Week 10

How can we tell different organisms apart?

success criteria

I can identify types of characteristics that can be used to identify an organism
I can construct and use a dichotomous key based on different organisms’ characteristics.

Tasks

Knowledge & understanding

Make and post a dichotomous key on the Padlet

Investigation Skills

Macroinvertebrate identification

Literacy & research

Knowledge and understanding

Scientists have catalogued 1.5 million species on Earth and estimate that there might be as many as 100 million more unidentified species. Classification keys are tools that provide a means to correctly identify different organisms, based on observable traits. Most such keys are created in a dichotomous format. Dichotomous literally means dividing into two parts. A dichotomous key provides users with a series of statements with two choices that will eventually lead to the correct identification of the organism. To use a dichotomous key, one must be able to make accurate observations and follow directions carefully.

Why is correct identification of organisms important?

The accurate identification of organisms is important when measuring the biodiversity of an area. It is also a prerequisite when attempting to find out more about the ecology of a species. And without accurate identification it is impossible to determine how many species exist in a given area. Identifying organisms is, however, a task fraught with difficulties. A single type of organism may be misidentified as several different species.

Macroinvertebrates are animals without a backbone that can be seen with the naked eye. These bottom-dwelling animals include crustaceans and worms but most are aquatic insects. Beetles, caddisflies, stoneflies, mayflies, hellgrammites, dragonflies, true flies, and some moths are among the groups of insects represented in streams. Macroinvertebrates are an important link in the food web between the producers (leaves, algae) and higher consumers such as fish. As we saw at Jerrabomberra Wetlands they are quite tricky to identify!

Classification is a system used by scientists to group and sort living and non-living things based on characteristics they share. Sorting things in this way helps us better understand the world we live in.

Here are a few ways scientists classify things.

Taxonomy

Taxonomy is the branch of science concerned with classification. Carolus Linnaeus, a scientist born in 1707, is known as the Father of Taxonomy. He divided all things into either plant or animal groups called kingdoms. He then divided these kingdoms into smaller and smaller groups, eventually giving us kingdom, phylum, class, order, family, genus, and species. Scientists still use these ideas today, though our current classification system contains 8 levels, with domain coming above kingdom.

Linnaeus also developed the system of giving organisms a scientific name in Latin. These two names form the genus and species of the organism. For example, the scientific name of a lion is Panthera leo, while the scientific name of a gray wolf is Canis lupus. This system of giving organisms two names is called binomial nomenclature.

Dichotomous Key

Dichotomous keys are tools that help users identify living and non-living things. The word dichotomous comes from two Greek words that together mean, "divided in two parts". In each step of a dichotomous key two choices are given with directions for what to do next. Each choice leads either to another choice or the identity of the object or organism. Some dichotomous keys are lists of questions, while some look more like charts. Here are two examples

How to use a dichotomous key

1 a. Backbone . . . . . . . . . . . . . . . . go to 2

b. No backbone . . . . . . . . . . . . . go to 5

2 a. Wings . . . . . . . . . . . . . . . . . . . bat

b. No wings . . . . . . . . . . . . . . . . . go to 3

3 a. Legs . . . . . . . . . . . . . . . . . . . . go to 4

b. No legs . . . . . . . . . . . . . . . . . .snake

4 a. Shell . . . . . . . . . . . . . . . . . . . .tortoise

b. No shell . . . . . . . . . . . . . . . . . lizard

5 a. Antenna . . . . . . . . . . . . . . . . . ant

b. No antenna . . . . . . . . . . . . . . spider

DIRECTIONS

• Choose one creature to start.

• Read steps 1a and 1b.

• Decide which statement is true and follow the directions.

• The directions will lead you to a new pair of choices.

• Keep doing this until you come to a step that gives you the creature’s name.

• Choose a new creature and repeat these steps.

• Do this until you identify every creature.

EXAMPLE

1 a. Backbone . . . . . . . . . . . . . . . . go to 2

b. No backbone . . . . . . . . . . . . . go to 5

2 a. Wings . . . . . . . . . . . . . . . . . . . bat

b. No wings . . . . . . . . . . . . . . . . . go to 3

3 a. Legs . . . . . . . . . . . . . . . . . . . . go to 4

b. No legs . . . . . . . . . . . . . . . . . .snake

4 a. Shell . . . . . . . . . . . . . . . . . . . .tortoise

b. No shell . . . . . . . . . . . . . . . . . lizard

Identifying Aliens with a Dichotomous Key

Look carefully at the aliens pictured below. Use the dichotomous key to find the scientific name for each one.

1 a. Mouth open . . . . . . . . . . . . . . go to 2

b. Mouth not open . . . . . . . . . . . go to 4

2 a. Arms . . . . . . . . . . . . . . . . . . . go to 3

b. No Arms . . . . . . . . . . . . . . . . .Alienus quadlegicus

3 a. Hairy . . . . . . . . . . . . . . . . . . . Alienus hairicus

b. Not hairy . . . . . . . . . . . . . . . . Alienus tritoothicus

4 a. No horns . . . . . . . . . . . . . . . . go to 5

b. Horns . . . . . . . . . . . . . . . . . . .Alienus stripicus

5 a. No legs . . . . . . . . . . . . . . . . . .Alienus blobicus

b. Legs . . . . . . . . . . . . . . . . . . . . Alienus fuzzicus

Compare you're answers to your neighbours.

Make Your Own Dichotomous Key

Create a dichotomous key for the animals pictured below and put it in the padlet. Since there are many traits to use to group these animals, there is more than one way to make a key. This means that there is more than one correct answer!

DIRECTIONS

• Carefully observe the traits of each animal.

• Make a list of the traits you can use to sort the animals into groups.

• For the animals above your list might look like this.

Number of legs Shell

Body covering (scales or hair) Tail

Exoskeleton Antenna

Backbone Wings

Classification (reptile, mammal, etc.)

• Pick one of the traits from the list to divide the animals into two groups.

• For example, you could start with body covering.

Step 1 a. Scales . . . . . . . . . . . . . go to 2

b. No scales

• Now look at all the animals with scales and choose another trait from the list to further separate them. Your next choice might be legs. In this step the first animal is named.

Step 2 a. Legs . . . . . . . . . . . . . . go to 3

b. No legs . . . . . . . . . . . . snake

• Continue these steps until all animals from the first group (scales) have been named.

• Repeat these steps with the second group of animals until each animal is identified.

Investigation skills

Who am I?
Use the macroinvertebrates key to find out the bug you have been given in class

StroudWebsiteMacroKeyFNL.pdf