Photosynthesis Rate Explorer
Explore how light intensity, CO₂ concentration, and temperature affect photosynthesis rates. View light response curves with compensation and saturation points, compare absorption and action spectra of photosynthetic pigments, and identify limiting factors.
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Results
Net Photosynthesis: 16.17 μmol CO₂/m²/s
Active carbon fixation (net CO₂ uptake)
Rate Breakdown
Limiting Factor
Key Light Points
Current Conditions
Overall Equation
Light Response Curve
Net photosynthesis rate vs light intensity at CO₂ = 400 ppm and T = 25.0°C
Reference Guide
Light Reactions (Thylakoid)
The light-dependent reactions occur in the thylakoid membranes of chloroplasts. Chlorophyll and accessory pigments absorb photons, which excite electrons through two photosystems (PSII and PSI).
- Water is split (photolysis), releasing O₂ as a byproduct.
- The electron transport chain generates a proton gradient used by ATP synthase to produce ATP.
- NADP⁺ is reduced to NADPH, which carries electrons to the Calvin cycle.
Calvin Cycle (Stroma)
The Calvin cycle (light-independent reactions) occurs in the stroma. It uses ATP and NADPH from the light reactions to fix CO₂ into organic molecules.
- Carbon fixation by RuBisCO combines CO₂ with RuBP (a 5-carbon sugar) to form two 3-carbon molecules (3-PGA).
- Reduction converts 3-PGA to G3P using ATP and NADPH.
- Regeneration of RuBP requires ATP, completing the cycle.
Limiting Factors
Blackman's law of limiting factors states that the rate of photosynthesis is determined by the factor closest to its minimum. Only one factor limits the rate at any given time.
- Light intensity limits rate at low levels. The relationship follows a rectangular hyperbola, saturating at high intensities.
- CO₂ concentration limits rate when light is sufficient. Atmospheric CO₂ (~400 ppm) is often limiting for C3 plants.
- Temperature affects enzyme activity. Rate increases with temperature up to an optimum (~25-30°C for most plants), then drops sharply due to enzyme denaturation.
The compensation point is the light intensity where photosynthesis exactly balances respiration (net rate = 0). The saturation point is where further increases in light produce no significant rate increase.
Absorption vs Action Spectrum
The absorption spectrum shows which wavelengths each pigment absorbs. The action spectrum shows which wavelengths actually drive photosynthesis.
- Chlorophyll a absorbs strongly in blue (~430 nm) and red (~662 nm), reflecting green light (which is why leaves appear green).
- Chlorophyll b has peaks at ~453 nm and ~642 nm, acting as an accessory pigment that broadens the range of usable light.
- Carotenoids absorb in the 400-500 nm blue range. They also protect chlorophyll from photooxidation damage.
The action spectrum closely follows the combined absorption of all pigments, confirming that absorbed light directly drives photosynthesis. The green trough (500-570 nm) shows minimal photosynthetic activity.