Lesson 2: Classifying with Class

In the last lesson we talked about the criteria for life – the characteristics a thing possesses that make it alive. We also learned some vocabulary that we can use to discuss the structure of organisms. The next step is to learn a bit about how we can classify and name living things.

But first there are a few other structural words that you should learn. Sometimes it is important to be able to describe exactly where on a living thing a certain characteristic exists…so we use special vocabulary to identify particular sites on their bodies. Did you ever hear of the dorsal fin on a dolphin? Where is the dorsal fin located?

The word “dorsal” refers to the back of an organism, and that is precisely where you would find a dorsal fin. The belly side of a creature is referred to as its ventral side. Most four-legged animals, and also multi-legged insects, walk with their ventral sides facing the ground and their dorsal sides on top. The ventral side of a human being faces front and the dorsal side faces back.

Here are two other position words that might sound familiar:

ANTERIOR means the front end.

POSTERIOR means the back end.

Study the diagram below. Then see if you can find the ventral and dorsal sides and the anterior and posterior ends of the animals in the pictures following:

Now…are you ready to do some classifying?

The study of classifying and naming organisms is called taxonomy. Scientists currently use a system of taxonomy developed in the 1700s by a Swedish scientist named Carolus Linnaeus. Watch this short video clip about Linnaeus and then we’ll talk some more about his system:

Linnaeus’s work was the foundation for the system we use today to classify organisms. This system divides all living things into five large groups , called kingdoms, into which organisms are placed based on similar characteristics they possess. There are all kinds of characteristics by which we can classify things. In a silverware drawer, we usually organize the utensils by type: knives here, forks there, and spoons there. In a grocery store, canned goods are stacked on the shelves according to what is in the cans. Soups are on their own shelf and vegetables are on another. The soup shelf is then further divided with chicken noodle on one side and tomato on the other, and the vegetable shelf has the corn separated from the peas.

Try this game and see if you are as good a classifier as Carolus Linnaeus:

CLICK HERE

The five large groups into which we classify organisms are called Kingdoms. Don’t worry if you dont understand all the words I use when I discuss these kingdoms. We will study each kingdom in detail in the coming months.

MONERANS – members of kingdom Monera – are tiny, one-celled organisms with no nuclei. Bacteria are classified into this kingdom.

2. PROTISTS – members of kingdom Protista – are also usually tiny one-celled organisms that usually live in the water. Euglena and Paramecium are Protists. The green scum you see floating on ponds is algae – also a member of kingdom Protista.

3. Kingdom FUNGI includes mushrooms, yeast, and molds.

4. Plants are members of kingdom PLANTAE.

5. All animals – from tiny insects to gigantic blue whales – are members of Kingdom ANIMALIA. Human beings are also considered part of this kingdom.

The kingdoms are further broken down into smaller subsets called PHYLA. Each phylum is made up of many CLASSES, which are further broken down into ORDERS, FAMILIES, GENUSES, and SPECIES. In our canned goods example, here is how we might classify a can of Green Giant green beans:

Kingdom: All foods in the grocery store

Phylum: Non-refrigerated foods

Class: Canned foods

Order: Canned vegetables

Family: Canned green beans

Genus: Green Giant canned green beans

Species: Green Giant French cut canned green beans

Do you see how each classification gets more and more specific? Let’s look at an example of an actual living organism’s classification into these specific subgroups:

Kingdom: Animalia (because a cat is an animal, of course)

Phylum: Chordata (because it has a backbone)

Class: Mammalia (because it is a mammal)

Order: Carnivora (because it eats meat)

Family: Felidae

Genus : Felis

Species: Catus

You may notice that the words to describe the cat’s taxonomy are a little weird compared to those I used to classify the green beans. This is because scientific classification is done in the Latin language. And in fact, scientists actually use only the Latin Genus and Species names when they refer to specific organisms. So the cat above would scientifically be known as Felis catus. Did you ever hear of a human being referred to as a Homo sapiens? These names are actually the Genus and Species names for humans. This two-name method of using Genus and Species names to classify organisms is known as binomial nomenclature. Notice that in my two examples I wrote both words in italics, capitalized the first (the genus name), and did not capitalize the second (the species name). This is the standard form for writing biological names using binomial nomenclature.

Which of these scientific names for a common radish is written correctly using the standard system of binomial nomenclature?

a. Raphanus savitus b. raphanus savitus c. Raphanus savitus d. raphanus savitus

So how, then, do scientists sort an organism into its proper genus and species? And how, when we come across a living thing, do we know its proper scientific name? Sometimes we use a biological key to determine the proper binomial nomenclature to use. A biological key is kind of like a “choose your own adventure” book – by answering a series of questions about a given life form, you can label it with the proper genus and species names. Let’s see how this works:

Look over this biological key:

This one isn’t specific for genus and species names, but it will show you how to use a biological key to identify common seashells. First, print the seashell pictures from this page. First, let’s use the biological key to classify the seashell on the top right.

We will start with question number 1: “Does the shell have a ROUNDED shape, or is it NOT rounded?” Look at the seashell picture. The shell is a funny shape, but I wouldn’t call it ROUND. If it WAS round, we would go directly to question number 8. But since it isn’t round, our key tells us to look next at question number 2:

“Is the surface of the shell full of holes, or is it NOT full of holes?” In the picture, the seashell we’re classifying is smooth. No holes at all, except for the big one where the creature once lived. So, according to our key, we should go next to question 4:

“Does the shell have radial symmetry, or does it have an elongated shape?” Look back at your glossary if you have forgotten what radial symmetry is. Does this shell seem radial? No…so it must be elongated. Next stop…question number 5.

“Does the shell have a spiral shape, or a non-spiral shape?” This shell is spiral – wrapped around and around itself. So we are off to question number 6:

“Does the shell have a wavy edge around its opening, or is the edge smooth?” Look closely. The edge around the opening is definitely wavy. So…we have a CONCH shell! See how it works?

Use the key to try classifying the other shells on the page, and then email me for a list of the answers! Seminar students wil do this activity in the seminar.

In later months, we will use some biological keys to classify organisms into their actual genus and species names.

Things you should study from this lesson:

Study the bold print words
Memorize the levels of classification: Kingdom, Phylum, Class, Order, Family, Genus, Species
Memorize the names of the five Kingdoms
Know Carolus Linnaeus
Understand how to use a biological key
Know the proper format for writing names with standard binomial nomenclature