The substance which resists change in pH is called buffer. Stable internal environment is maintained in animals. It requires a relatively constant pH of the body fluids. A strong acid or base can destroy cell stability. Similarly, opposite charges attract each other and form the ionic bond.

Change in pH may be destruethe. fine fluid systems of most animals contain chemicals. These substances help tc regulate the acid base balance. These substances are called buffers. They resist changes in pH. They accept 14″ ions present in excess “I hey donate IT ions when their amount is reduced.

The most important buffers are the bicarbonates, phosphates, and organic molecules, such as amino acids and proteins. The carbonic acid bicarbonate on system is important in buffering the blood of many vertebrates:

H2CO3 _________________ H’ + HCO;

Carbonic acid dissociates to lb-rm hydrogen ion and bicarbonate ion. In this example, if 1-1 ions are added to the system, they combine with HCO3. to form FI,CO3 (the reaction goes to the left). This reaction removes IT ions. So it does not allow changing the pH. If excess Olf ions are added, they react with the 11 ions to form water. So more EI,CO, ionize and replace the H. ions. Thus the reaction goes to the right. Again, p11 stability is maintained.

Role of buffers in biological system

Buffers play following role in the biological system

1. Protection of enzymes: Enzymes function within narrow pH range. A slight change in pH inhibits enzyme activity. For example, a slight change in pil affect phosphorylase enzyme. This enzyme converts starch in to glucose. The glucose increases the osmotic pressure of guard cells. Thus water enters into the guard cells and stomata are



opened. Phosphorylase is sensitive to pH changes. Thus change in pH can affect the opening and closing of stomata. Similarly Enzymes of glycolysis and Kerbs cycle are sensitive to change in pH. Thus buffer keeps pH stable in this system.

  1. pH of blood: The pH of blood remains within the range of 7.35 and 7.45. An increase in acidity causes acidosis. The decrease in acidity causes alkalosis. Both these conditions are dangerous Tor the body. Thus buffer keeps the pH of blood within normal range. The carbonate buffer is the principal buffer in blood. It is composed of carbonic acid and bicarbonate ion (I-12C01 and HCO3). Carbonic acid neutralizes off. The bicarbonate neutralizes H proton.
  2. Use of buffer in culture medium: Bacteria are grown in culture medium in microbiological labs. Bacteria produce acids during reproduction. It changes the pH of the medium. The buffers are added to these media. It stablizes the pH.

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