Video Transcript
Organisms belonging to the
Nostoc genus, shown in the picture, are examples of eubacteria. Which of the following is correct
about the nutrition of eubacteria? (A) They are exclusively
heterotrophic. (B) They can be autotrophic or
heterotrophic. (C) They are exclusively
autotrophic. Or (D) they are exclusively
parasitic.
This question asks about the
nutrition of eubacteria, specifically whether they are heterotrophic, autotrophic,
or parasitic. Let’s start with some
definitions. Autotrophs synthesize their own
food from inorganic materials. For example, many plants and algae
synthesize their food using simple inorganic materials and sunlight through
photosynthesis. Heterotrophs obtain their food by
consuming other living, or once living, organic matter. For example, a human who takes a
bite of an apple is a heterotroph. Any decomposers, like fungi or
bacteria, that break down the remains of the apple are also heterotrophs. Parasites are specific examples of
heterotrophs that live in or on a living host and gain food from, or at the expense
of, their host. For example, fleas, which feed on
the blood of animals like dogs, are parasites, as they gain their nutrition at the
expense of a host.
The microscope image from the
question showing some individuals belonging to the Nostoc genus give us some
clues about eubacteria nutrition. Nostoc appear green because
they are full of chlorophyll, a pigment used in photosynthesis, indicating that
Nostoc gain their nutrients from sunlight and are therefore
autotrophs. With this knowledge, we can
eliminate answers (A) and (D), stating that they are exclusively heterotrophic and
exclusively parasitic, respectively, because we know that at least some eubacteria,
such as those belonging to the Nostoc genus, are autotrophic. Some eubacteria are heterotrophs,
for example, organisms belonging to the genus Mycobacterium, some of which
cause diseases like tuberculosis in humans. This means answer (C), stating that
they are exclusively autotrophic, cannot be true because some eubacteria are
heterotrophs.
Now we know that some species of
eubacteria obtain their food from inorganic materials so are autotrophic, whereas
others obtain their food from organic materials so are heterotrophic, making the
correct answer (B). They can be autotrophic or
heterotrophic.
