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CBSE Class 12 · Biology

Ecosystem

Official NCERT chapter from Biology (book code lebo1). ExamMaster notes are original teaching at CBSE Class 12 depth.

This lesson follows the official chapter “Ecosystem” in Biology. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.

  • CBSE Class 12
  • Medium level
  • 8 concepts

1Ecosystem — Structure and Function

Structure and function: living and non-living looks plus the jobs (make, eat, break) as taught. An ecosystem is a place-plus-jobs, not a pretty park. One pond or a forest as the case is enough.

A single tree labelled ecosystem because it is “nature” is a miss.

Figure. An ecosystem is a place plus the jobs in it. Light, water and soil are the abiotic setting; producers, consumers and decomposers are the biotic jobs that run on that setting.

How it works

  1. Name the place and the jobsThe ecosystem.
  2. Keep living and non-living as two looksThe extra.
  3. Refuse a poster as the wholePlace-plus-jobs.

2Productivity

Productivity: how much food-make sits in a time as taught — GPP and NPP if split. Productivity is a rate of make, not a pretty green. One school sentence is enough.

A standing crop as the leftover rate is a miss if the lesson split them.

Figure. Gross primary productivity is the whole pile of plant production. NPP is what remains after plants burn some of it (R). Here NPP = GPP − R = 20 − 8 = 12 in schematic units, not a named forest census.

How it works

  1. Name make-per-timeProductivity.
  2. Split GPP/NPP only if taughtThe extra.
  3. Refuse a colour as the testA rate.

3Decomposition

Decomposition: break-down of the leftover as taught — detritus, a decomposer. Decomposition is a recycle-job, not a scare. One leaf-litter sentence is enough.

A predator labelled decomposer because it “eats” is a miss.

Figure. Decomposition is a chain of jobs on dead matter: break it (fragmentation), wash solubles (leaching), digest it (catabolism), leave humus, then release mineral ions plants can reuse. The boxes teach order, not duration.

How it works

  1. Name break-down of leftover bitsDecomposition.
  2. Keep a fungus or a named decomposer if taughtThe who.
  3. Refuse a scare as this headingA recycle.

4Energy Flow

Energy flow: one-way as taught — sun to make to eat, leftover heat. Flow is a direction, not a cycle (matter cycles). One arrow-sentence is enough.

A nutrient-cycle labelled energy-flow is a swap.

Figure. Energy enters as sunlight, is fixed by producers, then moves one way through eaters. At each living step some energy leaves as heat, so the flow is not a nutrient cycle.

How it works

  1. Name sun → make → eatThe flow.
  2. Keep it one-way; heat leftoverThe caution.
  3. Refuse a cycle-word as this headingEnergy ≠ matter.

5Ecological Pyramids

Ecological pyramids: number, biomass, or energy as taught — a stack of trophic looks. A pyramid is a count-map, not the place. Energy pyramids sit upright as framed.

A hill labelled pyramid because it is “triangle-shaped” is a miss.

Figure. A pyramid of energy is always upright: each higher trophic band holds less energy. Widths here are schematic so the top band stays readable; they are not a 10× scale. Numbers or biomass can invert; energy does not.

How it works

  1. Name number, biomass, or energyThe sort.
  2. Keep trophic levels as the stackThe map.
  3. Refuse a hill as this headingA count-map.

6Energy drops as you go up a trophic level

Energy drops as you go up a trophic level: a 10% look if taught. Drop is why stacks thin. One honest sentence is enough — not a precise farm-audit.

A 100% pass as the leftover is a miss.

Figure. Lindeman's school rule of thumb: about one tenth of the energy at one trophic level is available to the next. 10000 J → 1000 J → 100 J. The three boxes are drawn the same size because a true 10× width would hide the last box.

How it works

  1. Name the drop up the stackThe look.
  2. Keep 10% only if the lesson used itHonest extra.
  3. Refuse a full passA drop.

7A miss: treating a pyramid drawing as the place

A miss: treating a pyramid drawing as the place. The drawing is a map; the ecosystem is the pond or forest. A perfect triangle is a teach-sketch.

A printed pyramid as “this is the forest” is the miss.

Figure. A pyramid is a count of energy or numbers, not a map of a place. Treating the drawing as the pond itself is the miss: the pond is water, plants and fish in a location; the pyramid is a summary of one quantity by level.

How it works

  1. Keep the drawing as a mapA teach-sketch.
  2. Keep the place as the ecosystemTwo things.
  3. Refuse a swap of figure for placeThe miss named.

8Keep the claim at this class

Keep the claim at this class: jobs, a make-rate, one-way energy, a pyramid-sort. It is not a research carbon-model.

A journal-abstract tone is the wrong size.

Figure. Keep the Class 12 claim that is actually taught here: a pyramid of energy stays upright. An inverted pyramid of numbers (one tree, many insects) is a different quantity. Do not read that later picture as a failure of the energy claim.

How it works

  1. Stay on the school mapsThis class.
  2. Keep one pond or forestEnough.
  3. Refuse a model-dumpThe claim-size.
Energy flow is
  1. One-way as taught — not a nutrient-cycle
  2. A perfect recycle of energy
  3. A brand

Heat leftover.

Notes

  • Mapped to the official NCERT chapter “Ecosystem”. Original teaching only — no textbook sentences.
  • Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.

Recap

Hold these pegs from the official chapter “Ecosystem”. The wording is ExamMaster’s teaching, not a textbook recap.

Ecosystem — Structure and Function
Structure and function: living and non-living looks plus the jobs (make, eat, break) as taught.
Productivity
Productivity: how much food-make sits in a time as taught — GPP and NPP if split.
Decomposition
Decomposition: break-down of the leftover as taught — detritus, a decomposer.
Energy Flow
Energy flow: one-way as taught — sun to make to eat, leftover heat.
Ecological Pyramids
Ecological pyramids: number, biomass, or energy as taught — a stack of trophic looks.
Energy drops as you go up a trophic level
Energy drops as you go up a trophic level: a 10% look if taught.

Practise Ecosystem

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  • A 4-question practice set that ends the chapter
  • 1 quick check with worked explanations
  • Timed mocks scored with the real marking scheme
  • Readiness tracked per topic, kept on your device
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