essay about structure of amoeba

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Amoeba: Parts and Structure with Characteristics and Diagram

What is amoeba.

Amoeba is an aquatic, single-cell (unicellular) organism with membrane-bound (eukaryotic) organelles that has no definite shape. It is capable of movement. When seen under a microscope, the cell looks like a tiny blob of colorless jelly with a dark speck inside it. Some parasitic amoebae living inside animal bodies, including humans, can cause various intestinal disorders such as diarrhea, ulcers, and liver abscesses. Entamoeba histolytica is an example of such amoeba that causes a disease called amoebic dysentery or amebiasis in humans.

The term ‘amoeba’ is derived from the Greek word ‘amoibe’ meaning ‘change’. German naturalist August Johann Rösel von Rosenhof discovered and described amoeba in 1755.

Scientific Classification

Where do they live.

They are found in salt and freshwater bodiessuch as ponds, lakes, and slow-moving rivers and wet soils, the natural habitat of amoeba. Some parasitic amoebae are also found inside animal bodies, including humans. 

Characteristics

How do amoeba move.

They move by changing their shape, using temporary cytoplasmic extensions called pseudopodia, or false feet. The unique pattern has been named as amoeboid movement after the organism.

How Do They Eat

They catch food such as algae, bacteria , plant cells, microscopic protozoa, and metazoans through absorption using pseudopodia, a process termed phagocytosis . This mode of nutrition in amoeba is called holozoic nutrition where the food particles are engulfed to form a vacuole around it.

Other Important Features :

• Takes in oxygen and gives out carbon dioxide across the cell membrane through diffusion , which helps to produce energy in the form of ATP
• Exchanges water, ions and other small molecules across its cell membrane using the process of osmosis
• Has an average life span of 2 days
• Under unfavorable growing conditions, it transforms into a protective ball called the microbial cyst

It appears as an irregular, jelly-like tiny mass of hyaline protoplasm. Amoeba has no fixed shape, and the outline of the body continues to change due to the formation of small finger-like cytoplasmic outgrowths called pseudopodia.

How Big Can it Get

It varies widely in size and shape from being extremely small between 2.3 – 3.0 µm to exceptionally large such as 20 cm in diameter. The so-called ‘giant amoebae’, Pelomyxa palustris and Chaos carolinense , can be as large as 5 mm.

1. Cell membrane : Also called plasmalemma, it is a thin-layered membrane composed of protein and lipid molecules that restricts the entry and exit of substances in and out of the cell.

2. Cytoplasm : A mass of a jelly-like substance that holds all the other organelles. It consists of two parts:

a) Ectoplasm : The outer gelatinous, semi-solid layer called plasmagel, found just beneath the cell membrane.

b) Endoplasm : The less viscous fluid called plasmasol that surrounds the ectoplasm.

3. Nucleus : Small region within the cytoplasm that contains the genetic material or DNA in the form of chromatin granules along with the nucleoplasm , held within the nuclear membrane.

4. Pseudopod : Also called false feet, it is a temporary arm-like cytoplasmic extension that helps amoeba to perform locomotion and capture food. There can be multiple pseudopods in a cell, together known as pseudopodia.

5. Contractile vacuole : A clear transparent body filled with a watery fluid, found in the outer part of the endoplasm. The food captured using pseudopodia are digested, and the wastes are expelled using contractile vacuoles. It also helps to maintain proper water and salt concentrations within the organism.

6. Food vacuole : Different-sized vacuoles that help in the digestion of food. There are multiple food vacuoles unevenly scattered in the cytoplasm.

7. Water globules : Several small, spherical, colorless, and non-contractile vacuoles filled with water that helps to store water and essential minerals.

How do Amoeba Reproduce

Amoeba reproduces asexually in the following methods:

Binary Fission : The most common mode of reproduction in amoeba, where the parent cell divides equally to distribute its content into two daughter cells. This is the reason why amoeba is called immortal, as the parent cell itself lives on in the daughter cells, which will then give rise to more amoeba cells.

Multiple Fission : Occurs under unfavorable conditions where the parent cell undergoes multiple divisions to form 500- 600 daughter cells.

Sporulation : It is the inactive phase of reproduction during which the nucleus of amoeba undergoes multiple divisions to form numerous spores. Under favorable conditions of growth, the spores germinate back into reproductive cells. This is an important form of adaptation in amoeba.

Regeneration: A part of the amoeba’s body having a fragment of its nucleus develops into a completely new organism.

Ans. Amoeba changes its shape using pseudopodia that help in their movement.

Ans. Amoeba does not have a cell wall but has a cell membrane that forms the outer layer of the organism.

Ans. An amoeba is animal-like due to certain features such as an absence of cell wall, its inability to produce food, and its capacity to move from one place to another.

Ans. Amoeba is heterotrophic because it obtains food from other organisms.

Ans. Its food vacuoles are formed when the food is pushed inside the cell, causing the membrane to bend inward. As the food pushes against the membrane, it stretches inward until the food particles are completely inside the cell, when the membrane pinches off, forming a vacuole.

Ans. Naegleria fowleri popularly known as ‘ brain-eating amoeba’ is a species of the genus Naegleria , belonging to the phylum Percolozoa, which is technically not classified as a true amoeba. It is a free-living, bacteria-eating microorganism that can be pathogenic, causing an extremely rare fulminant and fatal brain infection called naegleriasis, also known as primary amoebic meningoencephalitis. They are commonly found in warm freshwaters such as lakes, rivers, and hot springs, and also in wet soil.

• Amoeba – Britannica.com
• Amoeba – Biologydictionary.net
• Learn About Amoeba Anatomy and Reproduction – Thoughtco.com
• What Is an Amoeba? – Livescience.com

Article was last reviewed on Thursday, October 29, 2020

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Facts about Amoeba, structure, behavior and reproduction

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What is Amoeba? A quick overview

Last updated date Feb 6th, 2023

Amoeba (plural amoebas/amoebae) is a group of primitive protists. Among the big family of Amoebas, Amoeba proteus is probably the best-known member – common in classrooms and research laboratories. Amoeba proteus is best known for the way they move, a primitive crawling manner – through extension and retraction of “false feet” (or pseudopods ) over varied substrates. Amoeba proteus does not have a fixed shape – it constantly changes because it extends its pseudopods. The ability to move by pseudopods is a common feature of the Amoeba family, although some of them look quite different from Amoeba proteus.

Classification of Amoeba – the Phylum Amoebozoa

Amoebas belong to the Kingdom of the protists (a protist is any eukaryotic organism that is not an animal, plant, or fungus). However, in terms of classification, the position of amoebas is just like their shape – consistently changing. In the early days, when microscopy was the only way to characterize microorganisms, amoebas were classified as Phylum Sarcodina with several other species like Heliozoa. Once molecular phylogenetics (classifying a species by its genetic materials) was introduced, amoebas are now in Phylum Amoebozoa. We have, however, to keep in mind that the classification of the protists is presently much debated. Below is the current scientific classification.

Scientific classification Kingdom: Protozoa Phylum: Amoebozoa Class: Tubulinea Order: Euamoebida Family: Amoebidae Genus: Amoeba Species: Amoeba proteus , Amoeba Pelomyxa , Amoeba Thecamoeba , Amoeba Vampyrella (Reference:  wiki )

[In this image] Heliozoa is commonly known as sun-animalcules. I personally like to call it a microscopic “Uni” (sea ​​urchin in Japanese)!

The Anatomy of Amoeba Cell

Amoeba is a single-celled organism, meaning one Amoeba consists of only one giant cell. Amoeba belongs to eukaryotic cells, which means that their genetic material (or DNA) is well organized and enclosed within a membrane by forming a “nucleus”. In this aspect, Amoeba is closer to our human beings (also eukaryotes) than bacteria (prokaryotes).

The microanatomy of Amoeba: an amoeba has a single granular nucleus containing most of the organism’s DNA. Amoeba move and hunt by extending pseudopods . A contractile vacuole is used to maintain osmotic equilibrium by excreting excess water from the cell. Several food vacuoles are used to digest food particles. The cytoplasm can be divided into two parts: a granular inner endoplasm and an outer layer of clear ectoplasm , both enclosed within a flexible plasma membrane . Crystals are condensed wastes produced by the cell.

Nucleus – extremely large genome

Amoeba proteus is a eukaryote, meaning that its genetic materials (DNA) are enclosed in the nucleus. Scientists call the entire DNA codes in a particular organism its “genome”. Guess how big the Amoeba proteus ’ genome is? Amoeba proteus has 290 billion base pairs (one base pair is equal to one DNA code), making it 100 times larger than the human genome (3 billion)!!! One of the largest genomes belongs to a very small creature, Amoeba dubia , a cousin of Amoeba proteus, which has 670 billion base pairs! However, a large genome size does not correlate with the number of genes. Amoeba proteus has such a large genome due to an extreme replication of the same set of genes (a classic example of polyploidy). It can have more than 500 chromosomes in a single nucleus. Human beings are diploid, and we have only two copies of the same genes (or chromosomes).

[In this figure] A comparison of genome sizes of different organisms. Early thinking held that the genome size should be directly related to the complexity of organisms. However, this is not true. Some simpler organisms can have even larger genome sizes than the species at the higher levels of the evolution tree. For example, Amoeba proteus and Amoeba dubia have a much bigger genome size than humans. Note: the genome size of Amoeba dubia (also called Polychaos dubium ) and Amoeba proteus were measured by the 1960s methods that analyzed the whole cell rather than single nuclei. The result could be muddled by including contributions from mitochondrial DNA, possible multiple nuclei, and anything the amoeba recently engulfed.

Pseudopods or Amoebas’ false feet

A pseudopod is a temporary arm-like projection that is developed in the direction of movement. When the Amoeba stretches its pseudopods, the cytoskeletons (like the cells’ skeleton system) inside the cell rearrange and extrude the cell membrane to change the cell shape. Once the tips of pseudopods adhere to the substrate, the cytoplasm of the cell flow to fill the space, so the whole cell moves forward. Under the microscope, you can see the components (including the nucleus and vacuoles) inside the Amoeba flow smoothly, like in a gel, as it moves. This form of movement by extension of cytoplasm is called “ amoeboid movement ”.

[In this figure] Amoeboid movement: an amoeba moves by stretching its pseudopods. Under the plasma membrane of the pseudopods, there are organized cytoskeletons that generate the force to drive the change of the cell’s shape.

In addition to using pseudopods to move around, Amoebae also use them to engulf food particles. Pseudopods are not exclusive to Amoeba. In fact, most eukaryotic cells can change their shapes by moving their cytoskeletons. For example, the white blood cells in our immune system can patrol and prey on invaded bacteria by pseudopods. (See video below).

Contractile vacuole – unique organelle

The third feature of Amoeba proteus is its built-in pumping system inside the cell, called “contractile vacuole”. The contractile vacuole is a water bubble within the cytoplasm of Amoeba proteus . Its function is to regulate the water content of the cell. Since Amoeba proteus is a unicellular organism, the water molecules can freely flow in or out through the semi-permeable cell membrane via osmosis. When Amoeba proteus moves to a place with fewer ions (minerals), the environment becomes hypotonic to the cell. This means more water molecules will move into the Amoeba proteus cell to achieve a balance. When this happens, the contractile vacuoles can store extra water and help in throwing them (together with the wastes) out of the cell. Without the contractile vacuoles, the amoeba may burst. Undoubtedly, it is a very important organelle with an essential function to the amoeba, as well as many freshwater microorganisms.

[In this figure] Osmoreulation in Amoeba. The contractile vacuole is the key regulator of osmotic pressure in the amoeba (also in many single-celled protists). The contractile vacuole serves as a reservoir to store excess water inside the cells. Once the water reaches its limit, the contractile vacuole moves and fuses with the plasma membrane to expel water.

Many microvilli on its cell membrane

The fourth secret of Amoeba proteus is its cell membrane is not as smooth as it shows under the optical microscope. In fact, the outside face of the membrane has many microvilli attached to it (only be seen under an electron microscope). These microvilli can help Amoeba proteus attach and release from the surface of the substrate.

Crystals – shiny particles inside Amoeba proteus

Another feature that you can easily observe is the abundance of crystal-liked inclusions inside Amoeba proteus . Most crystals of Amoeba proteus are in a bi-pyramidal shape. These crystals are contained in vacuoles and composed of triuret, a nitrogen waste product. Other species of Amoebas have their crystals in different shapes, like spheres, sheets, and even croissant-shaped crystals. Here are some examples of crystals in different species of Amoebas.

[In this figure] Crystals in different species of Amoebas. Source: https://www.arcella.nl/inclusions/

Some large Amoebas also have glycogen bodies to store their nutrient reserve. These glycogen bodies are glossy spheroids and vary in size. Glycogen is a form of sugar stored in our body, and we store glycogen in the liver and muscle. When the amoeba digests large amounts of diatoms, you can even see the oil droplets inside the Amoeba cell. This is because some diatoms are tiny oil producers! Some large amoebas contain bacteria and small green algae inside their cytoplasm. These organisms have a symbiotic relationship with their host and are called “endosymbionts”. For example, green algae that live inside can provide additional energy to their host (the amoeba), making the amoeba can live in nutrient-poor environments.

How does Amoeba proteus eat?

Amoeba proteus engulfs its food through a process called “phagocytosis”. As the amoeba moves towards its food, its pseudopods reach out, surround, and engulf the food inside the cell membrane by forming a food vacuole. Digestive enzymes are then released into the vacuole to break down the food into usable nutrients.

[In this figure] Amoeba phagocytosis. The pseudopods first surround and bring the food particle close to the Amoeba. Then a part of the cell membrane opens to allow the particle to move into the cell and into a food vacuole, where it is digested by enzymes.

What is Amoeba proteus ’ favorite food?

Amoeba proteus is a predator of bacteria , protozoa, and algae . It can eat almost any organic nutrients in its habitat. Paramecium is probably the most famous prey for Amoeba proteus . Check out the video of Amoeba hunting paramecia!

How big is the Amoeba proteus ?

Amoeba proteus is a large protozoan, and it can grow up to 1 mm long (average size 250-750 µm). The size ranges based on the amount of food it engulfs. It can almost be seen with the naked eye (still very difficult due to its colorless and transparent body).

[In this figure] Size of the smallest insect and two protozoans in comparison. (A)  Megaphragma mymaripenne . (B)  Paramecium caudatum . (C)  Amoeba proteus . Scale bar is 200 μm. Megaphragma mymaripenne, a parasitic wasp, is the smallest known flying insect. 

How fast the Amoeba proteus can move?

Amoeba proteus can move at a rate of 2-5 mm per minutes.

Does Amoeba proteus have eyes?

No, Amoeba proteus doesn’t have eyes (don’t forget it is a single cell). However, Amoeba proteus can sense light and tends to move away from it. Bright light can even make all movements cease suddenly. The scientists found that Amoeba proteus can respond to light stimulus because of reactions in its plasmagel, the gel-like cytoplasm at the tips of pseudopods. The light makes its plasmagel thicker and stiffer and, as a consequence, more difficult to move. Other than light, Amoeba proteus can also sense several stimuli, like chemicals, toughing, temperature, and even electric fields!

[In this figure] Even though the amoeba is just a single-celled organism, it can respond to various environmental changes. (1) Amoeba will avoid bright light. It also does not stay in the complete dark due to the lack of food. Amoeba prefers in a dim light environment, like under the shadow of water plants or rocks. (2) Amoeba can sense and avoid certain chemicals that are toxic. (3) Amoeba does not like to float around. If possible, it would like to adhere to the surface of the substratum. (4) Amoeba will avoid obstacles and sharp objects while it moves. (5) When scientists place an amoeba in an electric field, the amoeba tends to move toward the cathode. (6) Amoeba likes to stay at a temperature around 25 o C.

How does Amoeba proteus breathe?

Because the Amoeba proteus is a single-celled organism, oxygen, and carbon dioxide can freely diffuse in and out of its cell membrane. Also, other substances (water-soluble molecules like salt) are able to transport through the membrane by osmosis.

How does Amoeba proteus reproduce?

Binary fission.

Most of the time, Amoeba proteus reproduces asexually by splitting one cell into two cells, a process called “Binary Fission”. Just before it reproduces, Amoeba proteus retracts most of its pseudopods and rounds up into a ball. After replicating its genetic material (DNA) in the nucleus, the original nucleus of the Amoeba divides to form two daughter nuclei by the process of Karyokinesis. In this process, the long DNA molecules condense into chromosomes (rod-liked shape) to facilitate the separation. After the nucleus has divided into two, the process of Cytokinesis takes place in which the cytoplasm in the mother cell pinches in and divides into two daughter cells. This leads to the formation of the two daughter cells, having a nucleus and their own cell cytoplasm and organelles. Usually, the entire process may last anywhere from 30 minutes to an hour.

[In this figure] Two ways of amoeba reproduction: Binary fission and Multiple fission. Most of the time, amoebas reproduce by binary fission. When the environment is turning harsh, amoebas adapt to multiple fission to increase the chance of survival.

Multiple fission

Another rare way for Amoeba to reproduce is called Encystment or Multiple Fission. When amoeba senses the environment become unfavorable (eg. lack of nutrients, too acidic or too much bright light), it withdraws its pseudopodia and releases a protective coat (called a cyst) made of a chitin-like substance to cover its cell membrane. This cyst is able to survive in much harsher conditions. At the same time, mitosis occurs many times inside the cyst, producing more than two daughter cells. When the cyst wall ruptures (when the condition turns favorable), these daughter cells are then released to become several new amoebas. When the environment of habitat becomes extremely unfavorable, Amoebas will reproduce through spores. This sexual reproduction can create genetic diversity and increase its chance of surviving in harsh conditions.

Amoeba under the microscope – science project

Where to look for amoeba proteus .

Amoeba proteus resides at the bottom of clean freshwater. It feeds on decaying substances found in freshwater streams and ponds. You can use a transfer dropper to collect the bottom sediments to look for Amoeba proteus . Amoeba proteus can also be ordered from science supply companies. It is commonly used in classrooms to illustrate the movement of pseudopods in action.

[In this figure] Where to collect the amoebas? Here are some pictures of habitats where I recently spotted Amoeba proteus . (A-C) Amoebas like to hide in the bottom sediments (like leaves) of clear water ponds. (D-E) I used the forceps to collect some decaying leaves and water with sediments into my sample vial. I bring it home to look for amoebas and other pond lives under my microscope.

How to find Amoeba proteus under an optical microscope?

Amoebas can be directly observed under an optical microscope without additional stains. It takes patience to locate Amoebas under the microscope because they are transparent (colorless), slow-moving, and like to cover themselves under debris or bottom sediments.

Use a transfer pipette to get a drop of water with some bottom sediments onto a microscopic slide.

Gently cover the sample with a coverslip and mount it on the microscope stage for viewing. Wait 5-10 minutes to allow the microorganisms to adapt to the new environment (amoebas like to adhere to the surface of the glass).

Gradually increase the illumination (Amoebas are sensitive to bright light) and scan the field by low magnification (5x or 10x).

Looking for the tiny crystal-liked particles inside the cells of Amoebas may help you locate them. If you have phase contrast or polarized light filters, you may want to use them.

Amoebas can also be studied by dye staining to visualize cellular organelles. However, this requires the chemicals and equipment to fix and mount the dead Amoebas. If you want to know the detail, check out this link .

A stained Amoeba proteus slide .

What to look for under the microscope?

Direct observation of the Amoeba proteus has a significant advantage because the Amoeba proteus is still alive and actively moving when being viewed under the microscope. This allows you to see the finger-like projections (pseudopods) elongate and shorten as the Amoebas move or engulf food particles.

Some of the other organelles that are visible under the microscope include:

• Nucleus: The nucleus is found about 35 µm in diameter.
• Contractile vacuole: The size of the contractile vacuole may vary from 20 – 100 µm. Typically, it looks clear inside because it is actually a ball filled with water.
• Cytoplasm: The inner fluid containing all kinds of organelles and tiny crystals.
• Food vacuole: The food vacuoles are smaller than the nucleus. It is about 20 µm.

The color of the food vacuoles inside the Amoebas can also indicate the nutrient sources in the habitat. For example, I noticed that Amoebas collected in the late spring contain more green particles (could be green algae), while Amoebas from the early spring are more brownish (engrafted brown diatoms).

[In this figure] Examples of food sources that may affect the color of amoebas’ food vacuoles.

Sometimes, you may see Amoebas at rest and stay motionless with an oval shape. If you have a camera or cell phone mounted on your microscope, the slow-moving Amoebas are great models to practice your microphotography and video-making skills.

Do other Amoebas also look like Amoeba proteus ?

The answer is no. The family of Amoebas comprises very diverse members with over 15,000 described species. Although they all share one characteristic – moving by pseudopods, they can be totally different in shape and size.

[In this figure] Cousins of Amoeba proteus (A) Pelomyxa is a genus of giant amoeboids, usually 500-800 μm but occasionally up to 5 mm in length. (B) Thecamoeba. The body of Thecamoeba often forms a wrinkled cornucopia shape. (C) Vampyrella got its name from the way it feeds. Vampyrella sticks to its victims (usually algae), makes a large hole in the algal cell wall, and sucks the protoplast of the algae. (Credit: Pelomyxa and Thecamoeba – eol.org ; Vampyrella – Sebastian Hess)

Amoebas can be divided into two major groups: naked amoeboids (subclass: Gymnamoebae) and shelled amoeboids (subclass: Testacea). These Amoebas with soft, gel-like cell bodies, like Amoeba proteus, Pelomyxa, Thecamoeba, and Vampyrella , are all naked amoeboids. Surprisingly, some species of Amoebas make protective shells, called “tests”, around their cells. Some shelled Amoebas make the tests entirely by themselves, and the materials could be organics, siliceous (containing silica), or calcareous (containing calcium carbonate) components produced by the Amoebas. These tests are called autogenic tests. Some shelled Amoebas prepare their tests by collecting particles of sediment around them and gluing these mineral particles together with slime ingredients secreted from the cells. These tests are called xenogenic tests.

[In this figure] Left: Shell of Difflugia acuminata : the xenogenic test (about 300 µm long) made up of mineral particles glued together with secretions from within the cell. (Credit: Deuterostome on wiki); Right: The autogenic test (about 100 µm in diameter) of Arcella discoides , made up of organic plates produced by the cell. (Credit: Frank Fox on wiki)

These shelled amoebas can be collected with the same methods as naked amoebas. However, since the tests could easily break, you have to be careful when examining them under a microscope. The weight of the coverslip may crash the tests of shelled amoebas. Use the microscopic slides with a single concave or add some dots of Vaseline under the corners of the coverslip to provide more space for these creatures.

Where did the name “Amoeba” come from?

Amoeba proteus gets its name from two Greek words; “amoibe” meaning change, and “proteus” meaning Sea God. The Greek meaning describes this microbe as the Sea God Proteus that has a constantly changing shape.

[In this figure] Illustration of Proteus by Andrea Alciato from The Book of Emblems (1531)

I heard that Amoebas can eat human brains. Is it true?

Unfortunately, it is true. Although most amoebas are harmless to human beings, some rare species can be parasitic inside the human body. Naegleria fowleri , colloquially known as the “brain-eating amoeba”, live in freshwater ponds or streams in hot geographic areas. Naegleria fowleri has two flagella (like tails) so it can swim in the water. Most of the time, Naegleria fowleri is free-living and eats bacteria. In some very rare cases, Naegleria fowleri can be inhaled through the nose and travels to the brain, causing a deadly disease called Naegleriasis. Of 154 people known to be infected in the United States from 1962–2021 , only four people have survived.

[In this figure] Naegleria fowleri (commonly referred to as the “brain-eating amoeba”) is a free-living microscopic amoeba. At a certain stage of its life circle, the Naegleria fowleri can swim by two flagella.  (Source: CDC – https://www.cdc.gov/parasites/naegleria/ )

Did you know?

Amoeba Proteus , Euglena , Tardigrade , and Paramecium caudatum are the most frequently studied micro life creatures in classrooms and laboratories.

Monaco Nature Encyclopedia – Amoeba proteus by Giorgio Venturini and Mario Beltramini Amoeba proteus – An in-depth look at the protist, Amoeba proteus Microbus Microworld – world of amoeboid organisms “Amoebas are more than just blobs” by Wim van Egmond Wikipedia “The nature of response to light in Amoeba proteus (Leidy)” by S. O. Mast. Published on Zeitschrift für vergleichende Physiologie volume 15, pages139–147(1931) “Amoebae: Protists Which Move and Feed Using Pseudopodia” by David J. Patterson. Genome size: Genome News Network BioNinja Bionumbers Integrated Taxonomic Information System

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Learn About Amoeba Anatomy and Reproduction

The Life of an Amoeba

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Amoebas are unicellular eukaryotic organisms classified in the Kingdom Protista . Amoebas are amorphous and appear as jelly-like blobs as they move about. These microscopic protozoa move by changing their shape, exhibiting a unique type of crawling motion that has come to be known as amoeboid movement. Amoebas make their homes in salt water and freshwater aquatic environments , wet soils, and some parasitic amoebas inhabit animals and humans.

Key Takeaways: Amoebas

• An amoeba is an aquatic, single-celled protist characterized by a gelatinous body, amorphous shape, and amoeboid movement.
• Amoebas can form temporary extensions of their cytoplasm known as pseudopodia or "false feet" which can be used for locomotion or capturing food.
• Food acquisition is amoebas occurs by a type of endocytosis called phagocytosis. The food source (bacterium, algae, etc.) is engulfed whole, digested, and the waste expelled.
• Amoebas commonly reproduce by binary fission, a process in which the cell divides into two identical cells.
• Some species can cause disease in humans such as amebiasis, amoebic meningoencephalitis, and cornea infections of the eye.

Classification

Amoebas belong to the Domain Eukarya, Kingdom Protista, Phyllum Protozoa, Class Rhizopoda, Order Amoebida, and the Family Amoebidae.

Amoeba Anatomy

Amoebas are simple in form consisting of cytoplasm surrounded by a cell membrane . The outer portion of the cytoplasm ( ectoplasm ) is clear and gel-like, while the inner portion of the cytoplasm (endoplasm) is granular and contains organelles , such as a nuclei , mitochondria , and vacuoles . Some vacuoles digest food, while others expel excess water and waste from the cell through the plasma membrane.

The most unique aspect of amoeba anatomy is the formation of temporary extensions of the cytoplasm known as pseudopodia . These "false feet" are used for locomotion, as well as to capture food ( bacteria , algae , and other microscopic organisms). Pseudopodia may be broad or thread-like in appearance with many forming at one time or one large extension may form when needed.

Amoebas don't have lungs or any other type of respiratory organ. Respiration occurs as dissolved oxygen in the water diffuses across the cell membrane . In turn, carbon dioxide is eliminated from the amoeba by diffusion across the membrane into the surrounding water. Water is also able to cross the amoeba plasma membrane by osmosis . Any excess accumulation of water is expelled by contractile vacuoles within the amoeba.

Nutrient Acquisition and Digestion

Amoebas obtain food by capturing their prey with their pseudopodia. The food is internalized through a type of endocytosis known as phagocytosis . In this process, the pseudopodia surround and engulf a bacterium or other food source. A food vacuole forms around the food particle as it is internalized by the amoeba. Organelles known as lysosomes fuse with the vacuole releasing digestive enzymes inside the vacuole. Nutrients are obtained as the enzymes digest the food inside the vacuole. Once the meal is complete, the food vacuole dissolves.

Reproduction

Amoebas reproduce by the asexual process of binary fission . In binary fission , a single cell divides forming two identical cells. This type of reproduction happens as a result of mitosis . In mitosis, replicated DNA and organelles are divided between two daughter cells . These cells are genetically identical.

Some amoeba also reproduce by multiple fission . In multiple fission, the amoeba secretes a three-layered wall of cells that harden around its body. This layer, known as a cyst, protects the amoeba when conditions become harsh. Protected in the cyst, the nucleus divides several times. This nuclear division is followed by the division of the cytoplasm for the same number of times. The result of multiple fission is the production of several daughter cells that are released once conditions become favorable again and the cyst ruptures. In some cases, amoebas also reproduce by producing spores .

Parasitic Amoebas

Some amoeba are parasitic and cause serious illness and even death in humans. Entamoeba histolytica cause amebiasis, a condition resulting in diarrhea and stomach pain. These microbes also cause amebic dysentery, a severe form of amebiasis. Entamoeba histolytica travel through the digestive system and inhabit the large intestines. In rare cases, they can enter the bloodstream and infect the liver or brain .

Another type of amoeba, Naegleria fowleri , causes the brain disease amoebic meningoencephalitis. Also known as brain-eating amoeba, these organisms typically inhabit warm lakes, ponds, soil, and untreated pools. If N. fowleri enter the body though the nose, they can travel to the frontal lobe of the brain and cause a serious infection. The microbes feed on brain matter by releasing enzymes that dissolve brain tissue. N. fowleri infection in humans is rare but most often fatal.

Acanthamoeba cause the disease Acanthamoeba keratitis. This disease results from an infection of the cornea of the eye. Acanthamoeba keratitis can cause eye pain, vision problems, and may result in blindness if left untreated. Individuals who wear contact lenses most often experience this type of infection. Contact lenses can become contaminated with Acanthamoeba if they are not properly disinfected and stored, or if worn while showering or swimming. To reduce the risk of developing Acanthamoeba keratitis, the CDC recommends that you properly wash and dry your hands before handling contact lenses, clean or replace lenses when needed, and store lenses in a sterile solution.

• "Acanthamoeba Keratitis FAQs" Centers for Disease Control and Prevention , 6 June 2017, www.cdc.gov/parasites/acanthamoeba/gen_info/acanthamoeba_keratitis.html.
• "Naegleria fowleri — Primary Amebic Meningoencephalitis (PAM) — Amebic Encephalitis." Centers for Disease Control and Prevention , 28 Feb. 2017, www.cdc.gov/parasites/naegleria/.
• Patterson, David J. “Tree of Life Amoebae: Protists Which Move and Feed Using Pseudopodia.” Tree of Life Web Project , tolweb.org/accessory/Amoebae?acc_id=51.
• Protista Kingdom of Life
• The Role of Cytoplasm in a Cell
• A Definition and Explanation of the Steps in Endocytosis
• Cytoskeleton Anatomy
• Bacterial Reproduction and Binary Fission
• Euglena Cells
• What Are Prokaryotic Cells? Structure, Function, and Definition
• Biology Prefixes and Suffixes: phago- or phag-
• Differences Between Bacteria and Viruses
• 10 Facts About Cells
• Protists Organisms in the Kingdom Protista
• Binary Fission vs. Mitosis
• Differences Between Plant and Animal Cells
• Common Types of Asexual Reproduction
• Bacteria Shapes
• 7 Facts About Viruses

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Structure, Classification, Examples, and FAQs of Amoeba

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:

Domain: Eukaryota

Kingdom: Amoebozoa

Phylum: Tubulinea

Order: Tubulinida

Family: Amoebidae

Genus: Amoeba

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.

FAQs on Amoeba

1. At what temperature can amoeba die?

Mostly, amoeba does not bother people and can be free living. In some other cases, however, these can infect human beings and cause a host of problems. As we have discussed, the brain-eating amoeba can even cause permanent brain damage and death. Therefore it is important to know how long they can survive in the body. The temperature inside the body is optimum for these to thrive since they are mostly found in damp and wet environments. Most amoebae do not react to high temperatures, but they can be killed in very low temperatures. Freeing can be even useful in killing their offspring.

2. How do amoeba feed?

As can be understood from the structure of amoeba, they do not have hands and legs that can facilitate specific motor abilities. They move around with their whole body and this is also how they feed. They stretch out a pseudopod and engulf their food from all sides, and then digest it. A pseudopod is an arm-like extension that stretches from the body of an amoeba. Amoeba can eat a number of things, ranging from algae, other small plant matter, small bacteria, other protozoans, dead animal matter, fungi, and so on. Pathogenic amoeba can feed on the brains and organs of living beings as well. 

3. How can water be filtered to remove amoeba?

One of the main sources of amoeba infection is through drinking dirty water. It is not entirely possible to find water free from all microorganisms, since amoeba is found pretty much in all wet environments. However, making sure that the water we drink is purified and made fit for consumption is very important. Some varieties of amoeba can infect a person even when they do not drink it. In these cases, it is always advised to use chlorine treatments on water or use distilled water. For drinking purposes, only purified water should be consumed.

4. Is it possible for the amoeba to become larger in size?

While most amoebae are not visible to the naked eye, it is absolutely possible for them to get bigger in size to the point where they become noticeable. Some amoeba can grow up to 2 millimeters in length as well. The size of the amoeba depends on the kind of food they feed on. They get bigger and bigger as they keep feeding. Even when it turns big after engulfing food, it may not be particularly visible to the human eye, since it is colourless and has a very transparent body.

5. Is amoeba useful for the environment?

Amoeba forms a very important part of the ecosystem of the soil and the water they inhabit. They can regulate the number of algae that grows in these places by routinely feeding on them. They also feed on bacteria which may be harmful to the soil or which may consume too much of the algae for the system to be in balance. When amoeba are broken down, the soil derives nutrients from them. Research has been going on to see if amoeba can be employed in medical sciences to feed on harmful bacteria that affect human beings.

6. Is Amoeba Unicellular?

Yes. Amoeba is a single-celled eukaryotic organism that does not have a definite shape due to its pseudopodia.

7. Who Discovered Amoeba?

August Von Rosenhof, who was a German naturalist,  miniature painter, and entomologist discovered amoeba in 1755. He was a significant contribution to the field of modern entomology.

8. Why is Amoeba Called Immortal?

2 days is the general lifespan for an amoeba cell. Yet the daughter cells produced through binary /multiple fission are a replica of the parent cell. This is 1 reason why the amoeba is immortal in technical aspects.

9. At What Level of Organization is an Amoeba?

Ameboid cells will not be considered for a single taxonomic group. But they occur in multiple lineages of eukaryotic organisms. Examples include bacteria, fungi, protozoa, etc.

10. Can Amoeba Regenerate if Cut?

Yes. Amoeboid cells have the capacity of regeneration after cutting into pieces. Each piece cut will regenerate and form a new amoeba. But if a fragment does not have its nuclear components, then it cannot regenerate.

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28.7: Characteristics of Amoebozoa

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Skills to Develop

• Describe representative protist organisms from each of the six presently recognized supergroups of eukaryotes
• Identify the evolutionary relationships of plants, animals, and fungi within the six presently recognized supergroups of eukaryotes

In the span of several decades, the Kingdom Protista has been disassembled because sequence analyses have revealed new genetic (and therefore evolutionary) relationships among these eukaryotes. Moreover, protists that exhibit similar morphological features may have evolved analogous structures because of similar selective pressures—rather than because of recent common ancestry. This phenomenon, called convergent evolution , is one reason why protist classification is so challenging. The emerging classification scheme groups the entire domain Eukaryota into six “supergroups” that contain all of the protists as well as animals, plants, and fungi that evolved from a common ancestor (Figure \(\PageIndex{1}\)). The supergroups are believed to be monophyletic, meaning that all organisms within each supergroup are believed to have evolved from a single common ancestor, and thus all members are most closely related to each other than to organisms outside that group. There is still evidence lacking for the monophyly of some groups.

The classification of eukaryotes is still in flux, and the six supergroups may be modified or replaced by a more appropriate hierarchy as genetic, morphological, and ecological data accumulate. Keep in mind that the classification scheme presented here is just one of several hypotheses, and the true evolutionary relationships are still to be determined. When learning about protists, it is helpful to focus less on the nomenclature and more on the commonalities and differences that define the groups themselves.

Many of the protist species classified into the supergroup Excavata are asymmetrical, single-celled organisms with a feeding groove “excavated” from one side. This supergroup includes heterotrophic predators, photosynthetic species, and parasites. Its subgroups are the diplomonads, parabasalids, and euglenozoans.

Diplomonads

Among the Excavata are the diplomonads, which include the intestinal parasite, Giardia lamblia (Figure \(\PageIndex{2}\)). Until recently, these protists were believed to lack mitochondria. Mitochondrial remnant organelles, called mitosomes , have since been identified in diplomonads, but these mitosomes are essentially nonfunctional. Diplomonads exist in anaerobic environments and use alternative pathways, such as glycolysis, to generate energy. Each diplomonad cell has two identical nuclei and uses several flagella for locomotion.

Parabasalids

A second Excavata subgroup, the parabasalids, also exhibits semi-functional mitochondria. In parabasalids, these structures function anaerobically and are called hydrogenosomes because they produce hydrogen gas as a byproduct. Parabasalids move with flagella and membrane rippling. Trichomonas vaginalis , a parabasalid that causes a sexually transmitted disease in humans, employs these mechanisms to transit through the male and female urogenital tracts. T . vaginalis causes trichamoniasis, which appears in an estimated 180 million cases worldwide each year. Whereas men rarely exhibit symptoms during an infection with this protist, infected women may become more susceptible to secondary infection with human immunodeficiency virus (HIV) and may be more likely to develop cervical cancer. Pregnant women infected with T . vaginalis are at an increased risk of serious complications, such as pre-term delivery.

Euglenozoans

Euglenozoans includes parasites, heterotrophs, autotrophs, and mixotrophs, ranging in size from 10 to 500 µm. Euglenoids move through their aquatic habitats using two long flagella that guide them toward light sources sensed by a primitive ocular organ called an eyespot. The familiar genus, Euglena , encompasses some mixotrophic species that display a photosynthetic capability only when light is present. In the dark, the chloroplasts of Euglena shrink up and temporarily cease functioning, and the cells instead take up organic nutrients from their environment.

The human parasite, Trypanosoma brucei , belongs to a different subgroup of Euglenozoa, the kinetoplastids. The kinetoplastid subgroup is named after the kinetoplast , a DNA mass carried within the single, oversized mitochondrion possessed by each of these cells. This subgroup includes several parasites, collectively called trypanosomes, which cause devastating human diseases and infect an insect species during a portion of their life cycle. T . brucei develops in the gut of the tsetse fly after the fly bites an infected human or other mammalian host. The parasite then travels to the insect salivary glands to be transmitted to another human or other mammal when the infected tsetse fly consumes another blood meal. T . brucei is common in central Africa and is the causative agent of African sleeping sickness, a disease associated with severe chronic fatigue, coma, and can be fatal if left untreated.

Trypanosoma brucei

Watch this video to see T. brucei swimming. https://youtu.be/EnsydwITLYk

Chromalveolata

Current evidence suggests that species classified as chromalveolates are derived from a common ancestor that engulfed a photosynthetic red algal cell, which itself had already evolved chloroplasts from an endosymbiotic relationship with a photosynthetic prokaryote. Therefore, the ancestor of chromalveolates is believed to have resulted from a secondary endosymbiotic event. However, some chromalveolates appear to have lost red alga-derived plastid organelles or lack plastid genes altogether. Therefore, this supergroup should be considered a hypothesis-based working group that is subject to change. Chromalveolates include very important photosynthetic organisms, such as diatoms, brown algae, and significant disease agents in animals and plants. The chromalveolates can be subdivided into alveolates and stramenopiles.

Alveolates: Dinoflagellates, Apicomplexians, and Ciliates

A large body of data supports that the alveolates are derived from a shared common ancestor. The alveolates are named for the presence of an alveolus, or membrane-enclosed sac, beneath the cell membrane. The exact function of the alveolus is unknown, but it may be involved in osmoregulation. The alveolates are further categorized into some of the better-known protists: the dinoflagellates, the apicomplexans, and the ciliates.

Dinoflagellates exhibit extensive morphological diversity and can be photosynthetic, heterotrophic, or mixotrophic. Many dinoflagellates are encased in interlocking plates of cellulose. Two perpendicular flagella fit into the grooves between the cellulose plates, with one flagellum extending longitudinally and a second encircling the dinoflagellate (Figure \(\PageIndex{4}\)). Together, the flagella contribute to the characteristic spinning motion of dinoflagellates. These protists exist in freshwater and marine habitats, and are a component of plankton , the typically microscopic organisms that drift through the water and serve as a crucial food source for larger aquatic organisms.

Some dinoflagellates generate light, called bioluminescence , when they are jarred or stressed. Large numbers of marine dinoflagellates (billions or trillions of cells per wave) can emit light and cause an entire breaking wave to twinkle or take on a brilliant blue color (Figure \(\PageIndex{5}\)). For approximately 20 species of marine dinoflagellates, population explosions (also called blooms) during the summer months can tint the ocean with a muddy red color. This phenomenon is called a red tide, and it results from the abundant red pigments present in dinoflagellate plastids. In large quantities, these dinoflagellate species secrete an asphyxiating toxin that can kill fish, birds, and marine mammals. Red tides can be massively detrimental to commercial fisheries, and humans who consume these protists may become poisoned.

The apicomplexan protists are so named because their microtubules, fibrin, and vacuoles are asymmetrically distributed at one end of the cell in a structure called an apical complex (Figure \(\PageIndex{6}\)). The apical complex is specialized for entry and infection of host cells. Indeed, all apicomplexans are parasitic. This group includes the genus Plasmodium , which causes malaria in humans. Apicomplexan life cycles are complex, involving multiple hosts and stages of sexual and asexual reproduction.

The ciliates, which include Paramecium and Tetrahymena , are a group of protists 10 to 3,000 micrometers in length that are covered in rows, tufts, or spirals of tiny cilia. By beating their cilia synchronously or in waves, ciliates can coordinate directed movements and ingest food particles. Certain ciliates have fused cilia-based structures that function like paddles, funnels, or fins. Ciliates also are surrounded by a pellicle, providing protection without compromising agility. The genus Paramecium includes protists that have organized their cilia into a plate-like primitive mouth, called an oral groove, which is used to capture and digest bacteria (Figure \(\PageIndex{7}\)). Food captured in the oral groove enters a food vacuole, where it combines with digestive enzymes. Waste particles are expelled by an exocytic vesicle that fuses at a specific region on the cell membrane, called the anal pore. In addition to a vacuole-based digestive system, Paramecium also uses contractile vacuoles , which are osmoregulatory vesicles that fill with water as it enters the cell by osmosis and then contract to squeeze water from the cell.

Link to Learning

Watch the video of the contractile vacuole of Paramecium expelling water to keep the cell osmotically balanced.

Paramecium has two nuclei, a macronucleus and a micronucleus, in each cell. The micronucleus is essential for sexual reproduction, whereas the macronucleus directs asexual binary fission and all other biological functions. The process of sexual reproduction in Paramecium underscores the importance of the micronucleus to these protists. Paramecium and most other ciliates reproduce sexually by conjugation. This process begins when two different mating types of Paramecium make physical contact and join with a cytoplasmic bridge (Figure \(\PageIndex{8}\)). The diploid micronucleus in each cell then undergoes meiosis to produce four haploid micronuclei. Three of these degenerate in each cell, leaving one micronucleus that then undergoes mitosis, generating two haploid micronuclei. The cells each exchange one of these haploid nuclei and move away from each other. A similar process occurs in bacteria that have plasmids. Fusion of the haploid micronuclei generates a completely novel diploid pre-micronucleus in each conjugative cell. This pre-micronucleus undergoes three rounds of mitosis to produce eight copies, and the original macronucleus disintegrates. Four of the eight pre-micronuclei become full-fledged micronuclei, whereas the other four perform multiple rounds of DNA replication and go on to become new macronuclei. Two cell divisions then yield four new Paramecia from each original conjugative cell.

Which of the following statements about Paramecium sexual reproduction is false?

• The macronuclei are derived from micronuclei.
• Both mitosis and meiosis occur during sexual reproduction.
• The conjugate pair swaps macronucleii.
• Each parent produces four daughter cells.

Stramenopiles: Diatoms, Brown Algae, Golden Algae and Oomycetes

The other subgroup of chromalveolates, the stramenopiles, includes photosynthetic marine algae and heterotrophic protists. The unifying feature of this group is the presence of a textured, or “hairy,” flagellum. Many stramenopiles also have an additional flagellum that lacks hair-like projections (Figure \(\PageIndex{9}\)). Members of this subgroup range in size from single-celled diatoms to the massive and multicellular kelp.

The diatoms are unicellular photosynthetic protists that encase themselves in intricately patterned, glassy cell walls composed of silicon dioxide in a matrix of organic particles (Figure \(\PageIndex{10}\)). These protists are a component of freshwater and marine plankton. Most species of diatoms reproduce asexually, although some instances of sexual reproduction and sporulation also exist. Some diatoms exhibit a slit in their silica shell, called a raphe . By expelling a stream of mucopolysaccharides from the raphe, the diatom can attach to surfaces or propel itself in one direction.

During periods of nutrient availability, diatom populations bloom to numbers greater than can be consumed by aquatic organisms. The excess diatoms die and sink to the sea floor where they are not easily reached by saprobes that feed on dead organisms. As a result, the carbon dioxide that the diatoms had consumed and incorporated into their cells during photosynthesis is not returned to the atmosphere. In general, this process by which carbon is transported deep into the ocean is described as the biological carbon pump , because carbon is “pumped” to the ocean depths where it is inaccessible to the atmosphere as carbon dioxide. The biological carbon pump is a crucial component of the carbon cycle that maintains lower atmospheric carbon dioxide levels.

Like diatoms, golden algae are largely unicellular, although some species can form large colonies. Their characteristic gold color results from their extensive use of carotenoids, a group of photosynthetic pigments that are generally yellow or orange in color. Golden algae are found in both freshwater and marine environments, where they form a major part of the plankton community.

The brown algae are primarily marine, multicellular organisms that are known colloquially as seaweeds. Giant kelps are a type of brown algae. Some brown algae have evolved specialized tissues that resemble terrestrial plants, with root-like holdfasts, stem-like stipes, and leaf-like blades that are capable of photosynthesis. The stipes of giant kelps are enormous, extending in some cases for 60 meters. A variety of algal life cycles exists, but the most complex is alternation of generations, in which both haploid and diploid stages involve multicellularity. Compare this life cycle to that of humans, for instance. Haploid gametes produced by meiosis (sperm and egg) combine in fertilization to generate a diploid zygote that undergoes many rounds of mitosis to produce a multicellular embryo and then a fetus. However, the individual sperm and egg themselves never become multicellular beings. Terrestrial plants also have evolved alternation of generations. In the brown algae genus Laminaria , haploid spores develop into multicellular gametophytes, which produce haploid gametes that combine to produce diploid organisms that then become multicellular organisms with a different structure from the haploid form (Figure \(\PageIndex{11}\)). Certain other organisms perform alternation of generations in which both the haploid and diploid forms look the same.

Which of the following statements about the Laminaria life cycle is false?

• 1 n zoospores form in the sporangia.
• The sporophyte is the 2 n plant.
• The gametophyte is diploid.
• Both the gametophyte and sporophyte stages are multicellular.

The water molds, oomycetes (“egg fungus”), were so-named based on their fungus-like morphology, but molecular data have shown that the water molds are not closely related to fungi. The oomycetes are characterized by a cellulose-based cell wall and an extensive network of filaments that allow for nutrient uptake. As diploid spores, many oomycetes have two oppositely directed flagella (one hairy and one smooth) for locomotion. The oomycetes are nonphotosynthetic and include many saprobes and parasites. The saprobes appear as white fluffy growths on dead organisms (Figure \(\PageIndex{12}\)). Most oomycetes are aquatic, but some parasitize terrestrial plants. One plant pathogen is Phytophthora infestans , the causative agent of late blight of potatoes, such as occurred in the nineteenth century Irish potato famine.

The Rhizaria supergroup includes many of the amoebas, most of which have threadlike or needle-like pseudopodia (Figure \(\PageIndex{13}\)). Pseudopodia function to trap and engulf food particles and to direct movement in rhizarian protists. These pseudopods project outward from anywhere on the cell surface and can anchor to a substrate. The protist then transports its cytoplasm into the pseudopod, thereby moving the entire cell. This type of motion, called cytoplasmic streaming , is used by several diverse groups of protists as a means of locomotion or as a method to distribute nutrients and oxygen.

Take a look at this video to see cytoplasmic streaming in a green alga.

Foraminiferans, or forams, are unicellular heterotrophic protists, ranging from approximately 20 micrometers to several centimeters in length, and occasionally resembling tiny snails (Figure \(\PageIndex{14}\)). As a group, the forams exhibit porous shells, called tests that are built from various organic materials and typically hardened with calcium carbonate. The tests may house photosynthetic algae, which the forams can harvest for nutrition. Foram pseudopodia extend through the pores and allow the forams to move, feed, and gather additional building materials. Typically, forams are associated with sand or other particles in marine or freshwater habitats. Foraminiferans are also useful as indicators of pollution and changes in global weather patterns.

Radiolarians

A second subtype of Rhizaria, the radiolarians, exhibit intricate exteriors of glassy silica with radial or bilateral symmetry (Figure \(\PageIndex{15}\)). Needle-like pseudopods supported by microtubules radiate outward from the cell bodies of these protists and function to catch food particles. The shells of dead radiolarians sink to the ocean floor, where they may accumulate in 100 meter-thick depths. Preserved, sedimented radiolarians are very common in the fossil record.

Archaeplastida

Red algae and green algae are included in the supergroup Archaeplastida. It was from a common ancestor of these protists that the land plants evolved, since their closest relatives are found in this group. Molecular evidence supports that all Archaeplastida are descendents of an endosymbiotic relationship between a heterotrophic protist and a cyanobacterium. The red and green algae include unicellular, multicellular, and colonial forms.

Red algae, or rhodophytes, are primarily multicellular, lack flagella, and range in size from microscopic, unicellular protists to large, multicellular forms grouped into the informal seaweed category. The red algae life cycle is an alternation of generations. Some species of red algae contain phycoerythrins, photosynthetic accessory pigments that are red in color and outcompete the green tint of chlorophyll, making these species appear as varying shades of red. Other protists classified as red algae lack phycoerythrins and are parasites. Red algae are common in tropical waters where they have been detected at depths of 260 meters. Other red algae exist in terrestrial or freshwater environments.

Green Algae: Chlorophytes and Charophytes

The most abundant group of algae is the green algae. The green algae exhibit similar features to the land plants, particularly in terms of chloroplast structure. That this group of protists shared a relatively recent common ancestor with land plants is well supported. The green algae are subdivided into the chlorophytes and the charophytes. The charophytes are the closest living relatives to land plants and resemble them in morphology and reproductive strategies. Charophytes are common in wet habitats, and their presence often signals a healthy ecosystem.

The chlorophytes exhibit great diversity of form and function. Chlorophytes primarily inhabit freshwater and damp soil, and are a common component of plankton. Chlamydomonas is a simple, unicellular chlorophyte with a pear-shaped morphology and two opposing, anterior flagella that guide this protist toward light sensed by its eyespot. More complex chlorophyte species exhibit haploid gametes and spores that resemble Chlamydomonas .

The chlorophyte Volvox is one of only a few examples of a colonial organism, which behaves in some ways like a collection of individual cells, but in other ways like the specialized cells of a multicellular organism (Figure \(\PageIndex{16}\)). Volvox colonies contain 500 to 60,000 cells, each with two flagella, contained within a hollow, spherical matrix composed of a gelatinous glycoprotein secretion. Individual Volvox cells move in a coordinated fashion and are interconnected by cytoplasmic bridges. Only a few of the cells reproduce to create daughter colonies, an example of basic cell specialization in this organism.

True multicellular organisms, such as the sea lettuce, Ulva , are represented among the chlorophytes. In addition, some chlorophytes exist as large, multinucleate, single cells. Species in the genus Caulerpa exhibit flattened fern-like foliage and can reach lengths of 3 meters (Figure \(\PageIndex{17}\)). Caulerpa species undergo nuclear division, but their cells do not complete cytokinesis, remaining instead as massive and elaborate single cells.

The amoebozoans characteristically exhibit pseudopodia that extend like tubes or flat lobes, rather than the hair-like pseudopodia of rhizarian amoeba (Figure \(\PageIndex{18}\)). The Amoebozoa include several groups of unicellular amoeba-like organisms that are free-living or parasites.

Slime Molds

A subset of the amoebozoans, the slime molds, has several morphological similarities to fungi that are thought to be the result of convergent evolution. For instance, during times of stress, some slime molds develop into spore-generating fruiting bodies, much like fungi.

The slime molds are categorized on the basis of their life cycles into plasmodial or cellular types. Plasmodial slime molds are composed of large, multinucleate cells and move along surfaces like an amorphous blob of slime during their feeding stage (Figure \(\PageIndex{19}\)). Food particles are lifted and engulfed into the slime mold as it glides along. Upon maturation, the plasmodium takes on a net-like appearance with the ability to form fruiting bodies, or sporangia, during times of stress. Haploid spores are produced by meiosis within the sporangia, and spores can be disseminated through the air or water to potentially land in more favorable environments. If this occurs, the spores germinate to form ameboid or flagellate haploid cells that can combine with each other and produce a diploid zygotic slime mold to complete the life cycle.

The cellular slime molds function as independent amoeboid cells when nutrients are abundant (Figure \(\PageIndex{20}\)). When food is depleted, cellular slime molds pile onto each other into a mass of cells that behaves as a single unit, called a slug. Some cells in the slug contribute to a 2–3-millimeter stalk, drying up and dying in the process. Cells atop the stalk form an asexual fruiting body that contains haploid spores. As with plasmodial slime molds, the spores are disseminated and can germinate if they land in a moist environment. One representative genus of the cellular slime molds is Dictyostelium , which commonly exists in the damp soil of forests.

View this site to see the formation of a fruiting body by a cellular slime mold.

Opisthokonta

The opisthokonts include the animal-like choanoflagellates, which are believed to resemble the common ancestor of sponges and, in fact, all animals. Choanoflagellates include unicellular and colonial forms, and number about 244 described species. These organisms exhibit a single, apical flagellum that is surrounded by a contractile collar composed of microvilli. The collar uses a similar mechanism to sponges to filter out bacteria for ingestion by the protist. The morphology of choanoflagellates was recognized early on as resembling the collar cells of sponges, and suggesting a possible relationship to animals.

The Mesomycetozoa form a small group of parasites, primarily of fish, and at least one form that can parasitize humans. Their life cycles are poorly understood. These organisms are of special interest, because they appear to be so closely related to animals. In the past, they were grouped with fungi and other protists based on their morphology.

The process of classifying protists into meaningful groups is ongoing, but genetic data in the past 20 years have clarified many relationships that were previously unclear or mistaken. The majority view at present is to order all eukaryotes into six supergroups: Excavata, Chromalveolata, Rhizaria, Archaeplastida, Amoebozoa, and Opisthokonta. The goal of this classification scheme is to create clusters of species that all are derived from a common ancestor. At present, the monophyly of some of the supergroups are better supported by genetic data than others. Although tremendous variation exists within the supergroups, commonalities at the morphological, physiological, and ecological levels can be identified.

Art Connections

Figure \(\PageIndex{8}\): Which of the following statements about Paramecium sexual reproduction is false?

• The conjugate pair swaps macronuclei.

Figure \(\PageIndex{11}\): Which of the following statements about the Laminaria life cycle is false?

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The Structure and Life Cycle of Amoeba (With Diagram)

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Systematic Position

Phylum: Protozoa

Class: Rhizopodea

Order: Amoebida

Genus: Amoeba

Species: proteus

Plasma lemma is a very thin, delicate and elastic cell membrane of amoeba. It is composed of a double layer of lipid and protein molecules. This membrane is selectively permeable and regulates exchange of water, oxygen and carbon dioxide between the animal and the surrounding medium. From the outer surface of plasma lemma, small ridge like projections arise which helps in fixing the organism to the substratum.

The cytoplasm is differentiated into Ectoplasm and endoplasm. The ectoplasm forms the outer and relatively firm layer lying just beneath the plasma lemma. It is a thin, clear (non-­granular) and hyaline layer It is thickened into a hyaline cap at the advancing end at the tips of pseudopodia.

The ectoplasm has a number of conspicuous longitudinal ridges. Due to the presence of longitudinal ridges in the ectoplasm, it is considered as a supporting layer. The endoplasm forms the main body mass completely surrounded by the ectoplasm. It is granular heterogeneous fluid. The endoplasm is made up of an outer, relatively stiff plasmagel and a more fluid inner plasmasol.

The plasmagel is granular and more solid but its granules show no movements. Besides granules, endoplasm contains a number of important inclusions such as nucleus, contractile vacuole, food vacuoles, mitochondria, Golgi apparatus, fat globules and plate- like or bi-pyramidal crystals. Endoplasm contains a number of organelles or structures suspended in it. These organelles are nucleus, contractile vacuole, food vacuoles and water globules.

In Amoeba proteus, there is a single conspicuous nucleus. The nucleus appears as a biconcave disc in young specimens but it is often folded and convoluted in older specimens. The nucleus has a firm nuclear membrane or nuclear envelope and contains a clear achromatic substance with minute chromatin granules or chromidia distributed uniformly near the surface. The nucleoplasm is small in quantity. Such a nucleus is called massive or granular nucleus.

Contractile vacuole:

The outer part of the endoplasm near the posterior end contains a clear, rounded and pulsating vacuole filled with a watery fluid. This vacuole, called the contractile vacuole, is enclosed by a unit membrane.

Food vacuoles:

Numerous food vacuoles are scattered in the endoplasm. These are non- contractile and of different size. Each food vacuole contains a morsel of food under digestion. The food vacuoles are carried about by the movements of the endoplasm. Digestion of food takes place inside the food vacuole.

Water globules:

These are several small, spherical, colourless and non-contractile vacuoles filled with water.

Life cycle of Amoeba :

Reproduction in amoeba is a periodic process taking place at intervals. Reproduction in amoeba chiefly occurs by asexual method, i.e., by binary fission, multiple fission and sporulation.

(i ) Binary fission:

Under un-favourable conditions amoeba reproduces by formation of spores internally. It starts with the breakdown of nuclear membrane and release of chromatin blocks into the cytoplasm. Each chromatin blocks acquires a nuclear membrane and becomes a small daughter nuclei. The newly formed nuclei get surrounded by cytoplasm to form amoebulae.

The peripheral cytoplasmic layer of amoebulae forms a tough and resistant spore-membrane or spore case (fig. 9.9). About 200 such spores are formed inside a single parent amoeba. Finally the body of parent amoeba disintegrates to release the spores. The spore remain inactive for some time and on getting favourable conditions each spore forms a young amoeba.

In un-favourable conditions, amoeba divides by multiple fission. It withdraws its pseudopodia, becomes spherical and secretes three layered cyst around itself. Its nucleus undergoes repeated mitosis division forming 500- 600 daughter nuclei. Each daughter nucei gets surrounded by mass of cytoplasm and divides into minute amoebulae. On getting favourable conditions the cyst ruptures to release the amoebulae which soon grows into adult amoeba (fig. 9.10-9.11).

Amoeba has tremendous power of regeneration. If it is cut into small pieces, each piece regenerates into a new amoeba, however, a piece without nuclear fragment does not regenerate.

Related Articles:

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Amoeba: Diagram and Characteristics

Amoebae are microscopic unicellular organisms that belong to the family Amoebidae. They are freshwater organisms found at the bottom of ponds and streams in the decaying vegetation. They can be identified by their shape changing ability from their cytoplasmic extensions called pseudopodia.

Classification

Well-labelled diagram of amoeba.

Characteristics

• August Johann Rösel von Rosenhof, a German naturalist was the first person to reference amoebae in 1755.
• The distinguishing feature of the amoeba is its ability to change shapes with the help of cytoplasmic extensions called pseudopodia.
• Pseudopodia, also called false feet, are tubular extensions that are rounded at the end and help in movement of the organism.
• The amoeba is made up of jellylike cytoplasm which differentiates to form a thin outer plasma membrane, a stiff layer of clear ectoplasm just inside the plasma membrane and a central endoplasm that is granular in nature.
• The endoplasm houses a granular nucleus, food vacuoles and a contractile vacuole.
• The amoeba possesses no mouth or anus.
• They feed by surrounding their cytoplasmic extensions around the food particle and then forming a vacuole. Enzymes are then secreted to digest the food particles.
• The contractile vacuole functions to remove excess water from the amoeba and thus maintain the osmotic pressure of the organism.
• The mode of reproduction is asexual and it divides by binary fission.
• The amoebas can survive in extreme environmental conditions by undergoing encystation . It is the phenomenon of secreting a cyst membrane all around by becoming circular and losing all water. The amoebas get back to their original shape once the surroundings improve.

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Nov 08, 2022, 16:45 IST

An amoeba is a unicellular organism that can change its shape. They are usually found in bodies of water such as lakes, ponds, and slow-flowing rivers. Sometimes these single-celled organisms can get into the human body and cause various illnesses. One of the first reports referring to amoeba dates can be traced back to the 18th century. A German naturalist named August Johann Rösel von Rosenhof discovered the specimen in 1755 and made detailed illustrations of it.

Structure of Amoeba

Typically, most amoebae are characterized by the following characteristics:

• Movement occurs through pseudopodia, where the cytoplasm pushes the plasma membrane outwards or inwards, forming blunt finger-like projections.
• In one particular case, there may be several pseudopodia. Therefore its shape changes rapidly.
• The structure of amoeba primarily includes three parts – cytoplasm, plasma membrane, and nucleus.
• Cytoplasm can be divided into two layers – outer ectoplasm and inner endoplasm.
• The plasma membrane is a thin, double-layered membrane composed of protein and lipid molecules.
• Amoeba also contains the other cell organelles such as mitochondria, contractile vacuole, Golgi apparatus, and fat globules.
• An amoeba consumes food either through the process of pinocytosis or phagocytosis.
• The process of reproduction is through asexual means such as binary fission.
• The lifespan of a typical amoeba is two days, but because it undergoes binary fission, the resulting daughter cells are the same as its parent cell, so technically, amoeba can be described as immortal.
• When living conditions are not ideal, the amoeba can essentially turn into a protective ball called a microbial cyst. When living conditions improve, it can revert back to the trophozoite stage, where it can start feeding again.

Classification of Amoeba

Traditionally, amoebae are grouped under the kingdom Protista because they are not classified as a plant, animal, or fungus. However, amoebae fall under eukaryotes because they have a true nucleus. Although not technically a true amoeba, Naegleria fowleri, more commonly known as brain-eating amoeba, is an amoeboid organism that can burrow its way into the human body through the nose. It mainly feeds on neurons, destroying brain tissue. Not surprisingly, the mortality rate of this infection is high at 97%.

Frequently Asked Question (FAQs)

Q1. What is the size of an amoeba?

Ans. The amoeba size tends to vary greatly, from 2.3 micrometers to up to 2 00,000 micrometers. The marine amoeboid Massisteria voersi size is just 2.3 to 3 micrometers in diameter.

Q2. Where does amoeba grow?

Ans. They live in ponds, soil, lakes, rivers, and forests. If you scoop up a handful of dirt in the woods, it will contain hundreds of thousands of amoebas.

Q3. Do amoebas have hearts?

Ans. No, an amoeba can not grow a heart. Amoeba is single-celled organisms. Hearts only exist in complex, multi-celled organisms that belong to the taxonomic kingdom Animalia. Hearts are made up of muse tissue.

Q4. Where do most amoeba live?

Ans. They can be found in warm fresh water, such as rivers and lakes. Geothermal water, such as hot springs. Warm water discharge from the industrial or the power plants.

Q5. How many cells does an amoeba have?

Ans. One cell

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Amoeba: Structure, Osmoregulation and Sensitivity

In this article we will discuss about Amoeba:- 1. Introduction to Amoeba 2. Etymology of Amoeba 3. Structure 4. Osmoregulation 5. Sensitivity.

• Sensitivity of Amoeba

1. Introduction to Amoeba:

The genera Amoeba included under the naked amoebas by Ruppert and Barnes (1994), was first discovered by Rossel Von Rosenhof in 1755. Later in 1962, H. I. Hirschfield provided a detailed account of its biology. Amoeba serves as an interesting and suitable material, and is universally studied as an introduction to protozoa.

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The genus Amoeba has a single nucleus. Pseudopodia may be extensions of considerable size (.Amoeba proteus) or small, wart-like eleva­tions (A. verrucosa). Flagellated stages are unknown, but encystment has been reported in some species. There are several species of Amoeba, the most commonly studied species is Amoeba proteus.

2. Etymology of Amoeba :

Greek: amoibe, change.

The species name proteus is after the mythological Greek Sea God – Proteus, known for his power to change form variously.

Habit and Habitat of Amoeba:

A. proteus is a minute, free living form, occurring abundantly in the bottom of fresh water ponds, ditches, lakes and spring-pools. They are always found in association with aquatic vegetation.

External Structure:

Body resembles a tiny mass of irregular jelly and measures about 0-25 mm in diameter, but some large species (A. proteus) may reach a diameter of 0-5 mm (Fig. 1.6). The irregular shape of the body is due to constant throwing of its own surface as pseudopodium.

Externally the body is cove­red by a very thin, clear, elastic and semi­permeable layer of protoplasm, called the cell membrane or plasma membrane or plasma lemma. The thickness of plasma lemma may be between 0.5 µm to 2 µm. The existence of a very thin and flexible pellicle, covering the plasma lemma has been reported.

Internal Structure:

Inside the plasma membrane are placed a single nucleus and cytoplasm. Nucleus is disc-like and bicon­cave and occupies no fixed position in the endoplasm. Cytoplasm is differentiated into ectoplasm and endoplasm.

The ectoplasm is less extensive, gel in nature and non-granular, though in electron microscopy it shows thread and particles. The endoplasm is divi­sible into two parts — the stiff region beneath the ectoplasm, called plasmagel and an inner-fluid part called plasmasol. Embedded in the plasmasol are the following structures.

(a) Contractile Vacuole:

Single large and transparent vacuole, containing a space filled with a watery fluid. It gradually increases in size, travels to the surface and suddenly bursts to release its contents in the surroun­ding water and disappears. A new contractile vacuole is formed later.

(b) Food Vacuole:

One or more, spherical, non-contractile food vacuoles, containing water and food particles, are present at diffe­rent phases of digestion.

(c) Water Vacuole or Globule:

Several of these occur as transparent colourless drops which do not change in size.

(d) Stored Food:

Numerous granules of reserve food material of the nature of fats and carbohydrates are present.

(e) Mitochondria:

Present in the form of rods or more or less oval shape with tubular cristae.

(f) Crystals:

Different sizes and shapes of crystals are seen which are probably metabolic wastes.

Functions of the above mentioned struc­tures are given below.

Plasma Lemma:

Being the outer mem­brane it retains the inner contents. It is per­meable to respiratory gases and water. It plays important role in pseudopodia forma­tion and food capture.

It is responsible for main­taining the shape and also protects the inner parts.

It is the matrix, within which different organelles including the nucleus remain suspended.

Contractile Vacuole:

It is involved in osmoregulation, respiration and excretion.

Food Vacuoles:

These vacuoles are rela­ted with nutrition.

Water Vacuoles:

These control the water balance of the body.

Mitochondria:

These are considered as the ‘power house’ of the cell and are the seats of cellular respiration.

Locomotion :

Amoeba moves about by creeping and remains in direct contact with a substratum. This is performed by the production of finger-like projections called pseudopodia and the movement is called amoeboid move­ment.

Nutrition :

Nutrition in Amoeba is holozoic or zoo-trophic or heterotrophic. In this method animals and plants smaller than the body of the protozoa are used as food.

Respiration:

Dissolved oxygen in water enters the body through the general body surface and the carbon dioxide produced by oxidation goes out through the body surface by the process of diffusion.

Excretion :

The excretory bi-products are urea and uric acid. They pass out of the body through the plasma lemma by the process of diffusion.

4. Osmoregulation of Amoeba :

Water enters into the body by endosmosis through the general body surface. This water along with the water that is taken in during food intake is collected by the con­tractile vacuole. A contractile vacuole is about 20-30 µm in diameter and contains accumulated fluid which is less dense than the surrounding cytoplasm. A fully expan­ded vacuole contracts and the fluid is forced out through the cell surface.

As soon as the old vacuole disappears, its place is taken up by a new vacuole. The rate of contraction of a vacuole varies from a few seconds to several minutes. Schneider (1960) observed that the wall of a contractile vacuole is provided with contractile fibrils which bring about the con­traction of the vacuole.

Water discharged to the exterior by vacuoles contains traces of metabolic wastes and respiratory gases. The vacuolar activity increases when distilled water is injected and stops when the animal is put in salty water or is treated with potas­sium cyanide.

5. Sensitivity of Amoeba :

Amoeba has no nervous system and spe­cial sense organs to perceive the stimuli, although it is highly sensitive. It gives nega­tive response to mechanical obstacle. When pricked or touched by a rod it turns to avoid the obstacle. However, it is able to distin­guish between a particle of food and a non­food particle. It moves away from salt, sugar, acid and alkali to which it is unaccustomed.

Amoeba also avoids darkness as well as strong light, but shows positive response towards normal or diffused light. It becomes globular if an electric current is passed in the water which contains it. Even, extreme dis­turbance or injury causes it to become spher­ical and it remains motionless for some time.

It is most active at an optimal temperature of 20-25°C. Lower temperature retards its activity. Thus, the responses of Amoeba are so oriented so as to benefit the animal to the maximum.

Related Articles:

• Morphology of Amoeba | Protozoa | Microorganisms | Zoology
• Difference between Amoeba and Paramoecium
• How do Amoeba Reproduce? | Protozoa | Microorganisms | Zoology
• Term Paper on Amoeba | Protozoa | Microorganisms | Zoology

Table of Contents

Introduction

Amoeba is a type of microscopic organism belonging to the kingdom Protista. It is a unicellular organism that exhibits several distinct characteristics. Amoebas are classified under the phylum Amoebozoa and are commonly found in various aquatic environments such as freshwater, soil, and marine environments.

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Structure of Amoeba

Characteristics of Amoeba

• Shape: Amoeba has a distinct shapeless or irregular shape, often resembling a blob or a droplet of water.
• Locomotion: It moves by extending finger-like projections called pseudopodia , which help in crawling and capturing food.
• Feeding: Amoeba is a heterotrophic organism and feeds on microscopic organisms like bacteria and algae. It engulfs its food by forming temporary food vacuoles.
• Respiration : Amoeba performs respiration through diffusion, where oxygen enters and carbon dioxide exits through its cell membrane.
• Reproduction: Amoeba reproduces asexually by a process called binary fission , where it divides into two identical daughter cells.
• Contractile Vacuole: Amoeba has a contractile vacuole that helps regulate water balance by collecting and expelling excess water from the cell.
• Sensory Organelles: Amoeba lacks specialized sensory organs but can sense changes in its environment, such as light and temperature.
• Adaptability: Amoeba is capable of adapting to different environments and can form cysts when conditions become unfavorable, protecting itself until favorable conditions return.

It’s important to note that while these characteristics generally apply to most Amoebas, there can be variations within the group due to the diverse species of Amoeba.

Biology Articles Cytoplasm Protoplasm Nutrition in Amoeba

Amoebas are characterized by their shapeless and flexible bodies, which lack a fixed form. They have a single-celled structure , consisting of a cell membrane, cytoplasm, and a nucleus. One of the unique features of Amoebas is their ability to form temporary extensions called pseudopodia, or “false feet,” which they use for movement and capturing prey.

Amoebas are heterotrophic organisms, meaning they obtain their nutrition by ingesting other organisms or organic matter. They feed through a process called phagocytosis, in which they surround and engulf their prey, forming a temporary food vacuole. Inside the food vacuole, the prey is digested by enzymes, and the nutrients are absorbed into the Amoeba’s cytoplasm.

Reproduction in Amoebas primarily occurs through asexual means, such as binary fission, where the Amoeba divides into two identical daughter cells. Under certain conditions, Amoebas can also engage in sexual reproduction through a process called conjugation, where genetic material is exchanged between two individuals.

Amoebas play an important role in the ecosystem as decomposers, breaking down organic matter and recycling nutrients. They also serve as a food source for other organisms. However, certain species of Amoebas, such as EntAmoeba histolytica, can cause diseases in humans and animals, leading to infections and health issues.

Frequently Asked Questions on Amoeba

What is the habitat of amoeba.

Amoebas are found in a variety of freshwater, marine, and terrestrial habitats. They are commonly found in freshwater bodies such as ponds, lakes, and streams, where they inhabit the sediment or attached to submerged surfaces.

How does Amoeba obtain its food?

Amoebas are heterotrophic organisms and obtain their food by engulfing other microorganisms and organic particles. They extend their pseudopodia around their prey, forming a food vacuole, and then release enzymes to digest the captured food.

What is the reproduction process of Amoeba?

Amoebas reproduce primarily through a process called binary fission, where the parent cell divides into two identical daughter cells. They can also engage in sexual reproduction through conjugation, where genetic material is exchanged between two individuals.

Can Amoebas cause diseases in humans?

Yes, some species of Amoebas can cause diseases in humans. For example, the species EntAmoeba histolytica can cause amoebic dysentery, a gastrointestinal infection that leads to symptoms such as diarrhea, abdominal pain, and fever.

Are Amoebas harmful to humans?

While most Amoebas are harmless, certain species can be harmful to humans. For instance, Naegleria fowleri is a rare but deadly Amoeba that can cause a severe brain infection called primary amebic meningoencephalitis (PAM) if it enters the body through the nose.

How do Amoebas move?

Amoebas move by extending their pseudopodia, which are temporary extensions of their cytoplasm. They can change the direction of movement by extending pseudopodia in different directions.

Can Amoebas survive in extreme environments?

Amoebas are versatile organisms and can adapt to various environmental conditions. Some species can survive in extreme environments such as hot springs, frozen tundra, and even acidic or alkaline conditions.

What is the role of Amoebas in the ecosystem?

Amoebas play a vital role in the ecosystem as decomposers. They feed on organic matter, including dead plants and animals, and help in the breakdown and recycling of nutrients, contributing to the nutrient cycle in the environment.

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Biological, Economical, And Ecological Importance of Amoeba

Well! There’s a lot of importance about amoeba in our day to life. Here in this post, you’ll learn some of the most awesome importance of Amoeba.

Amoeba is really one of the simplest and primitive animalcules present on earth. It is the most popular free-living protozoan.

The most unique aspect of amoeba anatomy is the formation of temporary extensions of the cytoplasm known as pseudopodia or false feet that helps it in locomotion.

Their body is like a small spot of protoplasm resembling a tiny drop of jelly that has all the cell organelles to perform the movements and other mandatory activities.

There are several species of Amoeba, but the most commonly studied one is the large freshwater species  Amoeba proteus  which is an easy to find and useful experimental animal.

You can find Amoeba proteus on the bottom mud or on the underside of aquatic vegetation in freshwater ponds, ditches, lakes, springs, pools, and in slow-running streams as well.

Other Amoeba species can be found in hot springs, soil, mud, warm water coming from industrial plants, poorly maintained swimming pools, and at water heaters kept at temperatures below 117°F (47°C).

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Biological Importance of Amoeba

Economical importance of amoeba, ecological importance of amoeba.

1. Amoeba depicts body organization consisting of a protoplasmic mass or a single cell into a complete organism. Their cytoplasm and cellular contents are well-enclosed within a cell membrane. They have their genetic material in the nucleus with other cell organelles. This unicellular organism is so advanced that it executes all of the cellular functions including energy production and protein transport while taking care of respiration, movements, excretion, feeding, digestion, etc. all with a single cell.

2. The binary-fission of Amoeba is so straight forward and simple that it gives us a clear-cut understanding of the mitotic cell division happening in the animal kingdom. Binary fission is a process of asexual reproduction that occurs when the cell divides into two daughter cells. It is the most common mode of reproduction employed by Amoeba.

3. The responses of Amoeba represent the early beginning of sensitivity in animals. They have the simplest cell signaling patterns that helps detect the external and internal stimuli in the environment via. chemotaxis, phototaxis, thermotaxis, etc. These help in understanding the basics of cell signaling and stimuli patterns in the biological world.

4. Different organelles of Amoeba give the first indication of division of labour concerning the vital activities that defines a living organism. They have contractile vacuole, nucelus, cell membrane, proteins, endoplasmic reticulum, mitochondria, food vacuole, etc. and each of this is confined to its type of work that defines each and every function of life.

5. There are a great number of chromosomes present in the nucleus of Amoeba. Amoeba chromosomes are extremely small, and rough estimates of chromosome numbers are difficult to obtain to date. However, as many as 500-1000 small chromosomes have been observed in the nucleus of Amoeba proteus . This greatly suggests the occurrence of a wide variety of isolated genes in the animal kingdom, which in the higher animals are located in chromosomes.

6. The anatomy of Amoeba gives a faint idea regarding the anatomical structures of higher animals. For example: the food cup is comparable to the buccal cavity, food vacuole to gut, pseudopodia to legs, contractile vacuole to urinary bladder or kidney, and so on.

7. The absence of mitochondria in anaerobic amoebae explains how these anaerobic amoebae have developed mitosomes which are related to mitochondria and are thought to be highly altered versions of the same. This is the case for Entamoeba histolytica and a free-living amoeba, Mastigamoeba balamuthi, and more. This shows how biological organisms have developed various alternatives within themselves to fit their environment.

8. The pseudopodial movement of the amoeba helps it to move, locomote, and feed on its food. Pseudopodia are those short-lived outward projections of the cytoplasm that help the amoeba to grip a surface and propel themselves forward. These have explained the working of the various cells of the biological body like that of macrophages, leucocytes, etc.

9. An amoeba grows by gaining energy through absorbing food or making its own food from sunlight. This growth in one of the most primitive organisms like the amoeba, shows the basics of cellular growth in living organisms in order to withstand small changes in the environment. Scientists refer to this phenomenon as robustness and it is one of the distinct features that separate living systems from non-living materials and artificial machines.

10. Amoeba has its build-in pumping system inside the cell, called “contractile vacuole”. Its function is to regulate the water content of the cell. Without the contractile vacuoles, the amoebae cells may burst during hypotonic or hypertonic situations. Undoubtedly, it is a very important organelle with an essential function to the amoeba. This shows one of the most primitive mechanisms of how every biological cell has some kind of a protective mechanism that prevents the cell from absorbing too much water and possibly rupturing.

11. Amoeba shows encystment as a protective covering to save themselves. The main functions of cysts are to protect against adverse changes in the environment such as nutrient deficiency, desiccation, adverse pH, and low levels of O 2 , they are sites for nuclear reorganization and cell division, and even they are the infectious stage between hosts. This cyst formation shows how in the biological world organisms developed a way of protecting their cells and carry on their life history.

12. Amoeba proteus has 290 billion base pairs of DNA in its nucleus. This makes it 100 times larger than the human genome which only consists of about 3 billion base pairs of DNA. Amoeba dubia has about 670 billion base pairs of DNA. In biology, this explains the extreme replication of the same set of genes forming polyploid organisms.

1. Amoeba plays a key role in maintaining the fertility of the soil and they are also referred to as the friends of farmers. They add ammonium (NH 4+ ) to the soil thus providing nitrogen to be utilized by the plants.

2. Amoeba by feeding on the excess of bacteria present in the soil and then by digesting and excreting the bacterial wastes maintains the proper flow of nutrients in the soil, thus promoting the various agricultural practices.

3. Certain amoeba species can stay in close association with certain strains of bacteria, just like the amoeba Dictyostelium discoideum that stays in association with Burkholderia bacteria. This helps in the rapid spread of Burkholderia along with the amoeba in the agricultural field. This bacteria has been developed as a biopesticide for protecting crops against fungal diseases and has the potential to be a bioremediation agent for breaking down recalcitrant herbicides and pesticides. Thus, helping in agriculture overall.

4. Amoeba like Dictyostelium discoideum , during the scarcity of food, congregate and merge into a many-celled slug where many other bacterias also get packed. This slug gets a good place and forms a ball of spores that gets blown off due to wind pressure and reaches some other location in the field. When the spores land somewhere new, the bacteria along with the amoeba gets released, creating a ready supply of food for amoeba there. Dictyostelium discoideum can engulf and keep the bacteria within the cell. And, as agriculture seems to need bacterial survival and it is possible as various bacteria can live and replicate inside D. discoideum , making farming a lot easier.

5. Most of the economic impact of amoeba is secondary, the most obvious being that a few species make humans ill. Many people at some point encounter amoebic dysentery caused by the amoeba Entamoeba histolytica . Rarer cases of amoebic illness are caused by the amoeba Naegleria fowleri , the organism responsible for amoebic meningitis.

6. Amoeba like Entamoeba histolytica is a genus consisting of Amoebozoa. They are found in the intestines of animals they infect as internal parasites or commensals of animals. They can also cause amoebiasis in humans.

7. They enhance the rates at which bacteria decompose dead organic matter. Amoebas also excrete nitrogen and phosphorus, in the form of ammonium and orthophosphate, as products of their metabolism. And so, the presence of amoebae in soils enhances plant growth.

8. Bacteria, viruses, and parasites can be dangerous to other living creatures in soil or water plants. Biocides and pesticides can help you get rid of these microorganisms but most biocides are chemicals, many of which are toxic. So, promoting the growth of various amoeba can help get rid of these microorganisms as amoeba can happily feed on them.

1. Amoebae are an important part of the soil ecosystem. They regulate the bacterial population by feeding on them. It is possible that more than 60% of the decrease in the bacterial population of the agriculture field is due to the presence of naked amoeba, which is amoeba without a shell. Thus, it helps in balancing the abundance of bacteria in the soil and so balances the ecology and the environment as well.

2. The amoeba is considered as a primary consumer in the food web of any ecosystem. This type of organism does not produce its own food like plants, rather it obtains its food from other microorganisms or in some species by being photosynthetic. And, it is also important to note that all the food webs begin at the microscopic level and Amoeba is one of those simplest living organisms that play a key role at the beginning.

3. Amoeba is an ammonotelic animal because it excretes nitrogenous wastes in the form of Ammonium. The microorganisms they eat contain a much higher carbon to nitrogen proportion, so they can discharge the overabundance nitrogen as ammonium (NH4+). Ammonium is utilized by plants or other organisms by getting the nitrogen content from the soil. This nitrogen content thus enters the biochemical nitrogen cycle for functioning in the nucleic acids, amino acids, or chelating porphyrin rings for particles like hemoglobin or chlorophyll, and many more biological compounds.

4. Amoebae are very much essential for fulfilling the nutrient requirements of the soil. They do so by recycling nutrients in the soil. The bacteria take the nutrient that is available in the soil and when these bacteria are consumed by the amoeba, nutrients are released back into the soil due to amoeboid excretion. This brings the nutrients available to the plants.

5. Amoeba can engulf photosynthetic bacteria to become photosynthetic itself. Scientists have revealed in 2016 a fact that amoeba can engulf a bacterium and keep it within its cell alive and will eventually utilize the bacterial genes for the purpose of photosynthesis. This acquired photosynthetic power by the various heterotropic amoebae can help the organisms convert carbon dioxide into oxygen and sugar via solar energy. Thus the amoeba helps the ecosystem by being the simplest primary consumers.

6. Amoeba maintains bacterial growth in the soil. Bacteria actively promotes the decomposition of waste in soil and aquatic ecosystems. Moreover, they can also control the presence of those fungi that harms the plants. The amoebae attach to the surface of fungal hyphae and generate enzymes that eat through the fungal cell wall. The amoeba then sucks dry or engulfs the cytoplasm inside the fungal cell before moving onto its next victim.

7. Amoebae can enter deep into the soil reaching the groundwater systems from the soil surface. There are various amoebae known so far that can be seen in the deep groundwater systems, especially where the bacterial populations get to high densities. Thus, they help in better controlling the bacterial populations in soils at the deepest level possible which causes a positive impact on the ecology.

8. Amoeba plays a key role in the regulation of algae present in a pond or stagnant pool environment directly through their natural process of survival. They also feed on those overpopulating bacteria species that may be consuming too many algae within an environment. Thus, the amoeba helps in maintaining the overall balance in its environment.

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This post is written by Ronit Dey. Ronit Dey is a graduate in Zoology. Here, he has started sharing a lot of things that he has seen, learned, and researched so far related to Zoology. You can read more about here at the About page.

An amoeba refers to a single cell organism that is of a eukaryotic nature. Furthermore, this particular organism lacks a definite shape. Moreover, the movement of the amoeba cell takes place by means of pseudopodia. The temporary projections of the amoeba cell are pseudopodia or pseudopods, which literally means “false feet”. Also, the use of pseudopodia takes place by means of locomotion. The extremely small amoeba size cytoplasm contains the organelles. This cytoplasm is enclosed by a cell membrane. By using a process of phagoctyosis, the amoeba obtains its food. The digestion of the food particles takes place in its vacuole. Moreover, the reproduction of this single-cell creature takes place via mitosis.

Amoeba Meaning

Amoeba , in particular, refers to the genus  Amoeba  (true amoeba ). The amoeba classification takes place in the family Amoebidae. Also, the class in amoeba classification takes place in Tubulinea.

This genus comprises of protists that are single-celled. Furthermore, amoebas are free-living organisms. The extremely small amoeba size still requires food to survive. As such, this extremely small organism feed mainly feed on detritus, protists, and bacteria .

The amoeba classification takes place in the protoplasmic movement.  Furthermore, the cytoplasmic projections of this extremely small organism are called pseudopodia (false feet). Some references consider this single-cell organism with the capability to change cell shape and form pseudopods whose extension and retraction is possible.

The initial amoeba classification was under the subphylum Sarcodina. However, with the analysis of modern molecular phylogenetic, experts found the subphylum to be monophyletic.

Most of the free-living freshwater amoebae are commonly available in lakes, ditches, or ponds. Moreover, their size is microscopic in nature.

Members of this taxonomic group were not the result of a common ancestor. Therefore, one cannot consider it as a single group.

As such, the term  amoeba  includes those that have the characteristics of amoeboid. Some of the medically notable amoeboid protists examples are Naegleria and Entamoeba histolytica.

Experts commonly find them in decaying vegetation. However, experts are able to obtain them with ease.  As such, they are a common subject of study and are stored in laboratories.

Shape of Amoeba

The amoeba size tends to vary greatly; from 2.3 micrometres to up to 2, 00,000 micrometres. The marine amoeboid Massisteria voersi size happens to be just 2.3 to 3 micrometres in diameter. On the other extremity lies the shells of deep-sea xenophyophores whose size can go up to 20 cm in diameter.

However, one may see with the naked eye some species like the “giant amoebae” Pelomyxa palustris and Chaos carolinense. Also, at the trailing edge of the cell there exists one disc-shaped retractor.

The movement of the amoebas takes place due to protoplasmic flow. Furthermore, a change continues to happen in their appearance. That is why some experts believe that amoebas do not retain the same shape again in their entire lifetime.

However, it is not a completely amorphous form as many people generally believe. Moreover, the determination of the approximate shape takes place by genus and species. On the basis of a rough division, there are of the following three types.

• It always gives, at a time, one wide temporary foot. Furthermore, it becomes slugged or oval as a whole. Also, normally the travel’s direction will be wider.
• Gives two feet that are temporary. Furthermore, this is the most amebic figure and its shape intensely changes.
• Those that give plenty of feet that are temporary and are of the thin rod-shaped type.

It is necessary that the differences mentioned above are species differences. This is because there are things that change type on the basis of environmental circumstances and conditions.

Furthermore, its classification takes place by the temporary feet and the structure of the nucleus. However, even within the same species, there are various differences depending on lineage, and there seem to be difficulties.

Morphology of Amoeba

The typical structure of amoebae is that of a eukaryotic cell. Furthermore, this structure is that of various organelles, nucleus, and cytoplasm. Moreover, the division of cytoplasm takes place into a central granular mass. Experts call this granular mass the endoplasm while the ectoplasm is the lighter outer layer.

The movement of this single-cell creature takes place by the extension of the cytoplasm outward. Thereby, the amoeba forms extensions that are similar to tentacles. These tentacle-like extensions are what experts call false feet or pseudopods that wrap the food.

How do Amoebas Feed?

The amoeba cell depends on heterotrophic nutrition. This is due to the fact that it feeds on all kinds of microscopic bacteria, animals, and plants.

The formation of pseudopods takes place as a response to chemical stimuli. Furthermore, this generation of chemical stimuli takes place by the microorganisms that are the amoeba food.

The pseudopods introduce the food into the digestive vacuole and cavity. Moreover, this can take place at any point on the surface of the cell. This is because this single-cell creature lacks a mouth that is localized.

The secretion of acid takes place in the vacuole. Moreover, this acid leads to the decomposition of this food into soluble chemical substances.

Also, this type of digestion is known as intracellular digestion. Most noteworthy, this process is what call experts call as phagocytosis. Here, the elimination of unused parts also happens.

FAQs For Amoeba

Question 1: Do amoebas communicate among themselves?

Answer 1: Due to the extremely small size of amoeba cell , they lack a nervous system. Furthermore, their communication takes place through the interaction of the cell membrane with the surrounding outside world.

In response to a stimulus that is alimentary, irritant, and noxious, intracellular communication takes place. Due to the intracellular communication, there is a production of a reaction of the whole cell. Consequently, the whole amoeba cell either moves towards the stimulus or away from it.

Question 2: How does amoeba reproduction take place?

Answer 2: The mature amoeba reproduction takes place by asexual multiplication. Here, reproduction happens by binary fission, where the duplication of the genetic material takes place by mitosis.

During this reproduction, cell lengthens and the division of the cytoplasm takes place into two daughter cells. Moreover, each of the daughter cells keeps a copy of the DNA. Furthermore, experts have not made any observation of the sexual reproduction among amoebas.

Question 3: Can amoebas live forever?

Answer 3: Amoebas are pretty much immortal. The only way amoebas can die is by way of starvation or by suffering damage from their environment. Furthermore, amoebas can repair themselves indefinitely.

Amoebas are big proof that there is no separation between biology and death. Most importantly, amoebas do not die due to age.

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