Video Transcript
The following is a statement about
the characteristics of organisms belonging to the phylum Mollusca. Organisms belonging to the phylum
Mollusca have an blank body that has a calcareous blank. Which of the following options
provides the most appropriate replacements for the first and second blanks in the
statement, respectively? (A) Unspecialized and skin. (B) Unsegmented and shell. (C) Asymmetrical and appendage. Or (D) undifferentiated and cell
wall.
Let’s start by reviewing some of
the characteristics that organisms in phylum Mollusca have in common.
One of the most typical
characteristics of Mollusca is a mantle, which secretes a hard shell, which often,
but not always, covers the organism’s soft body. The mantle plays an important role
in respiration in these organisms, as well as secreting the shell. Also, the body is unsegmented,
meaning it does not have repeating parts and typically consists of a head, a
visceral mass, and a ventral foot. And mollusks are bilaterally
symmetrical, meaning that they look the same on both sides.
Let’s take a look through these
answer choices to determine which is the correct one. First, animal cells do not have
cell walls, so we can eliminate (D). And the cells of these organisms
are indeed differentiated or specialized in different tissues, so we can eliminate
(A). Since mollusks are bilaterally
symmetrical, we can also eliminate (C). The choice that does match
characteristics of Mollusca is (B). Organisms belonging to the phylum
Mollusca have an unsegmented body that has a calcareous shell.
