Energy Flow

Energy is the fundamental force behind all metabolic activities in living organisms. In an ecosystem, energy moves from one organism to another in a sequence, a process known as energy flow. Ultimately, all energy comes from the Sun, captured by plants during photosynthesis and passed on through various trophic levels.

TROPHIC LEVEL INTERACTIONS
Trophic levels explain how organisms in an ecosystem are linked by their nutritional needs.

Autotrophs (Producers):
Green plants convert solar energy into chemical energy through photosynthesis.  
Gross Primary Production (GPP) is the total energy captured.  
Net Primary Production (NPP) is the energy stored after respiration and is available to consumers.

Herbivores (Primary consumers): They feed directly on plants.  
Carnivores: Secondary or tertiary consumers that feed on herbivores or other carnivores.  
Omnivores: Feed on both plants and animals.  
Decomposers: Break down dead organisms and recycle nutrients back to the soil.

Energy always flows from lower to higher trophic levels and never in reverse.

Trophic level interactions include:
• Food chain  
• Food web  
• Ecological pyramids  

FOOD CHAIN
A food chain is the direct transfer of food energy from producers to various consumers.  
Example: Grass → Grasshopper → Frog → Snake → Hawk

Types of food chains:
1. Grazing Food Chain – Starts with green plants and moves to herbivores and carnivores.  
2. Detritus Food Chain – Begins with dead organic matter (detritus) and involves decomposers like bacteria, fungi, protozoa, mites, worms, etc.

FOOD WEB
A food web is a network of interlinked food chains in an ecosystem. It is a more realistic representation of energy flow.  
Disruptions such as species extinction or human interference can break these linkages.

ECOLOGICAL PYRAMIDS
Ecological pyramids visually represent trophic levels in terms of number, biomass, or energy.

Types:
1. Pyramid of Numbers  
   • Upright: Numbers decrease from producers to predators (grassland ecosystem).  
   • Inverted: Numbers increase at higher trophic levels (many birds feeding on one tree).

2. Pyramid of Biomass  
   • Upright in terrestrial ecosystems.  
   • Inverted in aquatic ecosystems because phytoplankton biomass is lower than the biomass of herbivores feeding on them.

3. Pyramid of Energy  
   • Always upright.  
   • Shows the total energy flow at each trophic level.  
   • Based on thermodynamics—energy decreases as it moves upward.

ECOLOGICAL EFFICIENCY
This is the ratio of energy transferred from one trophic level to the next.  
Only about 10% of energy stored in one trophic level becomes biomass in the next (10% law – Lindeman, 1942).

TROPHIC LEVELS AND POLLUTANTS
Non-degradable pollutants such as mercury, lead, and DDT move through trophic levels. Two key processes occur:

1. Bioaccumulation  
   • Pollutants accumulate in the tissues of organisms faster than they can be excreted.  
   • Aquatic species may absorb pollutants directly from water (bioconcentration).  
   Example: Phytoplankton absorbing DDT.

2. Biomagnification  
   • Pollutant concentration increases as it moves up the food chain.  
   • Persistent Organic Pollutants (POPs) such as DDT, dioxins and furans biomagnify.  
   Example: Microscopic organisms → small fish → big fish → humans.

For biomagnification, the pollutant must be long-lived, mobile, and biologically active.

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Subject: Environment

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