Question Video: Identifying Useful Characteristics for Scientists Classifying Organisms | Nagwa Question Video: Identifying Useful Characteristics for Scientists Classifying Organisms | Nagwa

Question Video: Identifying Useful Characteristics for Scientists Classifying Organisms Biology • First Year of Secondary School

Which of the following characteristics would be most useful for a scientist classifying organisms into distinct groups? [A] Mode of nutrition [B] Method of excretion [C] Rate of growth [D] Rate of cellular respiration

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Video Transcript

Which of the following characteristics would be most useful for a scientist classifying organisms into distinct groups? (A) Mode of nutrition, (B) method of excretion, (C) rate of growth, or (D) rate of cellular respiration.

Biological classification is the organization of species into groups, called taxa, based on meaningful shared characteristics. These taxa are ranked from the most general, typically a kingdom or domain, to the most specific, which can be a species, subspecies, or strain.

Taxonomy is the study of classifying and naming organisms. Modern taxonomy is based upon natural classification methods, which are based on genetic similarity and evolutionary relationships. These methods involve measuring the degree of genetic similarity between two or more organisms by comparing their DNA sequences. The more DNA two organisms or taxa have in common, the more closely related they are. For example, a turkey shares more DNA with a sea turtle than it does with a rattlesnake. This demonstrates that birds are more closely related to turtles than to snakes. A higher degree of genetic similarity also indicates a more recent divergence from a common ancestor.

In contrast, artificial classification refers to the classification of organisms based only on observable physical characteristics, for example, the number and shape of flower petals. It is called artificial because physical characteristics do not always guarantee that organisms are closely related or that they’re not. Artificial classification is the basis of systems devised by both Carl Linnaeus and Robert Whittaker. At the time these systems were created, scientists did not understand that the genetic code within DNA can reveal evolutionary relationships between taxa.

Although they are not the most accurate, artificial classification methods can still make useful contributions to taxonomy. One particularly useful artificial classification is the presence or absence of a nucleus. Classifying living organisms with this criteria creates two groups: the nonnucleated prokaryotes and the nucleated eukaryotes.

Now, let’s return to our question. Take a look at the answer options and see if you can determine whether each one is a natural or artificial classification method. If you said they are all artificial classification methods, you are correct. When using artificial classification, the observations should be ones that are relatively stable within an organism. They also should not be overly dependent on changing environmental variables. In light of this, we can eliminate options (C) and (D) because rate of growth and rate of cellular respiration change frequently depending upon an organism’s age, the time of day, the season, and whether the environment is ideal or stressful.

Method of excretion is a characteristic that is usually relatively constant in an organism, but it is not specific enough. There are many different substances that organisms excrete, such as water, salts, carbon dioxide, urea, and ammonia, just to name a few. So we can rule out option (B) as well.

Mode of nutrition describes how an organism obtains its energy. Although there are a few organisms that can use multiple modes of nutrition, this criteria typically doesn’t change throughout an organism’s lifetime. It is also quite a specific trait and is well conserved among closely related taxa.

Therefore, the correct answer is option (A). Mode of nutrition would be the most useful characteristic for classifying organisms into distinct groups.

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