Transport of Water in the Xylem Flashcards
Where is water absorbed in plants?
Water is absorbed by the roots through extensions called root hairs
What is the main force that pulls water through the xylem?
The main force is the evaporation of water from leaves, known as transpiration
What supplies the energy for transpiration?
The energy is supplied by the sun, making the process passive
Through which structures is most water transported in flowering plants?
The vast majority of water is transported through hollow, thick - walled tubes called xylem vessels
How does water move through the xylem?
Water moves through the xylem due to transpiration, starting when water evaporates from the surfaces of cells surrounding the stomatal air space and water vapour diffuses out of the stomatal pore
Why does water vapour diffuse out of stomata?
The humidity of the atmosphere is usually lower than that of the air spaces next to the stomata, creating a water potential gradient
What happens when the stomata are open?
Water vapor molecules diffuse out of the air spaces into the surrounding air
How is water lost by diffusion replaced?
Water lost by diffusion from the air spaces is replaced by water evaporating from the cell walls of surrounding mesophyll cells
How do plants control their rate of transpiration?
By changing the size of the stomatal pores
How is water lost from mesophyll cells?
Water is lost by evaporation from their cells walls to the air spaces of the leaf
Why do mesophyll cells take in water from neighbouring cells?
When mesophyll cells lose water by evaporation, their water potential decreases, so water enters by osmosis from neighbouring cells
How is water replaced in mesophyll cells?
Water is replaced by water moving from the xylem via cell walls or the cytoplasm
How do water molecules move across the leaf mesophyll?
A water potential gradient is established as neighboring cells lose water and take in water from adjacent cells by osmosis
How is water pulled from the xylem across the leaf?
The continuous loss of water and decrease in water potential creates a gradient that pulls water from the xylem, across the leaf mesophyll, and finally out into the atmosphere
What is the main factor responsible for water movement up the xylem?
The cohesion - tension theory
How does water movement in the xylem begin?
Water evaporates from mesophyll cells due to heat from the sun, leading to transpiration
What property allows water molecules to stick together?
Water molecules form hydrogen bonds and stick together due to cohesion
How does water form a continuous column in the xylem?
Cohesion between water molecules allows them to form a continuous, unbroken column across mesophyll cells and down the xylem
What causes more water to be drawn up the xylem?
As water evaporates from the mesophyll cells into the air spaces beneath the stomata, more water molecules are drawn up due to cohesion
What is transpiration pull?
It is the process where a column of water is puled up the xylem due to transpiration
Why is the process called the cohesion - tension theory?
Transpiration pull creates tension (negative pressure) in the xylem, pulling water upwards
