Problem 11 - Biology of Humans: Concepts, Applications, and Issues

Question

Choose the incorrect statement: a. Most biochemical reactions in the human body occur around \(\mathrm{pH} 7\) b. Buffers prevent dramatic changes in pH. c. \(\mathrm{HCl}\) is an important buffering system in the blood. d. Burning of fossil fuels causes acid rain.

Step-by-Step Solution

Answer

The incorrect statement is c.

Step 1: Understand the Question

The task is to identify the incorrect statement among the given options.

Step 2: Evaluate Statement a

Most biochemical reactions in the human body occur around \(\text{pH} 7\). This statement is correct because the pH of human blood and many cellular fluids is approximately 7.4, which is close to neutral pH.

Step 3: Evaluate Statement b

Buffers prevent dramatic changes in pH. This statement is correct because buffers are substances that help maintain a constant pH by neutralizing small amounts of added acids or bases.

Step 4: Evaluate Statement c

\( \text{HCl} \) is an important buffering system in the blood. This statement is incorrect because \( \text{HCl} \) (hydrochloric acid) is a strong acid, not a buffer. The primary buffer system in blood is the bicarbonate buffer system.

Step 5: Evaluate Statement d

Burning of fossil fuels causes acid rain. This statement is correct because the combustion of fossil fuels releases sulphur dioxide and nitrogen oxides, which can form sulfuric and nitric acid in the atmosphere, leading to acid rain.

Key Concepts

Biochemical Reactions in the Human Body

Biochemical reactions are processes that occur within living organisms to maintain life. These reactions involve enzymes that act as catalysts to speed up chemical reactions.

• Enzymes are highly sensitive to pH levels, which is why maintaining a stable pH is crucial for proper biochemical function.
• Most biochemical reactions in the human body occur around a pH of 7.4, which is close to neutral pH.

For example, the enzyme pepsin, which breaks down proteins in the stomach, works best in an acidic environment, while most cellular enzymes function optimally at a neutral pH. Understanding the pH requirements for different enzymes helps us grasp why pH balance is essential for health.

Understanding pH Levels

The term 'pH' refers to the potential of Hydrogen and measures the acidity or alkalinity of a substance on a scale from 0 to 14. A pH of 7 is neutral; values below 7 are acidic, and those above 7 are alkaline.

• Blood has a pH of approximately 7.4, making it slightly alkaline.
• The stomach secretes hydrochloric acid (HCl) maintaining a low pH of around 2, essential for digesting food.

Importantly, even small deviations from the normal blood pH range (7.35-7.45) can be life-threatening. Our body's homeostatic mechanisms, including buffer systems, help in maintaining this delicate balance.

Buffer Systems

Buffer systems are crucial in preventing drastic shifts in pH. They work by neutralizing small amounts of added acids or bases.

• The primary buffer system in the blood is the bicarbonate buffer system, consisting of bicarbonate ions (HCO3-) and carbonic acid (H2CO3).
• When the blood becomes too acidic, bicarbonate ions can neutralize excess hydrogen ions to form carbonic acid.
• Conversely, carbonic acid can dissociate to release hydrogen ions when the blood becomes too alkaline.

This buffering action helps maintain the blood pH within a narrow optimal range. Other buffer systems in the human body include the phosphate buffer system and protein buffer systems.

Acid Rain and its Sources

Acid rain is a type of precipitation that is significantly more acidic than normal rainwater. It is primarily caused by the release of sulfur dioxide (SO2) and nitrogen oxides (NOx) from burning fossil fuels like coal, oil, and natural gas.

• These pollutants react with water vapor in the atmosphere to form sulfuric acid (H2SO4) and nitric acid (HNO3).
• When it rains, these acids fall to the ground, causing environmental damage.
• Acid rain can lead to the acidification of lakes and rivers, harming aquatic life.

It can also erode buildings and monuments. Understanding acid rain's sources and effects helps in taking measures to reduce harmful emissions and protect the environment.