Red algae are known as Rhodophycae.
General characteristics of rhodophycae-
Algae are non-vascular, aquatic forms which possesses accessory spores for asexual multiplication and non-jacketed gametangial for sexual reproduction. But they do not have embryo forming stage. It includes in the kingdom plantae. According to presence of pigments algae can be divided into- chlorophyceae (green pigments chlorophyll is present), phaeophyceae (fucoxanthine for brown colour), and rhodophycae (phycoerithrin for red color).
Special Characteristics of the rhodophycae are mentioned below:
1. Maximum number of the algae are marine (except few are fresh water).
2. Some are color less and parasitic in nature that is they are unable to make their food themselves.
3. Rhodophycae do not have any motile stage and Thallophyta- in nature.
4. There structure can be unicellular, filamentous, parenchymatous and pseudoparenchymatous. Chloroplasts commonly discoid, without chloroplasts, endoplasmic reticulum.
5. Cell wall contains cellulose and phycocolloid like agar, carrageenan and funori.
6. Food is reserved as floridian starch formed in the cytoplasm, outside the chloroplasts.Mitosis closed,centrioles lacking, polar rings are present. Cleavage incomplete in most algae,presence of pit connection and pit plugs in most.
7. Rhodophycae contain female sex organ called carpogonium. It is flask shaped with long receptive neck called trychogyne.
8. Red algae contains male sex organ called spermatangium . Male sex organ contains non-flagellate gametes called spermatia.
9. External fertilization takes place. Post fertilization changes are complicated.
10. Some algae deposit calcium carbonate on their surface. This algae is know as coralline algae. Example of coralline algae is Corallina. This algae help in developing coral reefs along with corals.
11. Chloroplasts( chromatophores) have monothylakoid lamellae. Photosynthetic pigments include chlorophyll a, chlorophyll d (doubtful), carotenoids and phycobilins (phycoerithrin, phycocyanin, allophycocyanin). Red is due to phycoerithrin.
12. Life cycle is isoor heteroteromorphic, generally extended and triphasic.
Economic importance of red algae are:
• Used as edible food – Some red algae like Porphyra or Laver, Rhodymenia, Chondrus or Irish Moss (Gracilaria, Gelidium) are used as food or food processing.
• Extraction of bromine – At first bromine was extracted from red algae called Rhodomela.
• Used in microbiological media preparation - Gelidium, Gracilaria etc are used to yield agar which is used in culture media, media stabilizer and media thickener.
• Used as agrophyte – Gelidella acerosa. is used as an agrophyte.
• Uses as adhesive – funori acts as an adhesive agent.
• Clearing agent – Carrageenin acts as a clearing agent.
• Emulsifiers – Chondrus or Irish Moss act as emulsifiers.
• Anti bacterial agent - Polysiphonia kills microbes as it act as anti bacterial agent.
Questions and answers on Rhodophyceae:
1. Name a few fresh water representative of red algae?
Compsopogon, Lamanea, Thorea.
2. Name a red algae growing in mangroves?
3. Name some unicellular red algae.
4. What are pit plugs?
In a majority of red algae, cleavage is incomplete. Subsequently a protoplasmic connection is established between cells. Soon the connection becomes closed by a proteinaceous stopper called pit plug.
5. What is NAO?
Nuclear associated organelle (NAO) is a distinctive organelle occurring at mitotic spindle poles in red algae.