a) What is secondary growth? b) Describe the process of secondary thickening in a woody stem.
a) What is secondary growth? Type of growth that occurs due to cambium activity in woody plants/stems; resulting in an increase in girth/width of plants; 2 mks b) Describe the process of secondary thickening in a woody stem Facilitated by meristematic cells (cambium) located between the phloem and the xylem (intervascular cambium); it divides radially to form cambium tissues; with xylem forming the outer ring/to the inside; while the phloem forming the outer ring/to the outside; division of the cambium ring; form a secondary parenchyma; hence increases/forms the medullary rays; other xylems (secondary xylem) are formed; hence pushes the phloem and cambium ring outwards; this creates pressure on the outer cells; resulting in stretching and eventual rupturing of epidermal cells; a new band/volume of cambium cells are formed in the cortex beneath the epidermis (cork cambium cells/phellogen); to replace these ruptured cells; the phellogen cells divide on either side; where the inner cells become the secondary cortex; while those produced on the outside become cork cells; which are tightly packed; and become coated with an oily/waxy water-proof material/suberin; further multiplication of cork cells; lead to formation of the bark; which forms a protective layer (against water loss and damage by organisms); seasons results into annual rings; some cork cells form a loose mass/lenticels that allow gaseous exchange through the stem;
Max. 18 mks
Max. 18 mks
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