CO2 levels influence how oxygen is produced and transported in living systems, but the effects depend on the context (photosynthesis in plants vs. respiration in animals). Here’s a concise breakdown: Core idea

• In plants, photosynthesis uses CO2 and water to produce glucose and oxygen. Higher atmospheric CO2 up to a point can increase the rate of photosynthesis and thus oxygen production, but the gain saturates because enzyme Rubisco becomes limiting and other factors (light, nutrients, stomatal conductance) constrain the rate. In natural conditions, the increase in O2 production with CO2 is not linear and plateaus at relatively modest CO2 elevations.

• In animals (including humans), CO2 does not directly “produce” oxygen; rather, CO2 levels influence the oxygen affinity and delivery through hemoglobin via the Bohr and Haldane effects. Higher CO2 lowers hemoglobin’s affinity for O2 in tissues (and can facilitate O2 unloading where it’s needed), while lower CO2 can increase oxygen affinity in the lungs. This affects how efficiently oxygen is delivered to cells, not how oxygen is produced.

Key mechanisms

• Plant photosynthesis:
  • CO2 enters via stomata and is fixed by RuBisCO in the Calvin cycle.
  • Increased CO2 can raise the initial rate of carbon fixation and O2 output, but only until other factors (light, temperature, water, nutrient supply) limit the process. The response tends to saturate around certain CO2 concentrations (often cited around a few hundred ppm to a few thousand ppm, depending on species and conditions).

• Animal respiration:
  • CO2 in blood interacts with hemoglobin and bicarbonate buffering; elevated CO2 lowers the affinity of hemoglobin for O2 (the Bohr effect), promoting O2 release to tissues. In the lungs, CO2 is expelled and O2 uptake occurs more readily as CO2 is removed, effectively aiding oxygen delivery rather than production.

What to watch for

• In plants, long-term elevation of atmospheric CO2 can improve short-term photosynthetic rates in some species, but this does not guarantee proportional increases in net oxygen release, because factors like nutrient availability and stomatal behavior can offset gains. Also, ecosystem dynamics and plant community composition influence overall atmospheric O2 production.

• In humans and other animals, sustained extreme CO2 levels are hazardous, impairing respiration and acid-base balance, but the immediate relationship to atmospheric O2 levels is indirect and pertains to delivery efficiency rather than production.

Practical takeaways

• CO2 can boost plant oxygen production to a point, especially under ample light and nutrients, but gains plateau due to enzyme capacity and other constraints.

• In animals, CO2 modulates oxygen transport by altering hemoglobin’s oxygen affinity and the efficiency of tissue oxygen delivery, not by changing oxygen production.

If you’d like, I can tailor this to a specific system (e.g., crop plants under elevated CO2, or human physiology during exercise) and provide more detailed mechanisms and quantitative examples.