Critical concentration of nutrients

Options

A. are uniform for all micronutrients
B. control functioning of only micronutrients
C. vary widely for different micronutrients
D. can be determined on the basis of fresh weight

Answer

### Step-by-Step Solution:

1. **Understanding Critical Concentration**:
- Critical concentration refers to the specific range of nutrient levels in plants that is necessary for optimal growth and function. If the nutrient concentration falls below this range, it leads to deficiency, while exceeding it can cause toxicity.

2. **Defining the Range**:
- The critical concentration is not a fixed value; it represents a narrow range where the nutrient is most effective. Below this range, plants may exhibit deficiency symptoms, and above it, toxicity symptoms can occur.

3. **Variation Among Micronutrients**:
- Critical concentrations are not uniform across all micronutrients. Each micronutrient has its own specific critical concentration range that varies widely. This means that different micronutrients have different optimal levels for plant health.

4. **Evaluating the Options**:
- **Option A**: "Uniform for all micronutrients" - Incorrect, as critical concentrations vary.
- **Option B**: "Control functioning of only micronutrients" - Incorrect, as critical concentrations apply to both macronutrients and micronutrients.
- **Option C**: "Vary widely for different micronutrients" - Correct, as each micronutrient has its own critical concentration.
- **Option D**: "Can be determined on the basis of fresh weight" - Incorrect, as critical concentrations are not solely determined by fresh weight.

5. **Conclusion**:
- Based on the understanding of critical concentration and the evaluation of the options, the correct answer is **Option C**: "Vary widely for different micronutrients".