Biology · Ch 13 — Plant Growth and Development
Conditions for Growth
Conditions for Growth
Growth does not occur automatically simply because a plant's cells retain the biochemical capacity for it; a set of favourable external conditions must also be met, and if any one of them falls outside the range the tissue can tolerate, growth slows or stops regardless of how favourable the others are. Water is essential in two distinct ways: it provides the turgor pressure against the cell wall that physically drives the enlargement of cells during the elongation phase, and it serves as the medium in which the enzyme-catalysed metabolic reactions that support growth actually take place. Oxygen is equally essential, because the energy that powers growth -- the ATP consumed in building new cytoplasm, cell wall material and other structures -- is generated chiefly through aerobic respiration, so tissues deprived of oxygen (as in waterlogged soil) fall back on far less efficient anaerobic fermentation and grow poorly if at all. …
Worked out. A short explanatory note box on how temperature limits growth in every plant species through three species-specific reference points collectively called the cardinal temperatures: the minimum temperature, below which no measurable growth occurs at all; the optimum temperature, at which growth proceeds fastest and most efficiently; and the maximum temperature, above which growth again ceases, usually because heat begins to denature enzymes and other proteins essential to metabolism. These three cardinal points differ from species to species (and even between varieties adapted to different climates), which is part of why the same crop can grow vigorously in one region's climate and fail to thr …