2.3.1 - Making and using simple identification keys.

we continue our look at topic 2 the ecosystem this segment is concerned solely with topic two point three point one which is to construct simple keys and use published keys for the identification of organisms so lets find an organism that needs identifying suppose you are out doing a study of a polluted pond or lake and found you this floating as a result of maybe runoff from a farm and your job was to identify the species that you're looking at so that you can go ahead and write a report of what's going on your first step is likely to be take a sample of it to the lab and look at it with a microscope when you look in there your likely to find this this should tell you that you are looking at algae provided that you've got some basic knowledge of what you're doing and algae have chloroplasts in their cells lots of the green stuff used in photosynthesis and this particular algae that we have is made up of long unbranched filaments with this basic information in mind our next step in identification is this key..and see if you could figure out how it works just by looking at it this of course is a very simple version of a dichotomous key and the content of this is adapted from this URL here at the bottom so if you have had a look maybe you've figured out how it works but this is how it works if you have any trouble the key the dichotomous key is made up of a series of statements and each set of statements is aimed at dividing the big group into smaller groups so that you can eventually zero in on the identity of the unknown species that you're trying to identify for instance what we found in the pond is microscopic it's not macroscopic we needed a microscope to see details of it so the first statement or pair statements which is why we get the name dichotomous branching into two the first pair of statements says microscopic or macroscopic and our response should be that it's a microscopic so that means that we are directed to go to number two which then asks does it contain chloroplasts or not and it does contain chloroplasts so we go to three and in three are the cells solitary which means just by themselves or are they in colonies or are they filamentous well.. we might not be sure about what a colony is but if it's grouped with solitary we've already identified that the algae is filamentous so that takes us to five long thin unbranched filaments unbrached filaments so that takes us from five over to seven and at seven we're asked are the chloroplasts in a spiral like a spring or are they not in a spiral and we don't have any evidence that they are in a spiral so that leads us to eight do we have a single chloroplasts or many small chloroplasts and you can see here that our specimen has many small chloroplasts and that leads us to identify our specimen as microspora and this is how you use a simple dichotomous key having used it though you are likely to be asking why a key why do you need to go through this system when maybe you could just look through the pages of the book or go online and search for kinds of algae and that could very well work if you just had maybe fifty types of algae to pick from that could certainly work or maybe even a hundred but if you had eight thousand species and more of algae it could be the bit time consuming think about looking for somebody in a town with eight thousand homes it would take some time to carry out your search but if you had some important information about who we were looking for and each time you asked a question of somebody it narrowed your search down then it will be a whole lot easier so this is what a dichotomous key does it takes information that you know simple information that you can observe and it very quickly allows you to move toward identifying the name of what you have in front of you trying to figure out the keys are usually made by biologists for biologists so in the real world of biology in trying to identify things its definitely and asset if you have a basic knowledge of some of the terms like the terms we've used here to understand the key like microscopic and microscopic to know what chloroplasts are to know what filamentous means and what solitary and colonial mean that would also be helpful so a basic understanding of the structure of what you're looking at certainly is helpful because ultimately to identify we have to work with things that are easy to observe it is no point talking about things that are really complicated and hard to see we would like to..quickly identify what we are looking at so let's stop here now and have a look at your activity your activity requires you to make a key for eight organisms that..you are hopefully very familiar with a beetle scorpion centipede and dragonfly ladybug spider and butterfy so go ahead and look back at our sample key look at how it's made up pairs of statements and try to organize our eight specimens here in a key of your own and a hint is to look for features like body segments wings and legs things that are easy to observe and would be very useful in separating the members of this group your answer doesn't have to exactly match this to be right so you could have a very good answer that does not match this and if you have it totally wrong and you think you need to another shot at this go to your refrigerator and take out vegetables or some food items and try making a key to identify the names of what you have in the refrigerator for maybe for the purpose of some alien being that you have staying with you who won't know the names of what's in the refrigerator but they might be able to identify some of the features