Paramecium
The paramecium, phylum of protozoa class of Ciliophora, is often called slipper
animalcules because of their slipper-like shape. Paramecia are unicellular organisms usually less
than 0.25 mm (0.01 inch) in length and covered with minute hair-like projections called cilia.
Cilia are used in locomotion and during feeding.
When moving through the water, paramecia follow a spiral path while rotating on the
long axis. When a paramecium encounters an obstacle, it exhibits the so-called avoidance
reaction: It backs away at an angle and starts off in a new direction. Paramecia feed mostly on
bacteria, which are driven into the gullet by the cilia. Two contractile vacuoles regulate osmotic
pressure and also serve as excretory structures.
A paramecium has a large nucleus called a macronucleus, without which it cannot
survive, and one or two small nuclei called micronuclei, without which it cannot reproduce
sexually. Reproduction is usually asexual by transverse binary fission, occasionally sexual by
conjugation, and rarely by endomixis,- a process involving total nuclear reorganization of
individual organisms.
The pellicle, a stiff but elastic membrane that gives the paramecium a definite
shape but allows some small changes. Covering the pellicle are many tiny hairs, called cilia. On
the side beginning near the front end and continuing half way down is the oral groove. The rear
opening is called the anal pore.
HOW DOES A PARAMECIUM MOVE?
The paramecium swims by beating the cilia. The paramecium moves by spiraling through
the water on an invisible axis. For the paramecium to move backward, the cilia simply beat
forward on an angle. If the paramecium runs into a solid object the cilia change direction and
beat forward, causing the paramecium to go backward. The paramecium turns slightly and goes
forward again. If it runs into the solid object again it will repeat this process until it can get past
the object.
HOW DOES A PARAMECIUM EAT?
Paramecium feed on microorganisms like bacteria, algae, and yeasts. The paramecium
uses its cilia to sweep the food along with some water into the cell mouth after it falls into the
oral groove. The food goes through the cell mouth into the gullet. When there is enough food in
it so that it has reached a certain size it breaks away and forms a food vacuole. The food vacuole
travels through the cell, through the back end first. As it moves along enzymes from the
cytoplasm enter the vacuole and digest it. The digested food then goes into the cytoplasm and the
vacuole gets smaller and smaller. When the vacuole reaches the anal pore the remaining
undigested waste is removed.
Paramecium may eject trichocyts when they detect food, in order to better capture their
prey. These trichocyts are filled with protiens. Trichocysts can also be used as a method of selfdefense. Paramecium are heterotrophs. Their common form of prey is bacteria. A single
organism has the ability to eat 5,000 bacteria a day. They are also known to feed on yeasts, algae,
and small protozoa. Paramecium capture their prey through phagocytosis.
Reproduction of Paramecium
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.