What term describes substances required by a cell that the cell cannot synthesize?

The term that describes substances required by a cell that the cell cannot synthesize is referred to as growth factors. These are organic compounds that the organism must obtain from its environment since it lacks the metabolic pathways to produce them internally. Examples of growth factors can include vitamins or certain amino acids essential for cellular functions that cannot be manufactured by the organism itself.

Nutrients, while also necessary for cell growth and maintenance, cover a broader category that includes substances that can be either synthesized or must be acquired from the environment. Growth inhibitors are substances that prevent or slow down growth, which does not fit the context of the question. Trace elements are vital in small quantities for physiological functions but are not classified as substances that are compulsory for all cellular activities in the same way growth factors are. The specificity of growth factors highlights their role in supporting cellular needs that must be met externally.