ICSE Questions Set in Previous Years — Question 25

Biological importance of carbon dioxide dissolved in water :

1. Aquatic plants make use of dissolved carbon dioxide for photosynthesis, i.e., to prepare their food.
   6CO₂ + 12H₂O $\xrightarrow[\text{sunlight}]{\text{Chlorophyll}}$ C₆H₁₂O₆ + 6O₂ + 6H₂O
2. Carbon dioxide dissolved in water reacts with limestone to form calcium bicarbonate.
   CaCO₃ + CO₂ + H₂O ⟶ Ca(HCO₃)₂
   Marine organisms such as snails, oysters, etc., extract calcium carbonate from calcium bicarbonate to build their shells.