What gas do plants absorb from the atmosphere?

Plants primarily absorb carbon dioxide from the atmosphere during the process of photosynthesis. This gas is essential for the production of glucose and oxygen, which sustains both the plants themselves and the wider ecosystem. During photosynthesis, plants take in carbon dioxide through small openings in their leaves called stomata. Using sunlight as energy, they convert carbon dioxide and water into glucose, which serves as food for the plant, and oxygen, which is released back into the atmosphere.

While nitrogen is a significant component of the atmosphere, plants do not directly absorb it in its gaseous form for their nutritional needs. Oxygen is produced by plants during photosynthesis, but it is not something they absorb; rather, it is a byproduct of the process. Helium, while present in the atmosphere, is not utilized by plants in any biological processes. Thus, carbon dioxide is the correct answer as it plays a crucial role in the growth and energy production of plants.