Photosynthesis in Higher Plants
Class 11 · Biology
5 ideas in Class 11 Biology, explained in plain words, with games and quizzes to practise.
Discoveries and Site
Part of: Discoveries and Light Capture
Leaf-half tests prove CO2 need; Priestley restores air, Ingenhousz adds light, Sachs stores starch, Engelmann maps blue-red action, van Niel frees O2 from water. Membranes trap light into ATP and NADPH while stroma builds sugar; dark means unlit-supplied, not unlit-only.
Why it matters. Each experiment isolates one need. Site division explains light-dark teamwork.
Formulas
- 6CO2 + 12H2O -> C6H12O6 + 6H2O + 6O2
Key words
- Carbon dioxide
- : Gas whose need was shown by leaf halves in KOH tubes.
- Air purification
- : Restoring fouled air, shown by Priestley with mint sprigs.
- Thylakoid
- : Light-trapping membranes holding pigments and carriers.
- Stroma
- : Fluid ground where sugar is built from light supplies.
- van Niel insight
- : Oxygen shown to come from water, not carbon dioxide.
- Dark reaction
- : Sugar-building phase needing light-made ATP and NADPH.
Try it in two minutes
- Order five discoverers.
- Assign membranes versus stroma.
- Balance twelve waters.
Try at home. Cover leaf halves and test starch.
Pigments and Light Reactions
Part of: Discoveries and Light Capture
Four leaf pigments funnel blue-red light to chlorophyll a centres; helpers widen range and guard oxidation. Hundreds-strong antennae feed single P680 and P700 converters; electrons ride Z-shaped downhill runs, splitting water for O2 while cyclic loops spin ATP alone.
Why it matters. Funnel design explains efficiency. Loop choice balances ATP with NADPH.
Key words
- Chlorophyll a
- : Chief pigment that converts light at reaction centres.
- Accessory pigments
- : Helper pigments that widen range and guard oxidation.
- Antennae
- : Harvester groups feeding one central converter.
- PS II (P680)
- : Converter working first in the electron line.
- PS I (P700)
- : Converter feeding electrons toward NADP reduction.
- Z scheme
- : Downhill electron run linking the two photosystems.
- Cyclic flow
- : Loop spinning extra ATP without making NADPH.
Try it in two minutes
- Rank four pigments.
- Place P680 before P700.
- Trace Z from water to NADPH.
Try at home. Separate leaf pigments on paper.
Chemiosmosis and Calvin Cycle
Part of: Carbon Fixation
Water splitting, shuttling and NADP reduction pack lumen protons; CF channels spend gradients into ATP. Five-carbon RuBP catches CO2 into twin threes; reduction spends 2 ATP plus 2 NADPH per carbon while regeneration rebuys RuBP; six turns yield glucose.
Why it matters. Gradient spending explains ATP. Per-carbon costs scale to glucose.
Formulas
- One CO2 fixed costs 3 ATP + 2 NADPH
- One glucose built costs 18 ATP + 12 NADPH
Key words
- Chemiosmosis
- : Flow of protons through CF channels to build ATP.
- RuBP
- : Five-carbon CO2 catcher that splits into twin threes.
- PGA
- : First stable three-carbon product of carbon fixing.
- RuBisCO
- : Enzyme that both fixes carbon and wastes oxygen.
- Calvin cycle steps
- : Fixing, sugar-building and RuBP-rebuilding in stroma.
Try it in two minutes
- Name three proton sources.
- Order fix, reduce, regenerate.
- Multiply costs by six.
Try at home. Chart Calvin inputs and outputs.
C4 Pathway and Photorespiration
Part of: Carbon Fixation
Wreathed bundle sheaths host Calvin while mesophyll PEP traps carbon into OAA ferries; sheath CO2 floods favour carboxylation and silence wasteful oxygenation that plagues C3. Pumps buy heat tolerance and richer yields.
Why it matters. Anatomy plus chemistry beats heat. Pump logic explains crop yields.
Key words
- Kranz anatomy
- : Wreath of sheath cells around veins, home of C4 Calvin cycle.
- PEPcase
- : First carbon trap of C4 plants, working in mesophyll cells.
- RuBisCO
- : Main carbon-fixing enzyme kept in bundle-sheath cells.
- Oxaloacetic acid
- : Four-carbon first product of the C4 pathway.
- Malate and aspartate
- : Ferries that carry fixed carbon to sheath cells.
- Photorespiration
- : Wasteful oxygen fix that C4 pumps silence in heat.
Try it in two minutes
- Spot Kranz wreaths.
- Follow OAA to sheath.
- Weigh oxygenation loss.
Try at home. Compare maize with wheat leaves.
Factors Affecting Photosynthesis
Part of: Photosynthesis Factors
Scarcest inputs cap rates by Blackman's rule: light saturates early at a tenth of sun, thin air starves C3 while C4 sates sooner, warmth favours C4 enzymes, and thirst shuts pores and wilts blades. Greenhouses exploit CO2 hunger.
Why it matters. Limiting logic diagnoses fields. Factor curves guide greenhouse control.
Formulas
- Rate is capped by whichever factor runs scarcest
Key words
- Blackman law
- : Rule that the scarcest input caps the photosynthesis rate.
- Saturation point
- : Light level beyond which brighter light adds no speed.
- CO2 enrichment
- : Extra air CO2 that lifts yields of C3 crops in houses.
- Water stress
- : Pore shutdown plus wilting that slows thirsty leaves.
- Temperature optimum
- : Warmth-loving enzymes that favour C4 plants in heat.
Try it in two minutes
- Rank four factors.
- Spot the limiter.
- Enrich greenhouse air.
Try at home. Shade one plant and compare growth.
What your child will practise
- C4 Pathway and Photorespiration: Desert Quick Fire (Quick Fire)
- Chemiosmosis and Calvin Cycle: Space Puzzle (Clue Puzzle)
- Discoveries and Site: Ocean Quick Fire (Quick Fire)
- Factors Affecting Photosynthesis: Jungle Puzzle (Clue Puzzle)
- Pigments and Light Reactions: Candy Quest (Flip and Match)
- Quiz: C4 Pathway and Photorespiration (8 questions)
- Quiz: Chemiosmosis and Calvin Cycle (8 questions)
- Quiz: Discoveries and Site (8 questions)
- Quiz: Factors Affecting Photosynthesis (8 questions)