Question Video: Recalling the Classes of the Phylum Tracheophyta Biology

Which of the following is not a class of the phylum Tracheophyta? [A] Gymnospermae (conifers) [B] Filicatae (ferns) [C] Angiospermae (flowering plants) [D] Rhodophyta (red algae)


Video Transcript

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 algae?

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, and species.

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 algae.

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.

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