Page 116 - The Miracle in the Cell Membrane

The Miracle in the Cell Membrane

motion in this car riage, addi tion al ener gy is need ed.
In dif fu sion, as already stat ed, the sub stance behaves
accord ing to the pre vail ing den si ty. However, if a sub -
stance is to move from a lower den si ty to a high er one,
then ener gy is expend ed and active trans port takes place.
Passive trans port may be com pared to how water flows
down hill under the effect of grav i ty. Active trans port, on
the other hand, may be thought of as water being car ried
up a hill against the force of grav i ty, by the expend i ture of
ener gy. Similarly, some one car ry ing a load upstairs or
draw ing water from a well requires ener gy. In this form of
pas sage through the cell mem brane, there fore, requires
ener gy togeth er with enzymes.
Active trans port is required for sodi um, potas si um,
cal ci um, car bon, iron, nitro gen, urate ions, var i ous amino
acids and sug ars. Inside the cell, there must be con sid er a -
ble lev els of potas si um (K+), mag ne si um (Mg++), phos -
phate and sul fur for all kinds of func tions to take place in
our inter nal and exter nal organs, for cer tain con trol mech -
a nisms inside the cell to oper ate, and to ena ble cell reac -
tions. At the same time, there must be high lev els of sodi -
um (Na+), cal ci um (Ca++) and bicar bon ate in the outer
part of the cell.
If these sub stan ces entered and left through the cell
mem brane, not by active trans port but in the easy way,
involv ing no ener gy expend i ture—as water, urea, oxy gen
and car bon diox ide do—what would hap pen? In that
event the ions inside and out side the cell would be equal.
You could do noth ing with your mus cles because they
would not con tract. You could not taste the food that

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