by the way they look and act
their genome
The chart is a dichotomous key. It helps them classify things.
Scientists classify organisms by the dichotomous key. They classify by looking at if it moves or not, then they look at characteristics, then they can see what they are.
Scientists use morphological evidence, which includes physical characteristics like body shape and structure, and molecular evidence, which involves analyzing DNA or proteins, to classify organisms systematically.
Radial symmetry
scientists classify organisms into groups based on internal and external features.
DNA is the answer.
Scientists use the periodic table to classify the elements. The elements are arranged in the table based on their atomic number, electron configuration, and chemical properties. This organization helps scientists identify patterns and relationships among the elements.
Scientists use color, size, brightness, and temperature to classify stars.
I believe this is called magnitude, or apparent magnitude.
Taxonomy
Taxonomists usually use a set of criteria that have to do with reproduction. So even if two species can reproduce an offspring, taxonomists usually make the distinction that the offspring must be able to reproduce as well. If this is the case, then they are likely to consider the two organisms as one species.