4.4.2 - Transpiration Flashcards
How are xylem vessels arranged in a dicot root?
In a cross shape
How are xylem vessels arranged in a monocot root?
Arranged as tubes that surround the pith
Hoe does water vapour diffuse out of the leaf?
Less water in air than in the leaf so there is a water potential gradient.
Leaves have higher water potential
What happens when water is evaporated out of the leaf?
Replaced by water in xylem.
water can either move through the cytoplasm or cell wall of mesophyll cells.
Due to water potential gradient.
What are the 2 ways water is taken upwards by the xylem?
Cohesion tension
Root pressure
How does cohesion tension pull up water?
Water molecules form hydrogen bonds between each other.
A column of water is pulled up through the xylem, this is called transpiration pull
Evidence for cohesion tension?
During the day, the diameter of tree trunks is smaller.
Xylem vessels are narrower as they are pulling water upwards.
How does an osmotic potential arise in the roots?
Dissolved substances build up in epidermal cells by diffusion.
Gives roots a lower water potential than the soil.
What is the role of endodermal cells?
Actively transport solutes into the xylem to create a concentration gradient large enough to pull water up the xylem.
What are the 3 routes water can take when going from root hair cells into endodermis?
Apoplast route
Symplast route
Vacuolar route
How does water travel from root hair cells to the endodermis in the apoplast route?
Through the cellulose cell walls
How does water travel from root hair cells to the endodermis in the Symplast route?
Water diffuses along a water concentration gradient through the cytoplasm of cells
How does water travel from root hair cells to the endodermis in the vacuolar route?
Water moves along a water potential gradient but through vacuoles as well as cytoplasm.
