Transport through membranes either directly through the layers or
through carriers such as carrier proteins in cell membranes occur via one of
two basic processes: diffusion or active transport (Hall
and Guyton, 2016). Diffusion means random molecular movement of substances
molecule by molecule, either through intermolecular spaces in the membrane or
in combination with a carrier protein. In contrast, active transport means movement of ions or other
substances across the membrane in combination with a carrier protein in such a
way that the carrier protein causes the substance to move against an energy
gradient, such as from a low-concentration state to a high-concentration state.
In this exercise, the movement of
substances placed at different concentrations with respect to its surrounding
environment were observed. Our results show that substances with no active carriers
generally move from a place with higher concentration to places with lower
concentration in the purpose of reaching equilibrium. As substances naturally
move toward low concentrations, the presence of semi- permeable membranes aid
in the separation of different substances by restricting the movement of some
substances. This exercise will help us understand the physiological movements
of different substances and how membranes help achieve different movement
of gas in a gas
The scent of the
perfume was detected at different time intervals in different distances (Table
1.1). As the distance increased, the time it took for the perfume to be
detected also increased.
1.1. Times to reach the distances as the perfume was uncapped.
min 39 sec
min 05 sec
min 38 sec
min 56 sec
of a solid in a colloidal solution
differences in the rate of diffusion of the three substances placed in the
colloidal solution. After an hour, the substance with the lowest molecular
weight, KMnO4, diffused the fastest while the substance with the
highest molecular weight, methylene blue, was the slowest.
Potassium permanganate: =
Potassium dichromate: =
Methylene blue: =
Figure 1.1. Rate of diffusion of three substances in relation to its molecular
of a solid in a liquid
Upon addition of
the sodium permanganate crystal in the water, the color did not spread rapidly.
First, the color occupied the bottom of the water then it gradually rose to the
top part of the water. Eventually, after about 30 min, all of the water in the
beaker was colored equally (Fig. 1.2).
Figure 1.2. Diffusion of potassium permanganate.
Using the line
graph we were able to see the pattern of the changes of the weight of the
dialyzing membrane over time (with 5-minutes intervals). It is clear that the
dialyzing bag increased intensely on its first interval compared to the
following intervals. However, based on the graph, the dialyzing bag have lost
weight upon its 3rd interval, which was then again followed by a
weight increase on the 5th and 6th interval.
Figure 1.3. Weight changes of
the dialyzing membrane containing NaCl.
Based on the
projected line graph, the weight of the dialyzing bag decreased intensely on
its first 5-minute interval compared to the following intervals. There is also
an evidence that the weight of the dialyzing bag did not decrease constantly,
but rather followed an interchanging pattern per interval. Lastly, it can be
observed that the weight remained lower in all intervals compared to the
Figure 1.4. Weight changes of
the dialyzing membrane containing H20.
The red blood cells (RBCs) mixed with the 3% sodium
chloride (NaCl) was wrinkly in shape. The smooth edges of the RBCs were gone
and the original shapes of the cells were also lost (Fig. ). On the other hand,
the RBCs exposed to distilled water were also not the original shape. The cells
were rounder and some of the cells had burst (Fig. ). The RBCs exposed to the
0.9% NaCl, however, did not show any changes to the cell (Fig. ).
Figure 1.5. Effects of
hypertonic (A), hypotonic (B), and isotonic (C) solutions on cell volume.
A. Test for sodium chloride
Upon the addition of silver nitrate (AgNO3) to
the test water, the test water which was previously clear became turbid. This
is because of the slight formation of white precipitates. The result indicates
that the sodium chloride (NaCl) which was previously inside the dialyzing bag
was able to pass through the membrane of the bag.
Test for starch
When the IKI solution was added into the test
tube containing the test water, the IKI solution remained its color as it is.
The formation of a blue-black colored solution was expected in this test to be
able to confirm that starch is present in the test water. However, the solution
did not transform its color. This means that the dialyzing membrane did not
allow the starch to pass through.
Test for glucose
test, a precipitate with either of the colors: green, yellow, or brick red
should appear if glucose is positive in the test water. Upon the addition of
Benedict’s solution the resulting solution, however, did not change into either
of the anticipated colors. The solution remained blue as the color of the
Benedict’s solution is blue. Thus, we were able to confirm that the dialyzing
membrane did not allow the glucose to pass through it.
Test for albumin
nitric acid (HNO3) was added to the test water drop by drop.
However, a white coagulum, which is supposed to form in the presence of
protein, did not appear. This result indicates that the test water was negative
of any protein from the egg albumin. The dialyzing membrane did not allow the
protein components of the albumin to pass through it.
Figure 1.6. Results for
dialysis tests. a= test for sodium chloride b= test for starch c= test for
d= test for albumin
Diffusion, according to Hall and Guyton (2016),
is a random, constant motion of molecules that are moving from an area of high
concentration towards an area of low concentration. Furthermore, the rate of
diffusion is affected by certain factors such as temperature, viscosity of the
medium, and the molecular size of the particle. The experiment was able to
demonstrate how these factors affect the rate of diffusion.
are inclined to undergo diffusion due to the presence of kinetic energy (Malone and Dolter, 2010).
This energy enables the particles to move at a constant, random motion. As
stated previously, these particles will travel to an area with lower
concentration. This was observed during the experiment when there was a gradual
detection of the scent in order of the distances. The farthest distance was
able to detect the scent lastly which clearly displays the diffusion of gas in
experiment was performed to determine the effect of molecular weight to the
rate of diffusion. As molecular weight increases, the rate of diffusion decreases
(Fig. 1.1). This implies that the rate of diffusion of a substance in inversely
proportional to its molecular weight under the same conditions. The smaller
weighing substances are able to migrate more rapidly because they encounter
less frictional drag in the gel (Malone and Dolter, 2010)
which is why potassium permanganate diffused the fastest compared to potassium
dichromate and methylene blue.
The same concept
applies when a solid substance diffuses in a liquid solution – it travels down
its concentration gradient. The process is gradual until it can cover the whole
affect the rate of diffusion in different media. Gases diffuse faster than
liquids, and liquids diffuse faster than solids. Nonetheless, the same factors
apply to the different phases of matter.
a primary role in biological systems. The exchange of matter with the medium in
all living organisms occurs in such a mode. Osmosis is a physicochemical
process, in which the concentration difference between two solutions creates
pressure difference (osmotic pressure) across a separating semipermeable
membrane. Solvent transport takes place from the more diluted solution to that
of higher concentration, until equilibrium is reached (Minkov et al., 2013). A
solution is said to be isotonic when both sides of the membrane has an equal
concentration of solute. On the other hand, if one side of the membrane has
higher concentration of solute compared to the other, it is then considered as
hypertonic, where water tends to move in that direction. Lastly, the other side
which has lesser concentration of solute compared to the other is considered to
be hypotonic (Galindo, 2003).
In this experiment, we were able to see how the water
took its action as soon as the dialyzing membrane containing NaCl was immersed
in the beaker. The water moved into the bag rapidly which caused a sudden
increase of the weight of the bag. In addition, it can be observed in the graph
that the water movement has almost reached equilibrium since the following
intervals had already small changes of its weight. The NaCl inside the
dialyzing bag indeed caused a hypertonic solution and so thus the water went
inside to reach equilibrium for both the solute and the solvent.
The second dialyzing bag contained water and was immersed
in a beaker containing NaCl. As expected, the water went outside the membrane
which caused a rapid weight decrease of the bag. The solution has reached
equilibrium upon its first interval. It was expected that the weight of the dialyzing
bag would continually decrease or may stop decreasing when it reaches
equilibrium. However, there were some fluctuation in the data. This could be
due to improper handling of the test. As the dialyzing membrane was removed
from the beaker from time to time in order to weigh, the dialyzing bag may not
be dried as constantly as how it was dried on the other intervals. This case
could be the reason for the fluctuations of the data.
The cell membranes of the blood are also permeable to
water, like any other cell (Mader et al., 2013).
However, ions that are also in the solution cannot pass through the membrane
due to its larger size compared to water. The process that governs this
movement of water from one side of the membrane to the other is called osmosis
(Hall and Guyton, 2016). In addition, this process is controlled by the
difference in the ion concentration in the solution and inside the cell.
The shrinking of
a cell is called crenation (An et al., 2014).
Crenation occurs when the cell is exposed to a solution that has a higher
solute concentration than inside of the cell. The cell releases its water to
the outside in response to the concentration of the outside environment causing
it to shrink. When this happens the solution is said to be hypertonic (Hall and
Guyton, 2016). This suggests that 3% NaCl is hypertonic to the RBCs.
According to Hall
and Guyton (2016), when the cells are exposed to a solution with a lower solute
concentration than the inside of the cells, the cells take in water from the
outside. The solution is hypotonic to the cell. As the cells take in water,
this causes them to swell and eventually burst. This is called hemolysis (Hall and Guyton, 2016).
Exposure to distilled water caused the RBCs to swell and burst so the solution
is hypotonic to the RBCs.
The RBCs remained
in their original state when exposed to 0.9% NaCl. If it neither shrinks or
, the solution is
hence isotonic. Therefore,
solutions with concentrations of more than 0.9% is hypertonic to the cell and
solutions with concentrations lower than 0.9% is hypotonic to the cell.
Dialysis is known as the process of separating larger
molecules from smaller molecules (Galindo, 2003) by means of a passive movement in which
the mobility of solute particles between two liquid spaces is restricted,
mostly according to their size. Size restriction is achieved by using a porous
material, usually a semi-permeable membrane called dialysis membrane. This
membrane is permeable only for particles below a certain size. There are also
some cases where restriction of diffusion is driven via polarity or charge (Hegyi and Kardos, 2013).
In this experiment, a pork intestine is used as a
dialyzing bag which is supposed to allow the small molecules that are small
enough to pass through its membrane. Among the substances that was placed
inside the bag, it appeared that only NaCl was able to move into the outside of
the bag while the rest remained inside as the test water was confirmed to be
negative of it. Because of this ability to separate substances, the dialyzing
bag was considered to be selectively permeable.
The result of this test was more likely determined by the
sizes of the substance, as described by (Hegyi and Kardos, 2013). However, another factor could also be the reason for the restriction
of the other substances inside the dialyzing bag. Aside from the size of the
substance, its fat- solubility also controls its ability to pass through the
dialyzing bag since the one used in the experiment is an intestine which has a
characteristic of a lipid bilayer. Movements of water- soluble substances are
impeded in a lipid bilayer (Hall
and Guyton, 2016). Carbohydrate
molecules such as starch and glucose (Hall and Guyton, 2016), and albumin protein molecules are
generally water-soluble (Cooper, 2000). This explains why such
substances where not present in the test water since they cannot freely pass
through the membrane.