Growing Microorganisms

Microorganisms are organisms that are too small to be seen with the naked eye. In other words, they are organisms that you need a microscope to see. This includes bacteria, most other unicellular organisms and some small multicellular organisms.

Bacteria and other microorganisms can be grown in laboratories. A group of microorganisms being grown in a laboratory is called a culture. Cultures of microorganisms can be used in experiments.

This page will mainly focus on growing cultures of bacteria. However, many of the principles and techniques described here also apply to other microorganisms.

Bacteria can be grown in a nutrient broth solution or on an agar gel plate

In order to grow bacteria in a laboratory, you need to provide them with somewhere to live and you need to give them the nutrients that they need for growth. There are two main ways of doing this.

The first method is to grow the bacteria in a nutrient broth solution. A nutrient broth solution is a solution made by dissolving nutrients in water. The bacteria grow and divide in the solution, and form clusters of bacterial cells which are spread throughout the liquid.

Photograph of a conical flask on a bench in a lab. The flask contains a dark coloured solution which is frothy at the top. This is a nutrient broth solution with bacteria growing in it.

A nutrient broth solution with bacteria growing in it. Image by Nothingserious on Wikimedia Commons. (CC BY-SA 4.0 -

The second method is to grow the bacteria on an agar gel plate. Agar is a jelly-like substance. In liquid form, it can be mixed with nutrients and then poured into a Petri dish, where it sets to form a jelly-like solid. Petri dishes are sometimes called plates. Therefore, a Petri dish with agar in it is called an agar gel plate.

Photograph of two agar gel plates on a flat surface. The plate on the left has the lid on. The plate on the right has the lid off.

Agar gel plates (Petri dishes containing agar with nutrients mixed into it). Image: Y tambe via Wikimedia Commons (GNU Free Documentation License -,_version_1.2)

When bacteria are added to an agar gel plate, they grow on the surface of the agar, using the nutrients that have been mixed in with it for their growth. The bacteria form large clusters of cells called colonies. The colonies grow large enough to be seen with the naked eye.

Photograph of an agar gel plate with bacterial colonies growing on it. The plate is a circular Petri dish. The agar is a greeny yellowing substance that fills the plate. The bacterial colonies appear as dark green/blue circles on the surface of the agar. They very in size. Many of them are lined up in rows with each other.

Bacterial colonies growing on the surface of an agar gel plate. Many of the colonies are lined up in rows because this is the way that the scientist originally spread the bacteria on the agar.


Flashcards help you memorise information quickly. Copy each question onto its own flashcard and then write the answer on the other side. Testing yourself on these regularly will enable you to learn much more quickly than just reading and making notes.


What are microorganisms?


What is a culture?


What are the two main ways of growing bacteria?


What is a nutrient broth solution?


What is an agar gel plate?


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