Amoeba

All living beings that are present on the earth are composed of structures known as cells. Under microscopic levels this is the very basis of life . Each and every organism, including humans, begin their lives with a single cell and then branches into millions of these cells. Few organisms, moreover, remain single-celled for their entire lives. They are referred to as microscopic organisms and they require only a single cell to survive. Amoeba is one such common variety.

Amoeba

Amoeba are generally unicellular organisms that can only be viewed under a microscope. It is a simple eukaryotic organism that moves around with the help of a special structure known as the Pseudopodia (cytoplasm pushing the cell membrane); the word pseudopodia refers to ‘false feet’. They are mainly found on freshwater surfaces like ponds and rivers. The key feature of amoebae is their ability to change its body shape as required. The scientific name of amoeba is given as “Amoeba proteus”, that is also termed as the genus name. Amoeboid cells are usually found within animal species, in some forms of algae, and even in fungi. Asexual reproduction is the common method of amoebic cells division and the cells multiply through a biological process known as binary fission (or multiple fission). Many microbiologists often uses the term “amoeboid” and “amoeba” interchangeably in order to represent any organism that exhibits amoeboid movement. 

Few commonly known amoeboid protists are Chaos carolinense and Amoeba proteus, both of which are widely cultivated and studied in classrooms and laboratories. Other commonly known species involve the so-called “brain-eating amoeba” Naegleria fowleri, the intestinal parasite Entamoeba histolytica, that results in amoebic dysentery, and the multicellular “social amoeba” or slime mould Dictyostelium discoideum.

Features of Amoeba

Most amoebas are characterized by the following listed features:

• Movement in amoeba occurs via the use of pseudopodia, in which the cytoplasm pushes the plasma membrane outward or inward, thereby creating blunt and finger-like projections.

• Multiple pseudopodia can also be seen at one particular instance, thus its shape rapidly changes.

• Structure of amoeba is mainly divided into three basic parts – the cytoplasm, plasma membrane and the nucleus.

• The cytoplasm is further differentiated into two layers – the outer ectoplasm and the inner endoplasm.

• The plasma membrane is usually a very thin, double-layered membrane made up of proteins and lipid molecules.

• Amoeba also possess other cellular organelles like a contractile vacuole, mitochondria, Golgi apparatus and fat globules.

• Amoeba consumes food via the process of phagocytosis or pinocytosis.

• The process of reproduction is via asexual means, like the binary fission.

• The lifespan of a typical amoeba is only 2 days, but as it undergoes binary fission, the resulting daughter cells are similar to their parent cell, thus, amoebas can be termed as immortal.

• When living conditions are unfavourable,  the amoeba gets transformed into a protective ball, known as microbial cyst. When living conditions become suitable, they revert back to their trophozoite stage, where they can start feeding again.

Structure of Amoeba

The structure of amoeba is characterised by its cytoplasm along with cellular contents that enclose within a cell membrane. The DNA can be bundled into the main cellular compartment, known as the nucleus, and is covered via the plasmalemma. The nucleus is composed of various other varieties of membrane-bound genetic organelles which help in protein transportation and production of energy. Few of the structural features are discussed below:-

• Contractile vacuoles help in osmoregulation and represent a subcellular structure.

• Golgi apparatus are folded membranes with vesicles.

• Fat globules represent a hydrophobic intracellular structure. Food vacuoles are a storage unit for every food particle.

• Water globules are small, colourless, spherical vacuole water elements.

• Mitochondria are the powerhouse of a cell. The cytoplasmic entity of an amoeba possesses two layers- an inner endoplasm (granulated) and an outer ectoplasm (non-granulated). 

 Amoeba’s entire body is transparent and looks very similar to gelatin. The food consumption process of an amoeba is very unique, where a prey is usually ingested via pinocytosis or phagocytosis. An amoeba possesses the ability to turn itself into a microbial cyst, whenever its food and living food conditions are abnormal. Bacteria, plant cells, metazoa, algae, protozoa are some of the examples of amoeba’s food. It does not possess a well-defined mouth or anus for secretion or excretion. Though every amoeboid cell is a pseudopod, it does not have a definite shape. Moreover, the size of an amoeba cell is about 250 to 750 microns. There are even a few amoebae that are visible to a human’s naked eyes. Amoeba Proteus is the biggest known cell in the unicellular kingdom of organisms. 

Classification of Amoeba

The amoeboid cells are classified into various categories since it possesses only a true nucleus and is neither an animal nor a plant. To maintain balance, amoeboid cells are classified mainly under the Protista Kingdom. Below given is the scientific representation of the amoeba classification:

• Domain: Eukaryota

• Kingdom: Amoebozoa

• Phylum: Tubulinea

• Order: Tubulinida 

• Family: Amoebidae

• Genus: Amoeba

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

Current research studies mainly focuses on classifying amoeboid cells using its subunit ribosomal RNA (i.e. SSU rRNA) genes. ‘Sarcodina’ is the single-most accepted taxonomic group for the classification of amoeba cells. This is mainly classified based on certain observable characteristics and its morphology. We must note that this classification is not based on any evolutionary relationship and thus it is not to be considered as a family tree. 

Disease Associated with Amoeba

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

Another different variety of dangerous amoeba that lives in freshwater is Naegleria fowleri. They can also be free-living but invades the body of hosts and derives nutrition from them. The severity of this infection depends on the fact that this pathogen has the ability to enter the nasal mucosa and travel upwards towards the brain. It feeds on specific brain tissues like neurons. This can be fatal for human beings if not detected early, because it may lead to primary amoebic meningoencephalitis.

Lymph Vessels

Lymphatic vessels (also called as lymph vessels or lymphatics) are part of the human body’s lymphatic system. The lymphatic system also involves the lymph (it is a fluid found within the vessels) and lymphatic organs, like the lymph nodes.

Along with the rest of the system, lymphatic vessels help to maintain the body’s fluid balance, absorb fats from the digestive tract, and provide immune defence against microorganisms and diseases. Abnormalities in these functions cause issues such as lymphedema and the spread of cancer cells. 

Lymphatics are present throughout the body, except for the bone marrow, brain, and spinal cord. Lymph nodes are widely distributed along the lymphatic pathway that are connected via vessels. Clusters of lymph nodes are located in the armpit, groin, and neck.

Conclusion 

Amoeba refers to an organism that represents a simple eukaryotic organism that moves in a unique crawling fashion. However, a comparison of the genetic content of the various amoebas demonstrates that these organisms are not necessarily closely related to each other. So here we come to an end of this topic.