Introduction to Algae in Biology

Introduction to Phycology (Algae)

• Algae are photosynthetic organisms
• They carry out 50-60% of Earth's photosynthesis
• They use sunlight and chlorophyll to create food
• Range from microscopic single-celled organisms to large seaweed
• Most are aquatic, found in oceans, freshwater, ponds, lakes, streams, hot springs, polar ice, moist soil, trees, and rocks.
• Algae are non-vascular, primitive plants lacking roots, stems, and leaves.
• They reproduce both sexually and asexually using spores, rather than seeds.

Eukaryotes - Algae

• Euglenophyta
• Dinoflagellates
• Chrysophyta (EX. Vaucheria sp)
• Rhodophyta (Red Algae)
• Phaeophyta (Brown Algae)
• Chlorophyta (Green Algae; EX: Chlamydomona + Volvox sp. + Spirogyra sp)
• Importance of Algae

Kingdom: Protista or Algae

• Algae are divided into prokaryotic (cyanobacteria) and eukaryotic organisms
• Algae are photosynthetic.

Algal Classification

• Algae are classified based on pigment composition.
• Algae are classified into two kingdoms: Monera (prokaryotic algae: Cyanophyta (blue-green algae)) and Protista (eukaryotic algae). There are 6 divisions

4- Algal Pigments

• All algae contain photosynthetic pigments (chlorophyll a, b, c, d, e, f – 6 types).
• Carotenoids and Xanthophylls are yellow, red, or orange pigments.
• Phycobilins (phycocyanin – blue pigment; phycoerythrin – pink-red pigment) are present in Rhodophyceae and Cyanophyceae.

1- Euglenophyta

• Earlier, Euglenoids were classified with both plants and animals (protozoa).
• Molecular data shows Euglenoids are closely related to Zooflagellates.
• Euglenoids are unicellular with two flagella (one long, one short).
• They are plant-like in their pigments (chlorophyll a, b, and carotenoids).
• Some photosynthetic Euglenoids lose chlorophyll in the dark and become heterotrophic (ingesting organic matter).
• Other Euglenoids are always colorless and heterotrophic.
• Example: Euglena (evolutionary significance)

2- Dinoflagellates

• Unusual protists with different structures and two dissimilar flagella.
• Cells are often covered with interlocking cellulose plates or silicates.
• Pigments include chlorophyll a, c, carotenoids, and fucoxanthin.
• Ecologically important in marine ecosystems, producing oxygen.
• Can cause blooms (population explosions) that color water orange, red, or brown (toxic red tides).
• Examples: Gonyaulax, Ceratium

3- Chrysophyta (Golden Algae – Diatoms)

• Mostly unicellular; lack locomotory organs.
• Pigments: chlorophyll a, c, carotenoids, xanthophylls.
• Cell wall of two overlapping shells, resembling a petri dish, made of silica.
• Important in aquatic food chains.
• Examples: Diatom, Frequilaria, Pinnularia

4- Phaeophyta (Brown Algae)

• Multicellular; range from a few centimeters to 75 meters long.
• Largest are called kelps.
• Kelps have tough, leathery leaf-like blades, stem-like stipes, and root-like holdfasts.
• Non-motile; reproductive cells with two flagella.
• Pigments: Chlorophyll a, c, carotenoids, and fucoxanthin.
• Common in cooler marine water, especially along coastlines (intertidal zone).
• Examples: Fucus, Macrocystis

5- Rhodophyta (Red Algae)

• Multicellular; complex interwoven filaments.
• Filaments are delicate and feathery, or some form flattened sheets.
• Non-motile.
• Most multicellular species are attached to rocks or other substrates by a basal holdfast.
• Pigments: Chlorophyll a, carotenoids, and phycoerythrin (red pigment).
• Some incorporate calcium carbonate into their cell walls.

6- Chlorophyta (Green Algae)

• Unicellular, colonial, or multicellular.
• Pigments: chlorophyll a, b, and carotenoids.
• Most have flagella.
• Cell walls are made of cellulose.
• Similar characteristics to plants (pigments, products, and cell walls).
• A branch of the monophyletic plant lineage.
• Examples: Chlamydomonas (unicellular), Volvox (colonial), Spirogyra (filamentous), Ulva (sheet-like multicellular).

Importance of Algae

• Some algae (e.g., kelps) are edible; food source.
• Source of useful substances (algin, agar, carrageenan, fucoidan, carotenoids).
• Essential in aquatic ecosystems, forming the base of food chains, providing food and oxygen.
• Used in various products (cosmetics, pharmaceuticals, food production).

Vaucheria sp.

• Thallus is a single-branched tubular filament; multinucleate coenocytic.
• Contains a large central vacuole; cell wall is thin, weak, and non-elastic, made of pectic and cellulosic layers.
• Attached to the substratum by colorless rhizoids or holdfasts.
• Reproductive structures appear as septa.
• Found in freshwater.

Additional notes

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