Experiment 1: Dichotomous Key Practice A dichotomous key is an identification to

Question

Experiment 1: Dichotomous Key Practice

A dichotomous key is an identification tool that starts with a broad defining characteristics and splits into two options until an organism can be identified. In this experiment, you will identify organisms by their binomial nomenclature using a dichotomous key.

Materials

Dichotomous Key

Images of Organisms

Procedure

Start by observing organism i (Figure 2). Once you have taken notice of its physical characteristics, use the dichotomous key (Figure 3) to identify the organism.

Start at number 1 on the key and decide if the organism has feature “1a” or feature “1b”.

Which ever option you choose, follow the dotted line over to the next step that will state “Go to #”.

Go to that number and again decide between the two options.

Eventually you will wind up at a two name scientific name.

Once you have identified organism i record your finding in Table 3.

Repeat Steps 1 - 6 for all of the organisms in the dichotomous key (Figure 3).

Table 3: Dichotomous Key Results

Organism

Binomial Name

i

ii

iii

iv

v

vi

vii

viii

ix

x

xi

xii

xiii

Figure 2: Organisms to be identified

Figure 3: Dichotomous key

Post-Lab Questions

What do you notice about the options of each step as they go from number one up?

How does your answer from Question 1 relate to the Linnaean classification system?

Materials

Dichotomous Key

Images of Organisms

Explanation / Answer

Linnaeus introduced a new idea to classify living things (a hierarchy of nested groups within groups called hierarchical ordering). The Linnaeus proposed binomial classification system- which group organisms together based on common structures, functions, and resulting behaviors. We can say that all modern classification systems have their roots in the Linnaean classification. A dichotomous key is one such a tool which helps to determine the identity of items in the natural world (trees, wildflowers, mammals, reptiles, rocks, and fish) using their physical characteristics. Through a series of choices we can identify the correct name.

What do you notice about the options of each step as they go from number one up?

Dichotomous means divided into two parts and in dichotomous key each step tries to narrows the choices mainly based on the characteristics of an organism and help the user to identify the item. It begins with tree, flower, animal, vegetable or mineral, and will process until the other options have been ruled out.

How does your answer from Question 1 relate to the Linnaean classification system?

The Linnaean classification system, will group the organisms based on their physical similarities and Linnaeus did not consider the relationships between similar species and the classification is a rank based system. So, we can say that the Linnaean classification system and Dichotomous key use the physical traits shown by the organisms to group them together.

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