Chlorosis is:

Options

A. yellowing of leaves due to the absence of chlorophyll
B. yellowing of leaves due to low chlorophyll contents
C. greening of leaves due to high contents of chlorophyll
D. yellowing of leaves due to high contents of nitrogen

Answer

**Step-by-Step Solution:**

1. **Definition of Chlorosis**: Chlorosis is a condition in plants characterized by the yellowing of leaves. This occurs when the green pigment chlorophyll is deficient in the leaves.

2. **Cause of Chlorosis**: The primary cause of chlorosis is the lack of chlorophyll, which is essential for photosynthesis and gives leaves their green color.

3. **Role of Magnesium**: Magnesium ions play a crucial role in the formation of chlorophyll. When there is a deficiency of magnesium, the production of chlorophyll decreases, leading to the yellowing of leaves.

4. **Other Contributing Factors**: In addition to magnesium deficiency, other factors can contribute to chlorosis, such as:
- Poor drainage in the soil, which can affect nutrient uptake.
- Nitrogen deficiency, as nitrogen is also vital for chlorophyll production.
- Deficiencies of other essential minerals can also lead to chlorosis.

5. **Conclusion**: Therefore, chlorosis is defined as the yellowing of leaves due to low chlorophyll content, primarily caused by magnesium deficiency and potentially influenced by other nutrient deficiencies and environmental factors.