---
title: "Single-Celled Organisms"
description: "Explain how unicellular organisms such as bacteria and Amoeba carry out all the functions of life within a single cell"
canonical: https://lightmysky.com/learn/science/single-celled-organisms-mt_g9RcQOhU5d
source: https://lightmysky.com/learn/science/single-celled-organisms-mt_g9RcQOhU5d.md
retrieved: 2026-10-19
---

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# Single-Celled Organisms

Explain how unicellular organisms such as bacteria and Amoeba carry out all the functions of life within a single cell

Subject: Science · Area: Organisms & Life Processes · Ages 11 to 12
Page: https://lightmysky.com/learn/science/single-celled-organisms-mt_g9RcQOhU5d

## Ready when they can

- Names examples of unicellular organisms
- Lists the seven life processes (MRS NERG) and explains how a single cell performs each one
- Contrasts how unicellular organisms meet their needs compared to multicellular organisms

## Lesson: One Cell, Every Job

Most living things you know, like people, dogs, and trees, are built from trillions of cells working together. Some living things are different. A bacterium or an Amoeba is made of just one cell, and cells like these live in pond water and inside you. That single cell has to do every job a whole body does, all by itself. Scientists call the seven jobs MRS NERG: Movement, Respiration, Sensitivity, Nutrition, Excretion, Reproduction and Growth.

*(drawing: Scientists remember the seven life processes with MRS NERG. A single cell must do every one of them on its own.)*

**Example.** An Amoeba stretches part of itself out like a tiny arm to move toward a bacterium, then wraps around it and takes it in as food. Later, that same Amoeba splits itself into two new Amoebae. One cell just moved, fed itself, and reproduced.

*(drawing: A single-celled organism has one cell doing everything. A multicellular organism, like you, has many cells sharing the work.)*

**Tip.** In your body, a skin cell mostly protects and a muscle cell mostly moves you. A bacterium has no other cells to help, so its one cell must feed, sense, excrete, grow, and reproduce, and many can also move, all by itself.

**Recap.** A single cell, like a bacterium or an Amoeba, carries out every life process in MRS NERG completely alone, while your body shares those same jobs across many specialized cells.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Parts of Plant and Animal Cells](https://lightmysky.com/learn/science/parts-of-plant-and-animal-cells-mt_bABr-c2DfV)
- [Cells Under the Microscope](https://lightmysky.com/learn/science/cells-under-the-microscope-mt_VfA4xo4kUv)

## Opens up

- [Pathogens & the Immune System](https://lightmysky.com/learn/science/pathogens-and-the-immune-system-mt_1VIE8FlZvL)
- [Protists: the eukaryotes that are not plants, animals or fungi](https://lightmysky.com/learn/science/protists-the-eukaryotes-that-are-not-plants-animals-or-fungi-mt_CHb8H727nW)