Life cycle spirogyra Spirogyra is a genus of filamentous green algae of the order Zygnematales , named for the helical...
Life cycle spirogyra
Spirogyra is a genus of
filamentous green algae of the order Zygnematales, named for the helical or
spiral arrangement of the chloroplasts that is diagnostic of the genus. It is commonly
found in freshwater areas, and there are more than 400 species of Spirogyra in the world.[1] Spirogyrameasures
approximately 10 to 100μm in
width and may stretch centimeters long.
General characteristics
Spirogyra is unbranched with cells connected end to end
in long male reproductive system filaments. This genus of green algae undergoes
a haploid-dominant life cycle. The cell wall has two layers: the outer wall is
composed of pectin that dissolves in water to make the filament
slimy to touch while the innerd wall is of cellulose. The
cytoplasm forms a thin lining between the cell wall and the large vacuole it surrounds. Chloroplasts are embedded in
the peripheral cytoplasm; their numbers are variable (as few as one). The
chloroplasts are ribbon shaped, serrated or scalloped, and spirally arranged,
resulting in the prominent and characteristic green spiral on each filament.
Each chloroplast contains several pyrenoids, centers for the production of
starches, appearing as small round bodies.
Spirogyra is very common in relatively clean eutrophic water,
developing slimy filamentous green masses. In spring Spirogyra grows under water, but when there is
enough sunlight and warmth they produce large amounts of oxygen, adhering as
bubbles between the tangled filaments. The filamentous masses come to the
surface and become visible as slimy green mats. Mougeotia and Zygnema are
often found tangled together.
Reproduction
Spirogyra can reproduce both sexually and rarely asexually.
In vegetative reproduction, fragmentation takes place, and Spirogyra simply undergoes the intercalary
mitosis to form new filaments.
Sexual Reproduction is of two
types:
1. Scalariform conjugation requires association of two different
filaments lined side by side either partially or throughout their length. One
cell each from opposite lined filaments emits tubular protuberances known as
conjugation tubes, which elongate and fuse, to make a passage called the
conjugation canal. The cytoplasm of the cell acting as the male travels through
this tube and fuses with the female cytoplasm, and the gametes fuse to form a
zygospore.
2. In lateral conjugation, gametes are formed in a single filament.
Two adjoining cells near the common transverse wall give out protuberances
known as conjugation tubes, which further form the conjugation canal upon
contact. The male cytoplasm migrates through the conjugation canal, fusing with
the female. The rest of the process proceeds as in scalariform conjugation.
The essential difference is that
scalariform conjugation occurs between two filaments and lateral conjugation
occurs between two adjacent cells on the same filament.
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