Classification of organisms
You already use a simple classification system in your daily life. When you use words such as tree or bird you are using group words. The word tree covers a wide variety of different organisms. It includes pine trees, gum trees and wattles. Even though there are lots of different types of trees, trees is still a useful word to use, as the listener has a good idea of what you are talking about. Similarly, when a biologist is talking about a mammal, the listener knows a great deal of information about that particular organism without having to see it. Classification of organisms makes it easier to communicate facts and ideas about them.
What happens if we classify organisms by grouping together all those that look alike? For example, the cat, the lion, the tiger, the leopard and other cat-like animals could all be put into the "cat family". The dog, the wolf, the fox and the dingo could form part of the "dog family", and so on.
Under such a scheme, the whale might be classed as a fish and the bat as a bird. However, the whale and the bat are more like each other than one is like a fish or the other like a bird. Both the whale and the bat bear live young, while fish and birds have eggs. Both the whale and the bat breathe using internal lungs. If we look at the internal bone structure of their limbs below, we see that the whale and bat are similar. Because of these and other internal features biologists have placed the whale and the bat in the group called mammals.
What happens if we classify organisms by grouping together all those that look alike? For example, the cat, the lion, the tiger, the leopard and other cat-like animals could all be put into the "cat family". The dog, the wolf, the fox and the dingo could form part of the "dog family", and so on.
Under such a scheme, the whale might be classed as a fish and the bat as a bird. However, the whale and the bat are more like each other than one is like a fish or the other like a bird. Both the whale and the bat bear live young, while fish and birds have eggs. Both the whale and the bat breathe using internal lungs. If we look at the internal bone structure of their limbs below, we see that the whale and bat are similar. Because of these and other internal features biologists have placed the whale and the bat in the group called mammals.
Biologists look at internal structural features when classifying organisms. However, often organisms with structural features in common have other external features in common as well. This means that members of that group may look a lot like each other.
Organisms are classified at a number of levels. The largest groupings are called kingdoms. For many years, only two kingdoms were recognised: Animalia, consisting of all the animals and Plantae containing all the plants. However, there are thousands of organisms, mostly very small, that are neither plant nor animal, or have both plant and animal features. These organisms are grouped separately from plants and animals into other kingdoms including: Monera, Protista, Fungi. Today, many scientists recognise five kingdoms.
The kingdoms are further divided into a number of groups each known as a phylum. A phylum includes all organisms with the same body plan. For instance, the mammals, birds, reptiles, amphibians and fish are placed in one phylum because all have backbones and a maximum of four limbs. Each phylum is divided into classes, for example the Mammalia which includes bats, monkeys, horses, whales, kangaroos, apes and humans. The classes are divided into orders, the orders into families, the families into genera, and genera into species. The species is the smallest classification group. Members of a species can breed together to produce fertile offspring. Such a system is hierarchical.
Table 1. The hierarchical system used in classifying some organisms.
Organisms are classified at a number of levels. The largest groupings are called kingdoms. For many years, only two kingdoms were recognised: Animalia, consisting of all the animals and Plantae containing all the plants. However, there are thousands of organisms, mostly very small, that are neither plant nor animal, or have both plant and animal features. These organisms are grouped separately from plants and animals into other kingdoms including: Monera, Protista, Fungi. Today, many scientists recognise five kingdoms.
The kingdoms are further divided into a number of groups each known as a phylum. A phylum includes all organisms with the same body plan. For instance, the mammals, birds, reptiles, amphibians and fish are placed in one phylum because all have backbones and a maximum of four limbs. Each phylum is divided into classes, for example the Mammalia which includes bats, monkeys, horses, whales, kangaroos, apes and humans. The classes are divided into orders, the orders into families, the families into genera, and genera into species. The species is the smallest classification group. Members of a species can breed together to produce fertile offspring. Such a system is hierarchical.
Table 1. The hierarchical system used in classifying some organisms.
Many people use mnemonics to
help them remember things in order.
eg. Katy Perry Can Only Finish Good Songs
OR
Kittens Prefer Cream Over Fish, Generally Speaking.
Questions to answer in your exercise book:
1. Why is classification necessary?
2. Which is the largest classification group?
3. Which is the smallest classification group?
4. How many classes in the Animal Kingdom can you name?
5. Think of a mnemonic of your own to help you remember the KPCOFGS classification scheme.
eg. Katy Perry Can Only Finish Good Songs
OR
Kittens Prefer Cream Over Fish, Generally Speaking.
Questions to answer in your exercise book:
1. Why is classification necessary?
2. Which is the largest classification group?
3. Which is the smallest classification group?
4. How many classes in the Animal Kingdom can you name?
5. Think of a mnemonic of your own to help you remember the KPCOFGS classification scheme.
keys
When you study biology, you will often need to identify organisms. This might seem very easy, for instance, there are obvious differences between fleas and mosquitoes. However, in detailed studies it might be necessary to identify species. Having found a flea, how do you identify it from the 1500 or so other species of flea in the world? Devices, called keys have been constructed to make this task easier. Keys can take various forms, but the most common type is a list of questions about structural features of the organism to be identified.
To find out how to use a key, look at the one below. To classify the animal shown in drawing (a) follow the steps given.
- Start at 1 in the key. Does animal (a) have fins? No, so go to 3.
- Does animal (a) have feathers? No, so go to 4.
- Does animal (a) have hair or fur? Yes, so animal (a) is a mammal.
Now try to classify animals (b) and (c). Write the answers in your exercise book.
Keys to animals with backbones
1a) Fins present……………………………………………………Go to 2
b) No fins…………………………………………………………Go to 3
2a) Scales present (fish like)………………………………………Go to 6
b) Hair or fur present …………………………………………….Mammal
3a) Feathers present ………………………………………………Birds (Aves)
b) No feathers ……………………………………………………Go to 4
4a) Hair or fur present ……………………………………………Mammal
b) No hair or fur ………………………………………………… Go to 5
5a) Scales present ………………………………………………… Reptile
b) Slimy skin, no scales …………………………………………..Amphibian
6a) Jaws present ……………………………………………………Go to 7
b) Jaws absent ……………………………………………………. Jawless fish (Agnatha)
7a) Gills concealed under a flap, skeleton of bone …………………Bony fish (Osteiichthyes)
b) Gill slits visible on side of body, skeleton of cartilage …………Cartilaginous fish
To find out how to use a key, look at the one below. To classify the animal shown in drawing (a) follow the steps given.
- Start at 1 in the key. Does animal (a) have fins? No, so go to 3.
- Does animal (a) have feathers? No, so go to 4.
- Does animal (a) have hair or fur? Yes, so animal (a) is a mammal.
Now try to classify animals (b) and (c). Write the answers in your exercise book.
Keys to animals with backbones
1a) Fins present……………………………………………………Go to 2
b) No fins…………………………………………………………Go to 3
2a) Scales present (fish like)………………………………………Go to 6
b) Hair or fur present …………………………………………….Mammal
3a) Feathers present ………………………………………………Birds (Aves)
b) No feathers ……………………………………………………Go to 4
4a) Hair or fur present ……………………………………………Mammal
b) No hair or fur ………………………………………………… Go to 5
5a) Scales present ………………………………………………… Reptile
b) Slimy skin, no scales …………………………………………..Amphibian
6a) Jaws present ……………………………………………………Go to 7
b) Jaws absent ……………………………………………………. Jawless fish (Agnatha)
7a) Gills concealed under a flap, skeleton of bone …………………Bony fish (Osteiichthyes)
b) Gill slits visible on side of body, skeleton of cartilage …………Cartilaginous fish
Use the following key to name the beetles shown below. Write the answers in your exercise book.
Classify each of the fish shown below using the key provided. To use the key, select a fish. Start at number 1a and read the statement. If it applies, then go to the number allocated. Continue down the key until you reach the species name. For each fish, write its scientific name in your exercise book as well as a species description by writing out the steps you used.
eg. “This fish has scales that are fairly large. The body is compressed, long and slender. The dorsal fin is single and situated near the caudal fin of the fish. This fish has very large eyes and large scales. The mouth is hinged in front of the eye. The mouth has a long slender beak. The upper jaw is much broader than it is long. It has a slightly forked tail.”
eg. “This fish has scales that are fairly large. The body is compressed, long and slender. The dorsal fin is single and situated near the caudal fin of the fish. This fish has very large eyes and large scales. The mouth is hinged in front of the eye. The mouth has a long slender beak. The upper jaw is much broader than it is long. It has a slightly forked tail.”
Using Inspiration, create your own classification key for 6 different marine organisms of your choice. You may use google to select images of your organisms if this helps.