Food Chain in Ecosystem

Food Chain in Ecosystem

Food Chain

All organisms, including humans, need food that provides energy for growth, maintenance, and reproduction.

Any food or element required by an organism to live, grow, or reproduce is called a nutrient. Depending on the amount of which is needed, a nutrient can be classified as:

• Macronutrient – needed in large amounts, e.g., carbon, oxygen, hydrogen, nitrogen, phosphorus, etc.

• Micronutrient – needed in small quantities, e.g., iron, zinc, copper, iodine, etc.

A part of the energy provided by food is used for biological processes, and the rest is dissipated to the environment as heat energy by the process of respiration. Undigested food is excreted and enters the detritus path.

Food energy passes from plants & planktons to animals in a chain called the food chain.

On the Land

• The food chain is a sequence of organisms in a community, each of which uses the next lower member of the sequence as a food source, plants & planktons being at the base of the sequence on the land surface.

• The starting point in a food chain is always a green plant.

In the Seas & Oceans

Similarly, there are planktons in the seas and oceans that use sunlight to help them make their food. Fish, shellfish, and other crustaceans eat the plankton. These animals are eaten by bigger animals such as sharks and whales. Whales are killed by humans for meat.

In the Deep Sea and Oceans – Chemosynthesis

In deep sea and oceans, in the place of photosynthesis, a different process called chemosynthesis takes place. Her,e specialized bacteria convert simple compounds from their surroundings into more complex compounds without sunlight.

They use instead, a different source of energy instead. Deep in the Earth’s surface, heat is generated by the decay of radioactive elements. This heat is released at hot water vents in the ocean depths.

The bacteria use this geothermal energy for chemosynthesis. Later, these bacteria are consumed by many aquatic animals.

Ecological Pyramid (Producer & Consumer, Prophic Level and Usable Energy)

Types of Food Chains

There are two types of food chains— simple & complex food chains. A complex food chain is also called a food web.

1. Simple Food Chain

• In a grassland, grass is eaten by grasshoppers, grasshopper is eaten by frogs, frog is eaten by snakes, and snake is eaten by hawks.

  • Simple food chain: Grass < Grasshopper < Frog < Snake < Hawk < Decomposed by Fungi and so on.

Simple Food Chain

2. Complex Food Chain (Food Web)

• A number of food chains interwoven with one another give rise to a structure similar to the web of a spider.

• In cases where some organisms eat a variety of other organisms, the food chain becomes more complex. Such a complicated network of food chains is called a food web.

• As a variety of organisms live in the ecosystem and there is competition for food among them, food webs are very complex. Realistically, almost all ecosystems have food webs, not merely food chains.

Complex Food Chain i.e., Food Web

Ecological Pyramid of Trophic (Feeding) Levels

Each group of organisms occupies a trophic or feeding level.

Trophic Levels Classification:

• First Trophic Level: All green plants and other producers in the ecosystem occupy the first trophic level.

• Second Trophic Level: Herbivores, which feed on plants, are placed at the second trophic level.

• Third Trophic Level: (Primary carnivores) that eat herbivores occupy the third trophic level.

• Fourth Trophic Level: Top/Secondary carnivores that eat carnivores are placed at the fourth trophic level.

Ecological Efficiency and 10 Percent Law (Lindeman's 10% Law)

The different trophic levels are not equal in terms of energy available, as only a fraction of energy is transferred from lower to higher trophic levels.

• The percentage of energy transferred from one trophic level to another is called Ecological Efficiency. This efficiency varies from 5% to 20% depending on the types of organisms and environmental conditions.

• The 10% law of transfer of energy was introduced by American ecologist Raymond Lindeman (1915–42) in 1942.

• In the terrestrial ecosystem, only 10% of plant material is eaten by herbivores. That means on average, only 10% of energy is transferred from one trophic level to another.

• This means 100 kg of grain is needed to produce 10 kg of meat.

Such low efficiency is because not all the organisms present at one level become easily available as food for the consumers at a higher level. Predators may not be able to capture all the prey available. Those organisms that escape the predators eventually die, and they provide food for the decomposers.

Because ecological efficiency is low, the capacity of an ecosystem to support organisms at the higher trophic level is limited.

Energy and Matter Movement

Energy flow is the flow of energy from the sun through the materials and living things (as food) on the earth, then into the environment (as heat), and eventually into space as infrared radiation.

• A model of energy and nutrient movement in the ecosystem is discussed here. The sun provides radiant energy for the producer to manufacture food.

• The energy is transferred from the producer to the herbivores and then to the carnivores. Dead or decomposed remains of producers, herbivores, and carnivores provide energy for the decomposers.

• While a part (10%) of the food energy consumed is assimilated by organisms, the rest (90%) of it is dissipated as heat by respiration.

• Respiration is the reverse of photosynthesis. In the respiration process, the sugar molecule is broken down in the presence of oxygen and water into carbon dioxide, energy, and water.

  • Sugar + Oxygen + Water → Carbon dioxide + Energy + Water

• There is a unidirectional flow of energy from the sun until it is dissipated as heat into space.

• The movement of nutrient elements through various components of an ecosystem is called the biogeochemical cycle.

• The movement of matter in the form of mineral nutrients from the soil to the plants helps in the growth of the plants.

• These nutrients are consumed by herbivores and carnivores for their growth. When the plants and other organisms die, decomposers like bacteria and fungi feed on them and break them down into inorganic nutrients. These are available in the soil to be recycled by plants.

• The flow of mineral nutrients through the system is cyclic.

• Concerning the matter, the Earth is essentially a closed system. Matter cannot escape from its boundaries.

• In the words of Physics, energy can neither be created nor destroyed; it can only be transferred from one form to another (Law of Conservation of Energy).

• The ecological system maintains its stability by continuous input of energy from the Sun and the cyclic movement of nutrients through the system.

Bio-geo-chemical Cycle

The energy that enters the Earth's atmosphere as light and heat is balanced by the energy that is absorbed by the biosphere, plus the amount that leaves the Earth's surface as invisible heat radiation.

The term biogeochemical is a contraction/abbreviation that refers to the consideration of the biological, geological, and chemical aspects of each cycle.

Any of the natural cycles by which essential elements of living matter are circulated is called a biogeochemical cycle. For example: Water-cycle, Carbon-cycle, Nitrogen cycle, Oxygen-cycle, Phosphorus-cycle, etc.

Biogeochemistry

• It is a branch of science that was founded by Russian geochemist and mineralogist Vladimir Ivanovich (V.I.) Vernadsky (1863–1945) in 1926.

Carbon-Cycle

Carbon Dioxide in the Atmosphere

Carbon dioxide constitutes just 0.03% by volume of the atmosphere, yet it is vital to life.

Note: The percentage of carbon dioxide in the dissolved gaseous state/form present in the water is 0.3%.

Role of Carbon Dioxide in Photosynthesis

• Plants take carbon from carbon dioxide in the air, and they use chlorophyll to gather energy from the Sun.

• From these inputs and water, plants make glucose. In this process of photosynthesis, plants release oxygen.

• Animals breathe in this oxygen, and digest their food that comes from plants. This is called the carbon cycle.

  • Formula of Carbon Cycle: Photosynthesis process + Respiration process of organisms + Combustion process of coal, oil, etc. = Carbon Cycle

Combustion and CO₂ Emissions

• When we burn fossil fuels like coal, oil, etc., the carbon in the fuel combines with atmospheric oxygen to form carbon dioxide. This is called the combustion process.

Impact of Human Activities

• Since we burn a lot of fuel, there is a huge emission of carbon dioxide. This increase in carbon dioxide concentration upsets the carbon balance in the atmosphere.

• There are not enough growing plants to absorb all the excess carbon dioxide.

• Things become worse when we cut down forests and burn more trees.

The current excessive level of carbon dioxide, however, leads to a higher temperature, global warming, and climate change.

Final Thoughts

The food chain is a vital process that ensures the flow of energy through every ecosystem. From producers like green plants to top carnivores, each trophic level plays a crucial role in maintaining ecological balance. The 10% law highlights how energy transfer between levels is limited, making the efficiency of ecosystems naturally low.

This limitation means that resource management and biodiversity protection are essential. The biogeochemical cycles ensure that nutrients are continuously recycled, keeping life on Earth sustainable. Processes like photosynthesis, respiration, and chemosynthesis show nature’s adaptability in supporting life.

However, human activities such as deforestation and burning fossil fuels disrupt these delicate systems, leading to climate change and global warming. Protecting energy flow and nutrient cycles is not just an environmental issue but a necessity for our survival.

By understanding and respecting the interconnectedness of ecosystems, we can ensure a healthier planet for future generations. The Sun’s energy, once captured by plants, ultimately sustains all life, making it our most precious resource.