Amoeba Diagram & Characteristics

What is Amoeba?

Amoeba is found to be a unicellular organism that is made up of a single cell and can only be seen by a microscope. This organism is not visible with the help of the naked eye. It is usually a eukaryotic organism that shows the presence of true organelles and a nuclear envelope. This organism moves with the help of false feet which is termed as the pseudopodia. The pseudopodia is defined as the cytoplasm pushing off the cell membrane. A very important feature of the amoeba is to change its shape.

Classification of Amoeba

All the discussion of the amoeba from which domain and phylum it belongs is defined here:

• Domain: Eukaryota (True cells)

• Kingdom: Amoebozoa

• Phylum: Tubulinea

• Class: Lobosa

• Order: Tubulinida

• Family: Amoebidae

• Genus: Amoeba

• Species: many different species such as Proteus and animacule.

Nowadays, studies have been done on classifying the amoeba. This classification is done on the basis of the subunit that is located in their ribosomal RNA. Sarcodina is defined to be the most preferable form of the amoeba. It is found to be the single most accepted taxonomic group that is presented to the classification of the amoeba cell. It is divided on the basis of its observable character.

Well-Labelled Diagram of Amoeba

An amoeba's body is irregular in shape and covered by a plasma membrane. It has two parts to its cytoplasm: the outer part is called the ectoplasm and the inner part is called the endoplasm. The main organelles found inside its cytoplasm include the nucleus, contractile vacuole, and food vacuoles.

Structure of Amoeba

• Movement in the amoeba takes place with the help of false feet which is known as pseudopodia so it changes its shape.

• The structure and body of Amoeba are divided into three different parts namely cytoplasm, plasma membrane, and nucleus.

• The cytoplasm of the amoeba is further divided into two layers that are known as the outer ectoplasm and inner endoplasm.

• The plasma membrane of amoeba is observed to be very thin This layer is a double-layer membrane that is composed of protein. It is made up of lipid molecules.

• When we talk about other cellular organelles, amoeba possess contractile vacuoles, mitochondria, Golgi apparatus and some of the fat globules.

• The contractile vacuole helps in maintaining the osmotic equilibrium. This process is played by separating out most of the water from the cell.

Nutrition and Digestion in Amoeba

Nutrition in amebas is holozoic i.e., they ingest and digest liquid or solid foods. Most amebas are omnivorous, living on algae, bacteria, protozoa, rotifers, and other microscopic organisms. An ameba may ingest food at any part of its body surface just by producing a pseudopodium to engulf the food (phagocytosis). The enclosed food particle, along with some environmental water, becomes a food vacuole. As digestion occurs within the vacuole by enzymatic action, water and digested materials pass into the cytoplasm. Undigested particles are eliminated through the cell membrane.

Reproduction in Amoeba

Binary fission:

Binary fission in amoeba is a type of asexual reproduction. In binary fission , the organism first duplicates its genetic content and elongates and splits into two equal halves. Binary fission is relatively fast and a full cycle usually takes under half an hour. After karyokinesis has divided the nucleus, cytokinesis separates the cytoplasm into two cells that eventually can develop into an independent living organism.

Spore formation:

When there are unfavourable conditions, the amoeba divides with the help of spore formation. It starts to break its nuclear membrane, and some of the chromatin blocks get released into the cytoplasm. Each chromatin block now gets inside a nuclear membrane and becomes a small daughter nucleus. Unlike multicellular organisms, amoeba does not involve gamete fusion or sexual reproduction.

Size and Variation in Amoeba

Amoeba is present in different forms in both size and shape. When the earliest animals were found it was found to be 400 to 600 micrometers in size. There are many different sizes of amoeba that range from small to large size that is 2-3 nanometers in size to exceptionally large such as 20 cm amoeba. The body of the amoeba is found to be transparent and looks like gelatin.

Amoeba NEET MCQs

Q1. Amoeba moves and engulfs food with the help of:

1. Cilia

2. Flagella

3. Pseudopodia

4. Contractile vacuole

Correct answer: 3) Pseudopodia

Explanation:

Amoeba is a unicellular organism that moves by forming temporary extensions of its cytoplasm known as pseudopodia (false feet). These structures help the organism in locomotion as well as in capturing food through phagocytosis. Unlike cilia or flagella (used by other protists), pseudopodia provide flexible movement and are essential for the amoeba's survival.

Hence the correct answer is option 3) Pseudopodia.

Q2. The contractile vacuole in amoeba functions to:

1. Store nutrients

2. Maintain osmotic balance

3. Aid locomotion

4. Reproduction

Correct answer: 2) Maintain osmotic balance

Explanation:

The contractile vacuole of amoeba is a specialized structure that helps in osmoregulation, i.e., maintaining the water balance inside the cell. Since amoeba lives in freshwater, water constantly enters the cell by osmosis. The contractile vacuole collects excess water and periodically expels it out, preventing the cell from bursting. It does not play a role in nutrient storage, movement, or reproduction.

Hence the correct answer is option 2) Maintain osmotic balance.

Q3. Which condition is caused by Naegleria fowleri?

1. Amoebic dysentery

2. Primary Amoebic Meningoencephalitis (PAM)

3. Malaria

4. Sleeping sickness

Correct answer: 2) Primary Amoebic Meningoencephalitis (PAM)

Explanation:

Naegleria fowleri is commonly called the “brain-eating amoeba.” It enters the human body when contaminated water enters through the nose. From there, it travels to the brain and causes Primary Amoebic Meningoencephalitis (PAM), a rare but usually fatal infection. Amoebic dysentery is caused by Entamoeba histolytica, malaria by Plasmodium, and sleeping sickness by Trypanosoma.

Hence the correct answer is option 2) Primary Amoebic Meningoencephalitis (PAM).

Also read:

• MCQs on Characteristics of Kingdom Protista

• Lichens

• Amoebiasis

FAQs on Amoeba

What is Amoeba?

Amoeba is a unicellular eukaryotic organism that belongs to the kingdom Protista. It has an irregular, constantly changing body shape due to the presence of pseudopodia. The cytoplasm is differentiated into ectoplasm and endoplasm, and the cell contains a nucleus, contractile vacuole, and food vacuoles. Amoeba is found in freshwater, moist soil, and decaying vegetation. Being heterotrophic, it engulfs food particles through phagocytosis. It serves as a simple model to study basic life processes like locomotion, nutrition, and reproduction.

How does Amoeba move?

Amoeba moves with the help of pseudopodia, which are temporary extensions of its cytoplasm. The cytoplasm flows forward to form a pseudopodium, and the rest of the cell moves into it. This type of movement is known as amoeboid movement. Pseudopodia also help in capturing food particles, showing dual function. This simple mechanism of movement is important for survival in aquatic and moist environments.

What is the function of the contractile vacuole in Amoeba?

The contractile vacuole in Amoeba plays a vital role in osmoregulation. Since Amoeba lives in freshwater, excess water continuously enters the cell by endosmosis. The contractile vacuole collects this extra water and periodically expels it outside the cell. This process maintains osmotic balance and prevents the cell from bursting due to over-accumulation of water. Thus, it is essential for the survival of Amoeba in hypotonic environments.

How does Amoeba reproduce?

Amoeba reproduces asexually, mainly through binary fission. In this process, the nucleus divides by mitosis, followed by the division of cytoplasm (cytokinesis), resulting in two daughter Amoebae. Under unfavorable conditions, Amoeba may undergo multiple fission, where it forms a cyst and produces many daughter cells. Upon return of favorable conditions, these cells are released. This reproductive strategy ensures both survival and rapid multiplication of the species.