We all live in an ecosystem by interacting with different biotic and abiotic factors. An ecosystem is a biological community of interacting organisms and their physical environment. The existence of an organism depends on its adaptations to its particular ecosystem. One of the main requirements of an organism to sustain in its habitat or ecosystem is food. For example, we have seen lizards in our home eating insects. Lizards in turn preyed upon by a number of organisms, such as snakes, dogs and wolves. These organisms are then eaten by hawks and other top carnivores. These are examples of interactions happening in an ecosystem. This type of interaction is commonly called a food chain.
A food chain is a series of organisms in which transfer of energy takes place in the form of food from one organism to another organism. It also explains the feeding pattern or relationship between living organisms, flow of energy and nutrients. Every organism in the environment depends on one another for their food requirements as given below.
Fig: Grazing food chain
The sun is the ultimate source of energy that sustains life. The producers who occupy the first position use this solar energy to prepare food. The producers are then eaten by primary consumers which are then eaten by secondary consumers. The secondary consumers are then eaten by tertiary consumers which are preyed upon by the quaternary consumers. This is how energy flows from one species to another in an ecosystem.
When any of the organisms become dead, decomposers start acting on it. They release hydrolytic enzymes that break down organic substances into simple inorganic ones. These inorganic materials are then passed to the soil which is again used by the producers to prepare food. The decomposers are then eaten by detritivores which are then preyed upon by predators. This results in the continuous flow of energy and nutrients between different components in the ecosystem.
Fig: Detritus food chain
Table of contents
Food chain is described as a chronological series of organisms each depending on other organisms for food. It describes which organism in an ecosystem consumes other organisms. In a food chain, nutrients and energy are passed from one creature to the next in a sequential order. This occurs when one animal eats another. The food chain starts with the producer and ultimately ends with the decomposer. A trophic level describes the successive stages of a food chain, starting with producers at the bottom and moving up to primary, secondary, and tertiary consumers. Therefore, we can say that the trophic level is any point in the food chain.
Fig: Grazing food chain
Different organisms occupy different levels in the food chain and each level is referred to as trophic levels. In simple words, trophic level is described as the position of an organism along the food chain. For their energy needs, organisms at one trophic level rely on those at the lower trophic level.
Producers are present at the bottom or first trophic level of the food chain, synthesising their own food, followed by primary, secondary and tertiary consumers. The sun being the ultimate source of energy radiates sunlight which producers are able to utilise and synthesise the food. Consumers are dependent on plants for food. It includes herbivores (rats) that eat plants, carnivores that eat herbivores and other animals. Herbivores are known as primary consumers present at the second trophic level feeding on producers. Carnivores eat herbivores and come later in the food chain hence are known as secondary consumers. The herbivores are eaten up by secondary consumers or primary carnivores (snake) and present at third trophic level which is further eaten up by top carnivores (eagle) at fourth trophic level called secondary carnivores or tertiary consumers.
Fig: Different trophic levels in a food chain
There are four main elements of the food chain that are further divided into various trophic levels:
Sun is the ultimate source of energy for synthesis of food in all ecosystems except deep sea hydrothermal ecosystems. The producers are able to utilise this energy and prepare their own food which can be consumed by consumers. The decomposers have no role to play in receiving solar energy from the sun. Out of all the sunlight, 50% of all the solar radiation is photosynthetically active radiation (PAR). It is the portion of the light spectrum that can be used by plants. PAR refers to the light of wavelength ranging from 400 to 700 nm.
Fig: PAR in the light spectrum
Producers utilise only 1% of the available solar energy (PAR) to form organic matter or biomass that is available for the consumers. When primary consumers feed on the producers, they receive only 10% of the energy retained in the organic matter produced by the producers. Consequently, at each successive trophic level, only 10% of the energy retained at a lower trophic level is transferred to the next higher trophic level in a food chain.
Fig: Photosynthetically Active Radiation (PAR)
Out of this 50% PAR, 2 - 10% is captured by the plants and photosynthetic bacteria to prepare food.
Fig: PAR captured by producers
Deep sea hydrothermal ecosystems are an exception to the dependence of organisms on the sun for food. These ecosystems have extreme temperatures and pressures, toxic minerals and lack sunlight. The bacteria living in such ecosystems convert the toxic minerals or sulphur compounds and heat into food and energy and the process is known as chemosynthesis. These bacteria multiply and form thick mats on the floor which animals can graze and pass on the energy to them.
These specialised bacteria are present at the bottom of the deep hydrothermal food chain forming the first trophic level and many animals rely on their presence for survival, including deep sea mussels, giant tube worms, yeti crabs, fishes, etc.
Fig: Deep sea hydrothermal ecosystems
Producers are autotrophic organisms that prepare their own food. Producers like plants prepare their own food through the process called photosynthesis. The producers include phytoplankton, cyanobacteria, algae and green plants. The food chain starts from the producers. They occupy the first trophic level in the food chain and need mostly solar energy to prepare their food.
Consumers are those organisms that depend on plants or other organisms for their food and nutrient requirements. This is the most essential component of the food chain because it includes almost all the species of living organisms. They are further classified into various categories as follows:
Herbivores are those organisms that rely only on plants for their food requirement. They exist in the range of tiny insects to the large elephant. Herbivores are known as primary consumers and are occupying the second trophic level in a food chain. Examples include deer.
The organisms that eat other organisms are known as carnivores. They eat meat or flesh of other organisms. Carnivores eat herbivores or other small animals and come later in the food chain, hence are known as secondary or tertiary consumers. Examples include lions, tigers etc.
The organisms that consume plants, as well as animals, are known as omnivores. They occupy generally the tertiary trophic level in a food chain. Examples include human beings, dogs, bears, and many more.
Fig: Human being
A parasite is an organism that lives on or inside a host organism and obtains nutrition from or at the expense of the host. Parasitism is the type of population interaction here. It is a relationship between two living species in which one organism is benefited at the expense of the other (+/- interaction). The organism that is benefitted is called the parasite, while the one that is harmed is called the host. Examples include copepods, they are small crustaceans that are ectoparasites on many fishes.
Fig: Copepods on the mouth of fish
Scavengers are those living organisms that feed on dead biomass, such as meat or rotting plant material. These form the first level of the detritus food chain. Examples include jackals, hyenas, and wolves.
Fig: Hyenas waiting for leftover meat
Decomposers are microorganisms that feed on dead material and break down into simpler substances. They are heterotrophic organisms that convert organic substances into inorganic molecules and form nutrient-rich soil. These are normally microscopic organisms which help in chemically breaking down the complex organic compounds in freshly deposited detritus or fragmented detritus to simpler inorganic minerals or turning them into organic humus. Examples of decomposers include bacteria and fungi. They are also known as saprotrophs. They secrete digestive enzymes on a dead organism that break down dead and waste material into simple and inorganic matter. Decomposers contribute to the recycling of nutrients by adding nutrients to the soil or oceans that producers or autotrophs can utilise. An entirely new food chain is created as a result here.
These are animals which feed on freshly deposited detritus and fragments left over by scavengers and help in fragmenting and pulverising it. These include millipedes, earthworms, beetles, etc.
Food chain is classified into two types as follows:
The grazing food chain is a type of food chain that begins from the green plants and progresses via herbivores. Green plants or producers obtain food through a process of photosynthesis. The producers are directly dependent on the flow of solar energy. Energy is constantly added to the ecosystem through the grazing food chain. It fixes inorganic nutrients into organic compounds and includes all the macroscopic organisms.
In the grazing food chain, energy is produced by the producers which are then transferred to the primary consumers, secondary consumers , and then to the tertiary consumers.
A common example of a grazing food chain in the terrestrial ecosystem is given below. In this grazing food chain, energy is produced by the producers (plants) which are then transferred to the primary consumers (deer), secondary consumers (fox), and then to the tertiary consumers (tiger).
Fig: Grazing food chain in terrestrial ecosystem
Grazing food chain is also seen in an aquatic ecosystem, which is shown below. In this type, phytoplanktons are producers that produce food or energy which is then consumed by primary (clams), secondary (small fishes), and tertiary consumers (Shark).
Fig: Grazing food chain in aquatic ecosystem
The grazing food chain is further classified into two types as follows:
In this type of food chain, one animal consumes another animal. Predator refers to the animal that is consuming prey, while the prey is the animal that is being eaten. Predation is the type of population interaction here. For example, tiger (predator) hunting and feeding on deer (prey).
Fig: Tiger hunting and feeding on the deer
In this type of food chain, the plants, and animals in a grazing food chain are infected by parasites. The food energy transfers from the larger organisms to the smaller organisms without killing them in this food chain. Therefore, the larger organisms are referred to as ‘hosts’ whereas the smaller organisms that derive energy from the hosts are known as ‘parasites’. For example, Cuscuta (dodder or amarbel) is a parasitic plant that parasitises hedge plants (planted along the border like Bougainvillea). It lacks chlorophyll and leaves. It produces specialised roots called haustoria that penetrate the host vascular tissues (xylem and phloem) and derives its nutrition from the host plant.
Fig: Cuscuta with haustoria
The detritus food chain is a type of food chain that begins from dead organic matter called detritus. The decomposers act on the dead matter and break it down into simple and inorganic substances. The food energy is transferred to the decomposers and detritivores, which are then eaten by predators. Here, the primary consumers that act on detritus are fungus, bacteria, and protozoans and they are also known as decomposers. The secondary consumers that feed on bacteria and fungi are called detritivores and it includes earthworms. The tertiary consumers are those organisms that act as predators and feed on earthworms including sparrows.
Fig: Detritus food chain (DFC)
According to the 10% law of energy transfer, only 10% of the energy is transferred to each trophic level as we go up the trophic levels. Therefore, the energy flow decreases as we move up in the food chain. This law was given by Lindemann in 1942.
Sunlight is the ultimate source of energy for all ecosystems. It is trapped and utilised by the photosynthetic producers to prepare food. As organisms of one trophic level feed on another organism of a lower trophic level, energy flows through a food chain in the ecosystem. At each successive trophic level, only 10% of the energy is transferred from a lower to the next higher trophic level in a food chain.
For example, in the given scenario below, the energy trapped at the producer level = 20000 kJ
According to theory, only 10 % of energy is passed on from one trophic level to the next, So the energy transfer occurs in the following way:
Fig: 10% law of energy transfer
90% of energy is lost to the environment when it moves from one trophic level to another. The energy lost occurs mainly in the form of excretion and respiration.
Grazing food chain
Detritus food chain
Producers serve as the first trophic level in the grazing food chain
Dead material or detritus serves as the first trophic level in the detritus food chain
Energy is obtained directly from the sunlight
Energy is obtained from the organic debris
The grazing food chain releases energy into the ecosystem
The detritus food chain utilises energy from the ecosystem
In this type, all the macroscopic and sub-soil organisms are involved
In this type, microscopic organisms are mainly involved
This food chain is usually larger as compared to the detritus food chain
The food chain is usually smaller as compared to the grazing food chain
In an aquatic ecosystem, GFC is the major channel for energy flow
In a terrestrial ecosystem, a much larger fraction of energy flows through the detritus food chain than through the GFC
Fig: Grazing food chain
Fig: Detritus food chain
Organisms feed on alternate prey when one of their prey numbers is reduced. Both types of food chains, the grazing food chain and the detritus food chain can connect to one another. For example, the sparrow is a part of the detritus food chain and a fox is a part of the grazing food chain. This we saw above. Both food chains are connected and sparrows become the prey of foxes.
Fig: Grazing food chain (GFC) and detritus food chain (DFC) are connected
A food web is a complex interlinked network of food chains. The food chain begins with the producers which are able to make their own food in the presence of sunlight. The sun is the ultimate source of energy. However, it is not considered in food web. The capacity of organisms to feed on other organisms allows for the connection of numerous different food chains.
Autotrophs are the organisms which are able to synthesise their own food like grass that obtain the energy from the sun and convert it to chemical energy. Hence, it is a producer. This chemical energy is available in various forms depending on the plant. For example, it is available as fruits in the given example. Energy from the fruit here is obtained by consumers directly or indirectly (primary, secondary and tertiary). Primary consumers are herbivores whereas secondary and tertiary consumers are generally carnivores called primary and secondary carnivores.
Fig: Food web
The following are the importances of food chain:
Solution: The food chain is described as a chronological series of organisms each depending on another organism for food. It describes which organism in an ecosystem consumes which other organism. Producers constitute the first trophic level in the grazing food chain because they are capable of producing organic substances with the help of solar energy. Herbivores are those organisms that only feed on plants and therefore, constitute the second trophic level. Examples include deer. Hence, the correct option is a.
2. Identify the incorrect statement with respect to the detritus food chain?
Solution: The detritus food chain is a type of food chain that begins from dead organic matter called detritus. The decomposers act on the dead matter and break it down into simple and inorganic substances. The food energy is transferred to the decomposers and detritivores, which are then eaten by predators. Hence, the correct option is a.
3. Decomposers like fungi and bacteria are examples of ______________.
Solution: Decomposers are microorganisms that feed on dead material and break them down into simpler substances. They are heterotrophic organisms that convert organic substances into inorganic molecules and form nutrient-rich soil. Examples of decomposers include bacteria and fungi. They are also known as saprotrophs. They secrete digestive enzymes on a dead organism to break down dead and waste materials. Hence, the correct option is c.
4. The detritus food chain involves decomposers, organisms that feed on dead and decaying material (detritus) while the grazing food chain ________.
Solution: The grazing food chain is also known as GFC. It begins with autotrophs like green plants, cyanobacteria, etc., that are able to synthesise their own food and pass on the energy to herbivores and further to carnivores. Green plants or producers obtain food through a process of photosynthesis mainly. Hence, the correct option is a.
Answer: The food chain is crucial for the survival of various species and balance of an ecosystem. The extinction of a species can upset the balance of the ecosystem. It may also lead to the extinction of another species depending on the extinct organism for food. It will upset the predator prey relationship, if the extinct organism is a predator or prey.
Answer: Humans can be placed at the top level of most food chains because they can eat both plants as well as animals. Therefore, they are considered omnivores.
Answer: Apex consumers are those organisms that do not have their own predators and therefore, they are placed at the top of the food chain. This happens due to the reason that the predators at the top of the food chain are normally the biggest animals and usually nothing else eats them. A common example of an apex consumer is lion.
Answer: There are two major types of primary producers. They are the phototrophs and chemotrophs.
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