Water transport in plants Flashcards
Why do plants need water?
photosynthesis, transport minerals, maintain structural rigidity and to regulate temperature
Why do plants need nitrates?
produce DNA, amino acids and chlorophyll
Why do plants need phosphates?
make DNA and ATP
What is the structure of Xylem vessel?
Elongated tubes formed from dead cells (vessel elements) joined together in bundles
No end walls between cells
Thick walls made of Lignin
Pits in cell wall (gaps)
What is the function of Xylem?
Vessels transport water and mineral ions up the plant and provides support
How is the Xylem adapted to its function?
Hollow lumen makes an uninterrupted tube allowing water and mineral ions to flow
Lignin forms strong walls that prevent the tube from collapsing
Gaps in Lignin allow water to leave the vessels and pass between them
Lignin is waterproof to prevent water from adhering too much to the surface
What is the first step of the Cohesion- tension theory?
water evaporates from the mesophyll due to transpiration, leaves the cells will a negative water potential which causes more water to diffuse in through osmosis
What is the second step of the Cohesion- tension theory?
increase in water tension pulls more water into the leaf - Transpiration pull
What is the third step of the Cohesion- tension theory?
water molecules are cohesive so when some are pulled into the leaf others follow- cohesion. pulls whole column of water in the xylem up from roots to mesophyll tissue in the leaves
What is the fourth step of the Cohesion- tension theory?
water enters the stem through the roots
What is the evidence to support cohesion- tension theory?
if trunk or stem is damaged and a xylem cell is broken, water does not leak out, once air enters the tree can no longer draw up water because the continuous column has been broken
What is another piece of evidence to support cohesion-tension theory?
trunk of trees reduce in diameter during daytime when transpiration occurs, adhesion of water molecules to walls of xylem results in a tension which pulls the xylem walls in
