Photosynthesis & Calvin Cycle Tournament
Study the Calvin-cycle figure, then eight H2 rounds: Rubisco, why the cycle stops in the dark, carboxylation–reduction–regeneration, PSII/PSI/ATP synthase, 3 CO2 per G3P, stroma vs thylakoid, and photorespiration.
Take a moment with the full diagram
Drag to pan, scroll or pinch to zoom. Trace the substrates, products, and any regulatory inputs you see. When you hit Begin tournament we'll zoom in on each question, so this is your chance to study the full pathway end-to-end.
8 timed rounds - perfect run = 1600 points. You'll pick a leaderboard handle at the end.
What this tournament tests
Each task maps to a distinct GCE A-Level cognitive demand. The opening figure orients you; the next 8 test the high-yield mechanism, regulation, sequence and quantitative reasoning that consistently appear on test day.
Whole-Pathway Overview
Pan the Calvin-cycle WikiPathways figure.
Fill in the Blank
Name the carboxylase.
Disruptor
Why fixation stops in the dark.
Sequence Ordering
Three phases of the C3 cycle.
Match the Pairs
PSII, PSI, ATP synthase, NADP+ reductase, lumen.
Numeric Input
CO2 per net G3P.
Select All That Apply
Compartment and product facts.
Odd One Out
O2 is not a Calvin substrate.
Photorespiration Disruptor
Closed stomata on a hot bright day.
Public leaderboard
Your score posts to a global, persistent leaderboard scored by points first, time as tiebreaker.
Photosynthesis in 60 seconds
Light reactions on the thylakoid: water is split, O2 leaves, electrons run PSII → PSI → NADP+, protons in the lumen drive ATP synthase.
Calvin cycle in the stroma: Rubisco, reduction with ATP+NADPH, regeneration of RuBP. 3 CO2 → 1 net G3P.
Closed stomata raise the O2/CO2 ratio and push Rubisco into photorespiration.
H2 papers often ask why the cycle is called “light-independent” yet still stalls in the dark: the enzymes do not need photons, but they do need the ATP and NADPH the thylakoid only makes in the light.
FAQ
Is this mapped to SEAB H2 Biology 9744?
Yes. Energy transfer in photosynthesis — photolysis, chemiosmosis, the Calvin cycle, and photorespiration — is a core 9744 paper topic. This tournament is written for the Singapore-Cambridge syllabus, not AQA or Edexcel wording.
How many CO2 molecules make one net G3P?
Three. Rubisco fixes one CO2 per turn. Three turns produce six G3P; five of those rebuild three RuBP, so one G3P is the net sugar export. Six CO2 are needed for one glucose.
Why does fixation stop in the dark if Rubisco is still present?
The Calvin cycle is light-independent only in the sense that it does not absorb photons. Reduction of 3-PGA and regeneration of RuBP consume ATP and NADPH from the light reactions. Those pools collapse in the dark, so carboxylation stalls.
Do I need an account to play the Calvin cycle game?
No. The tournament is public, browser-based, and posts to a leaderboard under a random handle stored in your browser.