Brown Algae - Classification, Structure, Reproduction and Importance

Brown algae are classified as Phaeophyceae and are known for their distinct colors, which range from brown to olive green. These algae predominantly inhabit marine environments. There are approximately 1,500 species of brown algae, showcasing a wide variety in size and shape. They are multicellular organisms, and their coloration is determined by the balance of chlorophyll and the pigment fucoxanthin. Brown algae include seaweeds such as Fucus, Ectocarpus, Sargassum, and giant kelps. NEET Biology Notes on Brown Algae are provided in the article below.

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Brown Algae Structure

1. Size and Form: Brown algae exhibit a wide variety of sizes and shapes. The smallest types appear as tiny, feathery tufts of threadlike cells, only a few centimeters long. Some species have a life stage that consists of just a few cells, rendering them microscopic. Conversely, larger species, such as giant kelp, can grow up to 60 meters (200 feet) in length.
2. Thallus: The body of brown algae is known as a thallus, which means they do not have true roots, stems, or leaves.
3. Holdfast: Brown algae have a root-like structure called a holdfast, which anchors them to the substrate. Unlike roots in plants, the holdfast does not absorb nutrients or water but prevents the algae from being swept away by currents.
4. Stipe: Some brown algae possess a stalk-like structure called a stipe, similar to a stem. In the most complex species, such as Fucus, the stipe consists of three distinct tissue layers: a central pith, a surrounding cortex, and an outer epidermis.
5. Lamina: They feature a flattened structure known as the lamina, blade, or frond, which resembles leaves.
6. Pneumatocysts: Certain brown algae contain gas-filled bladders called pneumatocysts. These bladders provide buoyancy, keeping parts of the algae near the surface to facilitate photosynthesis.
7. Cell Wall: The cell wall of brown algae is composed of two layers: an outer gummy layer made of algin and an inner layer of cellulose, which provides structural strength.
8. Pigments: Brown algae contain the pigment fucoxanthin, which gives them their characteristic greenish-brown color.
9. Food Storage: They store food in the form of complex carbohydrates, such as laminarin or mannitol.

Cell The Unit of Life

Brown Algae Characteristics

• Habitat: Brown algae predominantly inhabit marine environments, especially in cold coastal waters. They may be free-floating or attached to the seabed.
• Size and Shape: They exhibit a wide range of sizes and shapes, from small species a few centimeters long to giant kelps that can grow up to 100 meters.
• Structure: These algae are multicellular and lack true roots, stems, and leaves. Instead, they have holdfasts (which anchor them), stipes (stalk-like structures), and blades or fronds (leaf-like structures). Some species possess gas bladders that aid in flotation.
• Cell Wall: Their cell walls are two-layered, consisting of an outer layer containing a gummy substance called algin and an inner layer made of cellulose, which provides strength.
• Pigments: Brown algae contain chlorophyll a and c, along with carotenoids and xanthophylls, including fucoxanthin, which gives them their characteristic brown color.
• Reproduction: They undergo alternation of generations, featuring both sexual and asexual stages in their life cycle.

Structural Organisation in Animals

Brown Algae Examples

• Ectocarpus: An epiphytic brown algae.
• Fucus: Typically found attached to rocks.
• Sargassum: Known for being free-floating.
• Kelp: Part of the order Laminariales, capable of growing up to 100 meters long.
• Macrocystis: A type of giant kelp that forms extensive underwater forests.
• Nereocystis: Another variety of giant kelp.
• Ascophyllum: A well-known species of brown algae.
• Durvillaea Antarctica: A specific type of brown algae.
• Dictyotales: A classification within brown algae.
• Chordariales: Another classification within this group.

Brown Algae Reproduction

• Brown algae can reproduce asexually by producing zoospores or aplanospores.
• Zoospores are generated within both unicellular (unilocular) and multicellular (plurilocular) sporangia and are always found on the diploid thallus (sporophyte).
• Vegetative reproduction occurs through fragmentation.
• The motile zoospores are pear-shaped and have two unequal flagella.

• Brown algae reproduce sexually using flagellated spores and gametes.
• These spores and gametes closely resemble the cells of single-celled Stramenopiles.
• Brown algae undergo two distinct stages: initially, they exist as spores released from the parent plant, which develop into male or female plants producing sperm or eggs. These gametes then fertilize to form the mature plant in the second stage.

Brown Algae Economic Importance

1. Food and Feed: Certain brown algae such as Sargassum, Laminaria, and Fucus are used as feed for livestock and poultry. Algin, a crystalline substance derived from the outer cell walls of large brown algae like kelps, is widely employed in food products.
2. Fertilizers: Brown algae contribute to fertilizer production, with species like Macrocystis providing Potash, a crucial element that enhances soil fertility for agriculture.
3. Cosmetics: The cosmetic industry benefits from the properties of brown algae, using them in various products.
4. Pharmaceuticals: Brown algae species like Ascophyllum are utilized in antibiotic production, while Laminaria is used in medicines for goitre treatment. Algin serves as a gelling agent in pharmaceutical applications.
5. Industrial Applications: Algin is extensively used in industries such as textiles.
6. Ecological Importance : Brown algae form expansive underwater forests known as kelp forests, which support diverse marine life.