What term refers to an organism's observable traits or physical appearance?

The term that refers to an organism's observable traits or physical appearance is "phenotype." The phenotype encompasses all the visible characteristics of an individual, such as height, skin color, and eye color, which result from the interaction between the organism's genetic makeup and its environment.

For instance, while two plants may have the same genotype (the genetic code that determines their traits), environmental factors such as soil quality, sunlight, or water availability can shape their phenotypes, leading to variations in their observable characteristics. This concept highlights the importance of both genetic information and external influences in determining how traits are expressed.

In contrast, the other terms have specific meanings that do not align with the definition of observable traits. The "genotype" refers to the genetic makeup of an organism—essentially the alleles it possesses, while an "allele" is one variant of a gene that can exist at a particular locus. The "genome" encompasses the complete set of genetic material in an organism, including all of its genes, rather than just the observable traits. Understanding these distinctions helps clarify the relationship between genetics and the traits we can see.