Transpiration & Stomates Flashcards
Stomates
Pores/openings guard cells
Guard cells
Cells that surround small openings on leaves used for water and gas exchange
Characteristics
Found on leaves/stems
Also found on flower parts and fruit
May occur on both lead surfaces but more common on undersides of leaves
The # of stomates varies according to the plant
Guard cell functions
Change shape due to turgor pressure caused by osmotic pressure. The parts most affected are the cellulose microfibrils in the cell wall
Transpiration
Water from soil leaves through leaves/heat and energy are consumed by the plant
Leaf gas exchanges
CO2 from PSN and resp.
H2O vapor
Organic matter
Influences on gas exchanges in leaves
Humidity Temperature Wind Radiation (inside and out) Opening and closing of stomates
Atmospheric pressure
Mixture of gases and the pressure exerted by those gases at certain temperatures
Partial pressure
Pressure each gas would exert if it alone occupied by volume of the mixture at the same temperature
Gas diffusion
Gases diffuse because of gradients in partial pressure
Vapor pressure
Partial pressure of water vapor (usually higher outside the leaf)
Diffusion into and out of cells
Vapor diffuses faster when differences in vapor pressure is greater and slower (ie. caused by partially closed stomates)
If CO2 is used inside leaf in PSN partial pressure will be less outside causing a gradient for CO2 diffusion into the cell
Relative humidity
Vapor pressure of a given sample of air at a given temperature compared to maximum saturation vapor pressure at that temperature (absolute humidity)
Increase in temp increases amount of water vapor air can hold
Diffusion of water vapor is related to pressure, not relative humidity (internal workings of leaf)
