Content Benchmark L.8.D.1
home / life science / diversity of life /

Students know species can be identified and classified based upon their characteristics.  E/S

The world is full of a vast variety of organism that range in size and complexity. Scientists estimate that there are between 25-50 million different species on Earth. Classifying and naming millions of organisms on Earth may seem like a daunting task, but that is the role of taxonomists. The organisms that need to be classified range from tiny microbes that require a microscope to been seen to the enormous blue whale. Due to the biodiversity on the planet, several classification systems have been proposed and modified over time to organize these organisms into groups based upon their structure and evolution. The work of the taxonomists provides insight into comparing organisms and determining how organisms are related. 

Characteristics Used in Classification
Biologists classify organisms into different categories by certain degrees of apparent similarities and differences. They compare internal and external anatomy, genetic make-up, and evolutionary relationships of organisms.  Organisms are also placed into groups based upon cellular characteristics such as whether or not they are prokaryotic (cells do not contain a nucleus) or eukaryotic (cells contain a nucleus). However, not all prokaryotic and eukaryotic cells are the same. Different types of bacteria (prokaryotes) appear to be similar, but differ in the biochemical composition of their cell wall. Organisms are also classified according to their mode that they obtain nutrients, such as autotrophs (can make their own food) or heteroptrophs (obtain food from another source).  Taxonomists also use biochemical evidence, such as protein analysis and DNA comparisons to classify organisms and determine evolutionary relationships among them.  

For more information on how the similarities of DNA sequences provides evidence that organisms are related, see HS TIPS Benchmark L.12.D.2

Using the classic method of taxonomy, insects, reptiles, and mammals are all classified as animals because they are multicelluar, heterotrophic organisms. Similarly, a cactus, a water lily, and a pine tree are all plants because they are multicellular, autotrophic organisms. Although each of these organisms are different from one another, they are classified into one of six kingdoms based upon general characteristics. There are subgroups (taxons) within the kingdoms into which organisms are categorized. For example, mammals are a taxon within the animal kingdom. The general characteristics of mammals include: vertebrates, warm-blooded, have hair on their bodies at some point during their life, have a four-chambered heart, breathe using lungs, and provide their young with milk. Humans, elephants, and dolphins are examples of mammals. Figure 1 contains a picture of a platypus which is a semi-aquatic, hairy, duck-billed, webbed-footed creature that lays leather eggs. It may seem like the platypus is similar to a duck and should be classified with the birds or with the reptiles because it lays leathery eggs. But, the platypus is a mammal because it possesses the general characteristics mentioned above.

Figure 1. Picture of a Platypus.
(From http://arstechnica.com/journals/science.ars/2008/
05/07/platypus-genome-as-distinctive-as-its-owner)

There are many taxons within each of the kingdoms. Biologists compare certain characteristics such as body plan, skeletal structure, and body covering to classify animals. In terms of body plan, taxonomists need to decide if the organism has radial symmetry, bilateral symmetry, or is asymmetrical.  Observations will also be made to determine the type of skeleton the organism possesses such as a hydroskeleton, endoskeleton, or exoskeleton. The body coverings may be assessed to scales, feather, hair, or a shell.  If it is a plant, then it can be classified as having vascular or nonvascular tissue. The plant may be an angiosperm (flowering) or a gymnosperm (no flowers, usually have cones). If the plant is an angiosperm, then it can be categorized as a monocot or a dicot based upon the number of flower parts, vascular tissue arrangement, and leaf structure.  

Binomial Nomenclature
The basic idea of the classification system used by modern biologists today, was developed in the 1700s by the botanist Carolus Linnaeus. He developed a system of grouping organisms into the hierarchical categories based upon similarities in structure and function. Linnaeus’ system consisted of seven taxons, each with subcategories divided into more specific categories.  The largest and most general category in his system was the kingdom. Linnaeus only had two kingdoms: Plants and Animals. The kingdoms were divided into phyla (for animals) or divisions (for plants), which were then divided into class, order, family, genus and species. The most specific category is the species and only contains one specific type of organism. Members of the same species can mate with one another and produce fertile offspring.  Modern biologists adopted Linnaeus’classification system and added four more kingdoms and as well as domains, which are categories above the kingdom level.

For more information on domains, go to http://www.ucmp.berkeley.edu/exhibits/historyoflife.php

The figure below provides an example of how a human and an armadillo are classified according to Linnaeus’ system.

Figure 2. Taxon levels comparing a human and an armadillo.
(From https://www.msu.edu/~nixonjos/armadillo/taxonomy.html)

The Six Kingdoms
In Linnaeus’ system, kingdoms are the broadest category. The following list provides a brief description of each kingdom.

1. Archaea: This kingdom contains very primitive forms of bacteria. The name archea means “archaic” or “ancient”. These types of bacteria live in extreme environments.

Figure 3. Example of Archaea.
(From http://www.learner.org/resources/series121.html)

2. Bacteria: This kingdom includes more advanced forms of bacteria that take on several shapes such as rod, spiral and sphere.

Figure 4. Example of an E. coli bacterium.
(From http://dearscience.org/2008/06/13/show-evolution-of-a-complex-trait-ok/)

3. Kingdom Protista: This kingdom includes a diverse group of mostly unicellular organisms that are plant-like, animal-like, or fungus-like. This kingdom is often referred to as the junk-drawer kingdom because the members to this kingdom do not fit well into any of the other kingdoms. Therefore, taxonomists created kingdom Protista for these unusual organisms.

Figure 5. Examples of Marine Protists.
(A) a diatom an autrophic protist, (B) a herbivorous oligotrich ciliate, (C) a herbivorous tintinnid ciliate,
(D) a dinoflagellate, and (E) a radiolarian. Images by J.R. Dolan
(From http://www.eoearth.org/article/Marine_microbes)

4. Kingdom Fungi: The organisms in this kingdom are heterotrophic and mostly multicellular. Example organisms found in kingdom Fungi are mushrooms, molds, and yeast.

Figure 6. Example of a fungus.
(From http://www.ucmp.berkeley.edu/fungi/fungi.html)

5. Kingdom Plantae: Organisms found in the plant kingdom share general characteristics. For example, they are all multicellular, autotrophic organisms with a cell wall. Example members of this kingdom include cacti, trees, and grasses.  

Figure 7. Example of a plant.
(From http://plants.usda.gov/java/profile?symbol
=ACMA3&photoID=acma3_001_ahp.tif)

6. Kingdom Animalia – Members of the animal kingom are multicellular, heterotrophic organisms that lack a cell wall. The animal kingdom includes a vast array of members from insects, to birds, to mammals.

Figure 8.  Examples of members of the animal kingdom.
(From http://www.perspective.com/nature/animalia/)

Scientific Names Using Binomial Nomenclature
Linnaeus’ system of classification is also used to provide organisms with a scientific name. Due to the different languages and regional names used throughout the world, a common system needed to provide organisms with a universal scientific name. Within the continental United States, people use several common names for the same organism. For example a mountain lion, puma, and cougar are in fact the same organisms. Although they have different common names around the country, the organism’s scientific name is a Felis concolor.  Another example includes different types of bears. One individual may incorrectly identify a grizzly bear (Ursus arctos horribilis) as a brown bear (Ursus arctos).  Scientists use the scientific names of organisms in order to effectively communicate which organism they are referring to. There are some individuals that may even be inclined to refer to a grizzly bear as some other bear name, such as polar (Ursus maritimus), simply due to ignorance and lack of knowledge. Below are several pictures showing the difference between these types of bears.

(1) Polar Bear	(2) Grizzly Bear	(3) Brown Bear

Figure 9. The physical differences between a polar, grizzly, and brown bear.
(From (1) http://www.defenders.org/wildlife_and_habitat/wildlife/polar_bear.php ,
(2) http://www.defenders.org/wildlife_and_habitat/wildlife/grizzly_bear.php and
(3) http://www.greatbear.org/brownbear.htm)

Linnaeus improved upon the previous classification system by giving organisms a scientific name with two parts. This two-name naming system is known as binomial nomenclature. The two-part name consists of the genus of the organism followed by its species identifier.  For example, a human’s scientific name is Homo sapien, which translates to “wise man.” When writing a scientific name, the genus is capitalized, but the species name is not. The entire name should be underlined or written in italics. Most of the scientific names come from Latin roots which are universal for every language. 

Dichotomous Key
A very important tool that is used in the world of taxonomy is a dichotomous key. This is a key that incorporates a set of choices that eventually leads to the naming of an organism. Even everyday common objects can be used to make a dichotomous key, but most often they are used in the field to help identify a newly discovered organism.

A dichotomous key, regardless of complexity and subject, always begins with the very first set of choices available to the person utilizing it. Within every set of choices there exists the possibility of reaching a solution/identification to the “mystery” organism or a path to another set of choices. The process continues until the user can clearly identify from one of the choices the organism that they are attempting to name or classify. One advantage to a dichotomous key is that the user always has to decide on one of the choices provided in each set and if at any point in time neither choice seems appropriate for the unknown object, then a mistake was made somewhere earlier in the dichotomous key. Below is an example of how a scientist would take a group of unknown organisms, in this case animals, and use a dichotomous key to aide in their identification.

Table #1 Sample Dichotomous Key: Use the key below to try to identify the organisms.

Adapted from Lab Manual B, Classification, Chapter 18 in Biology by Prentice-Hall

A website that can be visited to help solidify the idea of dichotomous keys can be viewed at http://www.dnr.state.wi.us/org/caer/ce/eek/veg/treekey/treestart.htm

back to top

Content Benchmark L.8.D.1

Students know species can be identified and classified based upon their characteristics.  E/S

Common misconceptions associated with this benchmark

1. Students incorrectly assume that the common name of organisms implies how the organism should be classified. 

For example, students may incorrectly believe that a jellyfish and starfish should be classified as fish. Just because the name of an animal contains the word “fish” or that the animal lives in the same habitat with fish, does not mean that they are categorized as a fish. This misconception has to do with the misleading common names that are given to some animals and the fact that not all aquatic organisms are classified with fish. This misconception can be expanded to include any misleading common names.

More information regarding this misconception can be found at the following sites
http://homepage.mac.com/vtalsma/misconcept.html#biology
http://www.nationalgeographic.com/ngkids/9608/jellyfish/
http://animals.nationalgeographic.com/animals/invertebrates/starfish.html

2. Students incorrectly believe that organisms such as plants and fungi are not living.

Elementary students and early middle school students use characteristics such as “movement” and “breath” to decide if an organism is alive. Students at this age rarely use criteria such as having cells or DNA to determine if an organism is alive. Due to their limited knowledge of these topics, students may not recognize similar sessile organisms as being alive.

For more information on this misconception, go to http://www.project2061.org/publications/bsl
/online/index.php?chapter=15&section=C&band=5

 
3. Students incorrectly do not classify invertebrates as animals.

Middle school age students hold a restricted preconception of the definition of an animal. Students at this age relate the term “animal” primarily to large land mammals that they are the most familiar with. Students often use characteristics such as body covering and habitat to determine if an organism is an animal. Due to their self-generated definition of an animal, students do not recognize invertebrates as sponges, arthropods, echinoderms, or mollusks as animals.

More information can be found at
http://www.project2061.org/publications/bsl/
online/index.php?chapter=15&section=C&band=5

4.Students have difficulty with a hierarchical classification system.

The current system of classification uses several levels of taxons to organize different organisms. For example, the animal kingdom contains a wide variety of organisms such as birds, mammals, reptiles, amphibians, fish, and invertebrates. It is difficult for younger students to comprehend that an organism can be classified into two categories. For example, a human can be a mammal and an animal.

For more information on this misconception, go to http://www.project2061.org/publications/bsl/
online/index.php?chapter=15&section=C&band=5

back to top

Content Benchmark L.8.D.1

Students know species can be identified and classified based upon their characteristics.  E/S

Sample Test Questions

1st Item Specification: Understand how to classify species based upon their characteristics (e.g. DNA, skeletal structure, body coverings, petal arrangement, and deciduous/coniferous) and behaviors.

Depth of Knowledge Level 1

1. Which of the following is the correct order from most broad to most specific of the taxonomic hierarchy?
1. Kingdom, Phylum, Class, Order, Family, Genus, Species
2. Phylum, Class, Order, Kingdom, Family, Genus, Species
3. Kingdom, Order, Family, Genus, Species, Phylum, Class
4. Genus, Species, Kingdom, Phylum, Class, Order, Family

2. Which of the following is NOT a characteristic typically used to classify plants?
1. DNA
2. Presence of seeds
3. Leaf type
4. Skeletal structure

3. Which of the following is the correct way to write the scientific name for human beings?
1. Homosapiens
2. Homo sapiens
3. homo sapiens
4. Homo Sapiens

4. Why do biologists use scientific names instead of common names?
1. There are more scientific names than common names.
2. To provide a consistent way to identify and classify organisms.
3. Common names are the same in every country and biologists need them to differ.
4. Scientific names are in Latin and describe organisms better than other languages.

Depth of Knowledge Level 2

5. The diagram below shows the arm bone structure of 3 organisms.

Based upon the arm bones of the following organisms, what is one reason these organisms are all classified into the same class?

1. They all have similar arm bones.
2. They all have different arm bones.
3. They are in the same order.
4. They are in the same family.

6. The chart below shows the eight basic levels of modern classification and several organisms that are found in specific categories.

Which two organisms will have the MOST similarities in their DNA according to the table above?

1. They will all have about the same amount of similarities.
2. The leopard and the cheetah.
3. The cheetah and the lion.
4. The lion and the leopard.
   
   

2nd Item Specification: Given a group of organisms and a key, classify organisms based on observable characteristics.

Depth of Knowledge Level 1

7. A tool used by scientists to identify unknown organisms based on observable characteristics is called a
1. dichotomous key.
2. scientific name.
3. taxonomic Tree.
4. homologous structure

8. Which of the following characteristics would be LEAST helpful in identifying an animal using a dichotomous key?
1. Number of limbs
2. Body covering
3. DNA
4. Color

Depth of Knowledge Level 2

9. Using the dichotomous key below, find the name of the organism C.

From: http://www.biologycorner.com/bio1/taxonomy.html

What is this organism’s name?

1. Deerus octagis
2. Deerus magnus
3. Deerus pestis
4. Deerus deafus

10. Using the dichotomous key below, find the name of organism A:

From: http://nerds.unl.edu/Pages/preser/sec/skills/dkeys.html

1. Coccinellidae novemnotata
2. Melanoplus differentialis
3. Arigomphus cornutus
4. Musca domestica
   
   

Constructed Response L.8.D.1

1. Below is a dichotomous key for the leaves of trees commonly found in the United States

1. Find the scientific name of each tree that the above leaves came from.
2. Based on the scientific names, which trees will have the most similarities in their DNA? Justify your answer.
   

back to top

Content Benchmark L.8.D.1

Students know species can be identified and classified based upon their characteristics.  E/S

Answers to Sample Test Questions

1. A, DOK level 1
2. D, DOK level 1
3. B, DOK level 1
4. B, DOK level 1
5. A, DOK level 2
6. D, DOK level 2
7. A, DOK level 1
8. C, DOK level 1
9. A, DOK level 2
10. B, DOK level 2

Constructed Response L.8.D.1 Score Rubric:
 

back to top

Content Benchmark L.8.D.1

Students know species can be identified and classified based upon their characteristics.  E/S

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. Classification of Living Things

Dr. Dennis O’Neil and the Behavioral Sciences Department has developed a web page devoted to educational activities relating to different topics from principles of classification to a look at the seven taxa. The site contains a section that presents topics of classification through flashcards and another that is dedicated to crossword puzzles covering the material presented throughout. There is also another area that allows the student to work through web expeditions.

The site can be found at http://anthro.palomar.edu/animal/default.htm

2. Working with Dichotomous Keys

A large part of identifying organisms that are found on this planet involves a tool known as a dichotomous key. Anything can be classified or categorized using a dichotomous key, but it is very important for scientists that are trying to identify both plants and animals and place them into the existing database of life. A few sites are listed below to help reinforce this idea of dichotomous keys.

The website http://webworld.freac.fsu.edu/cameras/keys/sa/tree.html provides an interactive plant dichotomous key.

At http://wow.osu.edu/experiments/plants/dichotkey.html students will learn how to make a dichotomous key.

3. Practice creating classification groups with another “Life Form”

Give students a chance to work with a tool known to us as a dichotomous key and incorporate life forms not from this planet. Hypothetically, where would other life forms fit into our current classification schemes? The creators of microbeworld.org have created an activity allowing students to classify and organize “Creepy Critters.” To learn more about these creatures and the use of dichotomous keys visit:

http://www.microbeworld.org/resources/experiment/pgs1-6.pdf

4. Sample dichotomous key activity

Most students have had a chance to play, walk, run or stroll through a park. But in the moment of all those activities they have probably failed to notice many of the endless possibilities of classification around them. This site allows students to once again step into the world of a local park and observe the things that might have gone unnoticed several times before. As an introductory lesson the students will classify shoes that they all should have worn to get to the park and as an extension an activity can be done with the trees and leaves. More information can be found at: http://edcommunity.apple.com/ali/galleryfiles/652/bsuactivity3.pdf

back to top