Why are cells so small?

Why are cells so small?

Biology is a fascinating life science that’s so complex it takes professional scientists years to fully grasp all of its intricacies and nuances (if ever, given our understanding of living things is ever-evolving). 

Cells are the smallest unit of life and are literally the building blocks of all living things. Some calculations estimate the average human body has upwards of 60 trillion cells inside of it, which is just mind-boggling when you start to imagine all those life-forms coursing through you. 

But just why are cells so small? 

There are several logical reasons why cells are so small. Being small allows them to regenerate en masse without the organism they’re supporting dying or shutting down. 

Cells inside an organism (like the human body) don’t live as long as the organism itself. The average person in some countries lives until they’re in their eighties, but the cells that power them die off long before then. 

Cell systems do their best to repair any damaged cells, but it’s often far more efficient for unhealthy or struggling cells to simply die off and be replaced by newer, improved cells. When this process of cell recycling takes place, it’s far better that the cells are small and plentiful than if they were large and scarce.

For example, imagine if your feet only consisted of two cells each. If the two cells in your left foot died off, you’d be unable to walk until the new cells were introduced and matured to perform the role of the dead cells. This would leave the human body, or any organism, woefully inhibited. 

There is also a more scientific reason why cells are so small. Cells are very complex living units that need to consume and excrete energy, and one of the ways they do this is via a process called ‘diffusion’, which involves the circulation of molecules to take on and eliminate waste. 

Diffusion as a process works best the faster it occurs, and it speeds up when a small is small and moves over shorter distances. So the fact cells are small helps the diffusion process, which helps a cell consume and eliminate the waste it needs to stay healthy. 

Importantly, too, as a cell increases in size, the ratio between the volume of the cell and its surface area diminishes, which means there is less surface area (relative to the volume of the cell) for the cell to exchange the material it needs to survive. A larger cell means a smaller ratio of surface area to volume, which leads to inhibitors on the cells exchanging vital materials, which can lead to their demise. 

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