LIFE WITHIN A SINGLE PLASMA MEMBRANE

LIFE WITHIN A SINGLE PLASMA MEMBRANE

Protozoa have unicellular (cytoplasmic) organization. But they are not simple organisms. Often, they are more complex than any particular cell in higher organisms. Some individual protozoans come together to form colonies. The individuals in a colony are not dependent on one another for most functions. However, some protozoan colonies are complex. Their individual cells become specialized. Therefore, it becomes difficult to differentiate between a colony and a multicellular organism.

Maintaining Homeostasis in Protozoans

Protozoans maintain homeostasis by following methods:

1. Support

The bodies of protozoans are supported by pellicle and cytoplasm.

(a)  A regular arrangement of microtubules is called the pellicle. Pellicle underlies the plasma membrane of many protozoa. The pellicle is a rigid structure. It maintains the shape of the protozoan. But it is also flexible.

(b) Cytoplasm: The cytoplasm of a protozoan is differentiated into two regions: The portion of the cytoplasm just beneath the pellicle is called ectoplasm. It is relatively clear and firm. The inner cytoplasm is called endoplasm. It is granular and more fluid like.

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Fig: Protozoan Protist

2. Osmoregulation

The maintenance of water and salt balance in the body is called osmoregulation. Most in wine protozoa have solute concentrations similar. to that of their environments. Fresh water protozoa must regulate the water and solute concentrations of their cytoplasm. There is higher solute concentration in the protozoan than in the environment. Therefore, water enters freshwater protozoa by osmosis. Contractile vacuoles remove this excess water. Contractile vacuoles are formed by the fusion of smaller vacuoles in some protozo the vacuoles are permanent organelles in other protozoans. These contracting vacuole arc composed of collecting tubules. These tubules radiate into the cytoplasm. The microfilaments contracts and empties the contractile vacuoles.

3.Ingestion of Food

There ar different methods of ingestion of food.

(i)  Mos protozoans absorb dissolved nutrients En acti \e transport.

(ii) Some protozoan ingests whole or particle of food by enducytosis. It forms food vacuole.

(iii) Some protozoa ingest food through cytopharynx or gullet.

5. Process of Digestion

Digestion and transport of food occurs in food vacuoles. These food vacuoles are formed during endocytosis.

(i) Food vacuoles fuse with Lysosmes.

(ii) These lysosomes contain enzymes. The change of  enzyme and acidity will help in digestion.

(iii) These food vacuoles circulate through the cytoplasm and distribute the products of digestion.

(iv) The vacuoles are called egestion vacuoles after completion of digestion.They release their contents by exocytosis. Sometimes a temporary pole is formed at a specialized region of the plasma membrane or pellicle. This pore is called the cytopyge.


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6. Respiration and Excretion

The protozoans have small size. But they have a large surface area in proportion to their volume. It helps in gas exchange or excretion. Both gas exchange and excretion occur by diffusion across the plasma membrane.

(i)    Gas exchange involves absorption or oxygen and elimination of the carbondioxide.

(ii)   Excretion is the elimination of the nitrogenous waste. Nitrogenous wastes by-products of protein metabolism. Byeproduct in protozoa is mostly ammonia.

1Fig: Asexual Reproduction in Protozoa. Binary fission begins with  mitosis. Cytoplasmic division (cytokinesis) divides the organelles between the two cells and results in two similarly sized protozoa.Binary fission is (a) longitudinal in some protozoa (e.g.mastigophorans) and (b) transverse in other protozoa (e.g., ciliates)

Reproduction

Both asexual and sexual reproduction occurs among the protozoa.

Asexual reproduction

Asexual reproduction in protozoans occurs bv following methods:

1. Binary fission: It is one of the simplest and most common forms of asexual reproduction. Mitosis produces two nuclei by binary fission. The cytoplasm divides. These nuclei are distributed into two similar-sized individuals. During cvtokinesis. some organelles duplicates. Therefore, each new protozoan gets all important organelles. The cytokinesis may be longitudinal or transverse.

2. Budding: It is another limp of asexual reproduction. Mitosis occurs during budding. It is followed by the incorporation of one nucleus into a cytoplasmic mass. This cytoplasmic mass is much smaller than the parent cell.

3. Multiple Fission or Schizogony: In this case, a large number of daughter cells are formed bv the division of a single cell. Multiple mitotic divisions occur in a mature cell in schizogony. Thus a large number of nuclei are formed. These cytoplasmic divisions occur. These cytoplasmic divisions result in the separation of each nucleus into a new cell.

Sexual Reproduction

Gamete formation takes place during sexual reproduction. These gametes fuse to form zygote. In most protozoa, the sexually mature individuals are haploid. Gametes are produced by mitosis. First division in zygote is meiosis. Ciliated protozoans takes places by conjugation.

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