Structure and Function of Amoeba’s Organelles
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, Classification, and Characteristics
1. Can amoebae be found in saltwater environments?
Yes, certain species of amoebae can survive in saltwater, but the most commonly studied Amoeba proteus typically inhabits freshwater.
2. How do amoebae detect their food?
Amoebae can sense chemical signals in the environment, moving towards higher concentrations of these signals. Once in contact with the food particle, they extend their pseudopodia to engulf it.
3. Are amoebae harmful to humans?
Most free-living amoebae are harmless. However, some species such as Naegleria fowleri (commonly called the “brain-eating amoeba”) can cause severe infections, although such cases are rare.
4. What happens during encystation?
During encystation, amoebae become nearly inactive. They retract their pseudopodia, expel excess water, and form a thick, protective cyst wall around themselves. This helps them survive harsh conditions.
5. Why do amoebae not have specialised organs like other organisms?
Amoebae are unicellular, meaning all life processes occur within a single cell. They rely on simple diffusion, osmoregulation through the contractile vacuole, and pseudopodia for movement and feeding, making specialised organs unnecessary.
