SATHEE: Spirogyra

Spirogyra

[Sexual Reproduction in Spirogyra](#Sexual Reproduction in Spirogyra)

[Frequently Asked Questions](#Frequently Asked Questions)

Spirogyra

Spirogyra is a genus of free-floating green algae found in freshwater habitats such as ponds, lakes, etc. It is commonly known as “water silk or pond silk” due to its filamentous and unbranched vegetative structure. There are approximately 400 species of Spirogyra, and the genus is named after the unique spiral chloroplast present in the cells of the algae.

Spirogyra are photosynthetic and contribute significantly to the total amount of carbon dioxide that is fixed. By doing so, they increase the oxygen level in their environment, making them an important food source for many aquatic organisms.

Spirogyra

Classification of Spirogyra

The genus Spirogyra, which contains around 400 species, is classified under Chlorophyta due to the presence of chlorophyll.

| Domain | Eukaryota |

| Kingdom | Plantae |

| Phylum | Chlorophyta |

| Class | Zygnematophyceae |

| Order | Zygnematales |

| Family | Zygnemataceae |

| Genus | Spirogyra |

Structure of Spirogyra

The vegetative structure of Spirogyra is an unbranched, filamentous thallus.

The thallus is multicellular, with each cylindrical cell joined end-to-end.

They are 10-100 µm in width and may grow several centimetres in length.

They are present as a slimy mass due to the presence of a mucilage sheath surrounding the filament.

The cell wall is composed of two layers: an inner layer of cellulose and an outer layer of pectin. The slimy mucilage sheath is a result of the dissolution of pectin in water.

In each cell, there is a nucleus, cytoplasm, a large central vacuole, and spiral chloroplasts.

Chloroplasts are ribbon-shaped and arranged spirally, with 1-16 being present in a cell.

The chloroplast contains many pyrenoids in a row, which store both starch and protein.

See also:

MCQs on Volvox

MCQs on Algae

Spirogyra Reproduction

Spirogyra undergoes vegetative, asexual and sexual reproduction. Its life cycle is haplontic, meaning that the dominant stage is a free-living haploid (n) gametophyte, while the sporophyte is represented only by the diploid zygote (2n).

Vegetative reproduction is achieved through fragmentation. When the environment is favourable, this is the most common form of reproduction.

Each fragment of the vegetative filament undergoes multiple divisions and elongations, leading to the formation of a new filament.

Fragmentation can occur as a result of mechanical damage or the dissolution of the middle lamella when salinity and temperature of the water changes.

Sometimes the middle lamella of one cell protrudes into an adjacent cell, resulting in the breakage of the filaments.

Asexual reproduction can be found in some species of Spirogyra, and is achieved through the formation of azygospores, akinetes or aplanospores.

Under unfavourable conditions, the protoplast shrinks and forms a wall around it, resulting in the formation of aplanospores.

Akinetes are also formed similarly, however they possess a thicker cell wall composed of cellulose and pectin.

Akinetes and aplanospores are non-motile spores that, when the parent filament decays, can develop into a new filament under favorable conditions.

Azygospores, also known as parthenospores, are gametes that failed to fuse during sexual reproduction and develop into a new filament asexually.

Sexual Reproduction in Spirogyra

Spirogyra undergoes isogamous sexual reproduction, meaning the male and female gametes are of similar size and fuse together.

Sexual reproduction is achieved through conjugation. There are two types of conjugation: scalariform conjugation and lateral conjugation.

Scalariform Conjugation:

In scalariform conjugation, two filaments of Spirogyra sp come together and are placed parallel to each other, forming a ladder-like structure. This is why it is referred to as scalariform conjugation or H-shape conjugation.

A tube-like structure develops from each cell of the two filaments when they are lying together.

The developing tube fuses to form a conjugation canal between two cells.

The male gamete fuses with a female gamete of the other filament, resulting in one filament becoming empty and the other containing zygotes.

These zygotes are released after the decay of the parent filament and germinate when conditions are favourable.

Lateral Conjugation:

In lateral conjugation, adjacent cells of a Spirogyra sp. act as male and female gametes. Conjugation tubes are formed between cells of the same filament, and this process can be divided into two types:

Direct Lateral Conjugation: Passage is formed between two adjacent cells through the middle lamella, allowing male gametes to fuse with female gametes and form zygotes in alternate cells.
Indirect Lateral Conjugation: The conjugation canal is formed when a cell with a male gamete joins an adjacent cell with a female gamete.

The entire protoplast of a Spirogyra act as a gamete. They are known as aplanogametes. Aplanogametes are formed in the gametangia, which are formed at the end of the growing season of Spirogyra.

The zygote in Spirogyra is known as zygospores. Zygospores are diploid (2n) and formed by the fusion of male and female gametes. Zygospores are the only diploid stage in the life cycle of Spirogyra.

The zygospore has a thick cell wall made up of three layers; exosporium (outer layer of cellulose), mesosporium (middle layer of chitin and cellulose) and endosporium (inner layer of cellulose).

The zygospore remains dormant until conditions that are favourable become available.

At the time of germination, the zygospore undergoes meiosis to form 4 haploid (n) nuclei, of which only one survives and the others disintegrate.

#The zygospore of Spirogyra bursts open to form a germ tube. This germ tube then divides repeatedly by transverse division, forming a new haploid filament.

Frequently Asked Questions

Spirogyra lives in freshwater ponds and lakes.

Spirogyra are filamentous, free-floating green algae found in freshwater habitats such as lakes and ponds. They are often referred to as pond silk or water silk, and there are approximately 400 species of Spirogyra present worldwide.