Which substances in xylem tissue are impermeable to water and prevent the collapse of the vessels?

7.1.1 draw plan diagrams of transverse sections of stems, roots and leaves of herbaceous dicotyledonous plants from microscope slides and photomicrographs

7.1.2 describe the distribution of xylem and phloem in transverse sections of stems, roots and leaves of herbaceous dicotyledonous plants

7.1.3 draw and label xylem vessel elements, phloem sieve tube elements and companion cells from microscope slides, photomicrographs and electron micrographs

7.1.4 relate the structure of xylem vessel elements, phloem sieve tube elements and companion cells to their functions