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Algae; Reproduction


 

REPRODUCTION

Algae reproduce vegetatively, asexually and sexually

VEGETATIVE REPRODUCTION

A part is detached from the plant body and develop into new plant. Vegetative reproduction may takes place by one of the following methods.

Fragmentation: parent plant is divided into small parts called fragments. Each fragment develop into new plant, e.g., Spirogyra.

Budding: outgrowths in the form of buds develop from cells. These buds develop into new plants after separation.

ASEXUAL REPRODUCTION

Asexual reproduction takes place during favourable conditions. Different type of spores are produced during asexual reproduction.

  1. Zoospores: Motile spores are called zoospores. They have flagella or cilia for locomotion. They are produced in special structures called zoosporangium.
  2. Aplanospores: Thenon-motile spores are called aplanospore, without any flagellum.
  3. Hypnospores: If cell secretes a thick wall around it & becomes rounded it is called hynospore.
  4. Akinetes: If parent wall of the vegetative cell becomes thick, it is called akinete.
  5. Palmella: If spores remain embedded in mucilaginous matrix and are not liberated. This condition is called Palmella stage.

SEXUAL REPRODUCTION

It takes place under unfavourable conditions. Gametes are produced in gametangia. Gametes fuse to form zygote. Zygote becomes zygospore after secreting a thick wall. Zygospore germinates during favourable conditions.

There are different forms of sexual reproduction in algae.

  1. Isogamy: In this case, the gametes are of similar size and form as well as both male and female gametes are motile.

    Fig: Algae isogamy

  2. Anisogamy: Gametes have similar structures but different sizes. The smaller active gamete is called male The larger less active gamete is called female gamete. They fuse to form zygote.

    Fig: Algae anisogamy

  3. Oogamy: In this case, the gametes have different forms and structures, sizes and behaviours. The smaller motile gamete is called They are produced in antheridia. The non-motile larger gamete is called egg or oosphere. It is produced in oogonium. The male gamete swims in water. It enters into to oogonium. After fusion of gametes zygote is formed which may secretes a thick wall and become oospore.

    Fig: Algae Oogamy

Parthenogenesis: Sometimes, oosphere (egg) is changed into oospore (zygote) without fertilization. It forms parthenospore. This condition is called parthenogenesis