How various mechanisms by which substances cross the cell me
How various mechanisms by which substances cross the cell meHomeostasis is essential to the cell’s survival. The cell membrane is
responsible for homeostasis. The membrane has a selective permeability
which means what moves in and out of the cell is regulated. Amino
acids, sugars, oxygen, sodium, and potassium are examples of substances
that enter the cell. Waste products and carbon dioxide are removed from
the cell. All of these substances cross the membrane in a variety of
ways. From diffusion and osmosis, to active transport the traffic
through the cell membrane is regulated.
Diffusion is the movement of molecules form one area of higher
concentration to an area of lower concentration. Concentration gradient
causes the molecules to move from higher concentration to a lower
concentration. The side of the membrane that has the higher
concentration is said to have the concentration gradient. It drives
diffusion because substances always move down their concentration
gradient. The pressure gradient also plays a role in diffusion. Where
this is a pressure gradient there is motion of molecules. The pressure
gradient is a difference in pressure between two different points. If
the concentration of one side of the membrane is greater than the
molecules will travel from the higher to lower concentration.
Eventually there will be a dynamic equilibrium and there will be no net
movement of molecules from one side to the other.
Osmosis is the diffusion of water. Like diffusion, the water moves
from a region of higher water potential to a region of lower water
potential. Solutions have three different stages that the solutes can
be classified in: isotonic, hypertonic, and hypotonic. Isotonic is when
the solutions have equal amounts of solutes. Like equilibrium, there is
no net change in the amount of water in either solution. When the
solutions have different concentration of solutes then the one with less
solute is hypotonic and the one with more solute is hypertonic.
Hypotonic takes in the solute from the hypertonic side that gives away
the solute. There will be a net movement in these types of solution.
The molecules will move from the hypotonic solution into the hypertonic
solution.
The third way a substance can cross the cell membrane is through
facilitated diffusion. This occurs when special carrier proteins carry
solutes dissolved in the water across the membrane by using active
transport. When the concentration gradient can not allow travel from
one side of the membrane to the other fast enough for the cell’s
nutritional needs, then facilitated diffusion is used. The transport
protein is specialized for the solute it is carrying, just as enzymes
are specialized for their substrate. The transport protein can be
changes or blocked just like...
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