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Unicellular and Multicellular Life
- The bodies of all living things are made of cells.
- Plants and animals are made of many cells.
- So they are called multicellular organisms.
- Some microbes, like bacteria, are made of one cell.
- So they are called unicellular organisms.
Example 1 — Unicellular Microbe
- A bacterium is made of a single cell.
- That one cell does all its life jobs.
- So it is a unicellular organism.
Example 2 — Yeast vs Mould
- Yeast is a single-celled fungus.
- Mould is a many-celled fungus.
- So fungi can be unicellular or multicellular.
Important Points
- Microbe cells also have a cell membrane, like plant and animal cells.
- Bacteria have no proper nucleus; they have a nucleoid instead.
- An electron microscope can magnify a cell about 10,00,000 times.
Definition — Unicellular Organism
A unicellular organism is a living being made of a single cell that carries out all life functions.
Definition — Nucleoid
A nucleoid is the region in a bacterial cell that holds its genetic material, since bacteria have no well-defined nucleus.
🧠 Test Yourself — Section 2.5
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What is a unicellular organism?
View Answer
A living being made of a single cell, like a bacterium. -
Is yeast unicellular or multicellular?
View Answer
Yeast is a unicellular fungus, while mould is multicellular. -
What do bacteria have instead of a nucleus?
View Answer
A nucleoid, since they have no well-defined nucleus. -
Why can fungi not make their own food?
View Answer
They have no chloroplasts, so they cannot do photosynthesis. -
Which microscope magnifies a cell about 10,00,000 times?
View Answer
An electron microscope.
