Reproduction of Paramecium (Sexual and Asexual) | Biology : Zoology

UNIT FOUR : KINGDOM PROTISTA
Class : 11

Reproduction of Paramecium

The paramecium reproduces both sexually and asexually 

Sexual reproduction 

It takes place by conjugation method. During the process following events occur 

• Two paramecia come close and get attached together from side of oral groove by some sticky substances. The Paramecia that take part in conjugation are called conjugants. 
• At the point of attachment, pellicle degenerates to form cytoplasmic bridge. 
• After formation of cytoplasmic bridge, the macronucleus of each conjugant disappeared. 
• The micronucleus undergoes meiosis division in each conjugant to give four nuclei. 
•  In each conjugant out of four nuclei, three nuclei degenerate and only one remain functional. 
•  The remaining one nucleus of each conjugant undergoes mitosis division to produce two nuclei. Out of two nuclei, one is larger and other is smaller. 
• Small nucleus of each conjugant migrates crosswise between two paramecia through cytoplasmic bridge. That nucleus is called migratory nucleus or male nucleus. The larger nucleus remains stationary and called stationary nucleus or female nucleus. 
• The migrated nucleus fuses with stationary nucleus in each conjugant to form zygote nucleus. 
• Now two paramecia separate together and then they are called exconjugant. 
• In each exconjugant the zygote undergoes mitosis division 3 times to produce 8 nuclei. 
• Out of eight nuclei, four becomes larger and 4 becomes smaller in each exconjugant. The larger nuclei are termed as macronucleus and smaller is micronucleus. 
•  Out of four micronucleus 3 degenerate and one remains functional. 
•  The functional micronucleus in each exconjugant divides into two and the conjugant divide by binary fission into two daughter paramecia from each exconjugant. The macronuclei are shared equally. 
• Again the micronuclei of two daughter paramecia divide into two and macronuclei are again shared and later the paramecia divide again to produce 8 paramecia. 

Significance of conjugation 

The vitality is stored, the hereditary materials or characters are exchanged between two paramecia. There are some other methods of sexual reproduction 

Autogamy 

It takes place in single individual. The micronucleus divides into two and fuses to form synkaryuon or zygote. Then the Paramecium starts to divide to produce daughter paramecia. 

Hemixis 

In this method fragmentation and division of macronucleus takes place without any activity of micronucleus. 

Cytogamy 

It takes place in two individuals. In this process micronucleus divides 3 times to produce 8 nuclei. in which 6 degenerate and remaining 2 fuse together to give zygote. 

Asexual Reproduction 

It takes place by binary fission method  At first, micronucleus divides into 2 nuclei by mitosis. Macronucleus divides into 2 by mitosis. The cytpharynx also divides into 2 parts. The cytoplasm is also divided into 2 parts. Then transverse constriction is made from two sides. New contractile vacuoles are formed. The constriction meet at centre and two daughter paramecia re produced.