Cellular slime moulds or communal slime moulds
General characters
1.Wallless, uninucleate myxamoeae present. Complete absence of flagellated cells during life cycle.
- Formation of pseudoplasmodium stage as a result of chemotactic movement of mycamoebae due to release of Camp and acrasin.
- Sporangia are naked.
4.Spores have cellulosic wall.
- Sexual reproduction is anisogamous.
Common cellular slime mould, Dictyostelium , is a colonial form in which hundreds of uninucleate, haploid amoeboid cells are aggregated without any fusion to form a colony. The colony gives the appearance of single multinucleate mass of protoplasm and thus, called pseudoplasmodium.
Under exhausted food supply and stimulation by cAMP and chemical acrasin,many cells come close together by chemotactic movement during the formation of pseudoplasmodium. Pseudoplasmodium exhibits primitive form of multicellularity and division of labour. So these are also called as communal smile moulds. On these basis cellular slime moulds are regarded as advanced protists and primitive fungi.
During unfavourable conditions, the myxamoebae may form a cyst called microcyst for perennation and dispersal.
Under dry conditions, the pseudoplasmodium produces stalked sporocarp , which may be branched or unbbranched, each branch bearing single sporangium terminally (monocentric). Sporangium is wall less. Within the sporangium , amoeboid cells become rounded to secrete a spore wall around. On the approach of favourable conditions, spores are liberated. Each spore germinates by rupturing cellulosic wall to form mycamoeba and the myxamoebae may live independently. Multiply by repeated mitotic divisions or get aggregated to form pseudoplasmodium.
Sexual reproduction is anisogamous type. During sexual reproduction, a number of myxamoebae form a clump. One of the myxamoeba becomes larger and engulfs the surrounding smaller myxamoebae. The macrocyst, karyogamy occurs and it thus, becomes zygote. It is followed by meiosis and several mitotic divisions to form a large number of haploid myxamoebae, which are released by rupture of macrocyst wall.
EXERCISE
31.Which kingdom includes nutritionally most diversed group of organisms and has no well defined boundaries ?
- Monera
- Protista
- Fungi
- Plantae
- Chrysophytes are
- Diatoms and desmids
- Diatoms and dinoflagellates
- Slime moulds and desmids
- Slime moulds and diatoms
- Red tide is caused by rapid multiplication of
- BGA
- Desmids
- Diatoms
- Dinoflagellates
34.Which of the following option for diatoms is correct?
- Pecto – cellulosic cell wall
- Silicified cell wall
- Multicellular eukaryotes
- Produce saxitoxin
- Acellular slime moulds show
- Haploid uninucleate plasmodium
- Naked sporangia
- Autotrophic nutrition
- Isogamous type reproduction
