THE PANSY AND THE PEA
(That is not the formal lab title. See the next page.)
● Water diffuses from soil into root xylem via osmosis => Root pressure
● Root pressure = osmotic pressure that causes sap to rise to the leaves; not sufficient force to account for movement of water to leaves at the top of tallest trees
● Without transpiration, ions will accumulate in root xylem and lower water potential
● Guttation = exudation of drops of xylem sap from tips/edges of leaves of some plants
(caused by root pressure at night)
● TACT Theory:
○ Tension => With adhesion/cohesion, generates “capillary action”, or spontaneous rising of fluid in a narrow tube
■ Water is polar, and Hbonds create surface tension, allowing plants to draw water from the root through the xylem to the leaf
■ Water’s polarity allows it to form Hbonds with xylem cell walls
■ Water’s polarity allows it to form Hbonds with itself
○ Transpiration => Primary mechanism of water movement in plants
■ Water constantly lost by transpiration through leaves when stomata open ■ 1 molecule lost, pulls the next up the column
● Water potential (Ψ) = tendency of water to move (always from high to low)
○ Ψ = Ψ Ψ w p s ● Germination = sprouting of seed under certain conditions
● Plant hormones
○ Auxins: cell elongation, responsible for tropisms, apical meristems
○ Cytokinins: cell division, cell differentiation, roots/fruits/embryos
○ Gibberellins: cell elongation, germination
○ Abscisic acid: seed dormancy, slowed growth, inhibition
○ Ethylene: fruit ripening, apoptosis
● Pansies are hybrid plants bred as garden flowers; round leaves, large flowers
● Blackeyed peas are a legume subspecies of the cowpea
Observing How Varying Water Levels Affects
BlackEyed Pea Germination Rate and How Varying
Wind Exposure Affects Pansy Transpiration Rate
● Group members
○ Supplies and Equipment Coordinator: Sarah Armstrong
○ Task Master and Safety Officer: Savanna Calchera
○ Lab Facilitator: Alicia Wang
○ Data Recorder and Lab Statistician: Hannah Whitaker
● College Board Objectives
○ Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow.
○ Enduring Understanding 2.C: Organisms use feedback mechanisms to regulate growth and reproduction, and to maintain dynamic homeostasis.
○ Essential Knowledge 2.C.2: Organisms respond to changes in their external environments. ○ Science Practices:
■ #2: The student can use mathematics appropriately.
■ #3: The student can engage in scientific questioning to extend thinking or to guide investigations within the context of the AP course.
■ #4: The student can plan and implement data collection strategies appropriate to a particular scientific question.
■ #5: The student can perform data analysis and evaluation of evidence.
● Background Information
○ Transpiration is the process by which vascular plants lose water through the stomata on their leaves, a combination of evaporation and other forces related to water potential. Stomata are small pores surrounded by “guard cells” which bow in and out to open and close the pore by actively altering the ion concentrations in their cytoplasm and thus swelling or emptying with water.
Water is taken up primarily by the cells in a plant’s roots, since the roots have a lower water potential than the soil surrounding. By osmosis, water travels through or between cells to reach the xylem of the vascular bundle, through which the water is transported to the leaves. Though root osmotic pressure
(due to differences in water potentials) is one factor in driving water upwards, transpiration, cohesion, adhesion, and the tension that these collectively create is the primary force for water transfer. As a water molecule is transpired, its cohesive attraction to adjacent water