7.2.1 PROTOZOA: The Animal Like Protists

Introduction

The term "protozoa" is derived from two Greek words: "proto," meaning "first," and "zoo," meaning "animals." It was originally coined in the 19th century to describe microscopic, single-celled organisms that exhibited animal-like behaviors, such as movement and ingestion of food particles. Protozoa are a polyphyletic group.

Definition

Protozoa: Protozoa are a polyphyletic group of unicellular, animal-like protists that inhabit a wide range of environments and exhibit animal-like behaviors such as movement and ingestion of food particles.

In simple words: Protozoa are single-celled, animal-like protists.

Core Concept

• The term "protozoa" is derived from Greek words:
• **"proto"** = first
• **"zoo"** = animals
• It was originally coined in the 19th century.
• It describes microscopic, single-celled organisms that exhibit animal-like behaviors.
• Protozoa are a polyphyletic group.

Detailed Explanation

Habitat of Protozoa

Protozoa inhabit a wide range of environments, including:

Structure of Protozoa

• Protozoa are unicellular.
• Their body is a single mass made of cytoplasm that holds all structures that are found in a typical cell.
• Protozoa do everything that living things do:
• They eat
• They breathe
• They move around
• They maintain fairly stable conditions necessary for survival (homeostasis)
• They reproduce

Vacuoles in Protozoa

Vacuoles are present in protozoans to perform specialized functions.

Shells in Protozoa

• Some protozoans have shells.
• Example: Foraminifera.

Reproduction in Protozoa

- Reproduction takes place both by asexual and sexual methods.

Locomotion in Protozoa

The organs of locomotion may be:

Other Features

• Regeneration is common in protozoans.
• Protozoans form resistant cysts to overcome unfavorable conditions.

Amoebas

• They are free-living microorganisms.
• They inhabit:
• Freshwater
• Oceans
• Soil
• They can also exist as parasites inside animals.
• Amoebas use pseudopodia for both movement and feeding.
• Examples:
• Amoeba proteus
• Entamoeba histolytica

Zooflagellates

• Protozoa that move using flagella are referred to as zooflagellates.
• Example: *Giardia intestinalis*
• A flagellated parasite.
• Infects the small intestine.
• Causes a gastrointestinal illness known as giardiasis in humans.

Choanoflagellates

• A choanoflagellate is a marine or freshwater flagellate organism.
• It is sessile and remains anchored in place by a stalk.
• It has a flagellum surrounded by a delicate collar.
• It resembles the collar cells found in sponges.

Ciliates

• Ciliates are named after a Latin word for "eyelash".
• Their cells are covered in tiny hair-like structures called cilia.
• Examples of ciliates include:
• Paramecium
• Stentor
• Vorticella

Summary Table of Protozoa

Intermediate Level

Habitat of Protozoa in Detail

Structure of Protozoa in Detail

Locomotion in Detail

Types of Protozoa

Vacuoles in Detail

Important Points

• 1. Protists are a diverse group that can be classified into several groups based on their characteristics and evolutionary relationships.
• 2. However, Protists include four major groups: Protozoa, Algae, Myxomycota and Oomycota, the salient features of which are discussed in following sections.
• 3. "Salient features" refer to the primary and easily recognizable characteristics or attributes of something, serving as the key points that define it.
• 4. Protozoa: The Animal Like Protists:
• - The term "protozoa" is derived from two Greek words: "proto," meaning "first," and "zoo," meaning "animals."
• - It was originally coined in the 19th century to describe microscopic, single-celled organisms that exhibited animal-like behaviors, such as movement and ingestion of food particles.
• - Protozoa are a polyphyletic group.
• 5. Habitat:
• - Protozoa inhabit a wide range of environments, including aquatic and terrestrial habitats.
• - They are commonly found in freshwater e.g., Amoeba and Paramecium, in marine ecosystems like Radiolaria and many protozoans are parasitic like Plasmodium and Entamoeba histolytica.
• - Protozoa can also live in soil, leaf litter, and decaying organic matter e.g. Spiromonas and Vorticella.
• 6. Structure:
• - Protozoa are unicellular and their body is a single mass made of cytoplasm that holds all structures that are found in a typical cell.
• - Protozoa do everything that living things do - they eat, breathe, move around, maintain fairly stable conditions necessary for survival (homeostasis), reproduce etc.
• - Vacuoles are present in protozoans to perform specialized functions. Food vacuoles help digestion by breaking down trapped food into simpler molecules with the help of enzymes. Contractile vacuoles found in many freshwater protozoa regulate the water content within the cell by pumping excess water out of the cell and help maintain the internal balance. Vacuoles can also serve as storage organelles in protozoa. Storage vacuoles help store waste products, nutrients, or other substances that the cell needs to keep separate from the rest of its cytoplasm.
• - Some protozoans have shell e.g., foraminifera.
• 7. Reproduction:
• - Reproduction takes place both by asexual and sexual methods.
• 8. Locomotion:
• - The organs of locomotion may be pseudopodia e.g., in Amoeba, cilia e.g., in Paramecium, flagella e.g., in Trypanosoma, while the parasitic protozoans do not have any specific means of locomotion e.g., Plasmodium (malarial parasite).
• 9. Other Features:
• - Regeneration is common in protozoans.
• - Protozoans form resistant cysts to overcome unfavorable conditions.
• 10. Amoebas:
• - They are free living microorganisms inhabiting freshwater, oceans, soil, and can also exist as parasites inside animals.
• - Amoebas use pseudopodia for both movement and feeding, as seen in examples like Amoeba proteus and Entamoeba histolytica.
• 11. Zooflagellates:
• - Protozoa that move using flagella are referred to as zooflagellates.
• - An example is Giardia intestinalis, which is a flagellated parasite that infects the small intestine and causes a gastrointestinal illness known as giardiasis in humans.
• 12. Choanoflagellates:
• - A choanoflagellate is marine or freshwater flagellate organism that is sessile and remains anchored in place by a stalk.
• - It has a flagellum surrounded by a delicate collar, resembling the collar cells found in sponges.
• 13. Ciliates:
• - Ciliates are named after a Latin word for "eyelash," which fits because their cells are covered in tiny hair-like structures called cilia.
• - Examples of ciliates include Paramecium, Stentor, and Vorticella.

Remember

• - Protozoa = animal-like protists.
• - Unicellular = single-celled.
• - Locomotion = pseudopodia, cilia, flagella.
• - Vacuoles = food, contractile, storage.
• - Reproduction = asexual and sexual.
• - Examples: Amoeba, Paramecium, Trypanosoma, Plasmodium.
• - Resistant cysts = to survive unfavorable conditions.
• - Four major groups of protists: Protozoa, Algae, Myxomycota, Oomycota.

Common Mistakes

• 1. Thinking protozoa are multicellular – Protozoa are unicellular.
• 2. Confusing protozoa with bacteria – Protozoa are eukaryotes; bacteria are prokaryotes.
• 3. Thinking all protozoa cause disease – Many protozoa are free-living and harmless.
• 4. Confusing the types of vacuoles – Food vacuoles = digestion; Contractile vacuoles = water regulation; Storage vacuoles = storage.
• 5. Confusing the types of locomotion – Pseudopodia = Amoeba; Cilia = Paramecium; Flagella = Trypanosoma.
• 6. Thinking all protozoa have shells – Only some protozoa have shells (e.g., Foraminifera).
• 7. Confusing amoebas and zooflagellates – Amoebas use pseudopodia; Zooflagellates use flagella.
• 8. Thinking protozoa only reproduce sexually – Protozoa reproduce both asexually and sexually.
• 9. Forgetting the role of resistant cysts – Resistant cysts help protozoa survive unfavorable conditions.
• 10. Confusing choanoflagellates and ciliates – Choanoflagellates have a flagellum and collar; Ciliates have cilia.
• 11. Thinking all protozoa are parasitic – Many protozoa are free-living.
• 12. Confusing the four major groups of protists – Protozoa, Algae, Myxomycota, Oomycota.

Quick Revision

• Protists are a diverse group that can be classified into several groups based on their characteristics and evolutionary relationships.
• However, Protists include four major groups: Protozoa, Algae, Myxomycota and Oomycota, the salient features of which are discussed in following sections.
• Salient features refer to the primary and easily recognizable characteristics or attributes of something, serving as the key points that define it.
• Protozoa: The Animal Like Protists:
• The term "protozoa" is derived from two Greek words: "proto," meaning "first," and "zoo," meaning "animals."
• It was originally coined in the 19th century to describe microscopic, single-celled organisms that exhibited animal-like behaviors, such as movement and ingestion of food particles.
• Protozoa are a polyphyletic group.
• Habitat:
• Protozoa inhabit a wide range of environments, including aquatic and terrestrial habitats.
• They are commonly found in freshwater e.g., Amoeba and Paramecium, in marine ecosystems like Radiolaria and many protozoans are parasitic like Plasmodium and Entamoeba histolytica.
• Protozoa can also live in soil, leaf litter, and decaying organic matter e.g. Spiromonas and Vorticella.
• Structure:
• Protozoa are unicellular and their body is a single mass made of cytoplasm that holds all structures that are found in a typical cell.
• Protozoa do everything that living things do - they eat, breathe, move around, maintain fairly stable conditions necessary for survival (homeostasis), reproduce etc.
• Vacuoles are present in protozoans to perform specialized functions. Food vacuoles help digestion by breaking down trapped food into simpler molecules with the help of enzymes. Contractile vacuoles found in many freshwater protozoa regulate the water content within the cell by pumping excess water out of the cell and help maintain the internal balance. Vacuoles can also serve as storage organelles in protozoa. Storage vacuoles help store waste products, nutrients, or other substances that the cell needs to keep separate from the rest of its cytoplasm.
• Some protozoans have shell e.g., foraminifera.
• Reproduction:
• Reproduction takes place both by asexual and sexual methods.
• Locomotion:
• The organs of locomotion may be pseudopodia e.g., in Amoeba, cilia e.g., in Paramecium, flagella e.g., in Trypanosoma, while the parasitic protozoans do not have any specific means of locomotion e.g., Plasmodium (malarial parasite).
• Other Features:
• Regeneration is common in protozoans.
• Protozoans form resistant cysts to overcome unfavorable conditions.
• Amoebas:
• They are free living microorganisms inhabiting freshwater, oceans, soil, and can also exist as parasites inside animals.
• Amoebas use pseudopodia for both movement and feeding, as seen in examples like Amoeba proteus and Entamoeba histolytica.
• Zooflagellates:
• Protozoa that move using flagella are referred to as zooflagellates.
• An example is Giardia intestinalis, which is a flagellated parasite that infects the small intestine and causes a gastrointestinal illness known as giardiasis in humans.
• Choanoflagellates:
• A choanoflagellate is marine or freshwater flagellate organism that is sessile and remains anchored in place by a stalk.
• It has a flagellum surrounded by a delicate collar, resembling the collar cells found in sponges.
• Ciliates:
• Ciliates are named after a Latin word for "eyelash," which fits because their cells are covered in tiny hair-like structures called cilia.
• Examples of ciliates include Paramecium, Stentor, and Vorticella.

60-Second Revision

• Protozoa = animal-like protists.
• Unicellular = single-celled.
• Locomotion = pseudopodia, cilia, flagella.
• Vacuoles = food, contractile, storage.
• Reproduction = asexual and sexual.
• Examples: Amoeba, Paramecium, Trypanosoma, Plasmodium.
• Resistant cysts = to survive unfavorable conditions.
• Four major groups of protists: Protozoa, Algae, Myxomycota, Oomycota.
• Warning: Protozoa are unicellular eukaryotes, not bacteria. Not all protozoa cause disease. Food vacuoles = digestion; Contractile vacuoles = water regulation; Storage vacuoles = storage. Amoebas use pseudopodia; Zooflagellates use flagella. Only some protozoa have shells. Protozoa reproduce both asexually and sexually. Resistant cysts help protozoa survive unfavorable conditions.