Unit 5 Flashcards
Define taxonomy
Taxonomy is the science of naming and classifying organisms. Taxonomy gives scientists a standard way to refer to species and organize the diversity of living things.
Describe Aristotle’s classification system
Aristotle classified things as either plants or animals. He grouped animals into land dwellers, water dwellers, and air dwellers. He grouped plants into 3 groups based on differences in their stems.
Explain why Aristotle’s classification system was replaced
Biologists realized that Aristotle’s categories were not adequate. They also found that using a common name, such as robin or fir tree, for an organism presented its own problems; common names varied from one locale to the next, just as they do today.
Why is the use of common names problematic?
Common names may not describe species accurately. For example, a jellyfish is not a fish at all. Some early scientists devised scientific names that consisted of long descriptions in Latin, but these names were difficult to remember and suggested nothing about how organisms were related to other organisms.
Explain Linnaeus’s system of classification and identify the main criterion he used to classify
organisms.
For the most part, Linnaeus used an organism’s morphology, that is, its form and structure, to categorize it.
List Linnaeus’s levels of classification from the most general to the most specific. (7)
Kingdom
Phyla
Classes
Orders
Families
Genera
Species
What is a phylogenetic tree?
A phylogenetic tree is a family tree that shows the evolutionary relationships thought to exist among groups of organisms. A phylogenetic tree represents a hypothesis, and it is generally based on several lines of evidence.
What information does a phylogenetic tree show?
A phylogenetic tree shows the evolutionary relationship thought to exist among groups of organisms.
List four types of evidence used to organize organisms in systematic taxonomy and briefly explain each type
The Fossil Record- The fossil record often provides clues to evolutionary relationships, but it is important to understand that the fossil record cannot be read like a history book. Some organisms, such as some ocean-living invertebrates, have fairly complete fossil records. Other organisms have incomplete fossil records; there may be series of strata in which no fossils of the organism appear. The fossil record may provide the framework of a phylogenetic tree, but a systematic taxonomist would seek to confirm the information it provided with other lines of evidence.
The Fossil Record
The fossil record often provides clues to evolutionary relationships, but it is important to understand that the fossil record cannot be read like a history book. Some organisms, such as some ocean-living invertebrates, have fairly complete fossil records. Other organisms have incomplete fossil records; there may be series of strata in which no fossils of the organism appear. The fossil record may provide the framework of a phylogenetic tree, but a systematic taxonomist would seek to confirm the information it provided with other lines of evidence.
Morphology
Taxonomists study an organism’s morphology and compare it with the morphology of other living organisms. Recall from Chapter 15 that homologous features suggest descent from a common ances-tor. Naturally, it is essential to separate those features that are truly homologous from those that seem homologous but are actually analogous.
Embryological Patterns of Development
Early patterns in embryological development provide evidence of phylogenetic relationships. They also provide a means of testing hypotheses about relationships that have been developed from other lines of evidence.
Chromosomes and Macromolecules
Taxonomists use comparisons of macromolecules such as DNA, RNA, and proteins as a kind of “molecular clock.” Scientists compare amino acid sequences for homologous protein molecules of different species. The number of amino acid differences is a clue to how long ago two species diverged from a shared evolutionary ancestor. This molecular-clock model is not a perfect one. It assumes that all changes in amino acid sequence are random and are not affected by natural selection. This is probably not true. Moreover, sequences of amino acids can change at different rates in different organisms. But the molecular-clock model is used, together with other kinds of data, to estimate degrees of relatedness between different species.
In a similar kind of analysis, biologists compare the karyotypes, or patterns of chromosomes, of two related species.
Define blastula
A ball of cells formed when a zygote undergoes repeated cycles of cell division
Why are echinoderms thought to be more closely related to vertebrates than they are to mollusks?
In echinoderms such as starfish and sand dollars, the blastopore becomes the posterior end of the
digestive system, as it does in chordates, which include vertebrates. This pattern of development suggests that echinoderms are more closely related to vertebrates than they are to other invertebrates, such as mollusks,
