Concept:The physical appearance of an organism refers to its observable traits, which is its phenotype.
Explanation:An organism’s phenotype includes features like height, eye color, and body structure.
These visible traits are determined by the genotype, which is the genetic makeup, and may also be shaped by environmental factors.
For example, two plants with the same genotype may show different heights if grown in different soil conditions.
The genotype refers to the actual alleles or variants of genes present in the organism.
Alleles are different forms of a single gene, while a chromosome is the thread-like structure carrying genes.
Hence, among the options, only phenotype directly describes the physical appearance.
Answer:A. phenotype