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Amoeba: Classification, Structure, Reproduction and Nutrition

Amoeba: Classification, Structure, Reproduction and Nutrition

Amoeba is one of the first microscopic organisms almost all of us viewed under the microscope. Also, it is one of the easiest drawn ones, where we just used to make an enclosed space with non-uniform space and put loads of dots inside. Commonly found in freshwater, saltwater and wet soil, it is the simplest and shapeless organism. The organism's in-depth structure, nutrition and reproduction are covered here. 

Table of Contents

  • Amoeba Classification
  • Structure of Amoeba 
  • Structural Divisions in Amoeba 
  • Modes of Reproduction 
  • Nutrition in Amoeba 
  • Practice Problems 
  • Frequently Asked Questions 

Amoeba Classification 

Amoeba is a member of the Kingdom Protozoa, a eukaryotic organism due to its placement in the Eukaryota domain. The reason for the latter is the presence of a true nucleus in the organism. It is not considered a plant, animal or fungus. It is a widely studied organism for evolution. The organism species are multiple such as proteus, animalcule, dubia and others. 

Structure of Amoeba

It is a shapeless organism owning a jelly-like structure that can change its shape. Commonly invisible organisms have microscopic asymmetrical bodies ranging between 0.05 to 1 mm. 

Structural Divisions in Amoeba

Beginning from environment facing side, the Amoeba comprises of following parts: 

  • Cell membrane

It is a thin proteinaceous, fatty layer surrounding the amoeba. It is responsible for the entry and exit of the compounds, acting as a barrier due to its selectively permeable nature. The membrane is double-layered. 

  • Nucleus 

Acting as the main controlling part, the amoeba's nucleus is constitutive of genetic material. It is responsible for managing the growth, development and functionality of amoeba. 

  • Vacuoles 

These air-filled spaces or sacs in the Amoeba are differentiated into three types. The contractile vacuole that can contract and expand is associated with osmotic regulation through the outward pumping of water. The food vacuole is a fixed shaped multi-sized food storage compartment. Water globules are water-filled and fixed shape spaces. 

  • Cytoplasm 

It is a gel-like material divided into outer ectoplasm and inner endoplasm. The former is non-granulated, while the latter is granulated in nature. Cytoplasm is the exact location of organelles of Amoeba such as Mitochondria, fat globules and Golgi apparatus. 

  • Pseudopodia

These are the finger-like projections that define the organism’s ability to move and eat food through the process of phagocytosis or drinking water via pinocytosis. 

Modes of Reproduction

Amoeba can reproduce both sexually and asexually. Asexual reproduction involves binary fission and multiple fission. The former is seen in favourable conditions, while multiple fission is witnessed during unfavourable conditions. 

Nutrition in Amoeba 

Amoeba ingests food through phagocytosis and gains nutrition via holozoic nutrition. The holozoic nutrition food intake pathway involves five steps, ingestion, digestion, absorption, assimilation and egestion of food material, primarily performed by pseudopodia. 

Ingestion: Food intake

Digestion: Breaking the food into soluble and smaller molecules

Absorption: Movement of food into cytoplasm except for the undigested particles. The process occurs through diffusion. It also involves storage as carbohydrates (glycogen) and fat (lipids). 

Assimilation: Action on the absorbed food material to derive energy from them. It involves different pathways and cycles. 

Egestion: It refers to the excretion or removal of undigested food material. 

Practice Problems 

Q1. Which organisms are the constituents of Kingdom Protista? 

A. Amoeba
B. Pseudomona 
C. Euglena 
D. Both a and c 

Ans. D. Both a and c 

Kingdom Protista constitutes eukaryotic organisms that do not lie in the category of plants, fungi and animals. 

Q2. Which form does Amoeba convert to in unfavourable conditions? 

A. Amoebic podia
B. Pseudopodia
C. Heterotopic amoeba 
D. Amoebic cyst

Ans. D. Amoebic cyst

Amoeba forms amoebic cysts characterised by the presence of a three-layer covering. It lacks pseudopodia. 

Q3. What does an amoeba feed on? 

A. Human blood
B. Microbes|
C. Air
D. Water 

Ans. D. Microbes

Assimilating food via digestive enzymes, they intake a variety of food such as plant cells, protozoa, algae and bacteria. 

Frequently Asked Questions 

Q1. Are Amoebas pathogenic in nature? 
Answer: A few Amoebas hold the potential to infect humans, though they are capable of surviving otherwise. They are opportunistic pathogens responsible for human diseases such as amoebic dysentery and amoebiasis. Another important and infectious Amoeba is Naegleria fowleri. 

Q2. Can Amoeba be ingested via tap water consumption? 
Answer. Amoebas may or may not be present in tap water. However, they can surely sustain themselves there. It is recommended to purify the water prior to drinking to avoid contamination and health issues. The chlorine-treated water and distilled water are safe for consumption from Amoeba and multiple other pathogenic organisms. 

Q3. What is Amoebic cyst?
Answer. Amoebic cyst is observed after the process of encystation. It refers to the phenomenon where pseudopodia are taken inside the Amoeba body followed by secretion of hard covering or cyst. It is a three-layered structure that protects the organism from harsh environments and unfavourable conditions.

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