Unicellular vs Multicellular

Unicellular vs Multicellular

Middle School

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Learning Objectives

• Define and differentiate between unicellular and multicellular organisms.

• Explain how unicellular and multicellular organisms carry out essential life functions.

• Identify and provide examples of both unicellular and multicellular organisms.

• Describe the concept of cell specialization in multicellular organisms.

Key Vocabulary

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Organism

An organism is any living thing that can carry out life processes on its own.

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Cells

Cells are the smallest units of life and the basic building blocks of all living things.

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Unicellular

A unicellular organism is a living being that is made up of only one single cell.

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Multicellular

A multicellular organism is a living being that is made up of more than one cell.

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Reproduce

To reproduce is the biological process of making more organisms of the same kind or species.

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System

A system is a group of interacting or interrelated parts that work together to form a whole.

What Are Cells and Organisms?

• An organism is any living thing, from a tiny bacterium to a large whale.

• Cells are the basic building blocks that make up all organisms.

• They perform different functions to keep the organism alive.

Multiple Choice

What are the primary roles of a cell in an organism?

• To take in nutrients and get rid of wastes.

• To store water for the organism.

• Only to help the organism move.

• Only to provide structure to the organism.

Unicellular Organisms

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Amoeba

• An amoeba moves around by changing its body shape.

• It eats by surrounding smaller food particles with its body.

• This organism has a very flexible cell membrane.

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Euglena

• A euglena moves forward using its long, whip-like tail.

• It can make its own food just like a plant.

• This organism has an eye spot to help it find light.

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Paramecium

• A paramecium moves using many tiny hairlike structures.

• These hairs also help it sweep in food to eat.

• This organism has a distinct slipper-like body shape.

Multiple Choice

Which unicellular organism is described as moving by changing its shape and surrounding its food?

• Amoeba

• Euglena

• Paramecium

• Bacteria

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What Are Multicellular Organisms?

• Multicellular organisms are living things made of more than one cell.

• ​They have different types of specialized cells that perform specific jobs.

• Transport systems move nutrients and gases throughout the organism's body.

• Humans, plants, and animals are examples of multicellular organisms.

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Multiple Choice

Why do multicellular organisms require specialized systems like a transport system?

• Because only their surface cells can directly exchange materials with the environment.

• Because they do not need to get rid of waste products.

• Because all of their cells perform the exact same function.

• Because they are simpler than unicellular organisms.

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Key Differences and Similarities

Similarities

• ​Both single-celled and multicellular organisms need to get rid of waste materials to survive.

• ​​This waste removal process is a shared characteristic that is essential for all living things.

• ​Getting rid of waste helps them maintain a stable and healthy internal environment.

Differences

• ​Multicellular organisms are more complex, with specialized cells that perform different jobs.

• ​​A single-celled organism has only one cell to carry out all life functions.

• ​The number of cell types helps scientists classify an organism as uni- or multicellular.

Multiple Choice

What is the most helpful factor for a scientist to determine if an organism is unicellular or multicellular?

• The number of different types of cells in the organism.

• The organism's color.

• Whether the organism can get rid of waste.

• Where the organism lives.

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Common Misconceptions About Cells

Misconception	Correction
Single-celled organisms are not real living things.	They are complete living things that perform all life functions in one cell.
All single-celled organisms are bacteria.	Besides bacteria, there are other types like amoebas, paramecia, and euglena.
Bigger living things must have bigger cells.	They have more cells that are specialized, not necessarily bigger cells.

Multiple Choice

Why do multicellular organisms need transport systems, while unicellular organisms do not?

• Because in multicellular organisms, not all cells are in direct contact with the outside environment.

• Because multicellular organisms are smaller and more compact.

• Because unicellular organisms reproduce by splitting, which moves materials automatically.

• Because unicellular organisms do not need to take in nutrients or expel waste.

Multiple Choice

How does the function of a single cell in a unicellular organism compare to the function of a single cell in a multicellular organism?

• A multicellular organism's cell does everything; a unicellular organism's cell is specialized.

• They both perform all the same life functions.

• Cells in both types of organisms only focus on reproduction.

• A unicellular organism's cell does everything; a multicellular organism's cell is specialized.

Multiple Choice

A scientist discovers a new organism that is composed of many different types of cells, including some that form a protective outer layer and others that help it move. What can the scientist conclude about this organism?

• It cannot be a living organism.

• It is a prokaryote because it can move.

• It is a complex, multicellular organism with specialized cells.

• It is a simple, unicellular organism like a bacterium.

Multiple Choice

A unicellular organism must perform all essential life functions (e.g., digestion, excretion, reproduction)

within a single boundary. This limits their:

• Need for energy

• Mobility

• Efficiency and complexity

• Rate of evolution

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Summary

• All living things are made of cells; unicellular organisms have only one cell.

• Multicellular organisms have many specialized cells that form complex systems.

• A key similarity is waste removal; a key difference is complexity.

• The number of cell types distinguishes unicellular and multicellular life.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4