Question

Which property of CO₂ makes it biologically and geo-Chemically important?

• A. Its acidic nature
• B. Its low solubility in water
• C. Its high compressibility
• D. Its colourless and odourless nature

Answer 1

The Correct Option is A

Correct Answer: Its acidic nature
 
Explanation:
The biological and geochemical importance of carbon dioxide (CO₂) largely comes from its acidic nature.

• In water, CO₂ reacts to form carbonic acid (H₂CO₃), which plays a crucial role in maintaining the pH balance of blood and other biological fluids.
• In geology, CO₂ dissolves in rainwater forming weak carbonic acid, which contributes to chemical weathering of rocks (especially carbonates).

Thus, its acidic nature is key to many biological and earth processes.

Answer 2

While multiple properties of CO₂ contribute to its importance, the property that *directly* and *most significantly* influences its biological and geochemical roles is its acidic nature.

Here's why:

• Acidic Nature and the Carbon Cycle: CO₂ reacts with water to form carbonic acid (H₂CO₃): $CO_2 + H_2O \rightleftharpoons H_2CO_3$ Carbonic acid then dissociates to form bicarbonate (HCO₃^-) and carbonate (CO₃^2-) ions: $H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$ $HCO_3^- \rightleftharpoons H^+ + CO_3^{2-}$ These reactions are crucial for regulating the pH of natural waters (oceans, lakes, rivers), which has profound biological and geochemical consequences.
• Biological Importance:
  • Photosynthesis: CO₂ is the primary carbon source for photosynthesis, where plants and other photosynthetic organisms convert CO₂ and water into glucose and oxygen. Its interaction with enzymes is determined by its electronic structure and thus to some degree on its acidity.
  • Respiration: CO₂ is a waste product of cellular respiration in animals and many microorganisms. The buffering capacity of blood (due to the bicarbonate system) is essential for maintaining pH homeostasis. Its acidity is directly responsible for how the respiration rate affects the pH of blood.
• Geochemical Importance:
  • Weathering: Carbonic acid contributes to the chemical weathering of rocks, releasing minerals and ions into the environment.
  • Carbonate Formation: Dissolved carbonate ions (CO₃^2-) are important for the formation of carbonate minerals (e.g., limestone, CaCO₃), which act as a major long-term carbon sink.
  • Ocean Acidification: Increased atmospheric CO₂ levels lead to increased CO₂ absorption by the oceans, resulting in ocean acidification, which poses a threat to marine ecosystems. Again, its acidity is directly responsible.
• Why the other options are less important:
  • Low solubility in water: Although CO₂ is *not* highly soluble in water, it *does* dissolve to a significant extent, and this solubility is crucial for the carbon cycle. If it were completely insoluble, it wouldn't participate in the aquatic processes.
  • High compressibility: Compressibility is relevant to its physical behavior as a gas, but is not a *direct* driver of biological and geochemical processes.
  • Colorless and odorless nature: This property has no direct impact on the chemical reactions or biological roles of CO₂.

Therefore, the acidic nature of CO₂ is the most important factor in its biological and geochemical significance.

Correct Answer: Its acidic nature