It is observed that deficiency of a particular element showed its symptoms initially in older leaves and then in younger leaves.
(a) Does it indicate that the element is actively mobilised or relatively immobile ?
(b) Name two elements which are highly mobile and two which are relatively immobile.
(c) How is the aspect of mobility of elements important to horticulture and agriculture ?

Explanation

(a) The plants try to supply more nutrients to its younger leaves than the older leaves. When nutrients are mobile, the deficiency symptoms are shown by the older leaves first because that particular nutrient reaches the top first and lower leaves does not get that nutrient.
Highly mobile elements are P, K and Mn. Less mobile elements are `Ca^(+)` and `K^(+)`.
(c) The aspect of mobility of essential elements is important in horticulture and agriculture in the following ways
(i) A crop in which older leaves are harvested if show deficiency symptoms , will decrease its economic value.
(ii) The crops in which flowers, fruits and inflorescence are harvested, the immobile nutrients will not reach to the apex/tip because of immobility , so this will reduce the yield.