Mass transport in plants Flashcards
The xylem vessel/ transpiration
Define transpiration
The process of water movement through a plant and its evaporation from leaves. Its the consequence of gas exchange in leaves as when stomata open, water evaporates from mesophyll cells and is replaced by water from the xylem.
Outline the movement of water through the leaf
When stomata are open, water vapour diffuses form the air spaces out through the stomata and down a water gradient. To replace this, water evaporates from the mesophyll cells into the air spaces, forming vapour which builds up air spaces. The water in the mesophyll cells is replaced by water from the xylem vessels.
Why do the xylem vessels contain lignin?
Their cell walls contain lignin for strength and waterproofing, and cause the cell contents to die leaving a hollow lumen with little to resist the mass flow of water.
Why do the xylem vessels contain pits and no end walls?
The walls also contains pits which divert the water laterally so it can continue in an adjacent flow if there’s a blockage. They have no end walls to form a continuous column from root to leaves.
What is mass transport?
The movement of materials over large distances, due to pressure differences
What does the xylem tissue do?
Transports water and dissolves minerals from the soil, through the roots, the stem and to the leaves.
What is the transpiration stream?
The continuous column of water that move from the soil through the roots, stems and leaves to the air.
