Plant transport Flashcards
2 plant vascular tissues
xylem and phloem
Label vascular tissues in root, stem and leaf
diagrams
Adaptations of xylem
-dead cells aligned from end to end to form tube
-tubes narrow so water column doesn’t break easily
-bordered pits in lignified walls allow water to move sideways from one vessel to another
-lignin allows xylem to stretch as plant grows
Features of phloem
-sieve tubes made of sieve tube elements and companion cells
-sieve tube elements- lined end to end, no nucleus, thin walls, sieve plates so sap moves to next element
-companion cells- large nucleus, dense cytoplasm, lots mitochondria
-holes between tube and companion cell= plasmodesmata
-sieve plates can close part of phloem if damaged to reduce loss of sap
Water pathways
Apoplast-passes through spaces between cells, moves by mass flow not osmosis
Symplast- water enters cytoplasm through membrane, then passes through plasmodesmata to the next cell
Vacuolar- water not confined just to cytoplasm, it can enter and pass through vacuole
Plasmolysis
when so much water is lost, the membrane loses contact with the cell wall
-tissue is now flaccid
Transpiration
-loss of water vapour from the upper parts of the plants
Pathway
-water enters leaf through xylem and moves by osmosis to cells of spongy mesophyll
-water evaporates from cells walls of spongy mesophyll
-water vapour diffuses out leaf through open stomata, down the water vapour potential gradient
Purpose of transpiration
-transport mineral ions up the plant
-maintain cell turgidity
-supply water for growth, cell elongation and photosynthesis
-keep plant cool on a hot day
Factors effecting rate transpiration
-Light intensity- higher rate as more photosynthesis, so stomata open for gaseous exchange
-Temperature- higher rate, as evaporation quicker, diffusion quicker and decreases water vapour in air (humidity)
-Humidity- lower humidity, higher rate
-Air movement- higher rate as maintains conc gradient
-Water availability- more water, higher rate
Practical to measure transpiration rates
-use a potometer
Valid results
-set up potometer under water so no air bubbles
-ensure healthy shoot
-cut stem under water so air doesn’t enter the xylem
-cut at angle so large SA
-dry the leaves
Water uptake at root
-root hair cells have large SA to absorb ions and water
-water moves across root cortex and down water potential gradient to the endodermis of the vascular bundle
-can travel via apoplast pathway, but then must enter symplast due to casparian strip
Role endodermis
-casparian strip blocks apoplast pathway between the cortex and medulla
-ensures water and ions pass into cell cytoplasm
-membrane contains transporter proteins that pump mineral ions from the cytoplasm of cells in the cortex, to the medulla and xylem
-this decreases WP, so water moves in via osmosis
-once water enters medulla, it can’t move back as blocked casparian strip
Root pressure
-action endodermis pumping minerals into medulla draws water in via osmosis
-pressure in medulla builds, pushing water up the xylem
Transpiration pull
-water molecules in xylem are attracted to each other due to H bonding- cohesion
-so as one molecule evaporates, the whole chain is pulled up the xylem
Capillary action
-same forces that hold water molecules together, attract them to the sides of xylem- adhesion
-xylem is narrow, so these forces can pull water up the sides of the vessel