[Solved] Which of the following would you expect to react fastest in an S<sub>N</sub>1 reaction (consider the mechanism)? D) All would react rapidly. E) None would react. Phenotype: The observable characteristics or traits of an organism, resulting from the interaction of its genotype with the environment. Visible Structure: The physical or organizational form of something as it appears to the naked eye. Organism's: Refers to any individual living entity, from single-celled microorganisms to plants and animals, including humans. Observable Characteristics: Traits or features that can be seen or measured directly.