Oedogonium: Classification, Structure and Life Cycle

Table of Contents

• Introduction
• Classification
• Characteristics and Structure
• Oedogonium Cell Structure
• Oedogonium Thallus Structure
• Ecology of Oedogonium
• Reproduction in Oedogonium
• Asexual Reproduction
• Sexual Reprodcution
• Frequently Asked Questions

Introduction

Oedogonium is a free-living, green algae that was first discovered by W. Hilse in the freshwater of Poland in 1860. It is a freshwater algae that are both planktonic and benthic in nature. It undergoes both sexual and asexual reproduction. Let us look at the structure and life cycle of the algae.

Classification

Characteristics and Structure

Oedogonium Cell Structure

• Cells of Oedogonium under microscope appear as narrow and cylindrical in shape.
• Each and every cell of the filament is similar, except for the uppermost cell (apical cell) and the lowermost cell (holdfast cell).
• The apical cell is wide but rounded at the tip with a cap.
• The holdfast cell has elongated growth on both the unattached sides that help in the tight gripping of the filament to the substrate.
• Also, the holdfast is the only colourless cell of the filament.
• The number of caps on the cells in a filament signifies how many times a cell has divided.
• Each cell of the filament is made up of three layers: cellulose (innermost), pectose (middle) and chitin (outermost).
• The three layers give rigidity to the cells and also provide protection.
• The plasma membrane contains the protoplasm that houses a nucleus, reticulate chloroplasts, a central vacuole and cytoplasm.
• The cell sap which is present inside the central vacuole is composed of inorganic compounds, secretions and excretions.
• The nucleus is large and oval-shaped and sits in the centre of the cell.
• The cells of the Oedogonium also consist of typical Golgi apparatus, endoplasmic reticulum and mitochondria.

Oedogonium Thallus Structure

• The algal body, also known as the thallus, is green and consists of unbranched, multicellular and end-to-end arranged filaments.
• The cells of the filament are either attached to the substratum by the holdfast or are free floating.
• The Oedogonium species exist in two forms:

1. Macrandrous species: The male and female sex organs (antheridia and oogonia, respectively) are borne on the filaments and are of normal size.
• In macrandrous monoecious species, the male and female sex organs are found on the same filament.
• In macrandrous dioecious species, the male and female sex organs are produced in different filaments.
2. Nannandrous species: In this type, the antheridia and oogonia are morphologically different. This type is always dioecious. The antheridia are very small as compared to the oogonia and are known as dwarf males. The small male filaments attach to the female filaments near the oogonium.

Ecology of Oedogonium

• Oedogonium is generally found residing in stagnant freshwater bodies such as lakes, ponds, marshes and reservoirs.
• It can grow in a pH range of 7.3 to 9.6 and shows wide flexibility to types of nutrients and the amount of water in the water body.
• The free-floating species form polyalgal patches or mat-like structures that give them a static habitat. It is also known as an algal bloom.
• The polyalgal mats are formed by secretions of different algal filaments.
• The benthic cells (residing at the bottom of the water body) are mostly juvenile. They mature and float to the surface to form polyalgal mats.
• The Oedogonium filaments usually thrive in warmer climates, such as in the months of July and August.
• The different algal species that are found in the polyalgal mats are Cladophora, Spirogyra and Rhizoclonium. These species hold onto each other with the help of holdfasts so that they can synthesise.

Reproduction in Oedogonium

Asexual Reproduction

Asexual reproduction in Oedogonium is achieved by fragmentation of the filaments, germination of aplanospores and akinetes and also zoospores.

• Fragmentation: In fragmentation, the filaments split apart, and each part gives rise to a new thallus. One position at the filament can split multiple times; that is why some cells have more than one cap.
• Zoospores: Asexual reproduction takes place by zoospores in benthic cells that are vegetative in nature. The zoospores are enclosed in a zoosporangium produced on the vegetative cells. The zoospores have a ring of flagella on the base. The zoospores are released from the vesicle, and they float freely for some time to find a substratum and start dividing to form filaments once they find a substratum.
• Akinetes and aplanospores: Akinetes are large, non-motile, thick-walled spores and their wall is attached to the wall of the parent cell. The thick walls are rich in food materials. Similarly, aplanospores are also non-motile, thick-walled spores, but their wall is separate from the parent cell. Both of these spores remain dormant in unfavourable conditions and start to germinate once favourable conditions are restored.

Sexual Reproduction

Sexual reproduction in Oedogonium is oogamous. The species can be macrandrous or nannandrous. Each oogonium consists of a single egg, while the antheridium may contain 1-2 multi-flagellated sperm cells. The motile gametes released from the antheridia are chemotactically attracted to the oogonia. Only one sperm cell enters the oogonia via a pore, and fertilisation takes place. The zygote divides by meiosis to form four multi-flagellated cells. These cells find substratum individually and divide to form new filaments. The life cycle of an Oedogonium is haplontic.

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Also Read:

• What is the Economic Importance of Algae?
• Difference between Algae and Plants
• Algae – Definition, Characteristics, Types and Examples