User:Gurcharanpreet Kaur

Food chain,

The sequence of transfers of matter and energy in the form of food from organism to organism. Food chains intertwine locally into a food web because most organisms consume more than one type of animal or plant. Plants, which convert solar energy to food by photosynthesis, are the primary food source. In a predator chain, a plant-eating animal is eaten by a flesh-eating animal. In a parasite chain, a smaller organism consumes part of a larger host and may itself be parasitized by even smaller organisms. In a saprophytic chain, microorganisms live on dead organic matter.

'Key points: ' Producers, or autotrophs, make their own organic molecules. Consumers, or heterotrophs, get organic molecules by eating other organisms. A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another. In a food chain, each organism occupies a different trophic level, defined by how many energy transfers separate it from the basic input of the chain. Food webs consist of many interconnected food chains and are more realistic representation of consumption relationships in ecosystems. Energy transfer between trophic levels is inefficient—with a typical efficiency around 10%. This inefficiency limits the length of food chains.

A food chain is a linear sequence of organisms through which nutrients and energy pass as one organism eats another. Let's look at the parts of a typical food chain, starting from the bottom—the producers—and moving upward. At the base of the food chain lie the primary producers. The primary producers are autotrophs and are most often photosynthetic organisms such as plants, algae, or cyanobacteria. The organisms that eat the primary producers are called primary consumers. Primary consumers are usually herbivores, plant-eaters, though they may be algae eaters or bacteria eaters. The organisms that eat the primary consumers are called secondary consumers. Secondary consumers are generally meat-eaters—carnivores. The organisms that eat the secondary consumers are called tertiary consumers. These are carnivore-eating carnivores, like eagles or big fish. Some food chains have additional levels, such as quaternary consumers—carnivores that eat tertiary consumers. Organisms at the very top of a food chain are called apex consumers.

Energy transfer efficiency limits food chain lengths 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. When energy enters a trophic level, some of it is stored as biomass, as part of organisms' bodies. This is the energy that's available to the next trophic level since only energy storied as biomass can get eaten. As a rule of thumb, only about 10% of the energy that's stored as biomass in one trophic level—per unit time—ends up stored as biomass in the next trophic level—per the same unit time. This 10% rule of energy transfer is a good thing to commit to memory.

As an example, let's suppose the primary producers of an ecosystem store 20,000 kcal/m^squared/year of energy as biomass. This is also the amount of energy per year that's made available to the primary consumers, which eat the primary producers. The 10% rule would predict that the primary consumers store only 2,000 kcal/m^ squared/year of energy in their own bodies, making energy available to their predators—secondary consumers—at a lower rate. This pattern of fractional transfer limits the length of food chains; after a certain number of trophic levels—generally three to six, there is too little energy flow to support a population at a higher level.

Why does so much energy exit the food web between one trophic level and the next? Here are a few of the main reasons for inefficient energy transfer^{1,2}

In each trophic level, a significant amount of energy is dissipated as heat as organisms carry out cellular respiration and go about their daily lives.

Some of the organic molecules an organism eats cannot be digested and leave the body as feces, poop, rather than being used.

Not all of the individual organisms in a trophic level will get eaten by organisms in the next level up. Some instead die without being eaten.