Stomata
Microscopic pores in the plant epidermis, each controlled by guard cells, that regulate carbon dioxide entry and water-vapor loss.
A single pore and its guard cells form a stoma; stomata is the plural. Guard cells change shape to adjust pore opening, balancing the carbon dioxide needed for photosynthesis against water loss through transpiration Transpiration Water moving up through the plant and evaporating out through the stomata. It drives nutrient uptake, and carries calcium, which moves almost entirely by that flow. .
Stomatal responses integrate light, internal carbon dioxide, humidity, temperature, water status, and plant hormones. Pores can respond over minutes, while stomatal size and density develop over longer timescales.
Cannabis gas exchange therefore depends on both the number of stomata and how open they are under the current conditions. An environmental change can affect carbon uptake and water loss together because both gases share the stomatal pathway.