Which gas is taken in by plants during photosynthesis?

During photosynthesis, plants take in carbon dioxide (CO2) from the atmosphere. This gas is crucial for the process, as it is used along with water and sunlight to produce glucose and oxygen. The carbon dioxide enters the plant primarily through small openings on the leaves called stomata.

Once inside the plant, CO2 is converted into organic compounds during the light-independent reactions (Calvin cycle) of photosynthesis. This process not only provides essential carbohydrates for the plant's energy needs but also contributes to the overall carbon cycle, which is vital for life on Earth.

The other gases listed, such as oxygen, nitrogen, and hydrogen, do not serve as the primary intake during photosynthesis. Oxygen is actually produced as a byproduct of the process, while nitrogen is more relevant in plant nutrition rather than photosynthesis itself. Hydrogen plays a role in the chemical reactions but is derived from water, not taken directly as a gas. Thus, the correct choice aligns with the fundamental understanding of photosynthesis and the role of carbon dioxide.