Final answer:
The presence of a gene coding for penicillin resistance is part of an organism's genotype, not its phenotype. The phenotype refers to observable characteristics, like the presence of the enzyme catalase or flagella, that result from the interaction of the organism's genetic makeup with the environment.
Step-by-step explanation:
Among the options provided, all except one are examples of a phenotype. The phenotype refers to the observable traits or characteristics of an organism, which result from the interaction of its genotype (genetic make-up) with the environment. The presence of the enzyme catalase, flagella, spherical cells, and pili are all phenotypic characteristics that can be observed or detected in an organism.
However, the presence of a gene coding for penicillin resistance is not a phenotypic trait but rather a part of the organism's genotype. The gene itself must be expressed, resulting in penicillin resistance, for it to be considered part of the organism's phenotype.
An example of a change in phenotype in response to environmental signals is the production of a red pigment by the Serratia marcescens cells at room temperature, which is an observable phenotypic trait that occurs under specific conditions.