Video Transcript
The kingdom Protista is divided
into multiple phyla. Which of the following statements
best describes organisms belonging to the Pyrrophyta phylum? (A) Organisms are unicellular, they
inhabit fresh water or salt water, and most contain chloroplasts to carry out
photosynthesis. (B) Organisms are mostly
unicellular algae, with their cells often containing chloroplasts and the cell walls
containing silica. (C) Organisms are unicellular, they
often inhabit water or moist soils, and they can act as parasites. Or (D) organisms move by the use of
flagella, their cells contain photosynthetic pigments, and nearly all species are
classed as phytoplankton.
The kingdom Protista is divided
into multiple phyla, including Protozoa, Euglenophyta, Chrysophyta, and Pyrrophyta,
which this question concerns. Many of the organisms that belong
to the Pyrrophyta phylum are commonly known as dinoflagellates. The suffix -flagellates refers to
the fact that they are motile organisms that use their two flagella for
locomotion. And the prefix dino- originates
from the Greek word dinos, which means whirling, describing how these flagella
move.
Organisms belonging to the phylum
Pyrrophyta contain photosynthetic pigments such as chlorophyll that often give them
a yellowish-green or golden-brown color. Some organisms belonging to this
phylum are even bioluminescent, from which their name derived, as the prefix pyr-
comes from the Greek word for fire, referring to the luminescent glow emitted by
some of these organisms in darkness.
Their photosynthetic pigments liken
them to plants, which are also usually photosynthetic and result in them often being
referred to as phytoplankton. This word derives from the Greek
words meaning plant wanderer, as they drift through their watery environment
photosynthesizing much like a land plant would, even though they are usually
classified in an entirely different kingdom to plants.
First, let’s talk about option (B):
organisms are mostly unicellular algae, with their cells often containing
chloroplasts and the cell walls containing silica. While these organisms are mostly
unicellular algae and often contain chloroplasts, their cell walls do not usually
contain silica and are instead made up primarily of cellulose like the cells of many
plants. Therefore, we can eliminate this
answer.
We can also eliminate option (C) —
organisms are unicellular, they often inhabit water or moist soils, and they can act
as parasites — because Pyrrophyta do not often inhabit moist soils. Instead, they mostly live in
marine, salt water, or sometimes fresh water habitats.
Now, let’s take a look at option
(A): organisms are unicellular, they inhabit fresh water or salt water, and most
contain chloroplasts to carry out photosynthesis. These are all true to the
Pyrrophyta phylum. However, it is not the best answer
because it misses a key component of the organisms that belong to this phylum, which
is the use of flagella for motility.
The best answer to describe
organisms belonging to the Pyrrophyta phylum would therefore be option (D):
organisms move by the use of flagella, their cells contain photosynthetic pigments,
and nearly all species are classed as phytoplankton.
