Which of the following organisms reproduces asexually by simple binary fission under suitable conditions?

Introduction / Context:
Asexual reproduction can occur through different mechanisms such as binary fission, multiple fission, budding, fragmentation, and others. Binary fission is a simple type where one parent cell divides into two nearly equal daughter cells. Recognising which organisms use binary fission is an important part of understanding basic microbiology and protozoology. This question asks you to choose the organism that reproduces by simple binary fission under suitable conditions.

Given Data / Assumptions:

• The organisms listed are Amoeba, liver fluke, Plasmodium, and Planaria.
• The focus is on asexual reproduction by simple binary fission.
• We assume knowledge of life cycles of common protozoa and worms.

Concept / Approach:
Amoeba is a unicellular protozoan that reproduces asexually by binary fission. In this process, the nucleus divides mitotically and the cytoplasm splits, producing two daughter Amoebae. Liver fluke is a parasitic flatworm with a complex life cycle involving multiple hosts and stages, but it does not simply divide into two equal individuals by binary fission. Plasmodium, the malaria parasite, reproduces asexually mainly by multiple fission (schizogony), producing many daughter cells at once. Planaria is a flatworm that reproduces asexually by regeneration and fission of body fragments, often considered fragmentation rather than classic binary fission of a single cell. Thus, Amoeba is the best example of simple binary fission.

Step-by-Step Solution:
Step 1: Recall that Amoeba is a single celled organism and divides into two daughter cells of similar size during reproduction. Step 2: Recognise that this division of one cell into two is termed binary fission. Step 3: Consider that liver fluke is a multicellular parasitic worm with eggs, larval forms, and host changes, not a unicellular organism. Step 4: Understand that Plasmodium undergoes multiple fission, releasing many merozoites from a single schizont. Step 5: Note that Planaria reproduces by splitting and regeneration, which is usually classified as fragmentation, not classic single cell binary fission. Step 6: Select Amoeba as the organism that clearly reproduces by simple binary fission.

Verification / Alternative check:
Protozoology textbooks describe Amoeba proteus and related species dividing by mitosis followed by cytoplasmic division, yielding two daughter Amoebae. Diagrams show the nucleus splitting and the cell constricting in the middle. In contrast, Plasmodium life cycle charts use the term schizogony for multiple fission, and liver fluke and Planaria diagrams show more complex multicellular reproduction. These references confirm that Amoeba is the classic example of binary fission among the options given.

Why Other Options Are Wrong:

• Liver fluke: This organism has a complex life cycle with eggs and larval stages, but it does not reproduce by simple binary fission of a single cell.
• Plasmodium: It reproduces asexually by multiple fission (schizogony), not by binary fission producing only two daughter cells.
• Planaria: It can reproduce asexually by splitting and regenerating body parts, which is better called fragmentation, not classic binary fission.

Common Pitfalls:
Learners often associate any kind of splitting with binary fission, but it is important to distinguish between single cell binary fission and multicellular fragmentation or multiple fission. Remember that binary fission is typical of unicellular organisms like bacteria and Amoeba, whereas complex parasites and flatworms use other modes of reproduction. Keeping examples like Amoeba and bacteria in mind for binary fission will help you avoid confusion.

Final Answer:
The organism that reproduces asexually by simple binary fission is Amoeba.