Leaves have air spaces to allow for carbon dioxide and oxygen to move into and o

Question

Leaves have air spaces to allow for carbon dioxide and oxygen to move into and out of cells for photosynthesis, which causes water to evaporate and creates greater tension on the mesophyll cells. How do xylem vessels and tracheids prevent collapse in these conditions?

A.photosynthesis is reversed at times to bring together oxygen and hydrogen ions B.metabolic dehydration reactions provide excess water to replace it C.the turgor pressure of surrounding cells pushes the mesophyll cells into shape D.lignin keeps water flowing through the cells E.rings maintain their tubular shape

Explanation / Answer

The xylem vessels and tracheids are elongated cells that have thickened walls which help them to prevent collapsing under tension.

As the water is drawn up by the transpirational pull, tension is produced in the xylem vessels which can be prevented when the side walls are reinforced with rings or spirals of lignin. - D,E

The removal of water from xylem vessels in the leaf reduces the hydrostatic pressure at the top than at the bottom.This pressure difference causes the water to move up in a continuous column.- B

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