mass transport in plants Flashcards
define osmosis
the movement of water molecules from an area of high water potential to an area of low water potential through a a partially permeable membrane
define transpiration
the movement of water up through a plant, to the leaves where evaporation occurs from the stomata
define evaporation
when water, that has moved to the surface of the leaf is released into the atmosphere
through which tube is water transported from the root to leaf?
xylem
what property of water allows them to counteract the force of gravity?
h bonds create cohesion
what is the name of the theory which explains the movement of water up the xylem column?
cohesion-tension theory
what does the xylem do?
it transports water and mineral ions around the plant
what are the main features of the xylem vessel?
. xylem cells are dead - no organelles. this means that no chemical reactions occur , so the flow of water is quicker
. long hollow tube
. covered in lignin. this makes xylem vessels waterproof, and it thickens the xylem vessel, making it stronger. it also allows plants to grow upwards
. pits in the walls allow water to move lateral to move into other xylem vessels
. no end walls. this allows for a continuous water column to be created
what is the stomata responsible for?
regulating water loss and controlling gas exchange
what is the apoplastic pathway?
the movement of water through the cell wall
what is the symplastic pathway?
the movement of water through the cytoplasm
what is the mesophyll layer?
the middle of the leaf
what would happen if air got into the xylem?
it would break the hydrogen bonds between the water molecules and cohesion would be lost
EXAM QUESTION
describe the cohesion-tension theory of water transport in the xylem, (6 marks)
the movement of water up through a plant, to the leaves where evaporation occurs from the stomata. this lowers the water potential inside the mesophyll layer. this creates a transpiration pull and water moves up the xylem vessel. water molecules have h bonds between each other causing cohesion. this allows the formation of a continuous water column, pulling water molecules up the plant. water also sticks to the walls of the xylem pulling them inwards (adhesion)
