Lesson 3 ·Class 9 · Five Kingdom Classification · Respond
Why Two Kingdoms Failed
The organisms that would not fit.
For centuries everything was either a plant or an animal. Here are the cases that broke the system.
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Situation 1 of 3
🦠 Euglena has chlorophyll and makes its own food in light — but it also has a flagellum, swims freely, and feeds on other organisms in the dark. Under the old two-kingdom system, where does it go?
Free play — read each situation and choose what you would do; each choice explains itself. Switch to when you're ready to test yourself.
Whittaker's five kingdoms use three criteria: cell structure (prokaryote or eukaryote), body organisation, and mode of nutrition.
What this lesson covers
Challenges to clear
- Work through all three cases correctly.
- Answer the Euglena case — the organism that broke the two-kingdom system.
The task
For centuries everything was either a plant or an animal. Here are the cases that broke the system.
What this lesson covers
- Euglena has chlorophyll and makes its own food in light — but it also has a flagellum, swims freely, and feeds on other organisms in the dark. Under the old two-kingdom system, where does it go? Best choice: Neither — it shows the two-kingdom system is inadequate — Exactly the reasoning Whittaker used. Euglena belongs in Protista, a kingdom created for such organisms.
- A mushroom cannot move and has a cell wall, so botanists long called it a plant. But it has no chlorophyll and absorbs food from dead matter. Should fungi stay in the plant kingdom? Best choice: No — it cannot photosynthesise, so it does not feed like a plant at all — Nutrition is the fundamental difference. Fungi are saprophytic or parasitic absorbers, which earns them their own kingdom.
- Bacteria have a cell wall but no true nucleus and no membrane-bound organelles. Where do they belong? Best choice: In a kingdom of their own, because they are prokaryotic — Prokaryote versus eukaryote is the deepest division in all of life — deeper than plant versus animal. Hence Kingdom Monera.
Hint
Whittaker's five kingdoms use three criteria: cell structure (prokaryote or eukaryote), body organisation, and mode of nutrition.