Amoeba Diagram & Characteristics
Amoeba is a unicellular organism studied from Class 7 to NEET level. Its diagram shows parts like nucleus, cytoplasm, pseudopodia, contractile vacuole, and food vacuoles. Learn about its structure, movement, nutrition, and reproduction with labelled diagrams and NEET MCQs.
This Story also Contains
- What is Amoeba?
- Classification of Amoeba
- Well-Labelled Diagram of Amoeba
- Structure of Amoeba
- Nutrition and Digestion in Amoeba
- Reproduction in Amoeba
- Size and Variation in Amoeba
- Amoeba NEET MCQs
- FAQs on Amoeba
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Amoeba is a fascinating unicellular organism widely studied in biology. Amoebas are members of the Kingdom Protista. They are known for their unique, simple structure and remarkable adaptability to various environments. Amoeba are unicellular, eukaryotic organisms that perform all the essential life functions within a single cell. They play a vital role in biological processes, such as nutrition and reproduction. Understanding the amoeba diagram is crucial for students as it offers insights into biology.
What is Amoeba?
Amoeba is found to be a unicellular organism that is made up of a single cell and can only be seen by a microscope. This organism is not visible with the help of the naked eye. It is usually a eukaryotic organism that shows the presence of true organelles and a nuclear envelope. This organism moves with the help of false feet which is termed as the pseudopodia. The pseudopodia is defined as the cytoplasm pushing off the cell membrane. A very important feature of the amoeba is to change its shape.
Commonly Asked Questions
Amoebae exhibit simple but effective responses to environmental stimuli, a behavior called taxis. They can move towards favorable conditions (positive taxis) or away from unfavorable ones (negative taxis). For example, they may move towards light (phototaxis), food sources (chemotaxis), or away from harmful chemicals.
Amoebae in freshwater environments face the challenge of constant water influx due to osmosis. They maintain osmotic balance primarily through the action of contractile vacuoles. These organelles collect excess water from the cytoplasm and periodically expel it from the cell, preventing the amoeba from swelling and potentially bursting.
Amoebae exchange gases, primarily oxygen and carbon dioxide, through simple diffusion across their cell membrane. Their large surface area-to-volume ratio allows for efficient gas exchange directly with their aquatic environment. Oxygen diffuses into the cell for use in cellular respiration, while carbon dioxide, a waste product of respiration, diffuses out of the cell.
The glycocalyx is a carbohydrate-rich layer on the outer surface of the amoeba's plasma membrane. It serves several functions, including protection against mechanical damage, aiding in cell-to-cell recognition, and helping the amoeba adhere to surfaces. In some species, it may also play a role in the formation of protective cysts.
Classification of Amoeba
All the discussion of the amoeba from which domain and phylum it belongs is defined here:
Domain: Eukaryota (True cells)
Kingdom: Amoebozoa
Phylum: Tubulinea
Class: Lobosa
Order: Tubulinida
Family: Amoebidae
Genus: Amoeba
Species: many different species such as Proteus and animacule.
Nowadays, studies have been done on classifying the amoeba. This classification is done on the basis of the subunit that is located in their ribosomal RNA. Sarcodina is defined to be the most preferable form of the amoeba. It is found to be the single most accepted taxonomic group that is presented to the classification of the amoeba cell. It is divided on the basis of its observable character.
Well-Labelled Diagram of Amoeba
An amoeba's body is irregular in shape and covered by a plasma membrane. It has two parts to its cytoplasm: the outer part is called the ectoplasm and the inner part is called the endoplasm. The main organelles found inside its cytoplasm include the nucleus, contractile vacuole, and food vacuoles.
Structure of Amoeba
Movement in the amoeba takes place with the help of false feet which is known as pseudopodia so it changes its shape.
The structure and body of Amoeba are divided into three different parts namely cytoplasm, plasma membrane, and nucleus.
The cytoplasm of the amoeba is further divided into two layers that are known as the outer ectoplasm and inner endoplasm.
The plasma membrane of amoeba is observed to be very thin This layer is a double-layer membrane that is composed of protein. It is made up of lipid molecules.
When we talk about other cellular organelles, amoeba possess contractile vacuoles, mitochondria, Golgi apparatus and some of the fat globules.
The contractile vacuole helps in maintaining the osmotic equilibrium. This process is played by separating out most of the water from the cell.
Nutrition and Digestion in Amoeba
Nutrition in amebas is holozoic i.e., they ingest and digest liquid or solid foods. Most amebas are omnivorous, living on algae, bacteria, protozoa, rotifers, and other microscopic organisms. An ameba may ingest food at any part of its body surface just by producing a pseudopodium to engulf the food (phagocytosis). The enclosed food particle, along with some environmental water, becomes a food vacuole. As digestion occurs within the vacuole by enzymatic action, water and digested materials pass into the cytoplasm. Undigested particles are eliminated through the cell membrane.
Reproduction in Amoeba
Binary fission:
Binary fission in amoeba is a type of asexual reproduction. In binary fission , the organism first duplicates its genetic content and elongates and splits into two equal halves. Binary fission is relatively fast and a full cycle usually takes under half an hour. After karyokinesis has divided the nucleus, cytokinesis separates the cytoplasm into two cells that eventually can develop into an independent living organism.
Spore formation:
When there are unfavourable conditions, the amoeba divides with the help of spore formation. It starts to break its nuclear membrane, and some of the chromatin blocks get released into the cytoplasm. Each chromatin block now gets inside a nuclear membrane and becomes a small daughter nucleus. Unlike multicellular organisms, amoeba does not involve gamete fusion or sexual reproduction.
Commonly Asked Questions
Amoebae regulate their cell cycle through a series of checkpoints and regulatory proteins, similar to other eukaryotic cells. The cycle includes phases of growth, DNA replication, and cell division (binary fission). Environmental factors such as nutrient availability and temperature also influence the rate of cell division.
Encystment is a survival mechanism where an amoeba forms a protective cyst around itself in response to harsh environmental conditions, such as drought or extreme temperatures. During this process, the amoeba becomes rounded, expels excess water, and secretes a tough, resistant outer covering. The encysted amoeba can remain dormant until conditions improve.
Microfilaments, composed of actin, play crucial roles in various cellular processes in amoebae. They are involved in cell movement by facilitating the formation and retraction of pseudopodia. Microfilaments also participate in cytoplasmic streaming, cell division, and maintaining cell shape. They form part of the cell cortex, providing structural support to the plasma membrane.
Mitochondria in amoebae, as in other eukaryotic cells, are the powerhouses of the cell. They are responsible for cellular respiration, a process that breaks down nutrients to produce ATP (adenosine triphosphate), the cell's primary energy currency. This energy is crucial for all cellular activities, including movement, feeding, and reproduction.
Size and Variation in Amoeba
Amoeba is present in different forms in both size and shape. When the earliest animals were found it was found to be 400 to 600 micrometers in size. There are many different sizes of amoeba that range from small to large size that is 2-3 nanometers in size to exceptionally large such as 20 cm amoeba. The body of the amoeba is found to be transparent and looks like gelatin.
Amoeba NEET MCQs
Q1. Amoeba moves and engulfs food with the help of:
Cilia
Flagella
Pseudopodia
Contractile vacuole
Correct answer: 3) Pseudopodia
Explanation:
Amoeba is a unicellular organism that moves by forming temporary extensions of its cytoplasm known as pseudopodia (false feet). These structures help the organism in locomotion as well as in capturing food through phagocytosis. Unlike cilia or flagella (used by other protists), pseudopodia provide flexible movement and are essential for the amoeba's survival.
Hence the correct answer is option 3) Pseudopodia.
Q2. The contractile vacuole in amoeba functions to:
Store nutrients
Maintain osmotic balance
Aid locomotion
Reproduction
Correct answer: 2) Maintain osmotic balance
Explanation:
The contractile vacuole of amoeba is a specialized structure that helps in osmoregulation, i.e., maintaining the water balance inside the cell. Since amoeba lives in freshwater, water constantly enters the cell by osmosis. The contractile vacuole collects excess water and periodically expels it out, preventing the cell from bursting. It does not play a role in nutrient storage, movement, or reproduction.
Hence the correct answer is option 2) Maintain osmotic balance.
Q3. Which condition is caused by Naegleria fowleri?
Amoebic dysentery
Primary Amoebic Meningoencephalitis (PAM)
Malaria
Sleeping sickness
Correct answer: 2) Primary Amoebic Meningoencephalitis (PAM)
Explanation:
Naegleria fowleri is commonly called the “brain-eating amoeba.” It enters the human body when contaminated water enters through the nose. From there, it travels to the brain and causes Primary Amoebic Meningoencephalitis (PAM), a rare but usually fatal infection. Amoebic dysentery is caused by Entamoeba histolytica, malaria by Plasmodium, and sleeping sickness by Trypanosoma.
Hence the correct answer is option 2) Primary Amoebic Meningoencephalitis (PAM).
Also read:
FAQs on Amoeba
What is Amoeba?
Amoeba is a unicellular eukaryotic organism that belongs to the kingdom Protista. It has an irregular, constantly changing body shape due to the presence of pseudopodia. The cytoplasm is differentiated into ectoplasm and endoplasm, and the cell contains a nucleus, contractile vacuole, and food vacuoles. Amoeba is found in freshwater, moist soil, and decaying vegetation. Being heterotrophic, it engulfs food particles through phagocytosis. It serves as a simple model to study basic life processes like locomotion, nutrition, and reproduction.
How does Amoeba move?
Amoeba moves with the help of pseudopodia, which are temporary extensions of its cytoplasm. The cytoplasm flows forward to form a pseudopodium, and the rest of the cell moves into it. This type of movement is known as amoeboid movement. Pseudopodia also help in capturing food particles, showing dual function. This simple mechanism of movement is important for survival in aquatic and moist environments.
What is the function of the contractile vacuole in Amoeba?
The contractile vacuole in Amoeba plays a vital role in osmoregulation. Since Amoeba lives in freshwater, excess water continuously enters the cell by endosmosis. The contractile vacuole collects this extra water and periodically expels it outside the cell. This process maintains osmotic balance and prevents the cell from bursting due to over-accumulation of water. Thus, it is essential for the survival of Amoeba in hypotonic environments.
How does Amoeba reproduce?
Amoeba reproduces asexually, mainly through binary fission. In this process, the nucleus divides by mitosis, followed by the division of cytoplasm (cytokinesis), resulting in two daughter Amoebae. Under unfavorable conditions, Amoeba may undergo multiple fission, where it forms a cyst and produces many daughter cells. Upon return of favorable conditions, these cells are released. This reproductive strategy ensures both survival and rapid multiplication of the species.
Frequently Asked Questions (FAQs)
Amoebae, like other organisms, can experience oxidative stress from reactive oxygen species. They cope with this through several mechanisms, including the production of antioxidant enzymes such as catalase and superoxide dismutase. Some species can also upregulate the production of these enzymes in response to increased oxidative stress.
The fluid mosaic membrane of an amoeba, like all cell membranes, consists of a phospholipid bilayer with embedded proteins. Its fluid nature allows for the movement of membrane components, which is crucial for the amoeba's ability to change shape, form pseudopodia, and engulf food particles. This flexibility is essential for the amoeba's survival and functioning.
The cytoskeleton of an amoeba is a network of protein filaments that provides structural support and enables cellular movement. It consists of microfilaments (actin filaments), intermediate filaments, and microtubules. The cytoskeleton plays a crucial role in the formation and retraction of pseudopodia, intracellular transport, and maintaining cell shape.
The endoplasmic reticulum (ER) in amoebae serves several important functions. The rough ER, studded with ribosomes, is involved in protein synthesis and modification. The smooth ER plays a role in lipid synthesis, calcium storage, and detoxification of harmful substances. The ER also helps in the transport of materials within the cell.
Amoebae primarily store energy in the form of glycogen, a polysaccharide similar to starch in plants. When the amoeba has excess glucose, it is converted into glycogen for storage. This stored glycogen can be broken down back into glucose when the cell needs energy. Some amoebae also store energy in the form of lipid droplets.
Lysosomes are organelles containing digestive enzymes that play a crucial role in intracellular digestion in amoebae. They fuse with food vacuoles to break down engulfed food particles. Lysosomes also help in cellular recycling by breaking down old or damaged cellular components, a process called autophagy.
Although amoebae lack a rigid cell wall, they maintain their shape through several mechanisms. The plasma membrane provides a flexible boundary, while the cytoskeleton, particularly the actin filaments, provides internal structure and support. The cytoplasm's gel-like consistency also helps maintain the cell's integrity. However, this flexibility allows amoebae to change shape as needed for movement and feeding.
The nucleolus is a structure within the nucleus of an amoeba. Its primary function is the production and assembly of ribosomal subunits. These subunits are then transported to the cytoplasm where they combine to form complete ribosomes, which are essential for protein synthesis. The nucleolus also plays a role in other cellular processes, including stress responses and cell cycle regulation.
Amoebae, like other cells, need to maintain a stable internal pH for optimal cellular function. They achieve this through several mechanisms, including the use of buffer systems in the cytoplasm, active transport of hydrogen ions across the cell membrane, and the action of organelles like contractile vacuoles. Some species can also adjust their metabolism to help maintain pH balance in different environments.
The cell cortex in amoebae is a specialized layer of cytoplasm just beneath the plasma membrane. It is rich in actin filaments and other proteins that give the cell its structure and allow for changes in shape. The cortex plays a crucial role in the formation of pseudopodia, cell movement, and phagocytosis.