蒸散

A potometer is a device used to measure water loss from leaves. Assemble it by attaching rubber tubing to a 5 mL calibrated pipette, submerging the device in water to fill it completely without bubbles, then capping the tube with a pipette bulb. Secure the potometer with clamps on a stand, keeping the capped end 1-3 inches below the bulb, and adjust the water level to zero using a transfer pipette before inserting a leaf.

Divide the total water loss measured in milliliters by the time the experiment ran in minutes to get the rate of water loss. Then divide this value by the leaf surface area in square meters. This calculation yields transpiration rate in standardized units, allowing comparison across different leaf species and environmental conditions.

Stomata are the primary sites of water loss in leaves. By counting stomata per unit area using microscope impressions made with nail polish, you can determine if a correlation exists between stomatal density and transpiration rate. This reveals whether plants adapted to drier environments have fewer stomata, a key adaptation for reducing water loss.

Trace each leaf outline on paper and cut it out. Weigh the tracing, then weigh a reference 4x4 centimeter paper square of the same type. Divide the tracing weight by the reference weight per square centimeter to calculate total leaf area. Convert the result from square centimeters to square meters for standardized transpiration rate calculations.

Paint the underside of each leaf with clear nail polish, covering at least one square centimeter, since most stomata are located on the leaf bottom. Once dry, press cellophane tape onto the painted area and peel it off to remove the polish impression. Mount the tape on a microscope slide and observe under low magnification first to locate stomata, then switch to higher magnification for counting.

The experimental hypothesis is that leaves from plants adapted to hotter or arid environments will have lower transpiration rates than those from humid or wet regions. The null hypothesis states that different plant species will not differ in transpiration rates. Data analysis should reveal whether environmental adaptation correlates with both transpiration rate and stomatal density.

Transpiration is a key plant process involving water movement through tissues and evaporation from leaves. Understanding this process connects to broader cellular metabolism. While transpiration itself is a physical process, it relates to cellular respiration and photosynthesis, as water availability affects metabolic rates and energy production in plant cells.