BIOLOGY Volume 1 - A Guide to General Biology - 2004

2. THE DIVERSITY OF LIFE ON EARTH

2.6. Kingdom Protoctista

2.6.3. Algae

Algae form a vast group of protoctists of immense biological significance and great importance to humans. They lack any single diagnostic feature. Most likely, they are photosynthetic eukaryotes that evolved in an aquatic environment and remained there. Some algae have emerged from Water and successfully adapted to terrestrial life, but unlike plants, the proportion of land algae is negligible compared to oceanic and freshwater forms. The algal body is not differentiated into a stem, roots, and leaves. Such a relatively undifferentiated body is called a thallus.

Algae form A number of distinct natural groups, differing mainly in their Photosynthetic Pigments. In modern Classification, these groups have been assigned the status of phyla (divisions). Fig. 2.28 shows only four algal phyla. The General characteristics of algae, as well as two of the major phyla, are described in Table 2.7. Two algal representatives, namely Chlorella (phylum Chlorophyta) and Fucus (phylum Phaeophyta), are examined in more detail below.

Class="center">Table 2.7. Classification and Main characteristics of two of the major algal groups

Algae
General features
Almost all species are adapted to an aquatic lifestyle
Great diversity of sizes and forms, including unicellular, filamentous, colonial, and thalloid forms. The thallus is an algal body that is not differentiated into true roots, stems, and leaves and lacks a true Vascular System (xylem and phloem)
Algae are often flattened in shape. Photosynthetic, eukaryotic organisms
Phylum Chlorophyta (green algae)	Phylum Phaeophyta (brown algae)
The primary photosynthetic pigment is chlorophyll, giving them a green color. Contain chlorophylls a and b (like plants)	* The main photosynthetic pigment is brown and is called fucoxanthin. Contain chlorophylls a and c
Store CARBOHYDRATES in the form of insoluble starch	* Store carbohydrates in the form of soluble laminarin and mannitol. Also store fats
Mostly freshwater species	Almost all species are marine (only three freshwater genera)
Great variety of types, e.g., unicellular, filamentous, colonial, thalloid	Filamentous or thalloid, often large
Examples: Chlorella (Chlorella) — a unicellular non-motile alga	EXAMPLES: Fucus (Fucus) — a thalloid marine alga
Chlamydomonas (Chlamydomonas) — a unicellular motile alga	Laminaria (Laminaria) — a large thalloid marine brown alga
Spirogyra (Spirogyra) — a filamentous alga Ulva — a thalloid marine alga
* Diagnostic feature.

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