Question

Yellowish edges appear in leaves deficient in
A. Potassium
B. Calcium
C. Magnesium
D. Phosphorus

Answer 1

Hint: Potassium is required in more abundant quantities in the meristematic tissues, buds, leaves and root tips. It is also absorbed from the soul in the form of potassium ions. It is required in the synthesis and translocation of carbohydrates, cell division, development of chlorophyll, stomatal movements and reduction of nitrate.

Complete answer
The first option is Potassium. Potassium deficiency starts with a characteristic mottled chlorosis of older leaves that gradually spreads to younger leaves. Due to loss of apical dominance, rosette or bushy habit of growth is shown by plants. Hence, the stem becomes weak and the resistance of plants to pathogens is lowered. Accordingly, the plants are easily lodged and attacked by diseases. Thus yellowish edges appear in leaves deficient in Potassium.
The second option is Calcium. Calcium deficiency hence, characterized by death of growing regions of stem and leaves, particularly leaf tissue, hence called necrosis which leads to blacck and brown colour of the leaves.
The third option is Magnesium. Magnesium acts as an important constituent of chlorophyll molecules where it occupies a central position. Its deficiency causes interveinal chlorosis in the leaves. As magnesium is easily transported within the plant body, the deficiency symptom is first seen in the mature leaves rather than younger leaves. Magnesium deficiency also leads to necrosis of the older leaves.
The fourth option is Phosphorus. Being a constituent of cell membranes, certain proteins, all nucleic acids and nucleotides, the maximum accumulation of phosphorus is found in rapidly growing regions, such as meristematic regions and maturing fruits and seeds. Phosphorus deficiency affects all aspects of plant growth and metabolism. Plants become stunted and older leaves fall down. In severe cases, necrotic areas develop on leaves, petioles and fruits.

So, the correct answer is ‘Potassium’.

Note:
Chlorosis is caused by the loss of chlorophyll leading to yellowing in leaves.
Apical dominance is the process where the main central part of the stem is dominant as compared to the side part of the stems.
Necrosis is the death of a leaf tissue.