Photosynthesis and Limiting Factors
Light intensity, carbon dioxide concentration and temperature each set a ceiling on the rate of photosynthesis, and at any moment one of them is the limiting factor. Includes the inverse square relation between lamp distance and light intensity.
What a learner can do afterwards
- Reads a rate graph and names the limiting factor in each region of the curve.
- Uses the inverse square relation to say what moving a lamp twice as far away does to light intensity.
- Explains why a greenhouse grower may add carbon dioxide rather than more light.
1 · Read
Light, carbon dioxide and temperature each set a ceiling on photosynthesis, so a grower who wants more food finds which one limits the rate. Read the graph in regions: where the line climbs, the thing on the axis limits. Where it flattens, something else holds it down.
Light obeys the inverse square rule. Move a lamp from 1 metre to 2 metres and the leaf gets a quarter of the light. At 800 lux from 1 metre, moving to 4 metres leaves 50 lux, since 4 squared is 16.
Raise one ceiling and the rate climbs until the next factor bottlenecks. That is why a grower adds carbon dioxide when light is already plenty. Push heat too far and the enzymes running the reaction fail instead.
Remember the net rate too: photosynthesis builds sugar while respiration burns some, and leftover sugar becomes growth. A limit on the leaf is a limit on the whole plant.
Find the flat part, name the ceiling behind it, and raise that one before touching the rest.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.