Calcium reduces the toxic effects of other salts in the water. A Lack of calcium reduces meristem activity or the activity of the cell wall. It is considered immobile, so calcium in older leaves cannot be removed to younger leaves. That means a deficiency will show up in the youngest areas of the plant. Young leaf margins curl back with brown spots.
Tomatoes show blossom end rot, which is the end of the tomato rots before the fruit ripens.