Exchange And Transport Flashcards
Structure of the waxy cuticle of the leaf?
Waterproof to reduce evaporation of water
Transparent to allow light through
Structure of the upper epidermis of the leaf?
Thin (only one layer) and transparent to allow light through
Structure of palisade cells in the leaf?
Many chloroplasts packed tightly at the top of the leaf
Structure of the vein of the leaf?
Contains xylem and phloem
Structure of lower epidermis of the leaf?
Contains guard cells which open and close the stomata to allow gas exchange
Structure of spongy mesophyll cells in the leaf?
Irregular shaped cells with large surface area with air spaces between to allow gases to reach all cells
Structure and function of plant root?
Absorbs water and minerals
Lots of root hair cells to increase surface area
Osmosis definition?
The diffusion of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane
Equilibrium definition in regards to osmosis?
Equal movement of water molecules in both direction, so no net movement
Water potential definition?
The pressure exerted by water molecules that are free to move in a system and so their tendency to move by osmosis
What is the kPa of pure water?
0, the highest possible water potential
What does water in the root need to go through to get the the xylem?
Epidermis, cortex, endodermis
Two water pathways in roots?
Apoplast and symplast
What does the apoplast pathway consist of?
Everything external to the plasma membrane of the living cells (cell walls and air spaces)
What does the symplast pathway consist of?
Cytosol and plasmodesmata
Through cell membranes
What is the casparian strip?
A waterproof strip in the endodermis made of Suberin. Blocks the apoplast pathway
How does water move past the casparian strip?
Moves inside the cells
How does water finally get into the xylem?
Water follows the lower water potential in the xylem to dilute it from the minerals
Structure of the xylem?
Cell walls contain lignin which is waterproof so cells die
End cell walls and cell contents decay creating a thin continuous tube
Lignin keeps the xylem strengthened
Function of bordered pits in xylem?
Lets water out of xylem sideways if needed
How does water move up the xylem?
Tension- as water evaporates from the leaf through the stomata the water in the leaf cell must be replaced from the xylem (transpiration pull)
Cohesion- water molecules are polar and attracted to each other forming hydrogen bonds allowing a continuous column of water
Adhesion- water molecules bond to sides of xylem which helps pull water up the stem as gravity is reduced
Root pressure- active transport of minerals into xylem water follows by osmosis. This pressure forces water upwards
Transpiration meaning?
Movement of water out of leaves
Guard cell function?
Controls water leaving the plant. Open and closes stomata by swelling when turgid
Transpiration process?
ATP used to transport potassium ions into guard cells lowing water potential
Water moves in by osmosis
Guard cells swell and open stomata
Factors affecting transpiration?
Stomata being open in response to light and low co2 levels
Stomata closing in response to drought
Temperature, high increase evaporation from stomata
Wind speed, wind blows water vapour away lowing water potential in surrounding air
Humidity, water vapour will increase in surrounding air so water will not diffuse out
What is a xerophyte?
A species of plant that is designed to deal with very little water
How are xerophytes adapted?
Rolled leaves to trap air, increasing humid and water potential in surround air
Extremely thick waxy cuticle
Reduced number of stomata
Stomata are in sunken pits reducing air movement
Lower epidermis have tiny hairs (trichomes) to trap moisture
Densely packed mesophyll so smaller surface area for evaporation
Leaf cells may have high salt concentration so lower water potential
Root system is deeper
The role of the mouth/nose in gaseous exchange?
Air enters through nose and mouth
Air filter by nose hairs and mucus to trap dust/bacteria
Air is warmed and humidified to match air in the lungs
The role of the pharynx in gaseous exchange?
Air enters, it’s an intersection where paths for oesophagus and trachea cross
The role of the larynx in gaseous exchange?
Closes during swallowing so food does not enter the trachea
The role of the trachea in gaseous exchange?
Supported by c-shaped rings of strong, flexible cartilage to prevent it collapsing