Algae Nucleus a) Chlorella Flagella Chloroplast Pyrenoid b) Chlamydomonas Oogonium Antheridium Central Vacuole c) Vaucheria Air vesicle Stipe Hold fast h) Fucus Lateral branch Air bladder i) Sargassum Hold fast Cap cell d) Oedogonium g) Ulva Seta e) Coleochaete f) Fritschiella a) Fragmentaion- Spirogyra b) Zoospore formation- Cladophora c) Isogamy Figure . : Reproduction in Algae d) Anisogamy e) Oogamy f) Scalariform conjugation- Zygnema membrane bound nucleus and cell organelles like chloroplast, mitochondria, endoplasmic reticulum, golgi bodies etc., Pyrenoids are present. They are proteinaceous bodies found in chromatophores and assist in the synthesis and storage of starch. The pigmentation, reserve food material and flagellation differ among the algal groups.
Algae reproduces by vegetative, asexual and sexual methods (Figure . ). Vegetative reproduction includes fission (In unicellular forms the cell divides mitotically to produce two daughter cells Example: Chlamydomonas) ; Fragmentation (fragments of parent thallus grow into new individual Example: Ulothrix ) budding (A lateral bud is formed in some members like Protosiphon and helps in reproduction) bulbils, (a wedge shaped modified branch develop in Sphacelaria ) akinetes (Thick walled spores meant for perennation and germinates with the advent of favourable condition Example: Pithophora ) and Tubers (Structures found on the rhizoids and the lower nodes of Chara which store food materials). Asexual reproduction takes place by the production of zoospores motile spores ( Ulothrix, Oedogonium ) aplanospore (thin walled non motile spores Example: Vaucheria ); autospores (spores which look similar to parent cell Example: Chlorella ); hypnospore (thick walled aplanospore – Example: Chlamydomonas nivalis ) and Tetraspores (Diploid thallus of Polysiphonia produce haploid spores after meiosis).
Sexual reproduction in algae is of three types . Isogamy (Fusion of morphologically and Physiologically similar gametes Example: Ulothrix ) . Anisogamy (Fusion of either morphologically or physiologically dissimilar gametes Example: Pandorina ) . Oogamy (Fusion of both morphologically and physiologically dissimilar gametes.
Example: Sargassum ). The life cycle shows distinct alternation of generation. The Oldest recorded alga is Grypania, which was discovered in the banded iron formations of northern Michigan and dated to approximately 2100Ma . .
. Classification F.E. Fritsch