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Lesson Eighteen: Classification of Living Organisms
The lesson can be extended to two periods (80 minutes)
Suggested teaching Methodology: - Lecture and Group work / Activity
The teacher is required to ask the following questions.
Activity – 1: Let the students list the names as many different organisms as they can, in a time period of two minutes. Let them examine the list of organisms that they have identified. How many of these organisms are animals? How many are plants? Are any of the organisms other than plants or animals listed? Where to group these organisms?
When asked to perform this task, many students may have a tendency to record the names of common plants and animals. However, many of these are neither plants nor animals.
Taxonomy – is one branch of biology deals with the study of principles, procedures, rules, and basis of classification.
Taxonomists: are scientists who classify organisms.
Taxon - The taxonomic unit at any level. Example: Panthera is a taxon at the genus level, and Mammalia is a taxon at the class level.
This lesson requires the active involvement of students in identifying the characteristics used to classify life forms into various groups.
With this information, students should identify similarities and differences in life forms and classify some examples of organisms according to identifiable features or characteristic and place them in the proper taxonomic categories.
Focus questions
The teacher should divide the class into different small groups.
Activity 2: For each of the kingdoms listed below, let the students state the cell type (prokaryotic or eukaryotic), identify the organisms as unicellular, multicellular, or both and their mode of nutrition (autotrophy, heterotrophy, or both).
Activity 3: (10 minutes). Provide each group with representative specimens or representations of specimens from the five kingdoms and allow students to use the text, other reference materials, or dichotomous keys to group the organisms into their appropriate kingdoms, phyla, classes, and possibly orders. Each group should be engaged in observing the features of some organisms provided. The teacher is expected to give guidance for each group. Each group should review by discussing or recording characteristics used to classify organisms into five major kingdoms. The teacher should inform each group to present their work after completing grouping of sample organisms.
The teacher is expected to give elaboration and summary of the classification scheme as this concept is very crucial in biology and biological investigations. It is recommended that the teacher is required to explain the basic concept in taxonomy. Thus, the students should be informed that taxonomy employs a hierarchical system of classification.
Why do scientists classify organisms?
Some of the reasons to Classify organisms are in order to:-
Taxonomy is the science of classifying organisms. The system currently used by taxonomists is called the Linnaean taxonomic system, in honor of Swedish biologist Carolus Linnaeus (1707 — 1778). The Linnaean system breaks down organisms into seven major divisions, called taxa (singular: taxon). These seven main ranks were defined by the international nomenclature codes: kingdom, phylum/division, class, order, family, genus, and species. The most basic rank is that of species, the next higher is genus, and then family. According to Carolus Linnaeus, each species has a two-part name ( namely genus name and species name). Such kind of naming is referred to as binomial nomenclature.
Note: There are many subdivisions of the seven main taxonomic levels, for example, Subphylum, Subclass, Infraclass, and so on.
The classification levels become more specific towards the bottom. Many organisms belong to the same kingdom; fewer belong to the same phylum, and so on. A species is one group of genetically distinct, interbreeding organisms. The average genetic differences within a species are less than the average differences between that species and a closely related group of organisms.
Binomial Nomenclature: In classification system, the scientific name for any organisms includes both the genus and the species name. The genus name is always given first, and the first letter is capitalized. The genus name is followed by the species name (it is not capitalized). Both names are always written in italics. As an example, the scientific name for human beings is Homo sapiens. That is, humans belong to the genus Homo, and the species sapiens. The full classification of human beings is thus,
Species that appear to be closely related are found in the same genus.
For example, the leopard, Panthera pardus, belongs to a genus that includes the African lion (Panthera leo) and the tiger (Panthera tigris).
Activity 4: (3 minutes)
Let the students practice how to write the scientific names of some organisms. The teacher is required to list the scientific names of certain organisms and then students should exercise how to write correctly those names.
Critical thinking
Taxonomy is largely based on structural similarity. However, modern biological science has allowed taxonomists to use additional traits to classify organisms. Can you name any of these additional traits?
Suggested Answers