Geology Reference
In-Depth Information
DNA. Furthermore, we found no organs of digestion, no gut, no stomach; so how does
the bacterium eat and excrete? The answer lies in our other discovery—that the mi-
crobe's cell membrane is made porous thanks to the multitude of tiny holes that pepper
its semi-fluid surface. The bacterium eats by absorbing tiny food molecules from its en-
vironment through these pores, and it excretes by sending wastes out through them. Life
of any kind is utterly impossible without cell membranes, and all cell membranes dis-
play a stunning degree of agency and sentience, for all of them, no matter where they
are found, are able to carefully select what goes in and out through their pores. We've
encountered this fact before; cell membranes are
semi-permeable.
Surprisingly, perhaps the most organised aspect of the bacterial cell is the chemical
soup that we so glibly ignored in our first exploration. Let's shrink ourselves down again
and return to the deep interior of our bacterium, but this time we'll stay in one place
and look very carefully at the teeming chemical melée in front of us. After a while we
recognise certain large molecular beings such as sugars, proteins and ATP, the univer-
sal energy-carrying molecule found in the cells of every single being, from microbes to
elephants. After a few hours of careful observation and sampling we come to a stun-
ning realisation: the overall composition of the cell's interior has remained relatively
constant, despite the fact that the molecular beings are ceaselessly creating and consum-
ing each other. This relative constancy is astonishing, for it suggests that the whole mo-
lecular network is able to regulate its own internal environment within limits favour-
able for its own existence. The cell does this by constantly re-making the components
of the complex networks that operate inside its semipermeable boundary. This continu-
al minute-by-minute, second-by-second re-creation is a major hallmark of life, which
the Chilean biologists Humberto Maturana and Francisco Varela have called
autopoies-
is
—'self-making', or more literally, 'self-poetry'. In order for autopoietic entities to
keep re-making themselves—in order to stay alive—it is indispensable that they have
access to an external source of usable energy that can be chemically captured within the
cell to be slowly released whenever and wherever it is required to build up molecules
that have been worn down or have simply fallen apart during the rough and tumble of
life itself.
But energy is needed not just for repair; it is also needed for eating and excretion.
Living beings absorb nutrients from the outside world to stay alive: sometimes as tiny
molecules brought in across a bacterial cell membrane, and sometimes as prey brought
down by a pride of lions after a long hard chase in the intense heat of an African after-
noon. After eating comes excretion. All life processes produce substances which would
be toxic if not removed, and so all living beings must excrete, or better, donate, these
substances to their surroundings to stay alive. The miracle of ecology is that the waste
products of one kind of being are food for another, which means that living beings or-
