Question Video: Recalling the Characteristics of the Chrysophyta Phylum | Nagwa Question Video: Recalling the Characteristics of the Chrysophyta Phylum | Nagwa

Question Video: Recalling the Characteristics of the Chrysophyta Phylum Biology • First Year of Secondary School

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Which of the following statements would correctly replace X in the Venn diagram? [A] Are exclusively heterotrophic [B] Have genetic material that is mainly stored in plasmids [C] Have a cell membrane that contains peptidoglycan [D] Have cell walls that contain silicon dioxide

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Video Transcript

Which of the following statements would correctly replace X in the Venn diagram? (A) Are exclusively heterotrophic. (B) Have genetic material that is mainly stored in plasmids. (C) Have a cell membrane that contains peptidoglycan. Or (D) have cell walls that contain silicon dioxide.

A scientist named Whittaker classified all life into five main kingdoms: Plantae, Animalia, Fungi, Monera, and Protista. Like the other kingdoms, kingdom Protista can be divided into several different phyla, including Protozoa, Euglenophyta, Chrysophyta, and Pyrrophyta. This question shows us a Venn diagram displaying some similarities and differences between the phyla Chrysophyta and Pyrrophyta. It asks about one difference in particular that is unique to Chrysophyta. So let’s talk about these organisms and what makes them different.

Protists, as well as plants, animals, and fungi, are all eukaryotic. This means that the majority of their genetic material is stored in a membrane-bound nucleus within their cells, which often contain other membrane-bound organelles too. In contrast, prokaryotic cells, which are exclusively found in kingdom Monera, do not have a nucleus or other membrane-bound organelles. Instead, their genetic material is found in the cytosol in the form of circular chromosomes and smaller loops called plasmids.

Option (B) suggests that the genetic material of organisms belonging to the Chrysophyta phylum is mainly stored in plasmids. With the information we have learned, we can eliminate this option as these organisms are eukaryotic. So the majority of their genetic material is not stored in plasmids.

As we can see in the Venn diagram, the organisms that are classified into both of these phyla have cell walls. However, organisms of the kingdom Protista do not have cell walls made of peptidoglycan. This is another property unique to some of the organisms in kingdom Monera. Protists certainly do not have cell membranes containing peptidoglycan. So we can exclude option (C): have a cell membrane that contains peptidoglycan.

Now that we have excluded two answers just by checking the characteristics of protists, we can take a closer look at the differences between Pyrrophyta and Chrysophyta. Organisms belonging to the Pyrrophyta phylum tend to have photosynthetic pigments, such as chlorophyll, which likens them to plants, even though they are classified in an entirely different kingdom. As a result of these pigments, many Pyrrophyta are often referred to as phytoplankton. This term derives from the Greek words meaning plant wanderer, as they drift through their watery environment photosynthesizing much like a plant would.

Another feature that likens these organisms to plants is that they have cellulose in their cell walls. Many of the organisms that belong to this phylum are commonly known as dinoflagellates. The suffix -flagellate refers to the fact that they are motile organisms that use their two flagella for locomotion. Organisms such as diatoms that are classified within the phylum Chrysophyta are also usually photosynthetic. As they are autotrophic organisms like those belonging to the Pyrrophyta phylum, they too are able to make their own food from simple inorganic materials. Knowing this, we can eliminate option (A), which proposes that chrysophytes are exclusively heterotrophic. As diatoms are autotrophic Chrysophyta, the phylum Chrysophyta cannot be exclusively heterotrophic.

Unlike the cellulose cell walls of pyrophytes, the cell walls of chrysophytes are made up of silicon dioxide and an organic matrix that allows them to withstand great pressure. With this information, we can deduce the correct answer to this question. A feature that distinguishes organisms in the Chrysophyta phylum from those in the Pyrrophyta phylum is (D). Chrysophyta have cell walls that contain silicon dioxide.

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