1. Algae :

- Chlorophyll-bearing

- Simple

- Thalloid

- Autotrophic

- Both fresh water and marine

- Occur in other habitats:

Moist stones
Soils
Woods

- Occur in association with:

Fungi (lichen)
Animals ( e.g., on sloth bear)

- Forms and size of algae s highly variable:

Microscopic unicellular forms like Chlamydomonas.
Colonial forms like Volvox.
Filamentous forms like Ulothrix and Spirogyra.

- Reproduction:

Vegetative reproduction: by fragmentation.
Asexual reproduction: by zoospore.
Sexual reproduction: by gametes ( Isogamous, Anisogamous, and Oogamous).

- Economic Importance of Algae:

Largest photo synthesiser, release O2.
Food for aquatic animals and humans.
Produce Algin (brown algae), Carrageen (red algae), agar (gelidium, gracilaria).
Chlorella and Spirullina are used as food supplements by space travelers as rich in proteins.

- Types of Algae:

Chlorophyceae (Green algae):
1. About 7000 species are known, mostly freshwater except a few (- 10%) marine forms.

2. The members are multi-cellular; but may be unicellular, colonial or coenocytic.

3. Chloroplasts contain photosynthetic pigments (Chl- a, b, carotenes and xanthophylls) similar to those of land plants.

4. Cell wall made up cellulose.

5. Reserve food is starch.

6. Sexual reproduction is isogamous, anisogamous, and oogamous type. Examples: Spirogyra, Ulothrix, Caulerpa,VoIvox, Acetabularia, Chlorella etc.
Phaeophyceae (Brown Algae):
1. It includes about 2000 species, mostly marine.

2. Unicellular forms absent.

3. They appear brown due to large amount of brown coloured xanthophyll pigments called fucoxanthin (C40H56O6).

4. Photosynthetic pigments include Chl-a, c, carotenes &xanthophylls.

5. The plant body is a thallus differentiated into holdfast, stipe and lamina (blade or frond). Photosynthetic lamina is annual while stipe is perennial. Holdfast helps in anchorage. A few species are free-floating e.g. Fucus (rockweed), Sargassum (gulf weed). Sargassum covered thousand of hectors in the Sargasso Sea in the North Atlantic Ocean and it is a menace to shipping as they get attached to the bottom of ships.

6. The larger forms of brown algae are called kelps or sea weeds e.g. Macrocystis (30-60m, the largest sea plant), Nereocystis (20-30m.). The giant kelps contain air vesicles or bladder for buoyancy.

7. Cell wall composed of a mixture of polysaccharides like cellulose, pectose and algin (non- sulphated phycocolloids). Chemically, algin is the calcium salts of alginic acid (a major phycocolloid). Phycocolloids are complex polysaccharides that store in the cell wall of algae, protect them from desiccation and prevent drying or freezing (in winter) when exposed to air in low tide.

8. Food reserve is laminarin and mannitol.
Rhodophyceae (Red Algae) :
1. About 5000 species are known, mostly marine except a few fresh water forms (Batrachospermum)

2. They appear red due to phycoerythrin (red pigment, C34H46O8N4) & phycocyanin (the blue pigment, C34H46O8N4). These pigments absorb blue-green region of spectrum i.e. 480-520 nm which can penetrate greater depth of water. Hence, the red algae are the deepest growing algae in the seas where other photosynthetic forms cannot grow.

3. Red algae appear more red in deep water because of excess phycoerythrin than chlorophyll is formed. When growing in shallow water, they appear green due to more chlorophyll. This property of change in pigmentation (colour) is called chromatic adaptation (Gaidukov phenomenon).

4. Nutrition is photoautopophic, except some colourless & parasitic forms like Harveyella which live on other red algae.

5. Reserve food is floridean starch.

6. Cell wall composed of cellulose, pectin & sulphated phycocolloids (agar, carageenin & funori).

7. Vegetative reproduction occurs by fragmentation & regeneration of holdfast. Some reproduce asexually by spores. Sexual reproduction is oogamous type.

8. The thallus of red algae may be unicellular (Porphyridium), filamentous (Batrachospermum, Polysiphonia), pseudofilamentous (Astocystis), parenchymatous (Porphyra), lace-like (Gelidium), ribbon-like (Chondrus) etc.

	Erstellt von Alishba Haider vor mehr als 7 Jahre

Notiz am Plant Kingdom , erstellt von Alishba Haider am 16/08/2017.