Download The plasma membrane of a cell is a boundary between the cell and

The plasma membrane of a cell is a
boundary between the cell and its
environment. One of the functions of
the plasma membrane is to allow a
steady supply of nutrients to come
into the cell no matter what the
external conditions are. One process
that helps the cell to transport
materials is selective permeability.
This is a process which allows the
plasma membrane of a cell to allow
some molecules into the cell while
keeping others out. Think about a
screen in a window and how it allows
air and light in but insects and other
critters out of your house.
If membranes show selective
permeability, what might happen if a
funnel is filled with starch molecules,
and a selectively permeable membrane is
stretched across the mouth of the funnel
and the funnel is inverted into a beaker
filled with iodine molecules?
Starch molecules are too large to diffuse
across the membrane; iodine molecules
are not. If iodine reacts with starch, the
starch turns blue-black. Suppose you
observe the setup for several hours.
In which direction did the iodine
move?
What is your evidence?
In which direction did the starch
move?
What is your evidence?