Phaeophyceae: Brown Algae Overview

Study Notes

Phaeophyceae (Brown Algae)

Brown algae thrive mainly in marine ecosystems, playing a significant role in ocean habitats.
They contain pigments including chlorophyll a, chlorophyll c, carotenoids, and xanthophylls, contributing to their coloration.
Variations in color, from olive green to various shades of brown, are largely due to the presence of fucoxanthin.
Size and form diversity is evident, with simple filamentous structures in Ectocarpus and large, complex kelps like Laminaria and Macrocystis reaching heights of up to 100 meters.
Food storage in brown algae consists of complex carbohydrates, primarily laminarin or mannitol.
The cell wall is composed of cellulose, often enveloped in algin, a gelatinous hydrocolloid known for its water-retaining properties.
Their cellular structure includes plastids, a central vacuole, and a nucleus within the protoplast.
The structure is differentiated into holdfasts for substrate attachment, stalk-like stipes, and fronds which serve as leaf-like photosynthetic organs.
Large brown algal forms frequently possess air bladders to aid in buoyancy, allowing them to float and access sunlight.
Vegetative reproduction occurs via fragmentation, enabling regrowth from broken pieces.
Asexual reproduction is facilitated by biflagellate zoospores, which are pear-shaped with unequal lateral flagella.
Sexual reproduction can be isogamous, anisogamous, or oogamous, with gamete fusion occurring in water; in oogamous species, fusion takes place in the oogonium.
The gametes are pear-shaped with two laterally attached flagella, contributing to reproductive processes.
Common species of brown algae include Ectocarpus, Dictyota, Laminaria, Sargassum, and Fucus.

Rhodophyceae (Red Algae)

Red algae contain pigments such as r-phycoerythrin, phycocyanin, chlorophyll-a, and chlorophyll-d, giving them a distinct coloration.
They are predominantly found in marine environments, where r-phycoerythrin is particularly abundant.

Economic Importance

Brown algae serve as primary producers, contributing significantly to photosynthesis and the food cycles of various marine life.
Certain species, like Spirulina, are used as food supplements due to their high protein content.
Hydrocolloids derived from brown algae, such as Gelidium, are commonly used in the food industry for products like ice creams, jellies, and chocolates.
Brown algae, including Fucus, are valuable sources of iodine, an essential nutrient.

Image Description

The diagram illustrates the structural diversity among brown algae, specifically comparing Laminaria, Fucus, and Dictyota.
Key anatomical features are labeled, showcasing parts such as frond, stipe, holdfast, air bladder, and midrib, highlighting the range of forms in brown algae from simple to complex structures.