THE STRUCTURE AND LIFE PROCESSES PARAMECIUM

Objectives       

This  blog post provides readers with the following objectives. The reader will be able to:

o   Describe the structure of  Paramecium.

o   Explain the life processes of  Paramecium.

Paramecium Caudatum

Kingdom: Protoctista

Phylum: Ciliophora

Habitat: muddy polluted, fresh water ponds and ditches

This image is credited to D G Mackean www.biology-resources.com

Structure of Paramecium

It has a fixed slipper shaped and is about 0.24mm in length. It has transparent body (with rounded anterior end and pointed posterior end), enclosed by elastic membrane called pellicle. 

Beneath the pellicle are oval bodies called trichocytes used for defense. 

The whole body is covered by tiny, hair-like protoplasmic threads called cilia. The cilia are interconnected at their basal bodies by fine fibers called neuronemes. 

The cytoplasm is divided into outer layer (plasmagel) and inner layer (plasmasol).

It has two nuclei; the large and bean-shaped nucleus called meganucleus and the smaller spherical nucleus called micronucleus which lies just close to the mega-nucleus. 

There are two star shaped contractile vacuoles lying at the anterior and posterior end. 

The ventral side of the body is hollowed out to form oral groove which leads into the gullets in the endoplasm. The gullet, in turn leads into the cytostome (mouth pore).

Life Processes of Paramecium

Excretion in Paramecium

Waste products such as carbon dioxide, urea and ammonia are diffuse through the cell membrane.

Excess water is carried out by the two contractile vacuoles that work alternatively.

Locomotion in Paramecium

Paramecium propels itself by whiplash movements of the cilia. The cilia move forwards and backwards acting as tiny paddles. The cilia propel the organism forward or backwards smoothly. Paramecium rotate on its long axis during movement.

Osmoregulation in Paramecium

Osmoregulation is carried out by contractile vacuoles, which actively expel water from the cell which frequently absorbed by osmosis from its surroundings.  

Nutrition in Paramecium

Paramecia feed on bacteria, algae, yeasts, diatoms and decaying organic matter. The cilia beat frequently to create water current, which drives food along the oral groove into the cytostome where they are ingested in a food vacuole.

Food vacuole circulate through the cytoplasm, and enzymes are secreted into the food vacuole to breakdown the content.

The digested nutrients are then absorbed into the cytoplasm. The undigested food is released through a special opening called anal pore.

Respiration in Paramecium

Paramecium requires oxygen to break down and absorb food in the cytoplasm. Oxygen diffuses into the cytoplasm and carbon dioxide produced as a result of this process, diffuses out in the reverse direction

Reproduction in Paramecium

Reproduction involves Asexual and Sexual reproduction.

Asexual reproduction

Paramecium reproduces asexually, by binary fission. The macronucleus splits and the micronucleus divide and move to opposite ends of the organism. The cell then divides transversally to produce two new paramecia.

Sexual reproduction

Sexual reproduction under unfavorable conditions paramecium undergoes sexual process known as conjugation. The two organisms involved in conjugation are called conjugants. During conjugation, two paramecia come together and unite at their oral grooves. The meganuclei disappears, and the micronucleus divides into four. Three of the four nuclei of each conjugant disintegrate and the remaining one divides into two active and passive nuclei. Exchange of active nuclei occurs between the two conjugants. Fusion occurs after interchange of nuclei to form a zygotic nucleus. The paramecia separate from each other and the zygotic nucleus in each divides thrice by mitosis to form eight nuclei. Each conjugant undergoes two binary fissions to produce four paramecia. Each daughter paramecium has two nuclei which develop into the meganucleus and micronucleus.

Adaptation

1.      It possesses numerous cilia for locomotion.

2.      It possesses contractile vacuole for osmoregulation.

3.   It possesses a pellicle, which gives it a definite shape

4.   It possesses trichocytes, which are used for defense and attack.

5.   The presence of oral groove enables it to feed.

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