Quantitative and multi‑factor analysis of photosynthesis
Bioenergetics • Photosynthesis
Flashcards
Test your knowledge with interactive flashcards
Key concepts
What you'll likely be quizzed about
Inverse proportion and the inverse square law
Light intensity from a point source decreases with the square of the distance. Light intensity (I) is proportional to 1 divided by the distance squared (d2), so doubling the distance reduces intensity to one quarter. Practical measurements of photosynthetic rate often use the 1/d2 relationship to convert lamp distance into relative light intensity for graphs and calculations.
Applying inverse square law to photosynthesis
Rate of photosynthesis increases as light intensity increases only while light is the limiting factor. Light intensity values derived from 1/d2 feed directly into rate-vs-intensity plots. Careful experimental design maintains other factors constant so the measured change in rate can be attributed to the change in light intensity. Experimental protocols commonly record oxygen production or bubble counts at set distances and convert distances using 1/d2.
Interpreting graphs with two or three factors
Rate-vs-factor graphs show characteristic regions: a rising region where the plotted factor limits the reaction, and a plateau where another factor becomes limiting. When two factors change, the steeper gradient indicates the factor currently limiting rate; when the curve flattens, a different factor limits further increase. Multiple curves on a single graph (e.g., rate against CO2 at two temperatures) reveal which factor becomes limiting under each condition by comparing maximum rates and plateau positions.
Identifying the limiting factor
A limiting factor is any condition that reduces or stops the rate of photosynthesis. Low temperature slows enzyme-controlled reactions; low CO2 reduces available reactant; low light supplies insufficient energy. On a graph, the limiting factor corresponds to the axis along which the rate still rises. If rate rises with increasing CO2 but plateaus with increasing light, light is not limiting while CO2 or temperature becomes limiting. Clear identification requires holding other variables constant during measurement.
Relating limiting factors to greenhouse cost-effectiveness
Investment in heat, light or CO2 increases yield only when that variable is limiting. Increasing a non-limiting factor wastes resources because the rate already sits on a plateau set by another factor. Controlled environments use sensors and feedback (e.g., increase CO2 as light increases) to match inputs to demand and avoid unnecessary cost. Economic decisions compare the marginal gain in yield from increasing a factor with the marginal cost of providing it. Practical guidelines advise balancing all three conditions to achieve profitable yield improvements.
Key notes
Important points to keep in mind