How do Organisms Reproduce? · Lesson 4 of 14
Fragmentation
“Sometimes breaking apart is the beginning of a whole new life.”
• Define fragmentation. • Describe fragmentation in Spirogyra. • Relate simple body organisation to fragmentation. • Explain why complex organisms cannot divide cell by cell. • Distinguish fragmentation from fission.
A long green Spirogyra filament can break into several pieces, yet each piece can continue growing. This works because the organism has a relatively simple, repeated body organisation.
Fragmentation is an asexual method in which a multicellular parent breaks into pieces and each suitable fragment grows into a new individual.
Fragmentation In Spirogyra
When a mature Spirogyra filament breaks, its fragments contain living cells arranged in the same simple filamentous pattern. Cell division lengthens each fragment until it becomes an independent filament. No specialised reproductive organ is required for this method.
Observing Spirogyra Filaments
Place one or two green filaments from pond water on a slide with a drop of glycerine and cover them gently. Under a microscope, observe the repeated cells and absence of complex organs. This simple organisation helps explain why a fragment can reproduce the entire filament.
Why Complex Organisms Cannot Simply Fragment
In complex multicellular organisms, specialised cells form tissues, tissues form organs and organs occupy definite positions. A random piece may lack the structures needed for feeding, transport or coordination. Reconstructing the entire arrangement requires organised development, so ordinary fragmentation is impractical.
| Feature | Fission | Fragmentation |
|---|---|---|
| Parent organisation | Usually unicellular | Simple multicellular |
| What divides | The whole parent cell | The body breaks into pieces |
| Growth needed after separation | Daughters grow | Each fragment grows and lengthens |
| Example | Amoeba | Spirogyra |
Problem
A Spirogyra filament breaks into three pieces and each grows. Identify the process.
- 1.The parent is multicellular and filamentous.
- 2.Its body breaks into fragments.
- 3.Each fragment grows into an individual.
- 4.The process is fragmentation.
Problem
Why can a middle fragment of Spirogyra grow without a head or root?
- 1.Spirogyra has no specialised head or root organs.
- 2.Its filament contains repeated, similar cells.
- 3.The fragment already contains the basic body organisation.
- 4.Cell division extends that organisation.
Problem
Why would a random fragment of a mammal not normally form a new mammal?
- 1.A mammal has highly specialised tissues and organs.
- 2.A random piece lacks a complete functional arrangement.
- 3.Most cells cannot independently produce all required cell types and positions.
- 4.Therefore, fragmentation is unsuitable as its reproductive method.
Fragmentation is not ordinary injury. It functions as reproduction only when fragments can organise growth into complete independent individuals.
Quiz
Which organism commonly reproduces by fragmentation?
Why does fragmentation suit Spirogyra?
What grows into a new individual?
Why is fragmentation unsuitable for most complex animals?
How does fragmentation differ from fission?
Practice Problems
- Describe fragmentation in Spirogyra.
- Relate the microscope observation to its reproductive ability.
- Compare fragmentation and binary fission.
- Explain why tissue and organ specialisation limits fragmentation.
- Classify three hypothetical organisms by whether fragmentation would be plausible and justify your choices.
Key Takeaways
• Fragmentation uses pieces of a multicellular parent. • Spirogyra fragments can grow into complete filaments. • Simple repeated body organisation makes fragmentation possible. • Fission usually concerns one whole cell. • Complex organisms require definite tissue and organ arrangements. • A random injury is not automatically reproduction.