# Ecosystem Notes, Class 12 Biology | SwaVid Ecosystem: NCERT Class 12 Biology notes with key ideas, key terms, common mistakes and 3 quick checks with worked answers. Written by SwaVid from the textbook. Canonical: https://www.swavid.com/cbse/class-12/biology/chapter/ecosystem Source: https://www.swavid.com/cbse/class-12/biology/chapter/ecosystem # Ecosystem ## Key terms ## Key ideas ## Common mistakes ## Quick checks ## Keep going ## Questions parents ask ## Class 12 Biology on SwaVid ### Structure and function of ecosystem ### Productivity ### Process of decomposition ### Energy flow and food chains ### Ecological pyramids ### Next chapter ### Related chapter ### Related chapter ### All chapters SwaVid › CBSE › Class 12 › Biology › Ecosystem Notes written by SwaVid from the NCERT textbook. Class 12 Biology, Chapter 12. Key ideas, formulas and common mistakes. CBSE prints 10 marks for Unit X, not for this chapter alone. Short answer. This chapter explains the structure and function of an ecosystem as a functional unit of nature. It covers productivity, decomposition, energy flow through trophic levels, and ecological pyramids. Source: NCERT Biology (Reprint 2026-27) , Chapter 12, Ecosystem An ecosystem consists of biotic and abiotic components interacting as a system. Key functional aspects are productivity, decomposition, energy flow, and nutrient cycling. Primary productivity is the rate of biomass production by autotrophs per unit area over a time period. Gross primary productivity minus respiration loss gives net primary productivity, which is the biomass available to heterotrophs. Decomposers break down complex organic matter into inorganic substances like carbon dioxide, water, and nutrients. The main steps are fragmentation, leaching, catabolism, humification, and mineralisation. Of the incident solar radiation, less than 50 percent is photosynthetically active radiation (PAR). Plants capture only 2 to 10 percent of PAR, and energy flows unidirectionally through food chains obeying the ten percent law. Ecological pyramids represent number, biomass, or energy at successive trophic levels. Pyramids of energy are always upright, whereas pyramids of biomass can be inverted, as seen in an aquatic ecosystem. Try each question first. Then tap it to see the answer. Use the relationship: NPP = GPP - R Substitute values: NPP = 120 - 35 85 kcal m⁻² yr⁻¹ Energy at primary consumer level = 10% of 20,000 J = 2,000 J Energy at secondary consumer level = 10% of 2,000 J = 200 J 200 J Producers are small phytoplankton with very short life cycles and low standing crop at any given time. Consumers such as fishes have longer life spans and accumulate far greater biomass than the phytoplankton. Because the biomass of fishes far exceeds that of phytoplankton Biodiversity and Conservation . Organisms and Populations . Microbes in Human Welfare . The 13 chapters of Class 12 Biology . CBSE does not give marks to one chapter. It prints 10 marks for Unit X, Ecology and Environment, which includes Ecosystem. No. They are written by SwaVid from the NCERT textbook. The CBSE curriculum is the reference for what is assessed. Biodiversity and Conservation. SwaVid is an AI tutor for Indian students in Classes 6 to 12. It finds the earlier ideas a child missed, then teaches today’s chapter. Start free to see how it works. - Ch 12 NCERT book - 10 marks, Unit X - 3 quick checks - Confusing PAR with total incident solar radiation . Remember that photosynthetically active radiation (PAR) makes up less than 50 percent of total incident solar radiation, not the whole amount. - Believing all pyramids of biomass are upright . Recall that in oceans or aquatic ecosystems, the pyramid of biomass is often inverted because the standing crop of phytoplankton is small compared to zooplankton. - Treating humification and mineralisation as physical breakdown steps . Fragmentation is the physical breakdown by detritivores, while humification and mineralisation are chemical transformations occurring in the soil during decomposition. ## Key Links - [CBSE](https://www.swavid.com/cbse) - [Class 12](https://www.swavid.com/cbse/class-12) - [Biology](https://www.swavid.com/cbse/class-12/biology/chapters) - [Start free →](https://www.swavid.com/signup) - [All 13 chapters](https://www.swavid.com/cbse/class-12/biology/chapters) - [NCERT Biology (Reprint 2026-27)](https://ncert.nic.in/textbook.php) - [Open notes](https://www.swavid.com/cbse/class-12/biology/chapter/biodiversity-and-conservation) - [Open notes](https://www.swavid.com/cbse/class-12/biology/chapter/organisms-and-populations) - [Open notes](https://www.swavid.com/cbse/class-12/biology/chapter/microbes-in-human-welfare) - [Class 12 Biology](https://www.swavid.com/cbse/class-12/biology/chapters) - [Start free →](https://www.swavid.com/signup)