In a greenhouse, which gas is commonly supplemented to enhance photosynthetic efficiency and growth?

• A. Oxygen
• B. Carbon Dioxide
• C. Nitrogen
• D. Argon

Answer: (B)

The main idea is that increasing the amount of carbon dioxide available to plants can boost photosynthesis and, as a result, growth. Photosynthesis uses CO2 along with light and water to produce sugars. When CO2 levels are low, the rate at which plants can fix carbon is limited; raising CO2 concentrations in a greenhouse provides more substrate for the Calvin cycle, allowing the photosynthetic machinery to operate more efficiently and produce more biomass, especially under strong light and with adequate nutrients. This is why CO2 enrichment is a common practice in controlled greenhouses, with careful monitoring to stay within safe and optimal levels.

Oxygen, on the other hand, is a by-product of photosynthesis and is not a limiting substrate that enhances photosynthesis when increased. Nitrogen is essential for plant nutrition, but it is typically supplied as fertilizer in soil or solution, not as a gas that directly drives the photosynthetic process. Argon is inert and does not participate in photosynthesis or plant metabolism.