▶️ Answer/Explanation
Process $X$ represents the conversion of ammonia into nitrate ions in the soil, which is known as nitrification; this is carried out by nitrifying bacteria. Process $Y$ shows the conversion of nitrate ions back into nitrogen gas in the atmosphere, a process called denitrification performed by denitrifying bacteria in anaerobic conditions. Other processes in the diagram include nitrogen fixation (atmosphere to ammonia/nitrates) and decomposition (waste to ammonia). Therefore, row $D$ correctly identifies both specific biological transformations.
✅ Answer: (D)
✅ Answer: (D)
▶️ Answer/Explanation
The process labelled $X$ represents nitrification. This biological process involves the oxidation of ammonium ions ($NH_4^+$) into nitrites ($NO_2^-$) and subsequently into nitrate ions ($NO_3^-$) by specialized nitrifying bacteria in the soil. Decomposition, or ammonification, is the preceding step where organic material is broken down into ammonium. Conversely, denitrification is the process shown on the right of the diagram, where nitrates are converted back into nitrogen gas ($N_2$). Nitrogen fixation is the process of converting atmospheric $N_2$ into ammonia, which is not what $X$ depicts here.
✅ Answer: (C)
✅ Answer: (C)
▶️ Answer/Explanation
To determine which processes increase atmospheric $CO_{2}$, we analyze the carbon cycle. Increased deforestation ($1$) leads to higher $CO_{2}$ levels because there are fewer trees to perform photosynthesis and remove the gas, and the clearing process often involves burning or decay. Increased fossil fuel combustion ($4$) directly releases stored carbon into the atmosphere as $CO_{2}$ through chemical oxidation. Conversely, tree planting removes $CO_{2}$, and decreasing combustion reduces the rate of addition. Therefore, only processes $1$ and $4$ contribute to an increase.
✅ Answer: (B)
✅ Answer: (B)