Describe various methods of asexual reproduction in algae

Asexual Reproduction:

Asexual reproduction involves the formation of certain type of spores — either naked or newly walled. It is a process of rejuvenation of the protoplast without any sexual fusion. Each and every spore germinates into a new plant. In this method, there is no alternation of genera­tions.

The asexual spores may be of various types:

a. Zoospores:

These are motile naked spores provided with two, four or many flagella and called as bi-, quadri- or multiflagellate zoospores, respectively. Biflagellate zoospores are found in Chlamydomonas, Ulothrix Ectocarpus etc., quadriflagellate zoos­pores are found in Ulothrix  and multiflagellate zoospores are found in Oedogonium 

But the multinucleate and multiflagellate zoospores as found in Vaucheria (Fig. 3.17D) are called synzoospores. Each zoospore has a chloroplast and an eye spot. The zoospores may be either haploid or diploid.

Asexual Spores in Algae 

They are formed within the zoosporangium. There may be sin­gle zoospore (e.g., Oedogonium) or many zoospores (e.g., Cladophora) per zoosporangium. Zoospores are either haploid or diploid depending on the nature of plant body, gametophytic or sporophytic on which it develops.

The zoospores are liberated either by the disintegration of the zoosporangial wall or by the formation of an apical pore on the zoosporangium. After liberation the zoospores swim for a while, then with­draw their flagella, encyst and ulti­mately germinate into new plants.

b. Aplanospores:

Aplanospores are non- motile spores. These spores are formed either singly or its protoplast may divide to form many aplanospores inside spo­rangium during unfavourable conditions, especially in drought (e.g., Ulothrix Microspora). The aplanospores may also be formed in certain algae of semiaquatic habitat.

When they appear identical to the parent cell, they are referred to as autospores (e.g., Scenedesmus, Chlorella etc.). Aplanospores with thickened wall and abundant food reserve are known as hypnospores (e.g., Pediastram, Sphaerella etc.).

They are formed to overcome prolonged period of desiccation. With the onset of favourable condition the hypnospores either directly germinate into a new individual or their protoplasts may form zoospores. Due to deposition of haematochrome pigment in their walls, the hypnospores of Chlamydomonas nivalis are red in colour.

c. Tetraspores:

Diploid plants of some algae (e.g., Polysiphonia, ) pro­duce a special type of haploid aplano­spores, called tetraspores, formed within tetrasporangium. The diploid nucleus of a tetrasporangium divides meiotically to form four haploid nuclei which — with little amount of protoplasm — are deve­loped into four tetraspores. After libe­ration the tetraspores germinate to form male and female gametophytes.

d. Akinetes:

The vegetative cells of certain filamentous algae develop into elonga­ted thick-walled spore-like structures with abundant food reserves, called akinetes (e.g., Gloeotrichia, ). They can tide over the unfavourable conditions. With the onset of favourable condition they germinate into new indi­viduals.

e. Exospores:

In some algae, spores are regularly cut off at the exposed distal end of the protoplast in basipetal succession, called exospores. These spores aggregate in groups and develop new colonies, e.g., Chamaesiphon 

f. Endospores:

These are small spores formed by the divisions of the mother protoplast. They are also called conidia or gonidia. They are set free after the dissolution of mother wail. Without taking rest, the spores germinate direct­ly and develop into a new plant, e.g., Dermocarpa

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hi Ella

Can u pls give me slightly a small answer to this question because this question is of 5 marks.

Thanks
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Its ok Ella
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According to the book i.e. NCERT textbook,only one method of asexual reproduction in algae is explained.since u hev said it is the question of 5 marks..so i will elaborate and give... Asexual reproduction in algae:-
  • Asexual reproduction is the production of progeny without the union of cells or nuclear material. Many small algae reproduce asexually by ordinary cell division or by fragmentation, whereas larger algae reproduce by spores.
  • Some red algae produce monospores (walled, nonflagellate, spherical cells) that are carried by water currents and upon germination produce a new organism.
  • Some green algae produce nonmotile spores called aplanospores, while others produce zoospores, which lack true cell walls and bear one or more flagella. These flagella allow zoospores to swim to a favourable environment, whereas monospores and aplanospores have to rely on passive transport by water currents.
thanks fr reading this..i hope dis helps u...

 
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