Cyanobacteria are used in agricultural fields for crop improvement because they cause 1.N 2 fixation 2.algal blooms 3.photosynthesis 4.all of these

Options

A. `N_(2)` fixation
B. algal blooms
C. photosynthesis
D. all of these

Explanation

To solve the question regarding the role of cyanobacteria in agricultural fields for crop improvement, let's analyze the options provided step by step.

### Step 1: Understanding Cyanobacteria
Cyanobacteria, also known as blue-green algae, are a group of photosynthetic bacteria. They are capable of photosynthesis due to the presence of chlorophyll pigment A.

**Hint:** Remember that cyanobacteria are not true algae but are often referred to as such due to their photosynthetic capabilities.

### Step 2: Analyzing Nitrogen Fixation
Cyanobacteria have the unique ability to fix atmospheric nitrogen (N2) into ammonia (NH3), which can be utilized by plants. This process is crucial for soil fertility as many plants cannot directly use atmospheric nitrogen.

**Hint:** Think about how plants obtain nitrogen and the importance of nitrogen fixation in agriculture.

### Step 3: Considering Algal Blooms
While cyanobacteria can cause algal blooms, this phenomenon is typically associated with negative environmental impacts, such as oxygen depletion in water bodies. Thus, it is not a beneficial aspect for crop improvement.

**Hint:** Algal blooms can lead to problems in aquatic ecosystems; consider whether this is a positive contribution to agriculture.

### Step 4: Evaluating Photosynthesis
Cyanobacteria perform photosynthesis, which contributes to the oxygen supply and can enhance soil quality indirectly. However, the primary benefit in agriculture is their nitrogen-fixing ability.

**Hint:** While photosynthesis is important, focus on what specifically aids in crop improvement.

### Step 5: Choosing the Best Option
Given the analysis:
1. Nitrogen fixation is a direct benefit to crops.
2. Algal blooms are not beneficial for crop improvement.
3. Photosynthesis is important but not the primary reason for their use in agriculture.

Thus, the best answer is **1. Nitrogen fixation**.

### Final Answer:
Cyanobacteria are used in agricultural fields for crop improvement primarily because they cause **nitrogen fixation**.

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