Which of the following is not a
class of the phylum Tracheophyta? (A) Gymnospermae, conifers; (B)
Filicatae, ferns; (C) Angiospermae, flowering plants; or (D) Rhodophyta, red
The question asks us about classes
within a phylum. So let’s start by reviewing what
these terms actually mean.
In biology, organisms are
classified into different groups based on shared characteristics and evolutionary
relationships. The study of this classification of
organisms is called taxonomy, and it uses different levels of organization arranged
in a hierarchy. We can see one example of a
hierarchical system in the diagram. Moving from the most general level
to the most specific level, they are kingdom, phylum, class, order, family, genus,
Scientists continue to engage in
lively debates about exactly how many taxonomic levels there should be and where
organisms should be placed among these levels. For example, some scientists
advocate using even broader levels than kingdoms, such as domains or empires.
For this question, we will focus on
kingdom Plantae, which contains over 400,000 described species of land plants and
algae. The diagram shows the major phyla
within an expanded kingdom Plantae, often referred to as Archaeplastida. The first three phyla are the
brown, red, and green algae. Algae is just a term for aquatic
organisms that, like plants, are photosynthetic but don’t have leaves, roots, stems,
or vascular tissue.
Algae can be microscopic, like the
freshwater green algae Spirogyra, or macroscopic, such as the brown algae known as
kelp, which can reach over 50 meters in height. There is active debate about the
inclusion of algae within kingdom Plantae, particularly about Phaeophyta, the brown
The next two phyla are Bryophyta
and Tracheophyta. Bryophytes are nonvascular, meaning
they don’t have specialized tissue for water, mineral, and sugar transport. In contrast, the tracheophytes
possess vascular tissues called xylem and phloem, which transport water and minerals
and sugars produced during photosynthesis.
The question is asking us about the
classes within Tracheophyta. Some taxonomic systems divide this
phylum into three classes: Filicatae, Gymnospermae, and Angiospermae. Filicates are ferns, which do not
have flowers or seeds but instead reproduce with spores. Gymnosperms are nonflowering plants
that use seeds to reproduce. Their seeds are not enclosed but
rather are found exposed on cones. The third class, the angiosperms,
are the flowering plants. After pollination, they produce
seeds that are enclosed in fruits.
We now have enough information to
answer our question. The class that is not part of the
phylum Tracheophyta is Rhodophyta, the red algae.