The Structure and The Life Processes of Spirogyra

 Objectives       

This  blog post provides readers with the following objectives. The reader will be able to:

o   Describe the structure of Spirogyra.

o   Explain nutrition and reproduction in Spirogyra 

Spirogyra

Kingdom: Protoctista

Phylum: Chlorophyta

Habitat: Freshwater, ponds, ditches, and slow-moving streams. 

Structure of Spirogyra

Spirogyra is a green free floating filamentous alga. It is unbranched with cylindrical cells connected end to end in long filaments.

The cell wall is two layered; the outer wall composed of thick, slimy, protective mucilage while the inner wall is of cellulose. 

The cytoplasm forms a thin lining surrounding a large vacuole. It also extends as a thread into the center of the cell to enclose and suspends the nucleus. 

The chloroplasts are ribbon shaped and spirally arranged in the cytoplasm. Each chloroplast contains several pyrenoids,

which stored starch.

The Life Processes of Spirogyra

Nutrition in Spirogyra

Photosynthetic autotroph: makes its own food using energy from sunlight. The chloroplast contains chlorophyll which absorbs energy from sunlight for synthesizing glucose. Excess glucose is converted to insoluble starch and stored in the pyrenoids.

Reproduction in Spirogyra

Asexual Reproduction: occurs in two forms; binary fission and fragmentation.

Binary Fission: This occurs frequently when conditions are favourable. The nucleus constricts and divides into two. A new cellulose cell wall develops transversely to separate the two nuclei and other cell structures. The two cells do not separate but grow to normal size increasing the length of the filament.

Vegetative Reproduction (Fragmentation): is another form of asexual reproduction. The filament breaks into small lengths. Each fragment becomes a new filament by cell division and cell elongation.

Sexual Reproduction (Conjugation)

This process occurs under adverse conditions such as drought or cold. Conjugation requires association of two different filaments called conjugants lined side by side. One cell each from opposite lined filaments develop protrusions known as conjugation tubes. Conjugation tubes elongate and fuse, to make a passage called the conjugation canal. The cytoplasm pulls free from the cell wall and the cell contents round off to form a gamete. Gamete from one cell moves through the tube and fuses with the other gametes to form a zygote. A resistant wall develops around the zygote to form a spore called zygospore. The spore can survive adverse conditions and when conditions become favorable, the resistant wall breaks open and a new spirogyra filament grows out.

This image is credited to D G Mackean www.biology-resources.com

Adaptation

    ¨  It’s protected by two layers of cell wall; an outer cellulosic layer and inner pectin layer.
¨   Presence of ribbon like chloroplasts for synthesis of glucose.
¨   Pyrenoids for starch storage.
¨ Filament has root-like structures for adhering to substratum.
¨ Each cell wall is surrounded by protective mucilage which prevents desiccation.

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