What is life?
This is the first article in an introductory biology series I’ll be writing over the next 4-6 weeks, starting from scratch and covering approximately final year high school/first semester university biology. My revision has begun, so buckle up: your learning is about to begin too.
The question of what is life? is as simple as it’s going to get, but also the most complex. Life is a weird, multi-faceted, conditional thing, and sometimes it’s hard to draw a line between what’s alive and what’s not. If I showed you a diamond, a virus, a fungus, a volcano, a dog, and a bacterium, how would you know which ones are living organisms?
There are a few key components of life, usually abbreviated to the acronym HOMER:
- Homeostasis: This is the regulation of internal conditions, like keeping pH and temperature constant. Polar bears, for example, help regulate their internal temperature with their thick coats.
- Organisation: Living things are built from complex assemblage of molecules, the smallest units of which are called cells.
- Metabolism: This is the transformation of energy for an organism’s use—for example, humans convert chemical energy from our food into energy that our cells can use to perform vital functions.
- Evolution: This is technically optional, because some living organisms don’t really evolve, but most are able to slowly change the genetic information passed down over generations, giving rise to diversity.
- Reproduction: Living organisms are able to pass on hereditary information into offspring.
Thinking about these five properties, let’s reconsider the list. A diamond and a volcano don’t tick any of our boxes and so are definitely not alive. A dog and a fungus are definitely alive. But the last two are more difficult to consider. What’s the difference between a bacterium and a virus? Well, we have to know a little bit more about them. Viruses are so harmful because they function by injecting their genetic material into a host, taking over the reproductive system in order to make more copes of themselves. They therefore don’t have their own reproductive system, since they have to hijack someone else’s—so they’re not alive.
Bacteria, on the other hand, tick all our boxes. We’ll find out a little more about them in the next article.
Further resources: “First Life" - David Attenborough documentary