Nitrifying bacteria

Options

A. reduce nitrates to free nitrogen
B. oxidize ammonia to nitrates
C. convert free nitrogen to nitrogen compound
D. convert proteins into ammonia

Answer

### Step-by-Step Solution:

1. **Understanding Nitrification**: Nitrification is a biological process that converts ammonia into nitrates. It occurs in two main steps and involves specific types of bacteria.

2. **Step 1 - Oxidation of Ammonia**: The first step of nitrification involves the oxidation of ammonia (NH₃) into nitrites (NO₂⁻). This reaction is primarily carried out by bacteria such as **Nitrosomonas** and **Nitrococcus**.

3. **Step 2 - Oxidation of Nitrites**: The second step involves the further oxidation of nitrites (NO₂⁻) into nitrates (NO₃⁻). This step is facilitated by another group of bacteria known as **Nitrobacter**.

4. **Role of Nitrifying Bacteria**: Nitrifying bacteria play a crucial role in the nitrogen cycle by converting ammonia, which can be toxic to plants, into nitrates, which are a more usable form of nitrogen for plants.

5. **Clarifying Misconceptions**: The statement "Nitrifying bacteria reduce nitrates to free nitrogen" is incorrect. Instead, nitrifying bacteria oxidize ammonia to nitrates.

6. **Conclusion**: The correct understanding of nitrifying bacteria is that they are responsible for the oxidation of ammonia to nitrites and then to nitrates, thus facilitating the process of nitrification.