Q.Differentiate between red algae and brown algae.

The classification of algae into Chlorophyceae (green), Phaeophyceae (brown) and Rhodophyceae (red) rests on differences in pigmentation, stored food, cell wall composition, and flagellar features.

Algae, though a highly diverse group, are traditionally divided into three main classes based on several structural and biochemical criteria:

1. Type of pigments present: Chlorophyceae (green algae) contain chlorophyll a and b, giving them a grass-green colour; Phaeophyceae (brown algae) contain chlorophyll a, c and the brown pigment fucoxanthin; Rhodophyceae (red algae) contain chlorophyll a, d and the red pigment r-phycoerythrin.
2. Chemical nature of the stored food: green algae store starch, brown algae store mannitol and laminarin (complex carbohydrates), and red algae store floridean starch.
3. Cell wall composition: e.g., cellulose in green algae, cellulose plus algin in brown algae, cellulose plus pectin (and sometimes calcium carbonate deposits) in red algae. …

(a) Green algae, (b) Phaeophyceae, (c) Red algae, (d) Mannitol and laminarin.

Algae are classified into three major classes based on their pigmentation and the type of food they store:

• Chlorophyceae, commonly called (a) green algae, store food mainly as starch, just like higher plants.
• (b) Phaeophyceae, commonly called brown algae, contain the pigment fucoxanthin along with chlorophyll a and c, and store food as complex carbohydrates, mainly (d) mannitol and laminarin. …

Red and brown algae are both mainly marine but differ in their characteristic pigments, food reserves, and cell wall composition.

Red algae (class Rhodophyceae):

• Get their colour mainly from the red pigment phycoerythrin, along with chlorophyll a, d and phycocyanin.
• Store food as floridean starch, a polymer very similar to amylopectin/glycogen, deposited outside the chloroplast in the cytoplasm.
• Cell walls typically contain cellulose along with polysaccharides such as agar and carrageenan (economically important, e.g., Gelidium, Gracilaria).
• Mostly found attached to the sea bed at greater depths in calmer marine waters, since phycoerythrin efficiently absorbs the blue-green light that penetrates deeper water.

Brown algae (class Phaeophyceae):

• Get their colour mainly from the brown/olive pigment fucoxanthin, along with chlorophyll a and c.
• Store food as complex carbohydrates — mainly laminarin (a polysaccharide) and mannitol (a sugar alcohol). …