Botany Question 19 – AP-EAMCET 2025
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Assertion (A) states: "Transport of plant growth regulators are always strictly polarized and unidirectional." While auxins are known for their strictly polar and unidirectional transport, other plant growth regulators (PGRs) such as gibberellins, cytokinins, abscisic acid (ABA), and ethylene do not exhibit such strict polar transport. Their movement can be non-polar, through xylem, phloem, or cell-to-cell diffusion, and can be multi-directional depending on the specific hormone and the plant part. Therefore, the statement that PGRs are *always* strictly polarized and unidirectional is false.
Remember that 'always' is a strong word in biological statements. Look for exceptions to such generalizations.
Reason (R) states: "Organic and mineral nutrients undergo multi directional transport." Organic nutrients (sugars) are transported via the phloem from source to sink, which can be in various directions (upwards, downwards, or sideways) depending on the location of the source and sink tissues. Mineral nutrients are primarily transported via the xylem in a largely unidirectional flow from roots to shoots. However, once in the shoots, they can be remobilized and transported via the phloem to other parts of the plant, such as developing fruits or storage organs. This remobilization and subsequent transport contribute to a multi-directional movement within the plant's overall nutrient economy. Therefore, Reason (R) is true.
Distinguish between the primary transport direction in xylem (unidirectional) and the overall movement of nutrients, which includes remobilization and phloem transport (multi-directional).
From the analysis:
Assertion (A) is false.
Reason (R) is true.
Comparing these findings with the given options, Option 4 states "(A) is false, but (R) is true", which perfectly matches our conclusion.
Carefully evaluate each statement's truth value before considering the relationship between them. This prevents errors in Assertion-Reason type questions.