Step-by-Step Amoeba Diagram Guide for Exam Success
Amoebae are microscopic, unicellular organisms that belong to the Family Amoebidae. They are usually found in freshwater habitats like the bottoms of ponds and streams, often hiding among decaying vegetation. One of the most notable features of amoebae is their ability to change shape through cytoplasmic extensions called pseudopodia. These extensions help them move and capture food particles.
In 1755, a German naturalist named August Johann Rösel von Rosenhof became the first person to reference these ever-changing organisms. Since then, our understanding of amoebae has expanded significantly, making them an important topic of study in biology and a key concept for exams like NEET.
Classification of Amoeba
Amoeba can be classified under the following ranks:
Domain: Eukaryota
Phylum: Amoebozoa
Class: Tubulinea
Order: Euamoebida
Family: Amoebidae
Genus: Amoeba
Structure of Amoeba (Well-Labelled Diagram)
A typical amoeba is composed of jellylike cytoplasm enclosed by a thin plasma membrane. The cytoplasm is divided into:
Ectoplasm: A clear, relatively firm layer just beneath the plasma membrane.
Endoplasm: A granular inner layer that contains organelles such as the nucleus, food vacuoles, and the contractile vacuole.
Key Characteristics of Amoeba
Shape-Shifting Ability: Amoebae can change shape by extending and retracting finger-like projections known as pseudopodia. These “false feet” enable movement and capture of food.
Feeding Mechanism: They do not possess a mouth or anus. Instead, they engulf food by surrounding it with pseudopodia and forming a food vacuole. Enzymes released into the vacuole help digest the food.
Contractile Vacuole and Osmoregulation: The contractile vacuole helps regulate the amount of water inside the cell, preventing it from bursting in a hypotonic (freshwater) environment. It collects excess water and expels it out of the cell.
Reproduction: The primary mode of reproduction is asexual reproduction by binary fission. The nucleus divides first, followed by the division of the cytoplasm, resulting in two daughter amoebae.
Encystation: In unfavourable conditions, amoebae can form a cyst by secreting a protective membrane around themselves. This process, known as encystation, helps them survive extreme conditions. When the environment improves, they emerge from the cyst and return to their active form.
Habitat: Amoebae thrive in freshwater environments, especially at the bottom of ponds and streams, where they often feed on decaying organic matter.
Additional Unique Adaptations
Sensitivity: Amoebae can sense chemicals in their environment, which helps them find food sources.
Locomotion Efficiency: Though seemingly random, the formation and retraction of pseudopodia are quite efficient, enabling amoebae to navigate their surroundings for optimal nutrient intake.
Short Quiz on Amoeba (With Answers)
1. What structure in Amoeba helps regulate water content?
Answer: The contractile vacuole.
2. Which scientist first referenced the Amoeba in 1755?
Answer: August Johann Rösel von Rosenhof.
3. Name the cytoplasmic extension that Amoeba uses for movement and feeding.
Answer: Pseudopodia.
4. What is the mode of reproduction in Amoeba?
Answer: Asexual reproduction by binary fission.
5. What is the primary habitat of Amoeba?
Answer: Freshwater habitats such as ponds and streams.
Related Topics
FAQs on Amoeba Diagram: Complete Structure, Classification & Key Features
1. What is an Amoeba and what are its key defining characteristics?
An Amoeba is a unicellular eukaryotic organism belonging to the Kingdom Protista. It is well-known for its irregular, constantly changing shape. Key characteristics include:
It lacks a fixed body shape due to the absence of a rigid cell wall.
Movement and feeding are accomplished using temporary finger-like projections called pseudopodia (false feet).
It has a distinct nucleus, cytoplasm, and various organelles like a contractile vacuole and food vacuoles.
Nutrition is holozoic, meaning it engulfs its food whole through a process called phagocytosis.
Reproduction occurs asexually, primarily through binary fission.
2. What are the important parts of an Amoeba cell as seen in a diagram?
A typical diagram of an Amoeba highlights several key organelles essential for its survival. These include the cell membrane which encloses the cell, the nucleus that controls all cellular activities, and the jelly-like cytoplasm. Within the cytoplasm, you can find the contractile vacuole, which regulates water balance (osmoregulation), and several food vacuoles where ingested food particles are digested. The pseudopodia are also visible as extensions of the cell body.
3. How is an Amoeba classified according to the taxonomic hierarchy?
The scientific classification of a common Amoeba, like Amoeba proteus, places it within the eukaryotic domain. Its taxonomic ranks are as follows:
Kingdom: Protista
Phylum: Amoebozoa
Class: Tubulinea
Order: Amoebida
Family: Amoebidae
Genus: Amoeba
Species: proteus
4. How does an Amoeba move and capture its food?
An Amoeba uses a fascinating method for both movement and feeding involving its pseudopodia. For movement, it extends a pseudopod in the desired direction, and the rest of the cytoplasm flows into it, effectively pulling the cell forward. This is known as amoeboid movement. To capture food, it senses a food particle, extends its pseudopodia to surround it, and fuses the tips to engulf the particle. This process, called phagocytosis, forms an internal bubble known as a food vacuole where digestion occurs.
5. What is the importance of the contractile vacuole in an Amoeba?
The contractile vacuole is a crucial organelle for an Amoeba's survival, especially in freshwater environments. Its primary function is osmoregulation, which is the process of maintaining a stable water balance. Because the concentration of solutes inside the Amoeba is higher than in the surrounding freshwater, water constantly enters the cell via osmosis. The contractile vacuole collects this excess water and periodically contracts to expel it, preventing the cell from swelling and bursting.
6. Why is an Amoeba often described as being biologically immortal?
Amoeba is considered biologically immortal because it reproduces through binary fission, a process where the parent cell divides into two genetically identical daughter cells. In this process, the original parent cell does not die or leave behind a corpse; its entire substance is distributed among its offspring. Therefore, barring accidental death or harsh environmental conditions, the cell lineage can continue indefinitely without ageing in the traditional sense.
7. How does an Amoeba survive in unfavourable conditions like a dry pond?
When faced with unfavourable conditions such as drought, extreme temperatures, or lack of food, an Amoeba undergoes a process called encystation. It retracts its pseudopodia, becomes spherical, and secretes a hard, three-layered protective covering called a cyst around itself. In this dormant state, its metabolic activities slow down significantly, allowing it to survive until environmental conditions become favourable again, at which point it emerges from the cyst.
8. If an Amoeba has no fixed shape, how does it maintain its cellular integrity?
Although an Amoeba lacks a rigid cell wall, its structural integrity is maintained by its flexible cell membrane, also known as the plasmalemma. This membrane is strong enough to contain the cytoplasm and all its organelles, yet elastic enough to allow for the formation of pseudopodia and changes in shape. It acts as a selective barrier, controlling the movement of substances in and out of the cell, thus preserving the internal cellular environment without breaking apart.
9. Are all types of Amoeba harmless to humans? Explain with an example.
No, not all amoebae are harmless. While most free-living species like Amoeba proteus pose no threat, some are parasitic and can cause serious diseases in humans. A well-known example is Entamoeba histolytica, which is a parasite that lives in the human intestine and causes a disease called amoebic dysentery or amoebiasis. Another extremely rare but deadly example is Naegleria fowleri, often called the "brain-eating amoeba," which can cause a fatal brain infection.
10. How does a single-celled Amoeba carry out all essential life processes without any organs?
As a unicellular organism, an Amoeba demonstrates the 'division of labour' at the organelle level, not the organ level. Each specialized part within the single cell performs a specific function necessary for life:
Respiration: Gaseous exchange occurs by simple diffusion across the entire cell membrane.
Nutrition: Ingestion happens via pseudopodia, and digestion occurs within food vacuoles.
Excretion & Osmoregulation: Waste removal and water balance are managed by the contractile vacuole.
Control & Coordination: All life activities are regulated by the nucleus.
This efficient system within one cell makes complex organs unnecessary for its survival.
