Quick answer: In binary fission one cell divides into two. Amoeba can split in any plane, while Leishmania, which has a whip-like flagellum at one end, splits in a definite (longitudinal) orientation relative to that structure. In multiple fission, as in the malarial parasite Plasmodium, the nucleus divides many times and the cell produces many daughter cells at once.
What is fission?
Fission is a type of asexual reproduction in single-celled organisms in which the parent cell divides to form two or more daughter cells. The parent ceases to exist as an individual; its contents are shared among the offspring.
| Type | Number of daughter cells | Examples |
|---|---|---|
| Binary fission | Two | Amoeba, Leishmania, Paramecium, bacteria |
| Multiple fission | Many, at the same time | Plasmodium (malarial parasite) |
Binary fission in Amoeba
Amoeba is a single-celled freshwater organism with no fixed shape; it moves using pseudopodia.
- Division of the nucleus (karyokinesis): The nucleus lengthens and divides into two.
- Division of the cytoplasm (cytokinesis): A groove forms in the cytoplasm between the two nuclei and deepens until the cell splits.
- Result: Two daughter amoebae, each with one nucleus.
Parent → Nucleus → Nucleus → Two
Amoeba lengthens divides daughters
Plane of division: Because Amoeba has no fixed shape or front and back, the split can happen in any plane.
Binary fission in Leishmania
Leishmania is a single-celled parasite that causes kala-azar (visceral leishmaniasis), a disease that can be fatal if not treated. It is spread by the bite of sandflies.
- Leishmania has a definite shape and a whip-like structure (flagellum) at one end of the cell.
- During binary fission, the cell divides in a definite orientation in relation to this structure, along the length of the cell (longitudinal fission).
- The flagellar apparatus and nucleus are duplicated, and the cell then splits lengthwise into two daughter cells.
NCERT line to remember: In Leishmania, "binary fission occurs in a definite orientation in relation to" the whip-like structure at one end of the cell.
Multiple fission in Plasmodium
Plasmodium causes malaria and is spread by the bite of the female Anopheles mosquito.
- Inside a host cell (for example a liver cell or red blood cell), the nucleus of the parasite divides repeatedly, forming many nuclei.
- Each nucleus gets surrounded by a small amount of cytoplasm, forming many small daughter cells.
- The host cell bursts and releases all the daughter cells (merozoites) at the same time. Each can infect a new cell.
Note on cysts: Some reference books describe multiple fission as happening inside a protective cyst under unfavourable conditions. That description applies to some other protozoa. In Plasmodium, multiple fission happens inside the host's cells. NCERT simply says Plasmodium "divides into many daughter cells simultaneously".
Summary table
| Feature | Amoeba | Leishmania | Plasmodium |
|---|---|---|---|
| Type of fission | Binary | Binary | Multiple |
| Plane of division | Any plane | Definite, lengthwise, relative to the flagellum | — (many cells formed at once) |
| Special feature | No fixed shape; pseudopodia | Whip-like flagellum at one end | Nucleus divides many times |
| Daughter cells | 2 | 2 | Many |
| Disease | Free-living, not a disease agent | Kala-azar | Malaria |
Exam tips
- For "how does binary fission in Leishmania differ from Amoeba?", mention the whip-like structure and the definite orientation of division.
- Name the disease with the organism: Leishmania → kala-azar; Plasmodium → malaria.
- Draw simple labelled diagrams showing the nucleus dividing before the cytoplasm.
- Remember that both binary and multiple fission are forms of asexual reproduction, so the offspring are genetically similar to the parent.
Common mistakes
- Saying Leishmania can divide in any plane. Only Amoeba does that.
- Writing that Amoeba causes amoebic dysentery. The disease is caused by a different organism, Entamoeba histolytica.
- Confusing multiple fission with budding or fragmentation.
- Saying the cytoplasm divides before the nucleus. The nucleus divides first.
Frequently Asked Questions
What is binary fission?
Binary fission is asexual reproduction in which a single-celled organism divides into two daughter cells, as in Amoeba and Leishmania.
How is binary fission in Leishmania different from that in Amoeba?
Amoeba can split in any plane because it has no fixed shape. Leishmania has a whip-like structure at one end and splits in a definite orientation in relation to it.
Which disease is caused by Leishmania?
Leishmania causes kala-azar, also called visceral leishmaniasis. It is spread by sandflies and can be fatal without treatment.
What is multiple fission? Give an example.
In multiple fission, the nucleus divides many times and the organism forms many daughter cells at once. The malarial parasite Plasmodium reproduces this way.
Which mosquito spreads malaria?
The female Anopheles mosquito spreads the malarial parasite Plasmodium.