LJ2 Lab 6 Transpiration

Lab Journal Setup Title on the appropriate page (remember we only use the front of each page) Lab 6 Transpiration Under the title date the left hand margin where you will begin today’s entry ( 10/30/18) Partner’s or partners’ name(s) Table of Contents (filled in later) Lab number and full lab title Beginning page (leave space for final page) Beginning date (leave space for final date) Objective (copy) Students will observe and understand the process of transpiration and understand the importance of water potential and capillary action in moving water upward in plants.

How are water, nutrients and hormones transported around a plant without a “pump” organ?

Transpiration is the process of water moving from the soil through the plant to the atmosphere, through a plant vascular system called the xylem. This movement of water upward is essential because it directly and indirectly transports water and nutrients throughout the plant. Water moves in part because the plant manages a gradient of water potential, ranging from the soil to the atmosphere. The water potential is higher in the soil than the root, so water will move from soil to root tissue. The water potential decreases as one moves up the plant and ultimately is very low in the atmosphere, ensuring osmotic movement upward and evaporation. Water potential gradient, capillary action and other phenomena allow a water column with upward movement (transpiration) to persist in plants.

What is water potential? ψW = ψP + ψS

Tonicity is the relative concentration of solutes dissolved in solution which determine the direction and extent of osmosis Tonicity: hypertonic, isotonic, hypotonic Refers to the solute concentration of the aqueous environment of the cell Indirectly tells us about water concentration “Hyper” – high solute/low water outside, so water flows out of the cell

Water potential - a value that describes the tendency of water to move across a membrane into or out of a solution A measure of the relative energy (in the tendency of water to move) in solutions separated by a permeable membrane Determined by the relative solute concentrations and pressure differences

Water potential  a value that describes the tendency of water to move across a membrane into or out of a solution is the free energy per mole of water is calculated from two major components: (1) the solute potential (ψS), which is dependent on solute concentration (2) the pressure potential (ψP), which results from the exertion of pressure — either positive or negative (tension) — on a solution. ψ = ψP + ψS Water Potential = Pressure Potential + Solute Potential In biological systems PP is typically equal on either side of the membrane, so PP is always 0 (pressure on either side cancels each other out) So ψ = ψS How do we calculate solute potential?

The water potential of pure water in an open beaker is zero (ψ = 0) because both the solute and pressure potentials are zero (ψS = 0; ψP = 0). The addition of solute to the water lowers the solute potential and therefore decreases the water potential. This means that a solution has a negative water potential because of the solute. The solute potential (ψS) = – iCRT i = the ionization constant C = the molar concentration R = the pressure constant (R = 0.0831 liter bars/mole-K) T = the temperature in K (273 + °C) Units = bars or megapascals (MPa) I = ionization constant Sucrose = 1 NaCl = 2 CaCl2 = 3

Evaporation(?) Soil: - 0.1 MPa

What is capillary action? Capillary action, brought about by cohesion and adhesion, is instrumental in maintaining the vertical water column in the plant.

At the end of the water column is the leaf and tiny pores in the leaf, called stomata. Water must evaporate into the atmosphere through the stomata to keep the flow of water through the xylem moving.

In this lab we will investigate the process of transpiration and the effect different environments have on the process. We will use an assembled devise called a potometer. A potometer is a devise that measures the amount of water transpired through a plant cutting. It is a simple devise, but one which must be assembled carefully if it is to work accurately. Measuring the amount of water movement over time gives a rate of transpiration.

Environmental variants – independent variables What would these conditions do to the transpiration rate??

Today we will… Tonight you will… Day 2 Day 3 Day 4 Start LJ Look over instructions Partner up Groups of two? Survey equipment and potometer setup for control group Assign independent variables Humidity Wind Bright light Choose plant Discuss data collection What data is collected? Amount of water transpired; leaf weight When is data collected? Tonight you will… Complete “Experimental Design” Day 2 Set up control group Take data control group Plan experimental group Day 3 Set up experimental group Take data experimental group Day 4 Analyze data

Data Analysis We want to express… amount of volume transpired in… amount of time transpired in… amount of leaf weight that did the transpiring How would we do this? What are our best units to do this? How do we crunch our data so that all of our numbers are comparable?

What is total transpiration? Major increments on pipette = 0.1 ml (100 ul) Minor increments = 0.01 ml (10 ul) What is total time? What is total leaf weight? Final values in microliters/1 minute/1 gram (?) To be compiled as class data Friday