Biology 2012 JAMB Past Questions - Question 22: In Which of the following is involved in secondary thickening in plants?

Correct Answer

C

Explanation

Vascular cambium is the cambium found in the vascular bundles between the 'xylem and phloem. The cells of the cambium divide repeatedly forming new cells which are added to the xylem and phloem resulting in increase in width or girth of the stem of dicotyledonous plants. This increase in girth of stem is called secondarygrowth or thickening. As new phloem cells are pushed outside, pressure ismounted on the epidermis which ruptures creating openings for germs to enter. To replace the ruptured epidermis, secondary cambium cells called cork cambium develops in the cortex. The cork cambium or secondary cambium cells divide producing new cells. These new cells move towards the epidermis to become the cork cells. Collenchyma is a tissue consisting of living cells which are thickened at their, corners to provide the plant with mechanical support. Sclerenchyma is also a tissue consisting of dead cells. The walls of these cells are heavily thickened with lignin to give the plant mechanical support.