The correct option regarding micro-nutrients is
B. are required by plants in very small quantities.
Detailed Explanation:
- Understanding Micro-nutrients:
- Micro-nutrients are essential elements that plants need for growth and development, but in much smaller amounts compared to macro-nutrients (like nitrogen, phosphorus, and potassium).
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Common micro-nutrients include iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), and boron (B).
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Why Option B is Correct:
- Micro-nutrients are indeed required by plants in very small quantities, typically measured in parts per million (ppm) or milligrams per kilogram (mg/kg) of soil.
- Despite their small required amounts, they play crucial roles in various physiological functions, including enzyme activation, photosynthesis, and hormone production.
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For example, iron is vital for chlorophyll synthesis, while zinc is important for protein synthesis and growth regulation.
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Why the Other Options are Incorrect:
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Option A: Promote formation of only root nodules:
- This statement is misleading because root nodules are primarily associated with nitrogen-fixing bacteria (like Rhizobium) that form symbiotic relationships with legumes. While some micro-nutrients may play a role in overall plant health, they do not specifically promote root nodule formation. This process is more about the plant's interaction with specific bacteria rather than the direct action of micro-nutrients.
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Option C: are fixed into the soil through microbial activity:
- This statement is incorrect because micro-nutrients are not "fixed" into the soil like nitrogen can be through the action of certain bacteria. Instead, micro-nutrients are often present in the soil in forms that plants can absorb. They can be influenced by microbial activity, but they do not undergo a fixation process similar to nitrogen.
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Option D: increase crop tolerance to pest attack:
- While some micro-nutrients may contribute to overall plant health and resilience, this statement is too broad and not universally true. The relationship between micro-nutrients and pest tolerance is complex and not solely dependent on the presence of micro-nutrients. Other factors, such as plant genetics, environmental conditions, and overall nutrient balance, play significant roles in pest resistance.
Summary of Key Points:
- Micro-nutrients are essential for plant growth but needed in very small quantities.
- They play critical roles in various physiological processes, despite their low concentration requirements.
- Other options either misrepresent the role of micro-nutrients or are overly simplistic regarding their functions in plant health.
Revision Summary:
- Micro-nutrients are required in small amounts (correct answer: B).
- They are crucial for enzyme function, photosynthesis, and growth regulation.
- Misconceptions about their roles can lead to confusion (e.g., root nodules and pest tolerance).
- Understanding the specific functions of each micro-nutrient can enhance agricultural practices.