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## Phaeophyceae 1. Brown algae are found primarily in marine habitats. 2. They possess the pigment chlorophyll a and c, carotenoids and xanthophylls. 3. They vary in colour from olive green to various shades of brown depending upon the amount of xanthophyll called fucoxanthin. 4. They show great va...

## Phaeophyceae 1. Brown algae are found primarily in marine habitats. 2. They possess the pigment chlorophyll a and c, carotenoids and xanthophylls. 3. They vary in colour from olive green to various shades of brown depending upon the amount of xanthophyll called fucoxanthin. 4. They show great variation of size and form. In *Ectocarpus* the body is simple branched and filamentous whereas in kelps the body is profusely branched e.g., *Laminaria*, *Macrocystis*. Kelps may reach a height of 100 meters. 5. Food is stored as complex carbohydrates which may be in the form of laminarin or mannitol (alcohol sugar). 6. Brown algae have cell wall made up of cellulose which is usually covered on the outside by a gelatinous coating of algin. Algin is a hydrocolloid which has good water holding capacity. 7. Their protoplast contains plastids, a centrally located vacuole and nucleus. 8. The plant body is often differentiated into holdfast for attachment to a substratum, stipe (stalk) and a leaf-like photosynthetic organ called frond. 9. The large forms often possess air bladders for providing buoyancy. 10. Vegetative reproduction takes place by fragmentation. 11. Asexual reproduction occurs with the help of biflagellate zoospores that are pear-shaped and have unequal laterally attached flagella. 12. Sexual reproduction may be isogamous, anisogamous or oogamous. Fusion of gametes takes place in water but in oogamous species, gametes fuse in the oogonium. Oogonium is the female reproductive structure, usually a rounded cell or sac containing egg cell or oosphere (the non-motile female gamete). 13. The gametes are pyriform, pear-shaped and bear two laterally attached flagella. 14. The common forms of brown algae are *Ectocarpus*, *Dictyota*, *Laminaria*, *Sargassum* and *Fucus*. ## Rhodophyceae 1. The pigments present in them are r-phycoerythrin, phycocyanin, chlorophyll-a and chlorophyll-d. 2. They are mostly found in marine habitats with abundance of the red pigment, r-phycoerythrin. ### Economic Importance: * **Photosynthesis:** As primary producers through photosynthesis * **Primary producers** of food cycles of all life * **Food supplements** are among the 70 species of algae. *Spirullina* are rich in proteins * **Hydrocolloids:** Hydrocolloids are obtained from brown algae (e.g., *Gelidium*) and are used in ice creams, jellies and chocolates. * **Iodine:** *Fucus* and other brown algae are the source to obtain iodine ## Image Description The image shows a diagram comparing three different types of brown algae: *Laminaria, Fucus* and *Dictyota*. The image is labeled with the different parts of each respective alga, including the *Frond, Stipe, Holdfast, Air Bladder* and *Midrib*. This image is a good representation of the diversity in forms that brown algae can take, from the simple branching patterns in *Ectocarpus* to the large, complex structures of kelps.