The Uni-Cellular Amoeba - Essay Example

BIOLOGY: ORGANISMS
Introduction
The Amoeba proteus is a uni-cellular, relatively large freshwater protozoan, lacking a defined shape. The amoeba as a one-celled organism is able to function efficiently in its environment “despite lacking the levels of organization present in more complex organisms” (Hunter, 2008, p.112). This is because its organellar structures perform all the life processes necessary to maintain homeostasis, in a manner similar to the tissues and systems found in multi-cellular organisms. The diagram of the Amoeba (Fig.1) given below clearly indicates all its organs and structures.
Thesis Statement: The purpose of this paper is to investigate the uni-cellular Amoeba, and examine how the organism is physiologically suited to its environment.
Fig.1. Amoeba proteus: A One-Celled Organism

(EnchantedLearning.com, 2010)

Physiological Suitability of the Amoeba to its Environment
Although amoebas are simple in form, they are highly successful organisms found in abundance in a large variety of habitats across the globe. Amoebas live in “fresh water, the oceans, and in the upper layers of the soil” (Columbia Encyclopedia, 2009, p.1703). Many species of amoebas have adapted to a parasitic life on the body surface of aquatic animals or in the internal organs of both aquatic and terrestrial animals.
The protozoan belongs to a much larger group of single-celled organisms called protoctists. There are over 40,000 species of amoeba or amoeba-like forms, most of which have an outer shell or case, and hard internal structures. “Amoebas are considered to be animal-like since they eat other organisms” (MCC, 2000, p.38); they move about and capture their prey by extending their pseudopodia in a process known as phagocytosis or amoeboid movement involving the formation of temporary extensions of the pseudopodia. Pseudopodia used in locomotion and feeding are of various shapes at the tip, they may be rounded, pointed, branched, and fused together, or rigid and pointed (Columbia Encyclopedia, 2009).
The pseudopodia are flowing extensions of the jelly-like protoplasm of the organism, which form a food vacuole after engulfing a food particle. Amoeba eat “algae, bacteria, plant cells, and microscopic protozoa and metazoa; some amoebas are parasites” (EnchantedLearning.com, 2010). Amoebas can distinguish between the different types of organisms that form their prey, from other materials, and use different strategies in approaching different food (Columbia Encyclopedia, 2009).
The food vacuoles ingest the food, digesting the particles with the help of digestive
enzymes manufactured and secreted by the organism, which are poured into these vacuoles. The resultant useful chemical compound is absorbed into the amoeba’s body. “Useless residues remain in the vacuoles and are ultimately expelled as the vacuole comes in contact with the membrane at the body surface” (Columbia Encyclopedia, 2009). Egestion is carried out through reverse pinocytosis at the cell’s plasma membrane (Hunter, 2008).
The single cell of the amoeba is surrounded by a porous cell membrane through which the organism breathes. Freshwater amoebas constantly take up water through the process of osmosis, and the organism’s water content is regulated by a pulsating contractile vacuole. Marine amoebas do not have a contractile vacuole. Respiration is by diffusion of gases through the cell membrane (Columbia Encyclopedia, 2009). Oxygen from the water passes into the amoeba, and carbon dioxide leaves through it (EnchantedLearning.com, 2010). Respiration takes place in the mitochondrion, which contains the required enzymes to release energy from food molecules (Hunter, 2008). The cytoplasm is a complex, jelly-like series of folded membranes filling most of the cell (EnchantedLearning.com, 2010). The organism moves with the help of the plasma membrane and the cytoplasm which allow the absorption and circulation of materials.
The nucleus is a large, disk-shaped structure that controls the growth and reproduction of the amoeba (EnchantedLearning.com, 2010). The nucleus also manufactures proteins that regulate the cell’s metabolic activities (Hunter, 2008). “Amoebas reproduce asexually by binary fission” (EnchantedLearning.com, 2010), during which the parent cell divides, while the nucleus also divides by a process called mitosis, and the organism produces two smaller copies of itself. Further divisions of the
two resulting organisms in a similar manner, lead to the amoeba’s proliferation.
Unlike most living cells, the amoeba and other protozoa living in water are not in osmotic equilibrium with their environment. “The protoplasm of an amoeba has a much higher concentration of salts than does the water in which it lives” (Heilbrunn, 1952, p.132). Excess swelling is avoided by the action of the contractile vacuole which continually pumps water out of the cell.
Similar to animals living in tidepools at the edge of the sea which can tolerate sharp changes in the salinity of their environment, the marine amoeba, Amoeba Mira, can live in solutions widely varying in osmotic pressure. Thus, marine organisms have a greater capacity to withstand the change in the osmotic environment than freshwater organisms. Similarly, protozoa like the marine amoeba termed Amoeba Mira, are able to face great differences in osmotic pressure. This amoeba can live in highly diluted seawater, with a “salt concentration reduced to 5 percent of normal, and it can also live in seawater concentrated to one-tenth of its original volume” (Heilbrunn, 1952, p.555). Additionally, the freshwater amoeba, Amoeba lacerate can live not only in seawater, but also in solutions of salts one-fourth more concentrated than seawater.
Conclusion
This paper has highlighted the unicellular protozoan amoeba. The organism functions successfully in its environment because its organelle is structurally adapted to carry out basic life processes efficiently. Thus, the amoeba’s anatomy, physiology, ability to change shape for locomotion and nutrition, and the activities performed by its
various organs and structures, help it to survive and thrive in different environments. Read More