Q.If a plant is provided with all mineral nutrients but, Mn concentration is increased, what will be the deficiency?

Step 1. The chapter's mineral-toxicity discussion states that increased manganese concentration prevents the uptake of iron (Fe) and magnesium (Mg), causing their deficiency.

Step 2. The same discussion states that excess manganese separately prevents translocation of calcium (Ca) to the shoot apex - a distinct process from uptake, since translocation is the internal movement of an already-absorbed mineral, not its absorption from the soil.

Step 3. So excess manganese does affect the availability of all three minerals where the plant needs them, but by two different mechanisms: it blocks Fe and Mg specifically at the uptake (absorption) stage, while it blocks Ca specifically at the translocation stage, not at uptake.

Step 4. Option (a) captures this precisely - Mn prevents the uptake of Fe and Mg, but not the uptake of Ca (Ca is instead blocked from translocating to the shoot apex). Option (d) is too broad because it claims Mn blocks Ca uptake, which is not what the text states; options (b) and (c) are wrong because excess manganese never increases uptake of these nutrients.

Distinguish 'uptake' (absorption from soil) from 'translocation' (internal movement) for each mineral affected by manganese toxicity.

• Treating 'blocks translocation of Ca' as equivalent to 'blocks uptake of Ca'.
• Assuming an excess of one mineral always increases, rather than decreases, availability of other minerals.