Question

Describe various types of Reproductive in Algae.​

Answer 1

Explanation:

Algae regenerate by sexual reproduction, involving male and female gametes (sex cells), by asexual reproduction, or by both ways. ... Many small algae reproduce asexually by ordinary cell division or by fragmentation, whereas larger algae reproduce by spores

Answer 2

Answer and Explanation:

The following points highlight the three modes of reproduction in algae. The modes are: 1. Vegetative 2. Asexual 3. Sexual.

Mode # 1. Vegetative Reproduction:

In this type, any vegetative part of the thallus develops into new individual. It does not involve any spore formation and there is no alternation of generations. It is the most common method of reproduction in algae.

The vege­tative reproduction in algae is of the follow­ing types:

a. Cell division or fission:

It is the simplest method of reproduction. The unicellular forms of algae commonly reproduce by this simple process, often called binary fission as found in Chlamydomonas, Synechococcus (Fig. 3.16A), diatoms etc. In this method the vegetative cell divides mitotically into two daughter cells, those finally behave as new indi­vidual.

b. Fragmentation:

In this method, the multicellular filamentous thallus breaks into many-celled fragments, each of which gives rise to a new individual. The fragmentation may be accidental or by the formation of separation discs or by some other mechanical force or injury. It is found in Spirogyra, Ulothrix, Oedo- gonium, Zygnema, Cylindospermum (Fig. 3.16B) etc.

Mode # 2. 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. Tetraspores:

Diploid plants of some algae (e.g., Polysiphonia, Fig. 3.17F) 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.  

b. 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, Fig. 3.17G). They can tide over the unfavourable conditions. With the onset of favourable condition they germinate into new indi­viduals.

Mode # 3. Sexual Reproduction:

All algae except the members of the class Cyanophyceae reproduce sexually. During sexual reproduction gametes fuse to form zygote (Fig. 3.18). The new genetic set up can develop by the fusion of gametes coming from the different parents.  

Types of Sexual Reproduction in Algae  

Depending on the structure, physio­logical behaviour and complexity of sex organs, sexual reproductions are of the following five types:  

a. Autogamy:  

In this process the fusing gametes are developed from the same mother cell and after fusion they form zygote. For the above, plant developed through autogamy does not show the introduction of any new characteristic, e.g., Diatom (Amphora normani).

b. Hologamy:

In some unicellular member the vegetative cells of different strains (+ and -) behave as gametes and after fusion they form zygote. It is an ineffi­cient process considering the point of multiplication, but new genetic combi­nations are developed by this process, e.g., Chlamydomonas.