Study GuidePlant Biology–Protista1. AlgaeAlgae are a diverse group of organisms, and they can look very different from one another. Somemarine algae, calledkelps, even resemble large plants. They havestem-like stalks,leaf-likeblades, and aholdfastthat anchors them to rocks on the sea floor. These kelps grow in cold northernoceans and can reach an incredible height of50–60 meters, making them thelargest protistsonEarth.However, most algae are much simpler and much smaller. Many areunicellular(made of just onecell) andmicroscopic. Others formcolonies,filaments,net-like structures, or longtubularbodies. Some move freely using flagella, while others remain fixed in place. This wide variety offorms shows how adaptable algae are to different environments.1.1How Do Scientists Classify Algae?Because algae come in so many shapes and sizes,body structure alone is not very usefulforclassifying them. Their reproductive structures also don’t help much. Instead, scientists focus onspecific features that are more reliable.Thefive main characteristicsused to classify algae are:1.Photosynthetic pigmentsthey contain2.Type of food they store3.Material of the cell wall4.Number, type, and position of flagella5.Details of cell structure, such as chloroplast shape or the presence of special structures likeeye spots or pyrenoidsA sixth and very important featureis now used:•DNA and RNA molecular sequencesModern genetic studies have greatly improved our understanding of algal relationships. In fact, thisnew data hasreshaped the algal family tree, changing many ideas scientists once believed werecorrect.Preview Mode
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