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Introduction

Class-XII/MEDICAL /Botany /Plant Kingdom /Algae /Introduction
  1. Red algae are second most ancient algae after blue green algae i.e. they are developed after blue green algae. eg. Polysiphonia

  2. Red algae mainly found in marine water. But exceptionally Batrachospermum is found in fresh water (river) and Porphyridium is found on land.

  3. Red algae are multicellular but exceptionally Porphyridium is unicellular.

  4. There is no motile stage found in life cycle of red algae and BGA i.e. cilia and flagella are absent.

  5. Cell wall of red algae is complex and made up of cellulose and pectin. The cell wall of red algae is also complicated like blue green algae. Their cell wall has many different type of substances such as xylan, galactose, polyuronic acid, polysulphate esters. But in some algae calcium carbonate is also present in the cell wall. Due to which their thallus become stony. These algae form lime stone and coral reefs. e.g. Corallina and Lithothamnion

1. Pigments

  1. Chlorophyll - Chl ‘a’ and Chl ‘d’
  2. Carotenes -
  3. Phycobilins - R - phycoerythrin (red coloured) and R - phycocyanin (blue coloured)
  4. On the basis of pigments red algae is similar to blue green algae.

  5. Colour of red algae changes according to depth in sea this is called as Gaudikov’s effect.

  6. When red algae are present on the surface of the sea then their colour is blue and when they are at the bottom, their colour is red. At the surface of sea the amount of R - phycocyanin is more while in depth the amount of R - phycoerythrin is more. Penetration power is maximum in ultra violet and violet light. R-phycoerythrin is only pigment to absorb ultra violet and violet light. Due to phycoerythrin red algae are deepest algae.

  7. Gaudikov’s effect is also found in Blue - Green algae.

  8. Red algae not always red, it may be blue coloured also. eg. Batrachospermum - This is a blue coloured algae.

2. Stored Food

  1. Floridean starch - It is a primitive type of starch. Structurally floridean starch is similar to the cyanophycean starch of blue green algae.
  2. Starch of higher plants is less branched yet floridean starch and cyanophycean starch is highly branched.
  3. Glycogen is also highly branched so that floridean and cyanophycean starch is structurally similar to glycogen and amylopectin

3. Phycocolloids

Agar -Agar, carrageenin and funori phycocolloids are found in the cell wall of red algae.

4. Reproduction

  1. Vegetative - By fragmentation

  2. Asexual - Non motile spores [By monospore, carpospores, tetraspore]

  3. Sexual reproduction

    • Sexual reproduction is oogamous type.
    • The female sex organs are called carpogonia. They are apparently similar to archegonia of bryophyta. Carpogonia is unicellular and jacketless but archegonia is multicellular and jacketed.
    • The male sex organs of red algae are known as spermatangia. Non motile spore like gametes are formed in spermatangia which are known as spermatia.
    • Life cycle of Polysiphonia is diplobiontic and Batrachospermum is haplobiontic

5. Special Points and Economic Importance

  1. Harveyella - It is a colourless parasitic alga. It remains as parasite on other alga.

  2. Porphyra - It is an edible algae.

  3. Gelidium and Gracilaria - Agar - Agar colloid is obtained from these. It is used to prepare culture medium

  4. Chondrus crispus - It is also called Irish moss. Carrageenin colloid is obtained from this alga. It is used as gelating agent in food industries (i.e. to make the food item viscous)

    • Capsule of medicines is also prepared from carrageenin.
  5. Haematococcus nivalis - “Red snow” - It likes to grow on snow and imparts red colour to snow.



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