An ecosystem is a functional unit of nature comprising biotic communities and their abiotic environment interacting through energy flow and nutrient cycling. It is important for NEET Biology because NTA frequently tests the 10% law of energy transfer, ecological pyramids, GPP vs NPP, and the decomposition process.
Sun (Solar Energy)
Ultimate source of energy for nearly all ecosystems. Drives photosynthesis in producers.
Producers (Autotrophs)
Green plants, algae, and cyanobacteria that convert solar energy to chemical energy via photosynthesis. Form the base of every food chain.
Primary Consumers (Herbivores)
Animals like grasshoppers, rabbits, and deer that feed directly on producers. Transfer roughly 10% of energy to the next level.
Secondary Consumers (Carnivores)
Predators such as frogs, snakes, and small birds that feed on primary consumers.
Tertiary Consumers (Top Carnivores)
Apex predators like eagles and lions at the top of the food chain. They have the least available energy.
Decomposers
Fungi and bacteria that break down dead organic matter through fragmentation, leaching, catabolism, humification, and mineralisation, releasing nutrients back into the soil.
Energy Flow
Unidirectional transfer of energy from sun to producers to consumers. Only about 10% of energy is passed to the next trophic level (Lindeman’s 10% law).
Nutrient Cycling
Cyclic movement of nutrients (N, P, C) from decomposers back into the soil and then to producers. Unlike energy, nutrients are recycled.
10% Law (Lindeman’s Efficiency)
Only 10% of energy is transferred from one trophic level to the next. The remaining 90% is lost as heat through respiration. NTA frequently tests this with numerical problems on energy available at different trophic levels.
Ecological Pyramids (Number, Biomass, Energy)
Pyramid of energy is always upright. Pyramid of biomass can be inverted in aquatic ecosystems. Pyramid of numbers can be inverted when a single large tree supports many organisms. Know examples for each type.
GPP vs NPP and Standing Crop
GPP = total rate of photosynthesis. NPP = GPP − Respiration. Standing crop = biomass per unit area at a given time. NTA tests the relationship between GPP, NPP, and respiration losses.
Decomposition Process
Five steps: fragmentation (by detritivores), leaching (water-soluble nutrients seep into soil), catabolism (enzymatic breakdown), humification (dark humus formation), and mineralisation (humus degraded to inorganic nutrients). Know the difference between humification and mineralisation.
Solve previous year NEET questions on ecosystem, energy flow, and ecological pyramids.
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