PELEKEKAE

TUMO LERANG SENWELO

201000004

BIO 211: CELL BOLOGY

EXERCISE 4: BUFFERS IN BIOLOGY

07/09/2011

INTRODUCTION

All living organisms are made up of living units called cells. The cells contain a structure called

the nucleus which is a site for chemical reactions. Chemical reactions are affected by

concentration, pressure and pH so the body needs to make sure that they are in the right amount

to maintain a constant internal environment (Stevens, 2008). One way to minimize pH changes

in a chemical solution is to add a buffer. A buffer in Jones & Atkins (2000) is defined as a

mixture of weak conjugate acids and bases that stabilizes the pH of a solution by both accepting

and providing protons for reaction with added acid or base. The Henderson-Hanselbach equation,

also called the buffer equation is:

pH= pKa+ log [conjugate base]

[Acid]

Buffer work best at controlling pH at pH values roughly equal to the pKa of the component

acid or base i.e. the [salt] is equal to the [ acid] (Cairns, 2000).

The aim of this experiment is to find to distinguish between extracellular and intracellular

buffers, to find out if there are natural buffers in higher animals and also to find out their

effectiveness in controlling hydrogen ion fluctuations.

METHODOLOGY

The groups were merged such that when others titrated with a base (NaOH) others titrated with

an acid (HCl) in order to cover all the solutions provided in three hours. Our group titrated with

HCl while the other titrated with NaOH.

Two solutions were provided; succinic acid (solution 1) and glycine (solution 2) working with

50ml of a 0.1M concentration. Measured out 25ml volume of succinic acid and poured it into a

conical flask provided. Read the pH of the succinic acid in the conical flask and titrated this

solution with hydrochloric acid (HCI). Small volumes of about 0.5ml were added at a time,

swirled the contents of the beaker before recording the pH, the volume added and the pH was

recorded after each addition. The titration was carried until the pH reached 2. The procedure

was repeated as above but in this case succinic acid was replaced with glycine.

The results from the titration with NaOH were collected from the other group that we had

merged with.

The results from this experiment were used to plot a graph and were analyzed.

RESULTS

The plotted graphs are in the next pages

From the graph on the titration of succinic acid with hydrochloric acid (HCl) it can be seen that it

requires less HCl for the pH to drop to 2 than it is required for glysin as the former needed only

10.02ml of HCl while the latter needed 32.98ml of HCl.

However it should be noted that when HCl was replaced with Sodium hydroxide the solutions

required even greater volumes to be added to raise the pH to 12. Because the NaOH is a base it

raises the pH of succinic acid and glysin, the graphs are upward sloping to indicate an increase in

pH whereas with HCl the graphs are downward slopping because the pH is being decreased.

DISCUSSION

With increasing amounts of added base, the overall slope of a graph of pH is downward but

without a buffer, the slope is steep. Inside the buffering range of an added buffer, the slope is

shallow. At very high and very low values of pH, where the buffer is ineffective, hence the

slopes are much steeper. Even when more NaOH was added to the solutions as it can be seen

from the graph, the pH changed slightly and this is in agreement with Sadava (2009) when he

says in the presence of a buffer, additions of even large quantities of base result in relatively

small changes in pH.

There are intra cellular and extra cellular buffers in the body. Intra cellular are buffers that are

inside/ in the interior of the cell while extra cellular refers to buffers outside of the cell. There are

different natural buffers, that can either be intra cellular or extra cellular found in higher animals.

Proteins, organic phosphates, inorganic phosphates (not natural) and in the erythrocytes,

haemoglobin (Cairns, 2000) are intracellular buffers. He goes on to say haemoglobin is the most

excellent because of its ability to bind to hydrogen ions forming a weak acid and carbon dioxide.

Extra cellular buffers include bicarbonate and ammonia and the bicarbonate is especially key as

carbon dioxide can be shifted though carbonic acid to H+ ions and bicarbonate.

Sadava (2009) goes on also to say that the major buffers in the blood are bicarbonate ions

(HCO3) that are formed from the dissociation of carbonic acid, which in turn is formed by the

hydration of CO2 according to the following equilibrium reaction:

CO2+ H2O ←→ H2CO3 ←→ H+ + HCO3-

If excess hydrogen ions are added to this reaction mixture, the reaction moves to the left and

absorbs the excess H+. If hydrogen ions are removed from the reaction mixture, however the

reaction will move to the right and supply more H+.

CONCLUSION

Most buffer systems in the body consist of a weak acid and the salt of that acid, which functions

as a weak base. Buffers prevent rapid drastic changes in the pH of body fluids by converting

strong acids and bases into weak acids and bases within fractions of a second (Tortora G J,

2009). The kidney is one of the organs that is involved in acid-base balance (Bulger, 1983)

In all multicellular organisms, the fluid within the cell and the fluids surrounding the cells have a

characteristic and nearly constant pH which can be maintained through buffer systems. There are

many buffers in higher animals but the principal of the body fluids are the protein buffer system,

the dihydrogen phosphate buffer system and the carbonic acid buffer systems. The phosphate

buffer system operates in the internal fluid of all cells which means that they are intra cellular

while the latter (carbonic acid systems) are extra cellular. Another most important buffer system

is found in the blood plasma because blood pH is a critical variable because it influences the

structure, and therefore the function, of proteins. In mammals, cellular fluid has a pH range 6.9

to 7.21 and the phosphate buffer is effective in maintaining this pH range

REFERENCES

D, C. (2000). Essentials of Pharmaceutical Chemistry. Chicago: Pharmaceutical Press.

E, B. R. (1983). The Urinary System. In W. L, Histology: Cell and Tissue Biology (pp. 867-912).

New York: Elsevier Science Publishing Co.,Inc.

Jones L, A. P. (2000). Chemistry: Molecules,Matter and Change. New York: W. H. Freeman and

Company.

Sadava D, H. D. (2009). Life: The Science of Biology. Sunderland, MA: Sinauer Associates Inc.

Stevens A, L. J. (2008). Human Histology. Philadelphia: Elsievier.

Tortora G J, D. B. (2009). Principles of Anatomy and Physiology. Hoboken: John Wiley &

Sons . Inc.