How do Organisms Reproduce? · Lesson 3 of 14
Modes of Reproduction Used by Single Organisms
“One cell, several clever ways to become more cells.”
• Relate reproductive mode to body design. • Compare binary and multiple fission. • Explain the plane of division in Amoeba and Leishmania. • Describe multiple fission in Plasmodium. • Describe budding in yeast. • Interpret microscopic observations of unicellular reproduction.
For a unicellular organism, one cell is the whole organism. When that cell divides successfully, reproduction has occurred. Different cell shapes and internal organisation produce different patterns of division.
Fission is an asexual process in which a unicellular parent divides to form two or more daughter individuals.
Binary Fission
In binary fission, the nucleus and cell contents divide so that two daughter cells form. Amoeba lacks a fixed body axis, so division can occur in any plane. Leishmania has a definite elongated shape and a whip-like structure at one end; it divides in a definite orientation along its length.
Binary fission is the division of one unicellular parent into two daughter individuals.
Multiple Fission
In multiple fission, repeated nuclear division is followed by division of cytoplasm, producing many daughter cells at once. Plasmodium, the malarial parasite, reproduces in this way during parts of its life cycle.
Multiple fission is the division of one parent cell into many daughter cells during one reproductive event.
| Feature | Binary fission | Multiple fission | Budding in yeast |
|---|---|---|---|
| Number produced | Two | Many | Usually one or more buds sequentially |
| Main pattern | Parent divides approximately into halves | Many nuclei and daughter cells form | Small outgrowth develops |
| Examples | Amoeba, Leishmania | Plasmodium | Yeast |
| Role of body design | Plane may be variable or definite | Many cells form together | Bud grows from a particular site |
Observing Budding In Yeast
Purpose: observe asexual reproduction in yeast. Prepare a dilute sugar solution, add yeast and keep it warm with a cotton plug. After growth, place a small drop on a slide and observe under a microscope. Small outgrowths on larger yeast cells are buds. A bud enlarges, receives hereditary material and may separate as a new cell.
Observing Binary Fission In Amoeba
Compare a permanent slide of an ordinary Amoeba with one undergoing binary fission. Look for nuclear division, constriction of cytoplasm and formation of two cell masses. The observations show that cell division directly creates two new unicellular individuals.
Problem
An organism divides into two nearly equal daughter cells. Identify the method.
- 1.One parent cell is involved.
- 2.Exactly two daughters form.
- 3.The parent divides rather than producing a small outgrowth.
- 4.The method is binary fission.
Problem
A cell produces many nuclei before separating into numerous daughters. Identify the method.
- 1.Many daughter cells form in one event.
- 2.The pattern is not division into two halves.
- 3.It matches the reproductive pattern of Plasmodium.
- 4.The method is multiple fission.
Problem
Why does Leishmania divide in a definite plane while Amoeba need not?
- 1.Leishmania has an organised elongated body and a flagellum at one end.
- 2.Daughter cells must receive an appropriate arrangement of these structures.
- 3.Division therefore follows the body axis.
- 4.Amoeba has no fixed axis, so its division plane can vary.
Quiz
Which organism can divide in any plane?
What distinguishes multiple fission?
Why does Leishmania divide longitudinally?
What is seen during yeast budding?
Why is cell division reproduction in Amoeba?
Practice Problems
- Compare binary and multiple fission.
- Explain the relationship between body shape and fission plane.
- Write the observation and conclusion of the yeast activity.
- Identify the mode used by Amoeba, Leishmania, Plasmodium and yeast, giving one reason each.
- A micrograph shows one large cell with a small attached cell. Explain how you would distinguish budding from unequal binary fission.
Key Takeaways
• Unicellular cell division directly creates new individuals. • Binary fission forms two daughter cells. • Amoeba can divide in any plane. • Leishmania divides in a definite orientation. • Multiple fission produces many daughters simultaneously. • Plasmodium uses multiple fission. • Yeast reproduces by forming buds.