The cell is the microscopic building block of most living organisms. Biology students learn about the parts of a cell and how they function, but it can be difficult to imagine how a cell really works. A useful way to gain a deeper understanding of what goes on inside a cell is to compare it with familiar objects and places in everyday life. Teachers often assign cell analogy projects for this reason. A cell analogy project requires a real-life place or object in place of a cell that describes how the place's or object's components are like those of a cell.
Cells are Like Schools
The hard exterior of a school building keeps it standing like a cell wall does in a plant cell. If you are late to school, you might find the doors locked. Doors are like the selective openings in cell membranes, which only open at certain times and only for certain chemical signals. In a cell, vacuoles operate as small spaces to store things, much like lockers work in a school. The main office functions like the nucleus in a cell, directing the action. The crowded hallways everyone walks through are comparable to the endoplasmic reticulum, which the cell uses to get information from the nucleus to other organelles.
The teachers follow curriculum guidelines to provide students with knowledge and critical thinking skills. Compare teachers to ribosomes in this cell analogy, which are tiny organelles made of proteins that translate information from the nucleus. Students are like mitochondria, converting learning materials into knowledge instead of converting glucose into a source of energy called adenosine triphosphate, or ATP. The Golgi apparatus packages and stores material before it leaves a cell, just like a classroom contains students until school is out.
Cells are Like Cities
In the past, many cities had walls surrounding them to provide structure to the city limits, and so that only people with permission could enter. In that way, they worked both like a cell wall providing a rigid boundary to a plant cell, and like a plasma membrane that only allows materials in with the correct chemical signal. City hall serves as a city’s headquarters, where laws are made and where historical records are often kept. The nucleus serves as a cell’s headquarters, where it stores genetic information in the form of DNA.
Many cities have industrial districts, where most of the factories cluster together. In a cell, the equivalent of an industrial district is the rough endoplasmic reticulum, home to the many ribosomes that assemble proteins. A city’s power plant serves as its energy manufacturer, converting a fuel like coal or gas into electricity. Mitochondria does the same thing in a cell, but it converts glucose into ATP. A post office stores all the city’s outgoing mail until delivery, like the Golgi apparatus in a cell. Visitors to the city might leave their cars in parking lots while they visit different sites. The parking lots provide storage for those cars like vacuoles do for materials in cells.
Cells are Like Cars
A car’s metal body maintains its shape even when it travels at high speeds. The structure its body provides makes it comparable to a cell wall. You can compare the windshield and windows to plasma membranes, since they protect the inside of the car from invaders like insects and dirt. Cars need power to drive, and this happens when fuel, converts to energy in the engine, much like mitochondria creating ATP. In a cell, the endoplasmic reticulum helps with the transport of material through the cell; In a car, the fuel line provides fuel to the engine from the gas tank.
A car's driver is equivalent to the nucleus of a cell. If the driver does not step on the gas, the car does not move. The gas pedal conveys the driver’s desire to move to the engine, similar to what a ribosome does with information from the nucleus. As the engine burns fuel, it creates exhaust, which passes through the catalytic converter to make the fumes less harmful to the air before exiting the vehicle. Like the catalytic converter, the Golgi apparatus does its own version of packaging up materials in transport. Both the car trunk and the glove compartment function as storage spaces as do vacuoles in cells.
Cells are Like Zoos
If you have ever gone to a zoo, you have seen many animal enclosures connected by walking paths. Somewhere in the zoo is the administration office where its staff make decisions about exhibits, animals and other zoo activities. This represents the nucleus of the zoo. Before you could get into the zoo, you buy a ticket before you pass through its gates. Zoos typically have wall enclosures around them to keep freeloaders out and to protect the animals, which operates like a cell wall. The gate is like an opening in a cell membrane that allows only ticket holders through. After entering the zoo, you might participate in a tour led by a zookeeper. Like ribosomes that translate information from the nucleus into fuel, the zookeepers take scientific knowledge about animals and share it with visitors.
The walking pathways connect the different parts of the zoo like endoplasmic reticulum does inside a cell. Enclosures serve as a kind of protective storage for the animals like vacuoles do for nutrients and other materials in a cell. The animals themselves provide the attraction for visitors, fueling zoo operations like mitochondria does in cells. Near the exit, the zoo might have a gift shop, where visitors can purchase stuffed versions of the animals they saw before leaving. If you had visited a microscopic cell instead of a zoo, the Golgi apparatus would have served the function of storing and packaging items before they left the cell.