Plant growth regulators (PGRs) primarily affect which of the following processes?

Plant growth regulators (PGRs) are substances that influence various aspects of plant growth and development. The processes primarily affected by PGRs include tissue development, which encompasses cell division, elongation, and differentiation. By regulating these processes, PGRs can impact various aspects of a plant's life cycle, including flowering, rooting, fruiting, and overall growth form.

For example, auxins, a class of PGRs, are known to stimulate cell elongation and are crucial in root development and apical dominance. Similarly, gibberellins can promote stem elongation and seed germination, while cytokinins are involved in cell division and shoot development. Since tissue development is directly influenced by these regulators, it is the most accurate choice in this context.

In contrast, while photosynthesis, nutrient absorption, and respiration are vital processes for plant health, they are not the primary targets of PGRs. Photosynthesis is largely a physiological process influenced by light, chlorophyll, and carbon dioxide, rather than by growth regulators directly. Nutrient absorption involves root structures and the surrounding soil environment, while respiration is a series of metabolic processes that, although they may be indirectly influenced by growth regulators, are not their primary focus.