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Class-XII/MEDICAL /Botany /Plant Kingdom /Algae /Introduction
  • Brown algae are found in marine water.

  • Brown algae are multi cellular filamentous.

  • Brown algae are the largest in size (up to 60 meter in length).

  • Largest brown algae - Macrocystis

  • Thallus of brown algae is divided into two parts

    • Lamina - Leafy part or photosynthetic part
    • Stipe - Elongated tubes called trumpet hyphae are present for food conduction in stipe. Trumpet hyphae are analogous to sieve tubes of vascular plants. Due to lamina and stipe brown algae look like leaf (leafy algae). e.g. Fucus, Dictyota, Ectocarpus

1. Pigments

  1. Chlorophyll - Chl ‘a’ , Chl ‘c’
  2. Carotene - Only carotene
  3. Xanthophylls - Mainly Fucoxanthin

Note : The amount of Fucoxanthin is more in brown algae due to which these algae are brown in colour. (Xanthophylls are mostly yellow but fucoxanthin is brown)

2. Stored Food

Laminarin and mannitol - both are derivatives of carbohydrates.

3. Phycocolloids

  • On cell wall of brown algae some colloid substances like fucinic acid, alginic acid and fucoidin are present which are known as phycocolloids.
  • Phycocolloids protects brown-algae against dessication and shocks. Phycocolloids are used in ice-cream as thickening agent. Alginates, salts of alginic acid used for dentury measurement.

Special Point : Life cycle of Ectocarpus and kelps are diplohaplontic, life cycle of Fucus is diplontic.

4. Special Name

  1. Postelsia - It is known as Sea palm.

  2. Ancyclonema - It is called Ice bloom because it grows on marine ice.

  3. Sargassum
    It is known as Gulf weed because Sargssum is a free floating alga. It grows rapidly in North Atlantic ocean and covers thousands of hectares of area. Therefore this region is called as sargasso sea.

  4. Laminaria (Kelps) - It is called as Devil’s Aprin.

5. Economic Importance

  1. Alginates or Alginic acid - Obtained from Laminaria, Fucus, Macrocystis. Alginates are used in the manufacturing of soap, ice-cream, polish, cream and plastic.

  2. Iodine and Bromine - Obtained from Laminaria.

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