mass transport in plants(3.6) Flashcards
what is transpiration
loss of water vapor from the stomata by evaporation
what is the role of the stomata
-allow gas exchange
-guard cells open and close the stomata to control transpiration
how does light intensity affect transpiration
more light causes more stomata to open as they are light sensitive this creates a larger sa for evaporation
how does temperature affect transpiration
more heat leads to more kinetic energy so molecules move faster therefore more evaporation
how does humidity affect transpiration
more water vapor in the air will create a more positive water potential outside the leaf therefore water potential gradient is reduced and diffusion slows
how does wind affect transpiration
more wind will blow away water vapor in the air this will maintain a strong water potential gradient
how does water have cohesion
water is a dipolar molecule this enables hydrogen bonds to form between the oxygen and hydrogen of different water molecules this creates cohesion between molecules so they stick together
how is cohesion beneficial for transpiration
water can travel up the xylem as a continuous water column which is easier than pulling up individual water molecules
what is adhesion
where water sticks to other molecules.Water adheres to the xylem walls
what is root pressure
as water moves into the roots by osmosis it increases the pressure in the root which forces up water above it
how does water move up the xylem
-water vapor evaporates from the stomata .This loss in water volume creates a lower pressure
-more water is pulled up the xylem to replace the lost water
-due to hydrogen bonds between dipolar molecules they are cohesive .This creates a column of water in the xylem
-water molecules also adhere to the walls of the xylem this helps pull the water column up
-as the column of water is pulled up it creates tension which narrows the xylem
what is translocation
Translocation is the movement of dissolved substances, such as sucrose and amino acids, from parts of the plant where the substances are made to other parts of the plant where they’re needed
what are the two key cells in phloem tissue and their role
companion cells-provide the atp required for active transport of organic substance
sieve tube elements-few organelles, no nucleus ,living cells to create hollow tube
what is the first stage of the mass flow hypothesis
-photosynthesis occurring in the chloroplasts of the leaves creates organic substances like sucrose
-the sucrose is actively transported into the sieve tube elements using companion cell atp
-this lowers the water potential in the sieve tube elements
what is the second stage of the mass flow hypothesis involving water
-water enters the sieve tube elements from the surrounding xylem vessels by osmosis
-this increase in water volume increases the hydrostatic pressure causing the liquid to be forced towards the sink
