Add respiration back to get gross photosynthesis
- The idea
- Predict
- See it
- Why
- Check
The idea
“The O2 a plant gives off in the light is the photosynthesis number, and I always subtract respiration.”
Respiration costs the plant O2, so subtracting it feels careful. The leaf already did that subtraction before the sensor saw anything.
The short version
The mistake: The O2 a plant gives off in the light is the photosynthesis number, and I always subtract respiration.
What's actually true: What a plant gives off in the light is net, with respiration already taken out. Gross is net plus respiration.
- Gross photosynthesis is all the O2 chloroplasts make. Mitochondria respire in the light too, so what leaves the leaf is net.
- To get gross, measure respiration in the dark and add it to net. This assumes respiration is the same in light and dark.
- Ecosystems work the same way. Gross primary productivity is all the energy producers capture. The net, NPP, is what's left after respiration and is stored as biomass.
On the exam: The light reading is net. Gross is net plus respiration.