Energy Flow in Ecosystems 🔄

☀️ Sun-powered life

• Except for a few deep-sea vents, every ecosystem runs on sunlight.
• Less than 50 % of incoming light is photosynthetically active radiation (PAR), and green plants lock up only 2 – 10 % of that PAR as chemical energy.:contentReference[oaicite:0]{index=0}
• This captured energy moves one way—from the sun ➜ producers ➜ consumers—never cycling back. (A neat example of the First Law of Thermodynamics in action.):contentReference[oaicite:1]{index=1}
• Living systems must keep “refilling” their energy tanks to fight the universal drift toward disorder, a nod to the Second Law of Thermodynamics.:contentReference[oaicite:2]{index=2}

🌱 Producers set the stage

Green plants (on land) plus phytoplankton, algae, and aquatic plants (in water) make food from simple inorganic molecules, forming the base of every food chain.:contentReference[oaicite:3]{index=3}

🕸️ Food chains & food webs

Grazing Food Chain (GFC) 🐐

• Starts with living plants.
• Example: Grass ➜ Goat ➜ Human.:contentReference[oaicite:4]{index=4}
• Main energy highway in aquatic habitats.:contentReference[oaicite:5]{index=5}

Detritus Food Chain (DFC) 🍂

• Begins with dead organic matter (detritus).
• Run by decomposers—fungi & bacteria—called saprotrophs that secrete enzymes and absorb the released nutrients.:contentReference[oaicite:6]{index=6}
• Dominant route of energy flow on land. GFC & DFC interlock to form complex food webs (think omnivores like cockroaches or crows).:contentReference[oaicite:7]{index=7}

📶 Trophic levels—energy “steps”

1. 1^st level: Producers 🌱
2. 2^nd level: Primary consumers (herbivores) 🐛
3. 3^rd level: Secondary consumers (primary carnivores) 🦊
4. Optional 4^th level: Tertiary consumers (secondary carnivores) 🦅

Energy dwindles with each step because only about 10 % moves up to the next level:

\( E_{n+1} = 0.1 \times E_n \) (“10 % Law”).:contentReference[oaicite:8]{index=8}

📊 Standing crop & biomass

• Standing crop = mass (or number) of living matter at a level right now.
• Measured as fresh or, more accurately, dry weight.:contentReference[oaicite:9]{index=9}

🎯 High-yield points for NEET

1. 10 % Law: Only one-tenth of energy climbs each trophic step.:contentReference[oaicite:10]{index=10}
2. GFC vs DFC: Aquatic systems rely on GFC; terrestrial ones on DFC.:contentReference[oaicite:11]{index=11}
3. Trophic level hierarchy: Producer → herbivore → carnivore; energy only flows upward.:contentReference[oaicite:12]{index=12}
4. Role of decomposers: Fungi & bacteria recycle detritus, closing nutrient loops.:contentReference[oaicite:13]{index=13}
5. PAR capture: Plants fix just 2 – 10 % of usable sunlight—small, yet it fuels the biosphere!:contentReference[oaicite:14]{index=14}

Keep these concepts handy, and you’ll shine on ecosystem-related questions 🌟