[Biology Class Notes] on Amoeba Pdf

All living beings on the earth are made up of structures called cells. Down at the microscopic level, this is the very basis of life. Every organism, including humans, begin their lives as a single cell and then branch into millions of these cells. Some organisms, however, remain single-celled for all their lives. They are microscopic organisms and they require only one cell to survive. One of the most common of this variety is an amoeba. 

What is Amoeba?

Amoeba is a unicellular organism that can only be viewed under a microscope. It is a simple eukaryotic organism that moves around through Pseudopodia (cytoplasm pushing the cell membrane); the word pseudopodia means ‘false feet’. 

They are commonly found on freshwater surfaces such as ponds and rivers. The ability to change its body shape as required is the key feature to amoebae (plural). The scientific name of amoeba is “Amoeba proteus”, also termed as the genus name. Amoeboid cells are generally found within animal species, some forms of algae, and even in fungi. Asexual reproduction is the typical nature of amoebic cells and the cells multiply through a biological process called binary fission (or multiple fission). 

What Does the Structure Of Amoeba Look Like?

Accounting to the amoeba’s characteristics, its cytoplasm along with cellular contents enclose within a cell membrane. The DNA is bundled into the main cellular compartment, called the nucleus, and is covered by the plasmalemma. The nucleus comprises other several membrane-bound genetic organelles that help in protein transportation and produce energy. 

To name a few:

• Contractile vacuoles (osmoregulation subcellular structures)

• Golgi apparatus (a folded membrane with vesicles)

• Fat globules (the hydrophobic intracellular pieces)Food vacuoles (a storage unit for every food)

• Water globules (small, colourless, spherical vacuole water elements)

• Mitochondria (the powerhouse of a cell)Speaking of its cytoplasmic entity, an amoeba has 2 layers namely the inner endoplasm (granulated) and outer ectoplasm (non-granulated). 

The entire body of an amoeba is transparent and looks similar to gelatin. When it comes to the food consumption process of an amoeba, a prey is usually ingested either through pinocytosis or phagocytosis. Adding to this, an amoeba can turn itself into a microbial cyst, when its food and living food conditions are abnormal. Bacteria, plant cells, metazoa, algae, protozoa are some of the common examples of what an amoeba eats. Yet, it does not have a well-defined mouth or anus for secretion or excretion. Since every amoeboid cell is a pseudopod, it does not have a definite shape. However, the size of an amoeba cell is around 250 and 750 microns. There are even amoebae that are visible to a human’s naked eyes. Moreover, A. Proteus is the biggest known cell in the unicellular kingdom of organisms. 

Amoeba Classification     

The classification of amoeboid cells has a few critics since it possesses only a true nucleus and is neither an animal nor a plant. To maintain consistency, ameboid cells are classified commonly under the Protista Kingdom. Following below is the scientific representation of the amoeba classification:

1. Domain: Eukaryota

2. Kingdom: Amoebozoa

3. Phylum: Tubulinea

4. Order: Tubulinida

5. Family: Amoebidae

6. Genus: Amoeba

7. Species: Proteus, animalcule, dubia, animalcule, etc.

Current research studies focus on classifying amoeboid cells using their subunit ribosomal RNA (SSU rRNA) genes. ‘Sarcodina’ is the single-most acceptable taxonomic group for the classification of amoeba cells. This is classified based on certain observable characteristics and after studying its morphology. Note that this classification is not based on any evolutionary relationship and hence it is not to be considered as a family tree. 

Some Examples Of Amoeba:

Many varieties of amoeba can be found in the surroundings, in places that are damp and watery. They are mostly seen in wet soil and freshwater environments. The most common example of free-living amoeba is the Amoeba proteus. This can grow up to a size of 2 mm, and unlike other varieties, this is not pathogenic and can not cause any diseases in humans or animals. 

Can Amoeba be Dangerous?

Some other varieties of amoeba are opportunistic pathogens. This means that they can be free-living, however, they prefer to infect and live inside a host and derive nutrition from them. These parasites can cause problems like amoebic dysentery and amoebiasis in human beings. These pathogens can be ingested with food and/or water and they can form a cyst-like structure inside the host’s body. These can be significantly harmful since sometimes the pathogens can invade the bloodstream and reach other vital organs. 

Another kind of dangerous amoeba lives in freshwater, Naegleria fowleri. It can also be free-living but can invade the bodies of hosts and derive nutrition from them. The severity of this infection lies in the fact that this pathogen can enter the nasal mucosa and travel upwards towards the brain. It feeds on specific brain tissues such as neurons. This can be fatal for human beings if not detected in a timely manner, since it may lead to primary amoebic meningoencephalitis.