Ecosystem
Class 12 · Biology
4 ideas in Class 12 Biology, explained in plain words, with games and quizzes to practise.
Structure and Productivity
Part of: System Parts
Ecosystems layer species vertically as stratification and run four functions: productivity, decomposition, energy flow and nutrient cycling. Gross production minus respiration leaves net production for heterotrophs; the biosphere makes 170 billion tons yearly with oceans contributing only 55 despite covering 70 per cent.
Why it matters. GPP-R equation plus ocean-share reasoning starts energy questions.
Formulas
- GPP minus R equals NPP
- Biosphere NPP is 170 billion tons yearly
- Oceans cover 70 percent but make 55 billion tons
Key words
- Stratification
- : Vertical layering of species.
- GPP
- : Total production by photosynthesis.
- NPP
- : Production left after respiration.
- Secondary productivity
- : Consumer biomass formation rate.
- Producers
- : Autotrophs fixing solar energy.
Try it in two minutes
- Layer forest top to bottom.
- Subtract R from GPP.
- Share 170 tons land-sea.
Try at home. Explain why ocean productivity lags behind land.
Rot and Return
Part of: System Parts
Detritus passes through fragmentation, leaching, catabolism, humification and mineralisation together. Humus resists decay and stores nutrients while mineralisation frees them. Lignin and chitin slow the work, sugars and nitrogen speed it; warmth and moisture help while cold and airless conditions stall it.
Why it matters. Step order plus rate prediction is classic reasoning.
Key words
- Detritus
- : Dead matter awaiting decay.
- Fragmentation
- : Shredding by detritivores.
- Leaching
- : Washing solubles downward.
- Catabolism
- : Enzyme breakdown to simples.
- Humus
- : Dark resistant nutrient store.
- Mineralisation
- : Release of inorganic nutrients.
Try it in two minutes
- Chain five steps in order.
- Split humus from minerals.
- Weigh chemistry against climate.
Try at home. Explain why earthworms are called farmer friends.
Chains, Levels and Ten Per Cent
Part of: Flow of Energy
Under half the sunlight is PAR, plants capture 2 to 10 per cent, and only a hundredth becomes NPP. Grazing chains start living while detritus chains start dead; each level passes about a tenth upward as heat escapes. Sparrows and humans occupy several levels at once.
Why it matters. Per-cent arithmetic plus chain sorting powers energy questions.
Formulas
- PAR is under half the sunlight
- Plants capture 2 to 10 percent of PAR
- Each level passes about one-tenth upward
Key words
- PAR
- : Usable light under half of sun.
- Trophic level
- : Feeding rank in chains.
- Grazing chain
- : Living-producer food path.
- Detritus chain
- : Dead-matter food path.
- Ten per cent law
- : A tenth passes upward.
- Standing crop
- : Living mass present now.
Try it in two minutes
- Shrink sunlight to NPP.
- Split grazing from detritus.
- Pass tenths up levels.
Try at home. Explain why food chains stay short.
Ecological Pyramids
Part of: Shaped Numbers
Number, biomass and energy pyramids usually stand upright, but tree insects invert numbers and sea fish invert biomass. Energy never inverts because heat escapes each step. Six million plants supporting three top carnivores shows the sharp drop, though pyramids ignore webs and saprophytes.
Why it matters. Exception cases plus always-upright energy are favourite traps.
Key words
- Pyramid of number
- : Counts stacked by level.
- Pyramid of biomass
- : Mass stacked by level.
- Pyramid of energy
- : Energy stacked by level.
- Inverted pyramid
- : Top heavier than base.
Try it in two minutes
- Draw three upright pyramids.
- Invert tree and sea cases.
- Note webs and saprophytes missing.
Try at home. Explain the sea biomass paradox.
What your child will practise
- Chains, Levels and Ten Per Cent: Candy Puzzle (Clue Puzzle)
- Chains, Levels and Ten Per Cent: Candy Quick Fire (Quick Fire)
- Ecological Pyramids: Desert Puzzle (Clue Puzzle)
- Rot and Return: Desert Quest (Flip and Match)
- Structure and Productivity: Ocean Quick Fire (Quick Fire)
- Quiz: Chains, Levels and Ten Per Cent (8 questions)
- Quiz: Ecological Pyramids (8 questions)
- Quiz: Rot and Return (8 questions)
- Quiz: Structure and Productivity (8 questions)