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Cells: Cell Structure


In order to develop a basic understanding of cells in general, they are sometimes compared to factories. So, let’s do that here as well. The factory itself is our cell in this analogy.

There are many different kinds of factories producing all kinds of things. There are small factories and large factories, simple ones and highly complex ones. But they all have certain things in common.

Firstly, a factory needs some kind of a border that separates the inside of the factory from the outside world and provides some protection against physical impact, and unauthorized invasion. This might be a fence or a wall. Within this border, guarded gates allow for controlled traffic in and out of the factory. They regulate who gets in and who gets out, and which products leave and enter the premises.

The outside fence is also where the factory would post banners and notices, communicating important facts, events and status-updates to passers-by, and the outside world in general.

In cells, this job is performed by the cell membrane. It can be found in all types of cells. Some cells also have a cell wall and even a capsule for additional protection and stability – but that’s a bonus.

Within these borders, we find the factory grounds. This is where the main work is conducted. It houses all the separate buildings and areas focusing on certain tasks of the production process. In a cell, we call this the cytoplasm. While the factory grounds are mainly air-filled space, the cytoplasm consists mainly of water, salts and some proteins. It embeds the cell organelles, protects them and facilitates their interaction and communication.

Every factory also needs a business plan, defining what and how much of it the factory is producing, and detailing how it is doing that. A Chief Operating Officer (COO) keeps an eye on everything going on within the factory and makes sure that everything goes according to the business plan and makes adjustments if necessary. If the company planned to expand and build a new daughter factory, he or she would make sure that this new plant would have an exact copy of the business plan, and somebody to oversee the operation.

In a cell, that is the DNA. Just like a COO may or may not have an office of their own, the DNA can be housed within a nucleus (eukaryotic cells) or not (prokaryotic cells). 

And, of course, a factory needs workers who create or assemble the product. They get hired and instructed according to the business plan.

In a cell, these are the ribosomes. They are created from instructions within the DNA, and their job is to assemble proteins following instructions also included in the DNA.

For the work performed within a factory, energy is needed. Most factories have their own generators supplying the plant with the energy needed by burning fuel.  In eukaryotic cells, these power plants are the mitochondria. In prokaryotic cells, the process of making energy available for the cell to use happens at enzymes embedded within the cell membrane.

Furthermore, some factories feature solar panels on their roofs in order to convert sunlight into energy usable within the factory. In plant cells, chloroplasts are the equivalent to those panels. 

In larger and more complex factories, workers don’t work on individual desks, but in assembly lines. They assemble or alter products according to instructions given to them by their superiors. Once they have completed their task on a specific item, they put it onto a conveyor belt which transports it elsewhere for further alteration, packaging or shipment. In a complex (eukaryotic) cell, the endoplasmic reticulum resembles such an assembly line and conveyor belt. Substances are created and/or altered here according to instructions encoded within the DNA, and then they are sent on for alteration elsewhere or excretion

In complex factories which are producing valuable products, the almost finished product is inspected by the quality control department. Here, final adjustments are made, extra material removed, minor changes carried out and final touches put on. Afterward, the product gets packaged and labeled for shipment

In a complex (eukaryotic) cell, this last step is performed by the Golgi apparatus. Here, proteins synthesized in the ER are modified and destined for transportation either to the cell membrane or another location within the cell.

To sum it all up, all factories must have a border, factory grounds, a business plan and a COO, workers and an energy supply – just like all cells have at least a cell membrane, cytoplasm, DNA, ribosomes and features supplying usable energy for the cell (mitochondria (eukaryotes) or enzymes embedded in the cell membrane(prokaryotes)).


The worksheet "Cell Structure" compares different cell types with regards to their composition. Which cell organelles do they all possess? Which cell organelles can only be found in certain cell types?

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Help for task No. 2 of the worksheet "Cell Structure" can be found in the document "Cell Structure - Help". In order to download this document, simply click the button on the left.

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(Cells - Cell Structure - Solution)