Amoeba
Will Sweet
















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Amoeba in Motion (AWC)

Classification/ Diagnostics characteristics:


Domain: Eukarya
Kingdom: Protista
Phylum: Protozoa
Class: Rhizopoda
Order: Amoebida
Family: Amoebidae
Genus: Amoeba
(2) (JLev)

Amoebas are a large group of protists, a group of eukaryotic microorganisms. The majority of amoebas have a distinct form of moving around; they have pseudopods, false feet. From the evidence that we have available to us now, it seems that amoebas may in fact be a polyphyletic group. This means that they are distantly related and do not share a common ancestor.


Relationships to Humans:


When people first tried to learn more about cell movement, two types of amoebas were used. These were Amoeba proteus and Chaos carolinense. In the present day; however, they are of a medical importance. Because many of amoebas can cause major impacts on human health, they need to be continuously studied. Naegleria fowleri, for example, is known as the "brain eating amoeba" because it can enter the human nervous system and cause an infection that is almost always fatal.

Dysentary is an example of another amoeba illness that can be detrimental to human health. It is especially dangerous for humans to be around raw sewage or other unhealthy areas, because the amoebas that live there can often cause infection. On a more ecological level, amoebas also control algae levels in lakes, ponds, and streams, and can also be helpful by providing smaller animals with nutrients ([2] ) (E.S.S.).

Habitat and Niche:


Amoebas can live in a variety of different habitats within an ecosystem but usually live in freshwater and saltwater ecosystems, soil ecosystems, and within the bodies of animals. Each type of amoeba is adapted to its specific environment and therefore occupy a specific niche. Losobeans, for example, are adapted to live on the bottoms of lakes, ponds, and other bodies of water. Their creeping manner of moving and way of consuming food are perfect for for a life close to sedentary organisms. This means that the role that the losobeans play is a predator. They feed on both parasites (live in a host organism) and scavengers (feed on dead organisms).



Predator Avoidance:


Amoebas secrete certain chemicals to ward off competing organisms and other amoebas. Also, many amoebas use their pseudopods to try and avoid predators. The nematode C. Elegansfeeds on the slime mold amoebae by rupturing the cell, but the slime mold can defend itself by releasing microcysts and macrocysts, which are bigger than the spores. (3) (BB-V) Other animals that eat amoebas include plankton feeders, such as mussels and water fleas (2) (KG).


Nutrient Acquisition:


Amoebas are able to change their body shape if they become aware that food is present. Amoebas use the same process that many other protists use to acquire nutrients: phagocytosis. In this process, the amoeba engulfs the prey using pseudopods, and the cytoplasm then forms food vacuoles. After this, digestive enzymes manufactured by the amoeba are put into the food vacuoles and the food is then digested. The important compounds that the cells needs are absorbed into the cell and the ones that the cell does use are kept in the vacuole to later be expelled from the cell via exoctyosis. Amoebas generally feed on algae, plant cells, metazoa, bacteria, protozoa, and other microorganisms.

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Amoeba Structure (MC)
Amoeba Structure (MC)




















Amoeba feeding on green algae [3] (SM)amoebfeed1b.jpgAmoeba feeding by engulfing its prey. (PS) (

Reproduction and Life Cycle:

Amoebas reproduce through the asexual process of binary fission, the splitting of one cell into two identical cells by mitosis and cytokinesis. Mitosis is the process of cell division that leads to the production of two daughter cells and nuclei that are nearly identical to the original cell and nucleus. At the end of mitosis cytokinesis occurs. This is the separation of the new cells. Because this process is asexual, the DNA is identical to the parent cell and the only way it will differ would be due to a mutation that occurs in DNA replication. The life cycle of an amoeba is simply the process of mitosis and the typical cell growth pattern.
The life span of amoebas can vary greatly depending on its conditions, from mere hours to years to almost immortality. When its food supply is unlimited, amoeba can keep reproducing with virtually no limit. When it is limited, the cells will age and die. The average life span of an amoeba in regular conditions is several days (until binary fission). (11) (DM)


Growth and Development:

Amoebas do not posses a specific growth and development pattern other than the pattern in mitosis. Because they do not have a definite shape, two amoebas will not have the same history of shape throughout their lives. Amoebas can, however, grow an organelle called a flagellum and transition from periods of sexual to asexual phases of growth. Amoebas have a distinct back end and are composed of a single cell. They have a nucleus floating within the cytoplasm of the cell.

Dysentary is an example of another amoeba illness that can be detrimental to human health. It is especially dangerous for humans to be around raw sewage or other unhealthy areas, because the amoebas that live there can often cause infection. On a more ecological level, amoebas also control algae levels in lakes, ponds, and streams, and can also be helpful by providing smaller animals with nutrients (2) (E.S.S.).

Integument:

The cells organelles and cytoplasm are enclosed within the cell with a lipid bilayer or cellular membrane. Some amoebas, however, have a more complex outer layer. Some loboseans, for example, have shells that are made by gluing sand and grains together.The lipid bilayer is a thin polar membrane. Because of their polarity, most hydophilic molecules find the lipid bilayer to be impermeable. This allows the cell to regulate salt concentration and intake of proteins and other nutrients. In environments that are potentially lethal to amoeba, they can excrete a protective mebrane called an amoebic cyst where it then becomes dormant until more favorable conditions are present. 8 (BS)





Movement:

The pseudopods that the amoebas have help the amoebas to move. They change shape continuosly as the amoeba reacts to food and stimuli. To move, the amoeba extends a pseudopodium and the endoplasmic fluid flows into the pseudopodium, moving the amoeba to a new location. The movement of an amoeba is also regulated by the chemicals in the water around the amoeba.
The movement of the amoeba can be explained using the Sol-Gel theory. The cytoplasm of the cell can be in two forms: a liquid or a a gel-like solid. The liquid phase is called plasmasol and the solid plasmagel. When in the liquid phase, the amoeba can propel itself forward. A pseudopod is extended and the plasmosol flows into the space, causing movement. Movement stops when the plasmasol loses water ad becomes plasmagel. (5) (AA)
Some relatives of the amoeba have hair-like structures called flagella instead of pseudopods that aid in movement (7) (KG).
pseudopod.gif (ES)


Sensing the Environment:

Amoebas can respond to stimuli such as food, changes in temperature, presence of light, alterations in chemical concentrations, and other organisms. When food sources are close to an amoeba, the amoeba can sense the chemicals that they release, causing the amoeba's movement mechanisms. This type of cell migration relying on chemical cues is called chemotaxis. In amoebas, chemotaxi is driven by chemical receptors on the cell membrane (4) (SJ). Also, if the temperature surrounding an amoeba is too cold, the amoeba will become inactive until the temperature warms.

Gas Exchange:

Amoebas do the process of gas exchange through the process of diffusion. Amoebas diffuse oxygen from areas of high concentration (outside the cell) to areas of low concentration (inside the cell) and diffuse carbon dioxide from areas of high concentration (inside the cell) to areas of low concentration (outside the cell). This is possible because of the make up of the cellular membrane and the concentration gradients of the gases.


Waste Removal:

exocytosis.jpeg
Figure 3. Exocytosis: Process Amoebas use to Excrete Waste[9] (AY)


Amoebas most often remove waste via the process of exocytosis. Exocytosis is when the vacuoles in the cell release waste from the cell into the external environment as the vacuoles attach to the cell membrane.

More specifically, the vacuole involved in waste removal is known as a contractile vacuole, which lies freely in the cytoplasm of the organism. This contractile vacuole collects excess water as fast as the water enters the body, and grows larger until it reaches its maximum size. The endoplasm surrounding the vacuole contracts and the fluid waste contents (containing urea and carbon dioxide) are released into its environment.[4] (JLau)
Amoebas cytoplasm is divided into ectoplasm and endoplasm. Within the endoplasm are cavities called vacuoles which help with digestion or which contract to move water into or out of the amoeba, depending on what is needed. (TM)


Environmental Physiology (Temperature, Water, and Salt Regulation):

Amoebas regulate water through osmosis. Osmosis is the process where water passes through a semipermeable membrane from areas where the solvent concentration is higher to areas where the solvent concentration is lower. Excess water in the cell of an amoeba is put into a vacuole that brings it to the exterior of the cell. Freshwater amoebas and saltwater amoebas regulate water slightly differently. Freshwater amoebas take up water all the time via osmosis while the cell uses a pulsating contractile vacuole to regulate the water content. The saltwater marine amoebas do not have a contractile vacuole, however.

During osmoregulation that regulates the amount of water present in freshwater amoebas, the membranes of the small vesicles and contractile vacuole contain aquaporin proteins. The aquaporin proteins are transmembrane proteins that help facilitate water passage through the membranes, and the small vesicles are responsible for collecting excess cytoplasmic water and channeling it to the central contractile vacuoles. Excess water is also put into the contractile vacuole from the cytoplasm and through exocytosis, the contractile vacuole fuses with the cell membrane, contracts, and releases water outside the cell. (6) (JF)

In particularly stressful environments, such as one that is particularly cold or dry or one that lacks food or water, the amoeba can enter a dormant state by forming a protective cyst membrane around its body. It can stay inside the protective cyst for a long period of time until environmental conditions became favorable again, at which point it emerges from the cyst.[5] [6] (FZ).


Internal Circulation:

Amoebas do not have a complex system of internal circulation, but they do have vacuoles. Vacuoles circulate waste, water, and other materials into and out of the cell.


Chemical Control (Endocrine System):


Review Questions

1. How do amoebas reproduce asexually through binary fission?(NC)
2. Do amoebas have a nervous system? What kinds of stimuli are amoebas sensitive to? (LC)
3. What is the difference between the water regulation of freshwater and marine populations and why does this difference exist? (AY)
4. What role does chemotaxis play in the life of an amoeba? (Shwetha)
5. Explain the process of how the amoeba is able to acquire foodstuffs from extracellular space to utilize in its body. (BH)
6. what is chemotaxis and how is it essential to the movement of amoebas?(HSC)
7. Explain the role of contractile vacuoles in the waste removal of amoebas. (JF)
8. How can an ameobic infection affect the human body? (DA)



References:

1. Hillis, David M., David Sadava, H. C. Heller, and Mary V. Price. Principles of Life High School Edition. Sudnerland, MA: Sinauer Associates, 2012. Print.
3. Kessin, Richard H. "How Cellular Slime Molds Evade Nematodes." Proc. Natl. Acad. Sci. USA. Proc. Natl. Acad. Sci. USA, May 1996. Web.

4. Willard, Stacy, and Peter Devreotes. "Signaling Pathways Mediating Chemotaxis in the Social Amoeba, Dictyostelium Discoideum." Hopkinsmedicine.org. Science Direct, 2006. Web. 11 Dec. 2012.

5. Sengupta, Saptakee. "Amoeba Movement." Buzzle.com. Buzzle.com, 23 Feb. 2012. Web. 11 Dec. 2012.

6.http://www.biolcell.org/boc/100/0179/1000179.pdf

7."Amoeba." UXL Encyclopedia of Science. 2002. Encyclopedia.com. 11 Dec. 2012 <http://www.encyclopedia.com>.

8.http://amoeba.ifmo.ru/species/amoebidae/aprot.htm

9. "Exocytosis" <http://www.tutorvista.com/content/biology/biology-iii/biomembranes/biological-processes.php>

10. http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artsep01/feed.html
11. Life Span Prolongation. http://books.google.com/books?id=9QrEjg_M3tMC&pg=PA138&lpg=PA138&dq=amoeba+life+span&source=bl&ots=OQ7zJS9Z9t&sig=gGMWbHDfC2OP7tmAHl5iCiOjVjk&hl=en&sa=X&ei=K_LTUNz5Kqjh0wGm5oDICQ&ved=0CHIQ6AEwCg#v=onepage&q=amoeba%20life%20span&f=false


  1. ^ https://www.youtube.com/watch?v=7pR7TNzJ_pA
  2. ^ http://www.fcps.edu/islandcreekes/ecology/amoeba.htm
  3. ^ http://www.youtube.com/watch?v=RegP_Lr_i94
  4. ^ http://www.tutorvista.com/content/biology/biology-ii/excretion-and-osmoregulation/excretion-and-osmoregulation-amoeba.php
  5. ^ http://www.scienceclarified.com/Al-As/Amoeba.html
  6. ^ http://www.biologycorner.com/worksheets/ameba_color.html