SCIENCE_BIOLOGY
KEY TO IDENTIFY THE RANGE OF ORGANISMS
Introduction
As biology is concerned with the study of living organisms, the characteristics of one organism is different from another though they belong to the same group or phylum. Identifying the characteristics of organisms is a challenging task for the biologist. After identifying the characteristics of an organism, they are classified and named. Naming of organisms is done with genus and species is termed as binomial system of nomenclature. Carolus linnaeus was the first Swedish scientist to classify the organism scientifically.
Charles Darwin was the first biologist to study and explain about the evolution of organisms and published an article Theory of Evolution. Complex organisms evolved from the simple existing organism. Here the complex organism refers to the organism with advanced characteristics. When the biologist explores nature and studies these organisms they use the reference character of the pre-existing organism. It is a completely complicated task for a layman to classify the organism by studying their character even which were already classified. So in order to make these tasks easy and convenient, scientists have developed a tool called dichotomous key, which helps a layman to identify objects and organisms.
The term dichotomous is derived from the two Greek word “Di” which means “two” and “tome” which means “cutting instrument”
A dichotomous key consists of a series of questions, when a question is answered, the key directs the user as to what question to ask next. Consider an example of dichotomous key to classify the vertebrates:
Mammals: We might ask, does it have fur? If the answer is “yes” it leads to mammals.
Birds: if said “no” next maybe next may be “does it have feathers”? If the answer is “yes” we identified birds
Reptiles: if the answer is “no”, we may ask if the organisms have dry or moist skin? If we say dry the organisms will be identified as reptiles.
Pisces: if the answer is “moist”, we might ask if the organism has smooth skin or scales? If the answer is scales we have identified as pisces.
Amphibians: if the answer is moist skin, it is an amphibian.
A dichotomous key looks like a flow chart a feature a series of images and text with two choices branching off at two each step: we choose the one that fits the organisms you want to identify
At each stage, we are presented with a choice of characteristics and answer ‘yes’ or ‘no’ until, we make an identification of an organisms
How to make a dichotomous key:
Step 1. Listing down the characteristics:
List down the character that you can notice. For example if we are trying to classify group of plants, you may notice that some of them have sharp leaves, cones ,whereas other have flat leaves and flowers
Step 2. Organising the characteristics in order:
While creating a dichotomous key the characters of an organism are identified and then they are assembled. While assembling the characters they are arranged from simple to complicated
Step 3. Divide the specimen:
We can use statements to divide our specimen into two groups. The first differentiation should be made on the first most general characteristics
Step 4. Divide the specimen even further:
Taking reference of more contrasting characters, we need to divide the specimen further. First we may group our organisms as they have sharp leaves or flat leaves, in which the plants with sharp leaves are classified as conifers and while the plants with flat leaves can be classified as angiosperm.
Step 5. Draw a dichotomous key diagram:
We can either create or draw graphical diagrams with images or text based dichotomous diagrams for the organism we are trying to identify.
Step 6. Test it out:
Once the dichotomous key is set up or created we need to test it whether it works or not. The specimens that are going to be classified should be checked with all the diagnostic characters and should coincide. Necessary adjustment or editing can be done if it is required.
Uses of dichotomous Key:
A dichotomous key is used for
Identifying and categorizing organism
Helping students easily understand complicated nomenclature concepts
Assembling large amount of information to make identification of an organisms much easier
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