Euglenoids, Definition, Structure, Classification, and Reproduction
Euglenoids, This article explains definition of Euglenoids, its classification, structure, nutrition mode, locomotion and reproduction with included MCQs and answers.
Krati Saraswat4 Jun, 2025
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Euglenoids are single-celled, flagellated organisms found primarily in freshwater environments. They possess both plant-like and animal-like characteristics, featuring chlorophyll for photosynthesis and flagella for movement. This unique combination makes them an important subject of study, bridging the gap between plant and animal life.
Euglenoids are significant for the NEET Exam as they illustrate key biological concepts such as cellular structure, mixotrophic nutrition, and evolutionary adaptations.Definition of Euglenoids
Euglenoids are a group of mostly unicellular, flagellated microorganisms primarily found in freshwater habitats, though some are found in marine waters. These organisms are particularly interesting because they exhibit both plant-like and animal-like characteristics. Euglenoids, such as Euglena, contain chloroplasts and perform photosynthesis like plants but can also switch to heterotrophic feeding when sunlight is unavailable.Classification of Euglenoids
Euglenoids belong to the kingdom Protista and are placed under the phylum Euglenophyta. The genus Euglena, from which euglenoids get their name, is the most studied group within this phylum. Based on their structure and characteristics, euglenoids have unique features distinguishing them from other protists, algae, and flagellates.| Kingdom | Protista |
| Phylum | Euglenophyta |
| Class | Euglenoidea |
| Order | Euglenales |
| Genus | Euglena |
Structure of Euglenoids
The structure of Euglenoids is unique and contributes to their adaptive versatility:- Cell Shape and Pellicle : Euglenoids have an elongated cell body covered by a flexible, protein-rich layer called the pellicle, rather than a rigid cell wall. This pellicle provides support and allows the cell to twist and change shape as it moves.
- Flagella : Euglenoids possess one or two flagella, which aid in movement. Typically, only one flagellum is visible externally, while the other is shorter and located within the reservoir (a pocket-like structure inside the cell).
- Chloroplasts : The presence of chloroplasts in Euglenoids allows them to perform photosynthesis, using sunlight to produce energy. These chloroplasts contain the pigment chlorophyll, giving Euglenoids a green color similar to plants.
- Eyespot (Stigma) : Euglenoids have an eyespot near the base of the flagellum, which is sensitive to light. The eyespot helps Euglenoids detect light sources, enabling them to move toward optimal lighting for photosynthesis.
- Contractile Vacuole : Euglenoids also have a contractile vacuole that helps maintain osmotic balance within the cell by expelling excess water.
Nutrition of Euglenoids
Euglenoids are notable for being mixotrophic, which means they can switch between autotrophic and heterotrophic modes of nutrition based on environmental conditions.- Autotrophic Nutrition : When exposed to sufficient light, euglenoids carry out photosynthesis using chloroplasts. They capture sunlight and convert carbon dioxide and water into glucose, similar to plant cells.
- Heterotrophic Nutrition: In the absence of light, euglenoids switch to heterotrophic nutrition, absorbing dissolved organic matter from the environment. They can ingest small particles or feed on organic molecules, making them adaptable to changing conditions.
Locomotion of Euglenoids
Euglenoids use a type of movement known as euglenoid movement or metaboly , which is a wavelike motion that allows the cell to move through the water. This form of movement is facilitated by the flexible pellicle, which lets the cell contract and expand, helping it glide. Additionally, the flagellum propels the Euglenoid through water, allowing it to navigate towards light sources or areas with abundant nutrients.Reproduction of Euglenoids
Euglenoids reproduce primarily through asexual reproduction, specifically by binary fission. During this process, the Euglenoid cell elongates, and its nucleus divides through mitosis. The cell then divides longitudinally to form two identical daughter cells. This mode of reproduction is relatively simple and allows Euglenoids to multiply quickly under favorable conditions.MCQs of Euglenoids
Q1. Euglenoids have flexible body due to the presence of;
- chlorophyll.
- cell wall.
- pellicle.
- cellulose.
Q2. Which of these bears two unequal flagella?
- Euglenoids
- Slime molds
- Diatoms
- Dinoflagellates
Q3. Which of the following is NOT present in Euglena?
- Chloroplasts
- Flagella
- Cellulosic cell wall
- Proteinaceous pellicle
Answers of MCQs of Euglenoids
Ans1 . Pellicle,| NEET Exam Important Links | |
|---|---|
| NEET Biology Syllabus | NEET Biology Diagrams |
| NEET Biology MCQ | NEET Biology Chapter wise Weightage |
| NEET Biology Notes | NEET Previous Year Question papers |
Euglenoids FAQs
Q. What is unique about euglenoids?
Ans. Euglenoids are unique because they exhibit both plant-like and animal-like characteristics. They possess chlorophyll pigments for photosynthesis, giving them a green coloration, and have flagella for mobility. This combination allows them to thrive in diverse aquatic environments.
Q. What do euglenoids feed on?
Ans. Euglenoids primarily feed on a combination of organic matter and light. They can utilize sunlight to produce their own food through photosynthesis and, when light is not available, they absorb dissolved organic nutrients from their surroundings, including bacteria and small algae.
Q. Can euglenoids produce oxygen?
Ans. Yes, euglenoids can produce oxygen during photosynthesis. When they use sunlight to convert carbon dioxide and water into glucose, oxygen is released as a byproduct, contributing to the oxygen supply in their aquatic environments.
Q. What are the characteristic features of euglenoids?
Ans. Characteristic features of euglenoids include their flexible pellicle, which allows for shape changes; the presence of chloroplasts containing chlorophyll; an eyespot (stigma) for light detection; and one or two flagella for movement. They also have a contractile vacuole for osmoregulation, enabling them to manage water levels within their cells.
Q. How do euglenoids reproduce?
Ans. Euglenoids primarily reproduce asexually through binary fission. In this process, a single euglenoid cell duplicates its genetic material and divides into two identical daughter cells. This method of reproduction allows for rapid population growth, especially in favorable conditions.
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