Lesson 1 - Page 1



Theories of Life  - Lesson 1

  Classification is one of the processes used by scientists in their search for explanations. In classifying, things that are similar with respect to a given feature or set of features are grouped together. Classification systems used to place things in a group are determined by humans. Thus, there may be many types of groupings. Early classifiers of plants and animals grouped them in entirely different ways from how they are classified today. Classification is a means of organizing knowledge. This process often indicates order where order does not appear to exist. Classification of living things is useful in learning to identify organisms and in acquiring insight into the relatedness of living things.

Classification is important in science because it attempts to discover order in a chaotic world. Classification itself is not a science, only logical divisions to arrange things so that they can be easily identified. Not all characteristics can be used to classify an organism, however. For example, librarians could classify books in two groups, large and small, but this would not help a person to locate a specific book.

Taxonomy is the science of classification, and is usually restricted to biology and paleontology. Taxonomic relationships try to find those characteristics that are natural and of some significance. Modern taxonomy depends upon organisms that reproduce through time. The basic method of taxonomy is to compare and weigh the characteristics of the structures of plants and animals by comparative anatomy or genetic coding. The most recognizable taxonomic unit is a species. The other arrangements include: Kingdom, Phylum, Class, Order, Family, Genus, and Species. Organisms change through time. Many times it can take only a change in one gene to create a different morphological creature.

In order to talk about organisms, scientists and naturalists had to develop a system to group organisms with like characteristics. Classification is a means by which objects with similar characteristics can be grouped together. A system of classification should be constructed in assisting people to discuss and understand the objects or animals that are being classified.

A Phylum is a subgroup of a kingdom that has similar tissue and organ development. A Class, Order, Family, and Genus are grouped according to characteristics determined by zoologists, biologists, or paleontologists working on that group of organisms. A species is a group of individuals that can successfully reproduce with each other.


.Ask students to discuss the characteristics of a dog and write down their responses on the board.

A  DOG   IS:

short or long haired creature 
4 legged animal 
an animal that barks 

small or large
has a tail
can bite

2. Next, ask the students to describe the characteristics of a poodle. They should list all the characteristics of a dog plus the characteristics of a poodle: for example curly hair which can be white, gray, or black.

3.Ask students to create an image in their mind of a tree-like organism that has long, thin needles and cones. Ask them to tell you something about this unknown organism. The organism that they describe should resemble a pine tree. Classification helps us predict what type of object something may be.

4.Discuss with students that living objects are classified into kingdoms, phyla, orders, classes, families, genera, and species. Stress that the species classification is very important to the classification scheme of an organism, but it is artificial. Nature does not always fit our artificial classification. A "Kingdom" is a grouping of living organisms that have similar eating and reproductive strategies.

The reasons for grouping organisms into certain kingdoms are not always obvious. The development of the kingdom classification dates back to Aristotle who divided organisms into animals and plants. Today, specialists working with different phyla change classifications when they derive more information. You must realize that we do not know all there is to know about organisms. The 5 kingdom classification system was first derived in the early 1960's, and there are many biologists today that use a 6 kingdom division.

The Monera group is now broken up into 2 other Kingdoms, the Archeabacteria and the Eubacteria. Examples include bacteria or blue-green algae. Monera as a group, have a very simple nucleus and do not have a nuclear membrane. The Kingdom Protista is made up of protozoa, consisting of one celled organisms, that have a well defined nuclear membrane. Protozoa will eat their food and reproduce asexually more commonly than sexually. The Fungi are characterized in that they lack chlorophyll and absorb food from the surrounding ground. Fungi possess organs and reproduce by sexual means (spores). The Plant Kingdom is characterized by its ability to produce by either sexual or asexual means. The animal kingdom is divided into invertebrates and vertebrates. To be an animal requires that an organism eat its food and reproduce mainly by sexual means. Organs are much more developed in the Animal Kingdom than the other kingdoms.





make their own food, mainly green

 (including Archeobacteria and Eubacteria)

one cell, primitive nucleus


one cell, eat food


absorb food


multicellular, eat food



Classification Theories of Life

Symmetry refers to, "the correspondence in size, form, and arrangement of parts on opposite sides of a plane, line, or point." If you look at the word in the dictionary, you will notice a list of definitions for subjects as diverse as geometry, botany, physiology, chemistry, and geology.  Symmetry can refer to two dimensional as well as three dimensional objects.  Some objects can have one or more symmetries.  In nature symmetry is not always perfect, but the terms are still applicable. 

            Bilateral symmetry is when one side looks like the other or is a mirror imagine.  Humans are bilaterally symmetrical .  If you make an imaginary line from the head to the ground; one side basically looks like the other.  However if you look at the organs inside a human, they are not bilaterally arranged. 

            Radial symmetry is when all segments are equal that radiate from a point.  A ball or a circle has radial symmetry.  Note that all objects that have radial symmetry also have bilateral symmetry.

            Pentagonal symmetry reflects a five-part symmetry.  The echinoderms (sea stars, sand dollars) are an excellent example of pentagonal symmetry.  This is easily recognized as a “star” shape.  Internally, echinoderms also have a five part symmetry.

            There are other ways of dissecting symmetry including hexagonal symmetry (six-part) and cubic symmetry (three-dimensional square).  Symmetry is all around us if we just look and describe.



1.  The objectives of this week's activities are to illustrate the difference between symmetry and patterns, especially in nature.  The first exposure to these concepts will give students a new vocabulary power to describe and observe the world.  Go over each of the above vocabulary words and illustrate with examples.  Reinforce the types of symmetry so children can learn by experience.  Listed below are a few ideas. 


2.  Use the Googolplex to illustrate the different types of symmetry.  Include bilateral, radial, pentagonal, hexagonal, and cubic.  Construct these examples (using the book as a guide) before class or have students follow the patterns in the worksheet.  Draw the different types of symmetry on the board and have students think of examples. 


            1. bilateral symmetry = one side looks like other

            2. radial symmetry = radiate from a point

            3. pentagonal symmetry = 5 part symmetry

            4. hexagonal symmetry = 6 part symmetry

           5.cubic symmetry = 4 part symmetry


            Symmetry and patterns are sometimes difficult to determine in nature.  Patterns are repeated; symmetry refers to the overall design.  Unit cells of patterns are not as well defined as in pattern blocks.  Symmetry can be considered as an “overall” descriptive term.  Humans and most vertebrates are bilaterally symmetrical.  All echinoderms have a 5 part pentagonal symmetry


            It is important to look at the overall symmetry first and then to describe the patterns that might be on organisms.  Organisms sometimes have different patterns on different parts of their body. 


3. In this lab, students will try to discover different symmetries by observing different organisms.


At each of the 10 stations, students observe the materials and first decide if the specimen has a particular symmetry.   Then see if they can detect a pattern.  Sometimes an object may not have a symmetry and sometimes it doesn’t have a pattern.  Let students determine for themselves.  You may want to give students about 2-3 minutes per station.  


4.  Review the following items after students look at them.   

            1.  Bubbles:  Students should blow just once through the bubble-maker.  Make sure this is clearly explained or you will have bubbles all over the room.  Bubbles have radial symmetry.  There is no pattern.

            2.  Sea cookie, sand dollar, and sea star:  Have students look closely.  Have students observe the pattern with a hand lens.  All of these organisms have pentagonal symmetry (5 part).  The pattern is of very fine holes throughout the skeleton of the organisms.

            3.  Glass sponge:  The sponge is very delicate and students should observe only.  This sponge is made up of silica dioxide (same ingredients as glass).  The sponge has bilateral symmetry and has groups of four patterns.

            4.  Snail shells:  These marine snails do not have any symmetry, but it has a coiled or spiral pattern.  This observation might be hard for students, but noticing the spiral pattern is important.  The pattern is different than a whorl which is coiled on the same plane; a spiral is off centered like a staircase.   

            5.  Pyrite:  This mineral has a "cubic" symmetry.  The symmetry can not be determined easily, because it is not continuous.  This is difficult to see unless you have a very good specimen.

           6.Nautilus:   A Mollusk that is related to the octopus and squid has perfect bilateral symmetry. Unlike its ancestor the gastropods (or snails) its growth is a “whorl” meaning it wraps itself directly over itself.  In snails the shell spirals.

            7.  Coral:  Many corals do not have symmetry because they grow in whatever shape they want.  The coral you have is not symmetrical, however, it has a pattern of pores all over the skeleton.  If you look at the individual pores they have a radial symmetry (may need hand lens or microscope).

            8.  Quartz:  Has a hexagonal symmetry if the crystal is complete.  There is no pattern.

            9.  Bivalves (clams):  Please note that this is an entire bivalve and it has bilateral symmetry.  The pattern reflects ridges and spines.

            10.  Slice of Tree:  Notice that it has not perfect radial symmetry.  The rings make up its pattern.




Activity: Do different organisms have different symmetries and patterns?


Materials: different living and non living items


Procedure:  Go to each station and write down the item, and describe or draw their symmetry and pattern (if there is one)
















































Display materials that are in the science room.



Classification of living organisms is a very difficult job. Life does not like neat little packages. If there is a rule to follow when naming species using strict definitions, it would be that exceptions are the rule.

In this program we will be using the 5 kingdom system, established in 1969 by S. Whittaker. In this system there are some groups that do not fit nicely into the kingdoms like Euglena or Dinoflagellates. But we feel that it is part of teaching to inform students that there are major problems in certain areas.

Follow the diagram below on the 5 kingdoms of Animalia, Fungi, Monera, Protozoa, and Plantae.




Students will look at the various displays of organisms around the lab and try to categorize them according to the different kingdoms. They will have a general guide on their lab sheet to help them decide which organisms belong to which kingdoms.


PROBLEM: Is it easy to identify the organisms from the different kingdoms?

HYPOTHESIS: __________________________________________________________________


MATERIALS: labeled specimens

Prior to lab you have talked about how organisms are classified. Use that information and try and determine what kingdom the specimens are in. Justify your decision. Remember there are 5 established kingdoms: Animalia, Plantae, Fungi, Protista, and Monera. Scientists are currently splitting the Monera kingdom as they learn more about this group.


predicted kingdom








































[Theories-Tree of Life]  [Biological Science]