When Cells Are Made Up of Organelles, Why Can't Organelles Be the Basic Unit of Life?
The cell is often referred to as the fundamental unit of life, but why is this so? To understand this, it's helpful to draw parallels between the micro and macro levels of biological organization.
Understanding Cells as the Fundamental Unit of Life
At the smallest level, cells are the building blocks that make up living organisms, such as humans and other organisms. Within the cell, metabolic processes occur that are essential for the organism's survival. This is why the cell is called the fundamental unit of life, as it is capable of maintaining life on its own.
Comparisons with Organ Systems
Just as organs in an organism depend on one another for function, so too do the organelles within a cell depend on one another. Analogies drawn from the macro level can be helpful here. If we remove an organ from an organism, such as the spleen, one kidney, or even a lung, the organism will often suffer degradation or even death. Similarly, if we were to remove the organelles from a cell and leave the cell structure alone, the cell itself would not function or survive.
Organelles, like mitochondria and chloroplasts, are essential subcellular structures, but they require a medium or environment in which to function. This environment is provided by the cell's plasma membrane. Without the confines of the cell, organelles cannot act as independent units of life.
Survival of Cells and Organelles
Organelles, such as mitochondria, are unique in that they contain genetic material and can code for some of the proteins they are made of. However, much of the genetic material necessary for a cell's metabolism and survival is located in the nucleus of eukaryotic cells. This nuclear genetic material dictates the steps involved in the cell's life cycle.
An analogy can be drawn between a cell and a human being. The nucleus and genetic material are akin to the brain, while the organelles are like the organs. Would we say that a liver is a living thing because it performs vital functions? No, because it is entirely dependent on its surroundings and has no level of self-determination.
Similar to how our body cells rely on our circulatory and nervous systems, cells function within a complex ecosystem within the organism. People need the infrastructure of cities, supermarkets, and means of transportation. However, cells, unlike organelles, still possess a significant degree of self-regulation, influencing yet not being completely determined by the environment around them.
Conclusion
In summary, while organelles are vital components of the cell, the cell as a whole is the fundamental unit of life. Organelles need the cell structure and environment to carry out their functions and cannot sustain life independently. This is why, when considering the basic unit of life, we must include the cell, not just its organelles.