Reproduction of unicellular algae
For some unicellular algae, for example, chlorella, only asexual reproduction is characteristic.
Usually, algae reproduce both asexually and sexually. The methods of sexual reproduction in algae are very diverse. Consider the reproduction of unicellular algae using the example of Chlamydomonas.
Under favorable conditions, chlamydomonas reproduces asexually. Before division, she stops moving and loses flagella. As a result of division, 2, 4 or 8 motile cells – zoospores – are formed in the mother’s cell. Zoospores leave the mother cell and grow to the size of an adult Chlamydomonas.
Chlamydomonas reproduces sexually when unfavorable conditions occur (cold snap, drying out of the reservoir). In this case, sex cells – gametes – appear inside the chlamydomonas. Gametes of different Chlamydomonas go out into the water and combine in pairs, forming a zygote, which is covered with a thick shell. With the onset of favorable conditions, the zygote divides, forming four cells – young chlamydomonas.
Reproduction of multicellular algae
Let us consider the reproduction of multicellular algae using the example of ulotrix. Like other multicellular algae, ulotrix reproduces asexually and sexually.
In favorable times, reproduction is asexual. Each cell, except for the one with which the thread is attached, can divide into 2 or 4 mobile cells with flagella – zoospores. They go out into the water, swim, attach themselves to some underwater object, and share. This is how new strands of algae are formed.
Under unfavorable conditions, numerous small mobile gametes with flagella are formed in some cells of the alga. In water, they merge in pairs, forming a zygote. Usually the gametes that have arisen in the cells of the filaments of different algae merge. The zygote is covered with a thick membrane and can remain dormant for a long time. When favorable conditions occur, the zygote is divided into 4 cells – flagellate spores. Each of them, having landed on an underwater object, can give rise to a new filamentous algae ulotrix.
Multicellular algae can also reproduce vegetatively – by pieces of thallus.