BIOL134 Design Experiment Forum

Running head:

The effect of Temperature, Wind and Humidity on the rate of Transpiration

Brittney Sierra

BIOL134

12/6/2019

Introduction

The process by which water moves through plants from the roots and then removed via the leaves is known as transpiration. Water from the soil is absorbed by plants through the roots by a process called osmosis. Water is transported through the plant as a result of water potential, this is a kind of energy that is created by water molecules in the stem of a plant. As a result of water potential water is capable of moving from a point of high concentration to that with lower concentration of water ("Evapotranspiration and the Water Cycle", 2019).

The leaves of plants contain tiny opening beneath them called stomata which allow water to leave the plant, this tiny openings also allow carbon dioxide and water to freely move inside the leaves. As water evaporates through the leaves a transpirational pull is experienced on water located in the xylem which is what results in water always moving up the plant. As a result of pressure water and other solutes are able to move through vessels and sieve tubes by a process known as backflow, this backflow results in negative pressure along the xylem vessels causing water and plant-sap to move to the leaves from the roots, this water movement is also aided by cohesion.

The coagulation of water molecules is what is known as cohesion, as water molecules stick together it makes it easier for it to move through the plant as it will be moving as a single molecule that is continuous. Due to the fact that water is cohesive as a result of the hydrogen bonds holding it together, water molecules in the xylem take up the place of molecules that evaporate from the leaves, which then evaporate continuing the transpiration cycle.

The rate of transpiration can either be increased or decreased by different factors in the environment, some of these environmental factors include the light, humidity and wind speed. The rate of transpiration is increased by wind movement due to the fact that the wind aids oxygen molecules in entering the leaf while light which is a source of heat energy also increases the rate of transpiration as a result of the heat speeding up the rate of evaporation from the leaves ("Environmental Factors Affecting Transpiration in Plants", 2019).

Humidity is one of the environmental factors that reduces transpiration as a result of additional water molecules being present in the air this is as a result of the water potential being able to move from regions of high concentration to those with lower concentration of water molecules. As a result of increased volume of water in the air there will be no need for water to move out through the leaves (Kuiper,1961).

Variables

The variables under investigation in this experimental design were

Independent variable

· Light – under what kind of light source or the environmental temperature condition in terms of time of day transpiration was measured

· Wind

· Humidity (mist)

Dependent variables

· The amount of water that transpired through the plant at a given time and the time of day.

In this experiment time of day is an independent variable due to the fact that it affects the dependent variable which in this case is the rate at which the plant transpires. This is as a result of different times of the day having different light intensity and environmental conditions which result in either the slowing down or increase in the rate of transpiration. The time the plants will be allowed to transpire also affects the dependent variable as increased time interval will result in increased transpiration and reduced time interval leads to little transpiration taking place

Constants and control

The following variables are those that will remain unchanged throughout this experiment:

· Species of plant being tested

· The location of the plant

· The time period allowed for the plants to transpire

Testable questions

This experiment aims to answer the following questions

What is the effect of light, wind and humidity on the rate of transpiration?

Hypothesis

In this lab experiment water will be lost in all the plants through the process of transpiration, those plants that will be affected by the fan and heat sink will end up losing a considerable amount of water as a result of changes in the environmental conditions. As a result of transpiration, water will be pulled from the photometer to the plant tissue.

Methods

Transpiration

The pipette was placed inside the plastic tubing using only the tip and then dipped into a tray of water, water is then drawn from the tray into the pipette and the tubing till bubbles had diminished. Petroleum jelly was then applied around the tubing so as to make an airtight seal around the stem of the plant. After this had been down the tubing was bent to make a u-shape then clamps two in general were taken and used to hold the photometer on the ring stand in place. The potometer was then left to reach equilibrium for about ten minutes.

The plants were then exposed to the fan which was set at low speed and situated about a meter away, the reading at zero seconds was recorded and then readings taken after an interval of 30 minutes. When the experiment was done all the leaves from the plant were removed using a razor blade and then massed using a 1cm2 box and then massed.

Stem structure

A microtome (Nut and bolt) was retrieved and then a small cup made by removing the bolt. The cut stem was placed in the microtome and the paraffin that had been melted prior poured around the plant stem. The poured paraffin was given time to dry then the excess stem cut out. A slice was then cut out by twisting the bolt and cutting using the blade, the cut slice was then placed in ethanol of 50% concentration. After being left in ethanol for a period of 5 minutes forceps were used to remove the slices and then placed in a dish of toluidine blue o strain and left to sit for a minute. These sections were then rinsed in distilled water then mounted on a slide and a drop of 50% glycerin added. Using a light microscope the cross-section was observed and observations recorded and drawn.

Results

Table 1. Parometer readings

Time	0	3	6	9	12	15	18	21	24	27	30
Room	0.53	0.54	0.55	0.56	0.57	0.58	0.59	0.6	0.61	0.62	0.63
Mist	0.34	0.36	0.38	0.40	0.42	0.43	0.43	0.44	0.45	0.45	0.46
Light	0.67	0.68	0.69	0.70	0.71	0.72	0.73	0.74	0.75	0.77	0.79
Fan	0.02	0.03	0.04	0.05	0.06	0.07	0.09	0.10	0.11	0.13	0.13

The mass of the leaves =1.1g

Leaf surface area=0.0044m2

Table 2. Individual water loss in ml/m2

Time interval (min)
	0-3	3-6	6-9	9-12	12-15	15-18	18-21	21-24	24-27	27-30
Water loss(ml)	0.01	0.01	0.01	0.01	0.01	0.02	0.01	0.01	0.01	0
Water loss per m2	2.27	2.27	2.27	2.27	2.27	4.55	2.27	2.27	2.27	0

Table 3. Average cumulative water loss (ml/m2)

Time	0	3	6	9	12	15	18	21	24	27	30
Room	0	5	5	5	5	5	5	5	5	5	5
Mist	0	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	4	4
Light	0	2.27	2.27	2.27	2.27	2.27	4.55	2.27	2.27	2.27	0
Fan	0	4.17	4.17	4.17	4.17	2.08	0	2.08	2.08	0	2.08

Analysis

Average water loss for each treatment per minute

Light – 0.93

Fan – 0.76

Mist – 0.83

Room – 1.67

Reasons why each condition resulted to an increase or decrease in transpiration rate as compared with the control experiment

Room

This was the control experiment in this lab and had no effect on transpiration

Fan

The fan led to an increase in transpiration rate due to the fact that the blown wind resulted in increased evaporation hence causing transpiration to be more rapid

Light

Increase in light increased the rate of transpiration due to the fact that heat increases the amount of water that is pulled by the plant from the tray as a result of increased evaporation at the leaves

Mist

Mist acts as humidity, this decreases transpiration as a result of increased volume of water in the air resulting to decreased evaporation.

How did each of the conditions affect the water gradient potential from stem to leaf?

Light and the fan led to a decreased water potential in the leaves of the plants resulting in water moving up the plants stem by transpiration. Being the control, room temperature did not have much effect on the water potential while mist/humidity led to an increase in water potential as a result of decreased transpiration

Discussion and conclusion

Water potential is the entity that controls transpiration in plants. A change in water potential at the leaves results in a gradient that enables water to be moved upward from the roots to the leaves via the xylem. The mist and plastic bag increased water potential resulting to reduced evaporation which in the end reduces the water potential between the roots and the stem of the plants reducing transpiration. The fan and light were used to imitate environmental conditions in terms of wind and heat, this resulted to increased evaporation which as a result increases the water potential gradient resulting to more water being pulled up the stem hence promoting increased transpiration rates.

References

Evapotranspiration and the Water Cycle. (2019). Retrieved 11 October 2019, from https://www.usgs.gov/special-topic/water-science-school/science/evapotranspiration-and-water-cycle?qt-science_center_objects=0#qt-science_center_objects

Kuiper, P. J. C. (1961). The effects of environmental factors on the transpiration of leaves, with special reference to stomatal light response (Doctoral dissertation, Veenman).

Zhang, W., Wang, Y., He, K., Zhou, Y., & Gan, X. (2008). Factors affecting transpiration of Pinus tabulaeformis in a semi-arid region of the Loess Plateau. Frontiers of Forestry in China, 3(2), 194-199.

Environmental Factors Affecting Transpiration in Plants. (2019). Retrieved 11 October 2019, from https://www.cropsreview.com/factors-affecting-transpiration.html