Moving Water Through A Plant Flashcards
What % of water passes through a plant an is lost via evaporation?
90%
What is transpiration?
The diffusion of water from a leaf via open stomata from a higher to lower water potential.
Is transpiration an active or passive process?
Passive, it uses energy from the sun.
What two factors help facilitate upwards water movement through the xylem?
The cohesion-tension theory, and water’s cohesive and adhesive nature.
What principles was the cohesion-tension theory based on?
The fact that water is cohesive and adhesive.
How far can water move upwards normally?
10m
Where does water evaporate from in transpiration?
The mesophyll cells.
Describe the cohesion-tension theory.
Water vapour evaporates out from the leaves, creating tension. This water is replaced by water from the xylem, as water’s cohesiveness means more water is automatically pulled up.
Describe xylem vessels.
Xylem vessels are long tubes comprised of dead cell walls linked end to end, lacking any cytoplasm.
How are xylem tubes created?
They are created when cells die and leave their cell walls. They elongate near the root tip.
What are cell walls strengthened with?
Lignin.
How does lignin first develop?
In rings.
What does this allow?
It allows cells to stretch, the between allows water to easily enter cells in younger rings.
How do older walls allow water in?
They use pits.
What are pits?
Small gaps that allow water to move sidewards into surrounding tissues or between blocked vessels.
What do conifers have instead of xylem?
Tracheids.
How do tracheids differ from xylem?
They’re smaller, they lack perforated ends. and the pits are only one way.
Why do xylem vessels allow water to travel further than 10m?
They’re very narrow, water cohesion, meaning the water column doesn’t break.
What happens to the water column in the xylem vessel?
The pulling force is so great that the water column is stretched, which pulls the walls slightly inwards.
What happens if the water column is broken?
The column ‘pings’ apart, leaving empty sections at each ends.
What does water use to move even when damaged?
Pits.
