1. Definition:

Unicellular organisms are simple living beings consisting of a single cell that performs all the essential life functions, including nutrition, respiration, excretion, reproduction, and movement.

2. Nutrition in Unicellular Organisms:

• Diffusion: This is the method of absorbing nutrients from the surrounding environment through the cell membrane.
Note: Diffusion occurs when the concentration of solutes is higher outside the cell than inside.
• Phagocytosis: This involves engulfing food by forming pseudopodia to wrap around it.
Note: Phagocytosis is commonly seen in larger unicellular organisms like amoeba.

3. Functions of the Ectoplasm:

• Transport: It transports nutrients into the cell and waste products out.
• Food Capture: The ectoplasm forms pseudopodia, helping unicellular organisms capture food during phagocytosis.
• Excretion: The ectoplasm eliminates waste products from the cell.
• Respiration: The ectoplasm carries out respiration to provide energy for the cell.
• Protection: The ectoplasm protects the cell from external environmental factors.

4. Functions of the Endoplasm:

• Containing the Nucleus: The endoplasm holds the nucleus, which stores the cell’s genetic information.
• Nutrition: The endoplasm contains organelles involved in the cell’s metabolic and energy processes.
• Reproduction: The endoplasm contains organelles that participate in the cell’s reproductive process.

5. Reproduction in Unicellular Organisms:

Asexual Reproduction:

• Binary Fission: This is the most common form of reproduction in unicellular organisms, where the parent cell divides into two identical daughter cells.
  Example: E. coli bacteria, amoeba.
• Multiple Fission: This involves multiple nuclear divisions followed by cell division, resulting in several daughter cells.
  Example: Plasmodium (malaria parasite).

Sexual Reproduction:

This is rare in unicellular organisms and involves the fusion of two gametes to form a zygote.

6. Transmission Pathways of Unicellular Diseases:

• Active Form: This is the disease-causing form of the unicellular organism, capable of movement and invading the host organism.
• Cyst Form: This form exists in the external environment, protected by a shell, allowing it to survive adverse conditions.
• Intermediate Host: This is an animal that facilitates the transmission of the unicellular organism from one person to another or from an animal to a human.
Note: Intermediate hosts can include flies, mosquitoes, cockroaches, snails, etc.

7. Examples of Intermediate Hosts:

• Houseflies: Carry amoeba that cause diarrhea.
• Anopheles Mosquito: Carries the Plasmodium parasite that causes malaria.

8. Differentiating Unicellular Organisms:

Based on Nuclear Structure:

• Prokaryotic Cells: Lack a nuclear membrane.
• Eukaryotic Cells: Have a nuclear membrane.

9. Classification of Unicellular Organisms:

Based on Locomotion Organs and Methods:

• Flagellates: Move using flagella.
• Amoebas: Move using pseudopodia.
• Ciliates: Move using cilia.

10. How Many Classes Are Unicellular Organisms Divided Into?

Unicellular organisms are divided into four classes: Flagellates, Amoebas, Ciliates, and Sporozoans.

11. Examples of Unicellular Organisms:

• Pig Amoeba (Entamoeba polecki): This is a type of amoeba that parasitizes the intestines of pigs.
• Dientamoeba fragilis: Recently classified as a flagellate due to its similar antigenicity and ultrastructural features to Trichomonas.
• Entamoeba dispar: A non-pathogenic amoeba in humans, distinguished from Entamoeba histolytica through molecular techniques like PCR.

12. Distinguishing Entamoeba histolytica / Entamoeba dispar:

PCR (Polymerase Chain Reaction): A highly accurate technique for differentiating these two amoeba species.