The following is a list of the
different classes of protozoa. (1) Sarcodina, (2) Ciliophora, (3)
Flagellata, (4) Sporozoa. A single-celled eukaryotic organism
is found that possesses a foot-like extension to aid its movement. Which of the classes listed is this
organism most likely to belong to? (A) Sporozoa, (B) Sarcodina, (C)
Ciliophora, or (D) Flagellata.
This question is asking us to use
the information provided and our prior knowledge to classify an organism into one of
the four classes of protists that’s listed. In order to answer this question,
we’ll first recall the traits that distinguish these classes of protozoa, and then
we’ll use the information provided about our mystery organism to choose the correct
The four classes of protozoa are
distinguished by their method of locomotion. Some organisms move by cilia or
hair-like extensions found on the outside of the cell. Some move using flagellum or
whip-like structures that allow them to swim. Some protozoa move using pseudopods
or moving extensions of the cell body. And finally, our last class of
protozoa have no special appendages that help them to move.
Now that we know what distinguishes
each class, we need to figure out which is which. Well, we can easily tell that
Ciliophora likely move using cilia, since that’s indicated in the name of the
class. Similarly, we can tell that
Flagellata use flagella. The last two are a little more
tricky. Sarco- is a word part that means
flesh or muscle. The Sarcodina use pseudopods or
extensions of their cell bodies to move from place to place. That leaves us with Sporozoa, which
are the class that possess no special appendages which help them to move.
Now that we’ve identified each of
the different classes of protozoa, we need to figure out which one our mystery
organism belongs to. Let’s start by recalling the fact
that all protozoa are single-celled or colonial, eukaryotic organisms. So those two traits do not give us
a clue as to which class our organism belongs to.
Our classes of protozoa are
distinguished by their modes of movement. And the organism in our question
has a foot-like extension which allows it to move. So, we can tell that it’s not a
Sporozoa, because it does possess a special appendage. And that appendage is described as
foot-like, so it doesn’t sound like it’s hair-like or whip-like.
Another clue is that the word
pseudopod actually means false foot. So, pseudopod is another name for
the foot-like extension of our mystery organism. Now, we have the answer to our
question. The class that this organism is
most likely to belong to is Sarcodina.