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Definition

noun

(botany)

(1) A plant that utilizes the C₃ carbon fixation pathway as the sole mechanism to convert CO₂ into an organic compound (i.e. 3-phosphogylycerate).

(2) A plant in which the CO₂ is first fixed into a compound containing three carbon atoms before entering the Calvin cycle of photosynthesis.

Supplement

C₃ plants involve direct carbon fixation of CO₂. That is, the initial steps involve the CO₂ being bound to ribulose bisphosphate to produce two molecules of three-carbon compound (i.e. 3-phosphogylycerate). The key enzyme that catalyzes carbon fixation is rubisco.

C₃ plants must however be in areas where CO₂ concentration is high, temperature and light intensity are moderate, and ground water is abundant. This is because in hot areas, the stomata are closed to prevent water loss. However, it results in the rise of O₂ level. When this occurs, rubisco reacts with O₂ instead of CO₂, and leads to photorespiration, which in turn, causes wasteful loss of CO₂ in C₃ plants.

Examples of C₃ plants include most broadleaf plants and plants in the temperate zones.

Compare: C4 plant, CAM plant.
See also: C3 carbon fixation pathway, Calvin cycle.