AP BIOLOGY

Detailed explanation-1: -So, the correct answer is ‘Xylem’.

Detailed explanation-2: -The transport of water in the xylem takes place only from the roots to the leaves. Therefore, the movement of water and nutrients in the xylem is unidirectional.

Detailed explanation-3: -Xylem is unidirectional, whereas, phloem is bidirectional.

Detailed explanation-4: -In case of plants, transport in xylem of both minerals and water is unidirectional (Polarised) from roots to stems. Plant growth regulators, hormones and chemical stimuli are also transported in unidirectional or polarized manner, in very small amounts, from where they are formed to other parts.

Detailed explanation-5: -Xylem sap analysis reveals that Nitrogen is primarily transported as amino acids and related compounds, in an organic form. And very little is transported in its inorganic form as nitrates or minerals. Therefore xylem also contains organic solutes and other compounds.