Biology 2012 JAMB Past Questions - Question 6: Plants that show secondary growth are usuaily found among the

Correct Answer

D

Explanation

The continuous increase in height in dicotyledonous plants is usually followed by corresponding increase in girth or width of the stems. The vascular bundles ary phloem. The cambium of each* vascular bundle divides repeatedly producing new or secondary xylem and phloem cells which' are added to the primary xylem and phloem to make the stem increase in girth or width. This is called secondarythickening -or growth.- Though plendophytes (ferns) and monocotyledonous plants eg. coconut trees have vascular bundles, they do no tundergo secondary thickening. This is because, their vascular bundles lack cambium (plural cambia). Thus, there is no increase in the number of xylem and p h l o e m cells. Thallophytes ie. the fungi and .!gae are non vascular plants.