Video Transcript
A simple dichotomous key used to
identify invertebrates commonly found in gardens is provided. A child finds an organism that has
no wings, no shell, and eight legs. Using this dichotomous key,
determine which organism it is most likely to be.
A dichotomous key is a tool created
by scientists to help identify an organism by responding to a series of statements
about the organism’s simple physical characteristics. The prefix di- means two,
indicating that each statement about a particular characteristic found at each
successive junction in the dichotomous key has two options. For example, the first
characteristic in this particular dichotomous key concerns the organism having
wings, the response to which can be one of two options. It has wings or it has no
wings.
The dichotomous key in this diagram
is useful for animals found in the garden, such as the organism that has been found
in this example, which might look something like this. When using a dichotomous key, we
start at the top.
It has already been determined that
this animal is an invertebrate, which means that it does not have a vertebral
column. Now, let’s move down the key to the
first branch. If the organism has wings, we
follow the left fork. If it has no wings, we follow the
fork on the right. We know that the animal has no
wings, so we move to the next branch on the right. We must now identify whether the
organism has a shell or no shell. As there is no shell present, we
take the left branch. Next, we need to identify the
number of legs the organism has. This organism has eight legs, so we
take the right branch.
This means that we can identify the
invertebrate correctly. The organism that has been found is
a spider.
