Chapter 2 – Orientation for the Bio-Curious 17
mechanical stimuli and also respond to changes in the environment with collective behavior.
For example, the evolution of antibiotic resistance in bacteria may be driven by selective
pressures not at the level of the single bacterial cell as such, but rather targeting a population
of cells found in the biofilm, which ultimately has to feedback down to the level of replicating
bacteria cells.
It is an intriguing and deceptively simple notion that putatively selfish genes (Dawkins,
1978), at a length scale of ∼10−9 m, propagate information for their own future replica
tion into subsequent generations through a vehicle of higher-order, complex emergent
structures at much higher length scales, not just those of the cell that are three orders of
magnitude greater but also those that are one to three orders of magnitude greater still. In
other words, even bacteria seem to function along similar lines to a more complex multi
cellular organism, and in many ways, one can view a multicellular organism as such an
example of a complex, emergent structure. This begs a question of whether we can truly
treat an isolated cell as the basic unit of life, if its natural life cycle demands principally
the proximity of other cells. Either way, there is no harm in the reader training themselves
to question dogma in academic textbooks (the one you are reading now is not excluded),
especially those of classical biology.
KEY POINT 2.4
“Unicellular” organisms exist in the context of many cells, of their own species, and of
others, and so our understanding of their biology should take this into account.
Cells can be highly dynamic structures, growing, dividing, changing shape, and restruc
turing themselves during their lifetime in which biologists describe as their cell cycle. Many
cells are also motile, that is, they move. This can be especially obvious during the develop
ment stages of organisms, for example, in the formation of tissues and organs that involve
programmed movements of cells to correct positions in space relative to other cells, as well
in the immune response that requires certain types of cell to physically move to sites of infec
tion in the organism.
2.2.2 CELLS SHOULD BE TREATED ONLY AS A “TEST TUBE OF LIFE” WITH CAUTION
A common misconception is that one can treat a cell as being, in essence, a handy “test
tube of life.” It follows an understandable reductionist argument from bottom-up in vitro
experiments (in vitro means literally “in glass,” suggesting test tubes, but is now taken to
mean any experiment using biological components taken outside of their native context in
the organism). Namely, that if one has the key components for a biological process in place
in vitro, then surely why can we not use this to study that process in a very controlled assay
that is decoupled from the native living cell. The primary issues with this argument, however,
concern space and time.
In the real living cell, the biological processes that occur do so with an often highly intricate
and complex spatial dependence. That is, it matters where you are in the cell. But similarly, it
also matters when you are in the cell. Most biological processes have a history dependence.
This is not to say that there is some magical memory effect, but rather that even the most
simple biological process depends on components that are part of other processes, which
operate in a time-dependent manner in, for example, certain key events being triggered by
different stages in the cell cycle, or the history of what molecules in a cell were detected out
side its cell membrane in the previous 100 ms.
So, although in vitro experiments offer a highly controlled environment to understand
biology, they do not give us the complete picture. And similarly, the same argument applies
to a single cell. Even unicellular organisms do not really operate in their native context solely
on their own. The real biological context of any given cell is in the physical vicinity presence