herbivores and other dead organic matter. Examples of decomposers are bacteria and fungi.

The flow of energy in an ecosystem can be explained in the form of a chain, web or pyramid.

Food Chain

A food chain refers to the order of events in an ecosystem, where one living organism eats another organism, and later that organism is consumed by another larger organism. The flow of nutrients and energy from one organism to another at different trophic levels forms a food chain.

The food chain also explains the feeding pattern or relationship between living organisms. Trophic level refers to the sequential stages in a food chain, starting with producers at the bottom, followed by primary, secondary and tertiary consumers. Every level in a food chain is known as a trophic level.

The food chain consists of four major parts, namely:

The Sun: The sun is the initial source of energy, which provides energy for everything on the planet.
Producers: The producers in a food chain include all autotrophs such as phytoplankton, cyanobacteria, algae, and green plants. This is the first stage in a food chain. The producers make up the first level of a food chain. The producers utilise the energy from the sun to make food. Producers are also known as autotrophs as they make their own food. Producers are any plant or other organisms that produce their own nutrients through photosynthesis.
Consumers: Consumers are all organisms that are dependent on plants or other organisms for food. This is the largest part of a food web, as it contains almost all living organisms. It includes herbivores which are animals that eat plants, carnivores which are animals that eat other animals, parasites that live on other organisms by harming them and lastly the scavengers, which are animals that eat dead animals’ carcasses.

Here, herbivores are known as primary consumers and carnivores are secondary consumers. The second trophic level includes organisms that eat producers. Therefore, primary consumers or herbivores are organisms in the second trophic level.

Decomposers: Decomposers are organisms that get energy from dead or waste organic material. This is the last stage in a food chain. Decomposers are an integral part of a food chain, as they convert organic waste materials into inorganic materials, which enriches the soil or land with nutrients.

Decomposers complete a life cycle. They help in recycling the nutrients as they provide nutrients to soil or oceans, that can be utilised by autotrophs or producers. Thus, starting a whole new food chain.

Food Web:

Several interconnected food chains form a food web. A food web is similar to a food chain but the food web is comparatively larger than a food chain. Occasionally, a single organism is consumed by many predators or it consumes several other organisms. Due to this, many trophic levels get interconnected. The food chain fails to showcase the flow of energy in the right way. But, the food web is able to show the proper representation of energy flow, as it displays the interactions between different organisms.

When there are more cross-interactions between different food chains, the food web gets more complex. This complexity in a food web leads to a more sustainable ecosystem.

Types of Food Chain

There are two types of food chains, namely the detritus food chain and the grazing food chain. Let’s look at them more closely:

Detritus food chain: The detritus food chain includes different species of organisms and plants like algae, bacteria, fungi, protozoa, mites, insects, worms and so on. The detritus food chain begins with dead organic material. The food energy passes into decomposers and detritivores, which are further eaten by smaller organisms like carnivores. Carnivores, like maggots, become a meal for bigger carnivores like frogs, snakes and so on. Primary consumers like fungi, bacteria, protozoans, and so on are detritivores which feed on detritus.
Grazing food chain: The grazing food chain is a type of food chain that starts with green plants, passes through herbivores and then to carnivores. In a grazing food chain, energy in the lowest trophic level is acquired from photosynthesis.

In this type of food chain, the first energy transfer is from plants to herbivores. This type of food chain depends on the flow of energy from autotrophs to herbivores. As autotrophs are the base for all ecosystems on Earth, the majority of ecosystems in the environment follow this kind of food chain.

Pyramids Of Number, Biomass, And Energy

Ecological pyramids are used to indicate trophic structures of an ecosystem. A diagram shaped likea pyramid is developed to represent the numbers of organisms, their biomass, and energy relationships. In a food chain, a fraction of energy is usually lost in the form of heat. Therefore, organisms usually pass lesser energy from one trophic level to the next. A pyramid is formed because of this loss of energy through a food chain. The high step in an ecological pyramid contains a lower number of individuals than the lower steps. There are three types of pyramids which may be found among organisms in the ecosystem.

Pyramid of numbers
Pyramid of biomass
Pyramid of energy

Pyramid of numbers.

This indicates the number of individual organisms at different trophic levels of a food chain. The numbers of organisms decrease rapidly above each successive link of the pyramid. In the pyramid, there must be enough plants to produce food at the bottom, and the number continues decreasing from one consumer to the other hence the shape of the pyramid. The number of a consumer cannot be similar to that of its prey; otherwise, they would risk being wiped out. A pyramid of numbers helps identify the number of organisms at each trophic level. It can also help to find out how one organism’s population can affect another.

Pyramid of Biomass.

The pyramid of biomass is formed by the biomass of the members of the food chain. This pyramid indicates a decrease in the biomass in each tropical level from the base to the apex of the pyramid. There are two types of the pyramid of biomass that is an inverted and upright pyramid of biomass. An inverted pyramid is where the mass of producers is higher than that of consumers. A pyramid of biomass helps in quantifying the biomass at each trophic level.

Pyramid of Energy.

This pyramid indicates the amount of energy flow at each level and the role that various organisms play in the transfer of energy. It also indicates the amount of energy needed to support the next trophic level flowing up. As you move from the bottom to the top through trophic levels, energy decreases. The pyramid of energy is useful in showing the transfer of energy from one organism to another.

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