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Regulation Of The Body Fluids Biology Essay

The movement of water molecules through a selectively permeable membrane down a water potential gradient is called Osmosis. Osmosis is the diffusion of water molecules from a high water concentration area to a low one. A selectively-permeable membrane is a membrane that allows some molecules to pass through, but stops other. In this experiment, a visking tubing is used (selectively permeable membrane) to imitate a biological membrane. The visking tubing is filled with a high concentration sugar solution, and submerged into a beaker containing water. The osmotic potential created, causes water molecules to move from the hypotonic water solution in the beaker to the hypertonic solution through the visking tubing. The small water molecules (solvent molecules) can pass through the artificial membrane (visking tubing), whereas the larger solute molecules cannot. This phenomenon (osmosis) is a passive one,which means that no energy is required for the process to occur.

Setting up the apparatus, as shown in Figure 1 and allowing the visking tube in the water (for a few minutes after experiment began), one could observe a slow raise in the level of the concentrated sugar solution. Approximately one hour later at the end of the experiment, the sugar solution had reached the capillary tube level shown in Figure 1. The color of the water didn’t change at any time, indicating that no dyed sugar solution diffused into the water in the beaker.

Discussion:

The experiment proved the osmotic theory, as the results predicted were obtained. The water molecules, moved from the hypotonic –low solute concentration- region (the water beaker) to the hypertonic –high solute concentration- region (the dyed sugar solution in the visking tube). According to the diffusion theory, the solute should normally move in the opposite direction of that of the water, so as a solute-solvent equilibrium could be achieved. Because of the selectively permeable membrane (visking tubing) though, the water molecules only were able to move and the sugar solution is kept in the tube; resulting to an increase in the volume of the mixture in the visking tube.

According to the pressure theory (of hydraulics), an increase in the number of molecules in a container, will cause an increase in pressure in the container. This occurs because of the atoms moving in random directions (Brownian motion) and colliding with the walls of the container. When the pressure of the fluid, is higher than the Atmospheric pressure, the volume of the fluid increases; this is how we observe the increase in volume in the capillary tube.

Osmotic pressure is what drives the movement of water. This pressure is regulated by the difference in concentration of the solute molecules in the solutions. The bigger the concentrations difference in the two solutions the greater the osmotic pressure. The osmotic pressure can be calculated by the formula Π = iMRT where i is the dimensionless van 't Hoff factor, M is the molarity, R=8.314472 L · kPa · mol-1 · K-1 is the gas constant and T is the thermodynamic absolute Temperature. (Voet, Donald; Judith G. Voet, Charlotte W. Pratt (2001). Fundamentals of Biochemistry (Rev. ed.). New York: Wiley. p. 30.)

Osmosis is very important in maintaining homeostasis in the human body (between the intracellular and extracellular water and solute concentrations). The reason why it is so important in biological systems can be explained by its ability to transport effectively between different parts of the body. Many biological membranes are selectively-permeable something which adds up to the importance of osmosis. Sixty percent in male and fifty-five percent of the female human body is made up of water. Cells are the main host of water, as 2/3rds of the water in the human body, is found intracellular whereas the remaining 1/3rd is found extracellular. Transport of all this water in the body occurs by osmosis, through concentration gradients without energy.

Disturbances may occur in the transport between various compartments (an example could be, the case of severe burns). The life threatening condition called Cerebral edema (also known as brain edema, brain swelling and wet brain) is a condition which accumulation of excessive fluid in the substance of the brain. The brain is especially susceptible to injury from edema, because it is located within a confined space and cannot expand (http://www.medterms.com/script/main/art.asp?articlekey=30899#). There are two types of brain edema, the vasogenic and the cytoxic. The Vasogenic edema occurs when integrity of the blood-brain barrier is disrupted, allowing fluid to escape into the extracellular fluid which surrounds the brain cells (it occurs in conditions like tumors). Vasogenic edema may impair the function of the blood-brain barrier and allow water and plasma proteins to leave the capillary and move into interstitium. Swelling of the brain cells due to an increase in fluid in the intracellular space (chiefly the gray matter) is called Cytoxic edema. Cytoxic edema can occur because of hypo-osmotic states, such as water intoxication that impair the function of the sodium potassium membrane pump. This causes rapid accumulation of sodium in cell, followed by movement of water against the osmotic gradient. (Carrol Mattson Porth, Essentials of Pathophysiology p.825)

The osmotic diuretic Mennitol can be used to tread cerebral edema. What this medication does, is that it decreases the pressure in the vascular system, by urinating more. C6H14O6 like all osmotic diuretics has a big molecular mass and has got the ability to inhibit the reabsorption of sodium chloride and water. This reduces the net osmotic force, since as Mennitol’s concentration increases the reabsorption of sodium chloride and water in the kidneys decreases (http://www.nature.com/ki/journal/v19/n3/abs/ki198136a.html and http://www.rxlist.com/mannitol_iv-drug.htm). As the concentration of Mennitol increase a higher osmotic gradient is created and water molecules move across the gradient; leading to a lower pressure in the brain due to a smaller number of water molecules.

Experiment One: Buffers

Title:

The effect of Buffer solutions on pH regulation and Acid-Base solutions’ effect on altering the pH.

Introduction:

Buffers have a very important role in regulating and maintaining a constant pH-level in the human body. Most biological processes are pH dependant; meaning that they can only work efficiently under a certain pH level, therefore small pH alternations cause big changes in the rate of a biological process. Protein, DNA and other molecules, get denaturized when pH irregularities occur. The resulting of such changes may the death of the cell and eventually the whole organism; therefore buffers are really important for the living organisms’ survival.

A buffer solution resists pH changes when small portions of an acid or a base are added. Such solutions are the mixture of a weak acid (HA) and it’s conjugate base (A-) which in comparison with the acid, it’s a strong base. A constant pH is achieved as, when an acid is added to the solution, the conjugate base neutralizes it and in the process the base is converted in to the weak acid (HA). In case a base (A-) is added, the weak acid (HA) can neutralize it and in the process it will be converted into a base (A-).

cm3

Method:

As per schedule.

Results:

Experiment 2 Part A

Flask

1

2

3

4

5

Volume of Acetic acid in cm3

40

30

25

20

10

Molecular concentration

(mol/ dm3)

0.08

0.06

0.05

0.04

0.02

Volume of sodium acetate cm3

10

20

25

30

40

Molecular concentration

(mol/ dm3)

0.02

0.04

0.05

0.06

0.08

Figure 1: shows the volume and concentration of the acid and the sodium acetate in each flask.

Flask

1

2

3

4

5

pH meter

4.03

4.41

4.58

4.80

5.23

Henderson-Hasselbalch equation

Where pKa of acetic acid is 4.7 and concentration of base over acid is in mol/dm3

4.10

4.52

4.70

4.88

5.30

Difference between the pH meter reading and the equation.

Henderson-Hasselbalch equation – pH meter

0.07

0.11

0.12

0.08

0.07

Percentage error.

% error = (estimate - actual) / actual * 100

(%)

1.7

2.5

2.62

1.67

1.33

Figure 2: shows the pH meter reading as well as the estimated pH using the Henderson-Hasselbalch equation. It also includes a pH difference between the ideal and the experimental results and a percentage error.

Experiment 2 Part B

Figure 3: shows the arrangement of the experiment and the amount of drops required for the color change in the indicator to occur.

Beaker

Drops required for color change to occur

Color Change

Percentage increase in the amount of drops needed for a color change to occur after adding 2 ml of buffer solution.

% increase= (new-old)/old*100

(%)

10ml of distilled water

2 drops of methyl orange indicator

1

From orangeto red

1400

0.1 mol/dm3acetic acid

(1 ml)

0.1 mol/dm3sodium acetate (1 ml)

8 ml distilled water

2 drops of methyl orange indicator

15

From orange to red

10 ml distilled water

2 drops of Phenolphthalein indicator

1

From colorless to pink

1700

0.1 mol/dm3acetic acid

(1 ml)

0.1 mol/dm3sodium acetate (1 ml)

8 ml distilled water

2 drops of Phenolphthalein indicator

18

From colorless to pink

Figure 4: describes the process and shows the amount of drops required for a color change to occur. The percentage increase is also calculated.

Discussion:

Experiment 2 Part A

In this experiment, acetic acid (ethanoic acid) was used as the acid and its conjugate base was Sodium acetate, creating a buffer solution. An acid is a proton donor whereas a base is a proton acceptor.

When an acid is added to the buffer solution, the H+ ions will combine with the Sodium acetate to form acetic acid. If a base is added to the system, the OH- ions react with H3O+ to produce water. By doing so, the solution’s pH is regulated and stays nearly the same. Buffer capacity is the limit at which a buffer can stop pH changes when an acid or a base is added. After the buffer becomes saturated it can no longer neutralise the effects of an acid or a base added, and on adding a base or an acid, a difference in the pH of the system will be observed. The buffer capacity depends on the amount of acid and base which the buffer solution was made.

On observing the pH results obtained, one is able to see that the pH range in the different flasks is between 4.03 and 5.23, which is not that big of a difference. The reason behind this is that because the solutions in the different flask react as buffering system to maintain a constant pH. One is able to see that, there is a percentage error of 1.33%-2.62% between the actual value and the experimental one; those errors may have occurred for numerous reasons.

The concentration of the acid and the base may have not been exactly 0.1 moldm-3.

The pKa constant was rounded up to 4.7 so errors may arise from that as well.

The pH-meter was not very reliable, since it was not calibrated.

Even though the pH meter was rinsed every time before inserted into the next flask, some cross contamination must have took place between the pH meter and the different flasks.

When measuring, a measuring cylinder was used which has a quit big % error and its not easy to take exact readings with it.

Experiment 2 Part B

In this experimental part, the buffers effectiveness was investigated. Distilled water buffer properties were also put to the test. The first two beakers contained 10 ml of distilled water and 2 different pH color indicators (Methyl orange and Phenolphthalein respectively). For either solution one drop of acid HCl (in beaker No.1) or a base NaOH (beaker No.2) was enough for a color change to be observed. A color change indicates a variation in pH. This explains that water has got very limited if any buffering abilities, since there was a phenomenal change in pH when a single drop of acid HCl or base NaOH respectively was dropped into the beakers.

When two 2ml of buffer solution was replaced by 2 ml of water in beakers number 3 and 4 (resulting to an 8ml of water and a 2 ml of the buffer solution) the number of drops required for a color changed to occur, increased dramatically. A 1400% increase in the number of drops needed was observed when HCl was added to the solution and a 1700% increase was observed when NaOH was added to the solution (slight pH changes occurred). This is an indication of a good buffer system, as the percentage increase in the volume of the acid/base added resembles the effect of the 2 ml of the buffer add.

Beaker 3

Beaker 4

As HCl is added to the buffer system, in beaker 3, the buffer tries to neutralize the acid maintaining a constant pH. This occurs as the acetate reacts with the H+ ions of the acid to produce more acetic acid CH3COOH. By doing so, the pH of thee solution decreases.

On addition of NaOH in beaker No.4, the OH- ion of the NaOH and the H+ ion of the CH3COOH react to produce water. Following on, the Na+ ion and the CH3COO- ion combine (by donating 1 electron from the CH3COO- to the Na+ ion) to form the basic CH3COONa and can act as a proton acceptor.

Buffer systems are used in modern industry as well. By maintaining a constant pH, one makes sure that the catalyst used to speed up the reactions will work under optimum pH. Agricultural, food industry as well as photography are some of the sectors where buffer solutions are used.

As mentioned before, buffers are really important in living organisms and especially in the human body, to maintain a relatively constant pH. Carbonic acid, also known as Bicarbonate is a buffer system of extracellular fluid in the human body. The bicarbonate buffer solution regulates the pH by shifting the concentration gradient of the products/reactant (H2CO3 dissociates to produce H+ and HCO3- or H2O and CO2). The Lungs act as the regulating organ, as when the CO2 concentration is high the equation shift to the right favoring the production of H+ ions. The body receptors will then inhibit a reflex where more frequent and heavier breathing will tend to decrease the CO2 concentrations and favor the backward reaction. Using this Buffer system, the body always maintains a pH of approximately 7.4.

Experiment Three: Tonicity and Red Blood Cells.

Title:

The effect of Tonicity on Red Blood Cells and there osmotic function.

Introduction:

The experiment designed is used to help one gain an understanding on how different concentrations of saline solutions affect the natural state of the red blood cells (RBCs), when mixed and observed under a microscope. The saline solutions represent extracellular fluid. The experiment is also providing information on the concentration at which red blood cells are able to maintain their normal shape and structure.

Method:

As per schedule

Results:

When conducting the experiment an excess amount of blood was used and because of insufficient mixing of the blood with the saline solution, no clear results were obtained. On studying another groups’ result, one could observe the results shown in Figure 1.

Figure 1: shows red blood cells under the effect of saline solutions used in different concentrations. The 0.9% saline solutions shows the Isotonic solution where the cell maintains it’s own shape and volume, the 0.45% saline solution is the hypotonic one, where the volume and size of the cell changes and increases. And the 1.8% saline solution is the hypertonic own where the red blood cells shrink and become spiky. (this pictures was taken from the book Principles of Anatomy and Physiology page 71)

Discussion:

When doing the experiment, the group’s slides did not turn out to be the way they should, due to an insufficient blood saline solution mixing. Under microscopic observation, the images were not very clear and no movement of red blood cells was visible at all. Due to the reason the Lab class’s time was running short, we did not repeat the experiment for more accurate results to be obtained, but instead we had the chance to observe another groups slides under the microscope. The other group’s glides were properly mixed and a clear view could be seen under the microscope.

Three different concentrations of saline solutions were used to observe the difference between normal 0.9% (which will be used as a reference point) smaller (0.45%) and greater (1, 8%) saline concentrations. When the red blood cells mixed in a 0.9% saline solution, and observed under a microscope, a normal cell size was observed. This is because of the isotonic motion (the osmotic potential inside the cell and in the solution outside the cell is the same, so no net osmotic movement is observed).

On comparing the 0.45% hypotonic saline solution slide with the 0.90% isotonic one, one is able to see the shape of the red blood cells altering (become more fat and rounded). Due to an osmotic gradient created between the concentration of saline on the slide and the cell there is a net movement of water (osmosis occurs) in the red blood cells; from a region of low solute concentration to a region of high solute concentration. In a Hypotonic solution like this one, the concentration of the salts inside the cells is greater than the concentration of the salts outside the cell. The phenomenon of Haemolysis -swelling up and eventually bursting of red blood cells, because no more water absorption can occur- is observed.

When the 1.80% saline solution is compared with the 0.90% which is the normal one, one can observe a decrease in the Red Blood Cell’s volume and irregularities in their shape. The reason is because in a hypertonic solution the concentration inside the cell is double the concentration outside the cell, thus an osmotic potential is created and water molecules move out of the cells. As water moves out of the cell, the cell is forced to decrease in volume and shrink. This process is called crenation.


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