Control Systems in the Living World - Building the Most Complex Structure on Earth - page 22

The Control System in Unicellulars
Both a unicellular and a multicellular organism are an architectural magnum opus ,
displaying incredibly high degrees of organization, and biology has not been able to
answer two important questions that are crucial to understanding the nature of uni-
cellular organisms. First, how do these microscopic beings determine the relative
size, number, and spatial arrangement of organelles within the microscopic cell? We
need to know where the “knowledge” necessary for producing and assembling the
highly ordered structures comes from.
Second, how do they determine their adaptive behavior in search of sources of
food and in avoidance behavior? They have to search for and find these sources and
get access to them. Only rarely provided with food by luck, they have to go after
food sources (it is the prophet that goes to the mountain, not the reverse). Simple as
this may seem, their foraging behavior implies that the unicellular is capable of dis-
criminating between the inorganic and organic debris and localize the latter. On its
way to the source, it may come across a barrier and has to figure out how to circum-
vent it. Sometimes they have to use environmental cues such as light (phototaxis) or
chemicals (chemotaxis) as leads to sources of food. Even their movement and neces-
sary corrections in the direction of the source of food require precise calculations
on the direction of the beating of cilia or flagella in ciliates or in determining the
form, size, and direction of the beating of pseudopodia in amoeba. All these func-
tions require adaptive changes in the structure of the cytoskeleton and microtubules
of cilia and flagella and in the actin subunits of microfilaments. We need to know
where all the calculations necessary for determining these adaptive changes in struc-
ture and behavior are made.
Both the spatial arrangement of organelles within the cell and the adaptive
behaviors mentioned above are not randomly occurring events that require specific
information to take place. Hence, they point in the direction of a specialized con-
trol center that receives information on the internal and external environment and
by processing that information, it produces instructions (chemical signals) that, via
effectors, determine the spatial arrangement of organelles and adaptive foraging
behaviors. But essentially, these are the functions of a control system. From a theo-
retical viewpoint as well, it clearly seems that complex systems such as unicellular
organisms could not subsist, let alone reproduce and evolve, without a control sys-
tem. The question, however, would arise whether central or separate local systems
of control are responsible for coordinating vital functions in unicellulars. We need
to know where the control system and its controller are located within the cell of a
unicellular organism. And the only rational approach in looking for the “controller”
of these functions is to trace back the possible causal chain by sequentially following
the described functions to their proximal causes and farther upstream.
The reductionist Zeitgeist still makes many of us focus on separate organelles
rather than on the whole unicellular organism; we see functions and behaviors of
unicellulars as products of specialized organelles, including chromosomes (for cell
reproduction), ribosomes (for protein synthesis), cytoskeleton (for cell shape and
transport of molecules throughout the cell), Golgi apparatus (for processing and