Factors (Independent variables for consideration)
Wind Speed
Light Intensity
Temperature
Humidity
Wind
carries
water Guard cells guarding the As stomata is opened to release As the relative humidity in the
released by transpiration stomata swell when in contact water
vapor
at
warmer surrounding air of the plant
and evaporates water in the with light, resulting in water temperatures, water evaporates in increases, the steepness of
layer
of
moist
air vapor escaping from leaves. a faster rate, leading to a water concentration gradient
surrounding the leaf, thus Light intensity also impacts the steepened water concentration is reduced. This shows
steepening
the
water rate of transpiration through and more water intake. Despite its saturated air lowers the rate of
concentration between the heat generation in the process. enhanced
transpiration
rate, transpiration due to less
stomata and surrounding (Kimball, 2016) Therefore, a extremely high temperatures may diffusion of water vapor out of
air. More water would be higher light intensity leads to also lead to heat stress, damaging the leaf through the stomata
diffused from the stomata to water leaving the leaves and the plant structure. As a result, and closing of guard cells.
the environment. Thus, increased photosynthesis rate stomata are closed to conserve Less abscisic acid is produced
higher
wind
speed that
generates
heat
to water, reducing transpiration rate. as stomata opens to facilitate
increases
transpiration evaporate water.
(Vaysl, 2023)
gas exchange. (Noaa, 2023)
rate. (Odle, 2022)
Chosen IV and justification: Light intensity has been chosen to be the most suitable independent variable due to efficient measures
that can be utilized to control the amount of light through using boxes in a confined space. A tight control of this factor can aid in the
production of accurate, valid, and reliable results. It’s easy manipulation make it a suitable candidate as the IV for the experiment.
Moreover, light is a major environmental cue that affects the opening and closing of stomata, having a link to photosynthesis and
hence increasing
Plant types
Xerophytes
Hydrophytes
Species and
Effect of chosen factor
Species and
Effect of chosen factor
Adaptations
Adaptations
Pineapple. The Due to the thick and waxy cuticle, the Water Lily. The water Despite having a consistent supply of
leaves
on
a pineapple leaves allow the fruit to lily has evolved to water, the water lily still utilizes the
pineapple
are experience reduced transpiration rates contain more stomata adaptation of more stomata on the upper
waxy, long, and through making a wax layer on the on the upper side of the leaf to facilitate gas exchange, also
bear
curved outside of the leaf to prevent water vapor leaf surface due to the adapting to the aquatic environment and
spines on the from escaping to the surroundings. This lower surface always maintain optimal water balance. By
edges,
also minimizes water loss and allows stronger being submerged in regulating the rate of water exchange, a
known as the resistance to hot and dry environments. water
smooth transpiration stream is ensured.
crown
(Li, Xueping, et al., 2018)
(Brainly, 2024)
Cacti. The needle As leaves are replaced by needle like Duckweed. Duckweed As duckweeds are submerged in or on
like
spines spines on the cacti, the surface area is are tiny floating leaves water, no roots are needed for absorbing
instead of normal significantly reduced. There is completely and does not contain a or up taking water. This simple structure
leaves
are no stomata on the spines, no evaporation stem, showing minimal also reduces its surface area and hence
located all over and exchange of water would occur, root system.
water loss through the leaf. The plant’s
the cacti and has suggesting water is not lost and locked
direct contact with water allows straight
no stomata at all. inside the plant, reducing transpiration.
uptake of water and reduces the rate of
(Biocircuits, 2022)
transpiration.
Chosen Xerophyte and Hydrophyte with justification: The pineapple is chosen as the Xerophyte for the experiment. This is due
to the plant’s easy accessibility, being able to be found in supermarkets everywhere. The adaptation of thick and waxy leaves on
pineapples is also a common adaptation found in other Xerophytes, which allows the experimental results to be potentially applied
to other plants. Water Lily is chosen as the suitable Hydrophyte due to its common presence in ecological environments, especially
in ponds and parks. This plant shows great importance in providing habitat for organisms like dragonflies and is also more accessible
than Duckweed.
Dependent Variable
The rate of transpiration will be measured in the experiment. Transpiration refers to where plants gain and evaporate water. Water
is first absorbed by the root of the plant through osmosis along the concentration gradient. It then moves along the Xylem of the
plant with the aid of properties including cohesion and adhesion. The plant then arrives to the leaf and is evaporated through stomata.
The rate of transpiration is chosen as it reflects transportation of water throughout the plant, which is a vital part of plant functioning.
(Melissa, 2019)
Method of measurement for DV: To accurately measure the rate of transpiration, a potometer should be used. The potometer
should first be submerged into water with a plant inserted at the lobe of the apparatus. An air bubble should then be introduced into
the capillary tube to observe its movement along the tube. By taking the distance travelled by the air bubble, the rate of transpiration
can be found with the division of time. This measurement method should be adapted due to its high precision in recording distance
and allows transpiration to be measured quantitively. The process of transpiration can also be observed in real time through air
bubble movement. (Oxford Biology, 2021)
Controlled variables
Extraneous variables
Duration of experiment – 10 minutes will be used to record Plant individual differences – Plants have own individual
each plant’s rate of transpiration through the potometer. The circadian rhythms that determine the opening and closing of
exact start and finishing times will be recorded.
stomatal pores disregarding external factors. This may lead to
Time to complete – All trials would be done in the same lower accuracy of results with the circadian rhythm disrupting
period to ensure the same temperature and humidity in the transpiration.
experimental setting. This variable is controlled to secure the Plant origins – Original environment of plants cannot be located
same level of other major variables aforementioned that affect but can influence plant growth. As the growth is influenced,
the rate of transpiration in plants.
individual characteristics within plants develop leading to slightly
Plant size – As plants of different sizes have varying leaf sizes different features, hence impeding the general applicability of
leading to uncertain amount of stomata available for substance results.
exchange, the same sizes of pineapples and water lilies
should be used to ensure same surface area for transpiration.
This can be controlled by measuring sizes of plants before
buying them.
Water type – Distilled water should be used consistently
throughout all trials. The type of water must remain uniform as
different water contains minerals that can affect transpiration.
Tap water is avoided as minerals can clog plants’ roots.
Plant age – The age of plants impact the development of root and
shoot systems which in turn affects rate of transpiration. Older
plants have the ability to increase water uptake whereas younger
plants don’t, again limiting accuracy of results.
Ethical considerations: While plants are not sentient, the
specimens should be protected through minimizing unneeded cuts.
To protect and aid in creating a sustainable ecological environment,
the use specimens and water should also be limited to prevent
waste.
Safety considerations: Although the plants and experimental procedures are generally harmless, lab coats and safety goggles
should be always worn during procedures to prevent any unexpected irritation to eye and skin. All glassware and apparatus should
also be properly handled to prevent breakage and safety hazards in the lab.
Final question: How does the adaptations of pineapple and water Lily affect transpiration under different light intensities?
Justification: After the deconstruction process, the independent variable of light intensity was decided to be used on the xerophyte
pineapple and the hydrophyte water lily through measuring the dependent variable of rate of transpiration, hence developing the
final question. With the specific adaptations of both plants and the large impact light intensity has on plant transpiration rate, the
research question can show how the adaptations of waxy leaves and focused stomata would lead to different transpiration rates in
the manipulation of light.
How does the adaptations of pineapple and water Lily affect transpiration under different light intensities?
Part B – Practical Design
Introduction
The practical experiment aims to determine the impact of adaptations in plants (xerophytes and hydrophytes) and light
intensity have on their transpiration rates. The chosen xerophyte, pineapple, is used due to its wide accessibility and
the common feature of thick waxy leaves, which can be seen in other xerophytes, allowing potential generalization of
experimental results. The chosen hydrophyte, water lily, is chosen due to its practicality and dominant presence in
natural environments. Among plants, the rate of transpiration is extremely vital due to it maintaining water regulation
and nutrient support, moving water and dissolved nutrients from the roots to the leaves through the xylem and
transpiration stream. Hence, the rate of transpiration in the two specimen will be measured. This will be done through
using a potometer via dividing the distance travelled by the air bubble to time. There will be a control group with normal
light settings during the day, which allows normal transpiration. This will allow a direct comparison to experimental
groups that are subjected to different light intensity, hence measuring changes as a result of the independent variable.
Aim
To investigate the impact of varying light intensity on transpiration of xerophytes (pineapple) and hydrophytes (water lily)
through measuring the change in distance of potometer over time.
Hypothesis
As the light intensity surrounding the plants decrease, the rate of transpiration measured by the potometer will decrease.
The lowest light intensity of 10000 lux will result in the lowest distance travelled by the air bubble, vice versa for the
plant with the highest light intensity.
A lessened amount of light energy leads to a lower rate of photosynthesis, as light is an essential fuel in conducting
photosynthesis process, stomatal pores will only remain closed or partially open, leading to less water loss through
transpiration.
Independent Variable
The independent variable for this experiment will be the light intensity exposed to plants. There will be 3 groups, 10000,
20000, and 30000 lux and a control group with light intensity of a normal daylight setting. The maximum light intensity
is 30000 as a research suggests 20000 Lux is the most suitable for plant growth, and light intensity of over 30000 may
wither plants.
Dependent Variable
The rate of transpiration of the two plants, given by the average rate of distance covered (mm/s-1) using a potometer.
Potometers will be used as they are easily accessible and user friendly, while providing an accurate means to find the
average distance change. By measuring distance covered in mm, precise results can be used for comparisons between
groups. Measuring transpiration rate through potometers would enable in depth analysis on the optimal transpiration
stream for plants under different light intensities.
Controlled Variables
Table 1) Controlled variables for suggested experiment.
Variable
temperature
and humidity
Size of plants
Duration
of
experiment
Water
Distance
of
light box and
plant
Significance
An increased temperature can lead to more openings of
stomatal pores, steepening water intake. Hence, unstable
temperature will result in more intake of water, affecting
the transpiration rate. Humidity also determines how
much water plants can absorb from the air, affecting water
intake.
The size of plants leads to varying surface area of leaves
that determines the area available for transpiration. More
surface area suggests a larger number of stomata on the
leaf, which leads to more evaporation in the same time
frame and higher transpiration rate.
If less time is offered for plants’ transpiration during
different trials, the cumulative amount of water lost
through transpiration will be limited as the full variability of
plants’ transpiration is not known, hence diminishing its
reliability.
The type and quality of water can affect transpiration rates
as they have varying salinity and minerals. Chlorinated
water, for example, contains chlorine ions that may affect
the root health of plants, which reduces transpiration rate
as water absorption is lessened.
As the light intensity is changed directly using the light
box, the distance of light box and the plant affects the rate
of transpiration and photosynthesis directly. The closer
they are, the higher the transpiration rate. This is due to
more amount of light energy the plant receives for cellular
functioning
Method of Control
The temperature and humidity will be
kept constant at room temperature.
Controlling these conditions allow the
rate of water evaporation to be
constant, also ensuring that the
experiment is done in same conditions.
The leaves of each type of plant should
be ensured to have the same surface
area, allowing similar number of
stomata for gaseous exchange and
expelling water from transpiration.
The same duration of 10 minutes will be
used for all experiments such that the
same amount of time would be given
for the specimen to transpire.
Distilled water will be used in all trials
as the water is purified, which prohibits
the presence of harmful ions that can
potentially deteriorate plant health.
The light box and plants will have a
fixed distance of 15cm between them to
ensure they absorb uniform amount of
light throughout the experiment and
allows the light intensity for each trials
in experimental groups is constant.
Materials
- 8 specimen each for pineapple and water lily (2 per group). This ensures a low cost while still providing adequate
results with 2 trials for each group and preventing a waste of plants to minimize environmental risks.
- 1 potometer. This is needed to provide an accurate measurement on the amount of water absorbed by the plant, thus
calculating rate of transpiration.
- 1 beaker. To contain distilled water and pour into the potometer.
- 1 stopwatch to indicate the 10 minute duration of each trial.
- 1.2 L Distilled water (200 mL for each trial). The water is used to be poured into the potometer.
- 2 light bulbs. They are used to provide light energy to plants to manipulate light intensity.
- 1 ruler. It is used for measuring distance between plant and light box to ensure that they have a constant distance.
- 1 Paper towel roll. Paper towel should be used to pat the plant dry before conducting the experiment to prevent water
clogging on leaves.
- Food coloring. It is used to distinguish parts separated by the air bubble of water in the potometer.
Safety and Hazards
Table 2) Safety concerns for suggested experiment.
Safety
Glassware
Significance
Broken glassware, such as the potometer, can
fall onto the ground, causing slippery and
potential injuries in the lab.
Allergic
reactions
Allergic reactions may occur to some
individuals when in contact with pineapples and
waterlilies due to histamine and pollen
exposure, hence having the risk to cause
irritation, sneezing, etc.
Ethics
Mitigation
All apparatus must be handled with care and
placed on the center of the working tray when
not in use. Lab coats and safety goggles should
be worn to reduce risks of injuries.
Researchers should be informed of any
potential allergic reactions by participants
before commencing the experiment. First aid
tools must be situated in the lab for severe
reactions.
While plants are not sentient, researchers still have the responsibility to handle all plant specimens carefully through
reducing unnecessary harm towards them and aid in constructing and eco-friendly environment. The specimen should
also be cut in a smaller size to minimize wastage. All wastes should be directly put into the compost bin afterwards.
Methods
1. Wash all specimens carefully by rinsing with tap water. Pat them dry. The process cleans the plant off any excess
impurities and removes water from it.
2. Cut all pineapples and water lilies into 10 cm strips with 3 leaves attached such that the size allows perfect fitting into
the inserting tube of the potometer. This allows easy handling to fit into the potometer and controls the amount of water
uptake due to uniform number of leaves. This is to be repeated to cut all the 8 specimens for each plant.
3. Fill a tub up with water and add food coloring for a uniform color. The amount of water should allow the potometer to
be fully submerged into it. After submerging the potometer. No air bubbles should be seen inside the tube of the
potometer. The use of food color in distilled water allows the air bubble in the potometer to be more visible during the
transpiration process.
4. Inside the tub with water, fit the specimen tightly into the bubble potometer under water. This ensures that no excess
air would remain in the potometer tube as the specimen is fit underwater.
5. Take the potometer with the plant out of the water and immediately close the tap. Pat the specimen dry with paper
towel. The use of paper towel again removes water from the specimen and allows a regular expulsion of water from
stomata.
6. Put a 50 ml beaker with water at the end of the capillary tube. The tail of the potometer should be submerged in water.
The connection of the beaker with water and potometer ensures that there is a constant water source available for the
plant to continuously transpire and absorb water through osmosis.
7. Turn on the light bulb with the designated light intensity in which the box is situated 15cm between the plant. The light
bulb would provide the designated light intensity for each experimental group to manipulate the independent variable.
8. Introduce an air bubble into the capillary tube by lifting it out from the beaker for 5 seconds and submerging it again.
Record the initial position of the air bubble. The air bubble is used to determine the initial and final position which can
then be used to calculate the rate of transpiration of the specimen, providing valuable results.
9. After 10 minutes (recorded by stopwatch), Record the final position of the bubble. The final position of the bubble is
recorded to aid in calculating the rate of transpiration.
10. Turn open the tap of the potometer to reset it after finishing a trial. This process resets the potometer to its original
status and the air bubble to the initial position for other trials.
11. Steps 4-11 should be caried out repeatedly until all trials have been completed.
Calculations
To calculate the rate of transpiration after conducting the experiment. The values of time, initial and final distances of
the air bubble inside the potometer would be used. The time used is 10 minutes, which equals to 600 seconds. The rate
of transpiration would be calculated using the following formula:
𝑅𝑎𝑡𝑒 𝑜𝑓 𝑡𝑟𝑎𝑛𝑠𝑝𝑖𝑟𝑎𝑡𝑖𝑜𝑛 =
𝐹𝑖𝑛𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑜𝑓 𝑎𝑖𝑟 𝑏𝑢𝑏𝑏𝑙𝑒(𝑚𝑚) − 𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑝𝑜𝑠𝑖𝑡𝑖𝑜𝑛 𝑜𝑓 𝑎𝑖𝑟 𝑏𝑢𝑏𝑏𝑙𝑒(𝑚𝑚)
𝑡𝑖𝑚𝑒(𝑠)
After calculating the rate of transpiration of each trial, the answer should be presented in the unit of mm/s -1.
Aim
To investigate the effects of different distances between the plant and the light source (20, 40, 60, 80 cm) on the
transpiration of Callistemon by measuring the rate of transpiration (mL 10min-1) using a potometer.
Background Information
Transpiration is the physiological loss of water in the form of water vapor in plants. The process of transpiration involves
the movement of water from root to leaf and its exertion to the atmosphere (Brittanica, 2019). The water in soil is
absorbed into roots through root hairs via osmosis, referring to passive transportation of water along the concentration
gradient. Due to the formation of pressure gradient in the plant, water will flow within the xylem to mesophyll cells in
leaves, aided by cohesion and adhesion. As water is expelled out of the leaf by stomata in the mesophyll cells, a
transpiration stream is formed to ensure the balanced flow of water (BBC, 2020). This allows the plant to facilitate
gaseous exchange, where stomatal pores would be opened to expel water vapor, and nutrients including oxygen and
carbon dioxide, could be absorbed by it. The continuous water and nutrient transport would benefit cellular activities of
the plant, including aerobic respiration and photosynthesis, contributing towards its growth (Brittanica, 2019).
Light affects plant transpiration. Increased light intake augments the responses of guard cells controlling the stomata by
provoking an increase in cell turgor, consequently opening the stomata and allowing water vapor to be released from
the plant, hence increasing transpiration rate (Libre Texts, 2016). Further distance between the light source and the
plant would reduce transpiration as less light provided by the source, which makes plants lose turgor pressure to
facilitate opening of stomata. The transpiration rate can be measured by a potometer, which measures the amount of
water the plant absorbed from the tube of the potometer. This ensures that the reduction in water volume is due to water
uptake of the plant. Other factors besides from light intensity (see Table 3) also affects transpiration rate.
Table 3) Other factors that affect rate of transpiration in Callistemon.
Other factors affecting rate of transpiration
Temperature
As temperature increases, water evaporation occurs, steepening water concentration. Hence,
more water intake is required for the plant to maintain a regular transpiration stream, thereby
increasing transpiration rate. (Vasyl, 2023)
Humidity
A higher relative humidity in the surrounding air would reduce water concentration gradient
between the surrounding and the plant. The saturated air lowers transpiration rate with less water
vapor being expelled from the stomata. (Noaa, 2023)
Wind speed
Wind aids in evaporating water and carrying it away from the plant. More water would be diffused
from the stomata in high wind speed, which increases transpiration rate. (Odle, 2022)
Hypothesis
As the distance between the specimen and light source increases and lowers the light intensity, increasing from 20, 40,
60, 80 cm, a lower rate of water uptake and transportation of the plant will be observed, resulting in lower transpiration
rate.
Justification of Hypothesis
As the distance between the plant and light source increases, the reduction in light energy that comes in contact with
the plant would reduce the turgor pressure in guard cells, making them closed and unable to expel water from the
stomata, resulting in decrease of transpiration rate.
Independent Variable
The distance between the plant specimen and the light source. (20, 40, 60, 80cm)
Dependent Variable
The initial amount of water present in the potometer compared to the final amount of water present inside after 10
minutes (mL), used to calculate the rate of transpiration (mL 10min-1)
Controlled Variable
Table 4) Controlled variables for the experiment.
Controlled Variable
Plant Species
Time (10 minutes)
Plant size
Light source
Justification
Different species of plants contain varying features that alter their
efficiency in transpiration, such as thick waxy leaves and a larger
root system. These features would determine how well mesophyll
cells are protected, and the area provided for stomata for gaseous
exchange, in result affecting rate of transpiration.
The duration of the experiment should be kept constant such that
the time allowed for the plant to absorb water would remain the
same, allowing for accurate results measurement and easier
comparisons with other trials.
The root system of the of the plant would affect the efficiency of
water uptake via osmosis from the roots. If the size of leaves vary,
the surface area available for stomata would differ and the number
of stomata cells would lead to alterations in water evaporation,
hence changing transpiration rate.
While light sources (light bulbs) can be produced by different
manufacturers, their efficiency in light emission and excess heat
given out would vary. The differences in light and heat energy that
comes in contact with the plant would influence water evaporation
and transpiration rate.
Method of control
The same plant species,
Callistemon, would be
used for all trials in the
experiment.
Timers were set to
record each trials for ten
minutes.
Only 2 plant specimens
of the same size would
be
used
in
the
experiment.
The same light bulb is
used for the trials and is
set at the same height
with a stand and clamp.
Extraneous Variables
Table 5) Extraneous variables in the experiment.
Extraneous variable
Light from surroundings
Influence
The experiment is done simultaneously with other groups
and the light energy emitted from the nearby groups
would impact the light intensity of the trials, leading to the
inability to control the condition of guard cells and
stomatal pores.
All plants have unique biological rhythms that determine
the optimal time for transpiration, sometimes opening
more stomatal pores for gaseous exchange. As the
experiment is done in a span of 2 hours, the transpiration
efficiency for trials would have been changed.
Optimal transpiration time
Suggested improvement
The experiment should be
done in individual settings
with completely no other
affecting light source .
The experiment should be
conducted simultaneously
through
using
more
specimens at the same
time.
Materials
- 2 light bulbs
- 100mL water with food colouring
- 2 stand and clamps
- ruler
- 1 Lux reader
- 2 plant specimens (Callistemon)
- 2 potometers
- 2 stopwatches (not included in setup)
- Blue tac
- 1 beaker
Practical Setup
Callistemon
Stand and Clamp
Light bulb
Beake
r
ruler
Water with food
colouring
Method (Provided by teacher)
Blue tac
Potometer
Lux reader
1. Fill up the potometer to the 0mL mark with food coloring from a beaker and put it on a flat surface, i.e. lab table for
accurate measurement. The mark of 0mL would be the initial starting reading.
2. Insert the bark of the plant specimen into the stopper of the potometer and use blue-tac to ensure that the hole is
sealed such that no air would escape. The stopper and specimen is fixed onto the top of the tube of the potometer.
3. Set up a stand and clamp and adjust the clamp for the light bulb to be fixed in place on it. This light source is placed
in the same duration for the entirety of the experiment and the electric cable of the light bulb is connected.
4. Set a ruler between the light source and the potometer. The distance between the two objects is then measured by
the ruler. For the first 3 trials, the distance of 20 cm is used.
5. After fixing the light source and the potometer in place, the light bulb is switched on.
6. The Lux meter is turned on and set to ‘100’. It is put beside the potometer to measure the light intensity the plant
receives. The light intensity in Lux is then recorded.
7. After measuring the light intensity, the stopwatch for 10 minutes is immediately started. This marks the start of the
trial and the change in water volume in the potometer is observed throughout.
8. After 10 minutes, record the final reading by observing the mark on the potometer that touches the surface of the food
coloring water. The difference between the starting and final reading is calculated and presented in the unit of mL 10min1.
9. After conducting the first trial, the above steps are carried out again until each experimental group of distance 20, 40,
660, 80 cm has been done for 3 trials each.
10. Calculate the rate of transpiration for each trial and the average rate of transpiration for each experimental group.
Ethical Considerations
The plant specimen should be treated appropriately to ensure proper protection of the environment. The size of the
specimen used should be limited and not used excessively such that less resources would be wasted due to the
experiment. After trials, the specimen should be properly disposed into the same container to be recycled. The use of
food colouring water should also be properly controlled to prevent spilling and waste of resources.
Safety Considerations
Table 6) Safety considerations for the experiment.
Safety Concern
Glassware
Potential Hazards
Broken glassware may lead to the
creation of sharp shards that would
cut and injure the human body if
improperly handled.
Light bulb
Due to the high light intensity of the
light bulb, continuous observation
would potentially lead to irritation of
eyes.
People may be allergic to pollen in
Callistemon, and may lead to
symptoms including sneezing, puffy
eyes and breathing troubles.
Allergic reaction to
Callistemon
Results
Mitigation
Glassware should be properly inspected before being
used in the experiment. During trials, all apparatus should
be properly handled and put on the experimental area
when not in use. If breakage occurs, brooms and
dustpans should be immediately used for proper clean
up.
While observing the change in water levels, the light bulb
should be situated at least 30cm from the experimenter.
The experimenter should also avoid direct eye contact
with the light bulb to prevent eye irritation.
Prior to the experiment, participants should be informed
of the specimen Callistemon that would be used.
Participants should voice out their concerns and allergies
immediately before commencing the experiment.
Qualitative data: The rate of transpiration remained constant during most of the time in all trials. However, while other’s
participants’ light bulbs were switched off, it can be seen that the efficiency of water absorption in the trials of the same
experimental group decreased.
Quantitative data:
Table 7) The rate of transpiration in Callistemon exposed to different distances from the light source.
Sample Calculations
To calculate the amount of water the specimen used for transpiration in 10 minutes, the difference between the finishing
and starting reading of water level is compared, given by: 𝐹𝑖𝑛𝑖𝑠ℎ𝑖𝑛𝑔 𝑟𝑒𝑎𝑑𝑖𝑛𝑔 − 𝑠𝑡𝑎𝑟𝑡𝑖𝑛𝑔 𝑟𝑒𝑎𝑑𝑖𝑛𝑔.
Example calculation – Trial one for experimental group with 20cm distance
𝐹𝑖𝑛𝑖𝑠ℎ𝑖𝑛𝑔 𝑟𝑒𝑎𝑑𝑖𝑛𝑔 − 𝑆𝑡𝑎𝑟𝑡𝑖𝑛𝑔 𝑟𝑒𝑎𝑑𝑖𝑛𝑔
0.1 − 0 = 0.1 𝑚𝐿 10𝑚𝑖𝑛−1
To obtain the average in water level distance for each experimental group, the mean of the difference in mL for 3 trials
were calculated, given by: (𝑡𝑟𝑖𝑎𝑙 1 + 𝑡𝑟𝑖𝑎𝑙 2 + 𝑡𝑟𝑖𝑎𝑙 3) ÷ 3.
Example calculation – Average difference for experimental group with 20cm distance
(𝑡𝑟𝑖𝑎𝑙 1 + 𝑡𝑟𝑖𝑎𝑙 2 + 𝑡𝑟𝑖𝑎𝑙 3) ÷ 3
(0.1 + 0.09 + 0.1) ÷ 3 = 0.096666 …
= 0.0967 𝑚𝐿 10𝑚𝑖𝑛 −1 (𝐶𝑜𝑟 𝑡𝑜 3 𝑠𝑖𝑔. 𝑓𝑖𝑔. )
Avg. rate of transpiration in 10
min (mL 10min-1)
Graph
Average rate of transpiration of
Callistemon exposed to different
distances with light source
0,1
0,08
0,06
0,04
0,02
0
0
20
40
60
80
100
Distance between specimen and light source (cm)
Graph 1) Transpiration rate of Callistemon exposed to varying lighting conditions.
Analysis
Graph 1 indicates a negative correlation between the rate of transpiration in Callistemon and their distances with the
light source. This is shown through the shortest distance between the two variables, 20cm, having the highest
transpiration rate of 0.0967 mL 10min-1, while the experimental group with the longest distance of 80cm having the
lowest transpiration rate of 0.0293 mL 10min-1, supporting the hypothesis. Hence, the results drawn from the experiment
concludes that the difference in light intensity created by distance between plants and light source holds significant
impact against the transpiration rate of plants, and showing that as the distance increases from 20, 40, 60, 80 cm, the
rate of transpiration will decrease. The lower transpiration rate suggests that the expulsion of water in the plant is limited
with less light energy provided by the light source. This further demonstrates that the results validate the background
information provided that the loss of turgor pressure in guard cells protecting the stomata would lead to stomata pore
closure, therefore reducing the amount of water to be expelled and limiting transpiration rate.
While the results obtained in the 40,60 and 80cm group showed a negative correlation and decreasing pattern in
transpiration rate, the decrease has lessened with only a 0.003 and 0.01mL 10min-1 difference in transpiration rates
between each value. This is likely the result of a significant outlier in Trial 3 of the 40cm group, which showed only 0.03
mL 10min-1 transpiration rate, while both Trials 1 and 2 yielded the result of 0.05 mL 10min -1, this confirmed that the
outlier of trial 3 has skewed the data to a lower value. This outlier could have arisen from the surrounding light being
manipulated by others. As reported in qualitative observations, the water uptake by the specimen dropped when
surrounding light bulbs were switched off, and hence demonstrated a lower transpiration rate in Trial 3 of 40cm
experimental group. Overall, the results expectedly correspond to the hypothesis and supports the biological information
regarding light energy’s manipulation of guard cells. However, the conclusion is limited by the outlier.
Evaluation
Precision
In Graph 1, a high level of scatter can be observed as data points from experimental groups are dispersed against the
trendline. This is especially seen in the outlier of experimental group of 40cm distance with average transpiration rate
of 0.0433 mL 10min-1, indicating a significant impact created by a series of random errors. While experimental groups
20,60,80 had a stable range of +/-0.01, the outlier in group 40 recorded a range of +/-0.02, which shows a 2 times
increase in the fluctuation of results. Thus, the precision of the results have been negatively affected.
Reliability
The average results from the 3 trials of each experimental group was taken to minimize the impact of random error.
However, the modest sample size of using only 3 trials with the same specimen is not sufficient and does not consider
all variants of the Callistemon plant. Hence it is not applicable to the wider population of every Callistemon, limiting the
consistent interpretation of results. The lack of sample size compromises the justification of conclusions and creates
variance across repeated trials.
Validity
The experiment has demonstrated a moderate level of validity, where the results satisfied the aim of the experiment and
showed that the decrease in rate of transpiration is due to a longer distance between the light source and the Callistemon
specimen. However, the apparatus used for data measurement, the potometer, was damaged as reported in qualitative
observations, leading to the presence of systematic errors and reduced the experiment’s internal validity.
Accuracy
Accuracy refers to how close the value of results is compared to the true value. In this case, the true value cannot be
determined. Hence, the accuracy of results remains unknown. However, the expected trendline showed a negative
correlation, and the results have aligned with previously introduced biological information. Hence, the results’ validity is
estimated to be at a moderate level.
Errors
Random Errors are factors that causes inconsistency between trials, and randomly affects the quality of results by
creating scatter in trials.
Table 8) Random errors present in the experiment.
Random Error
Surrounding
light sources
Parallax error
Significance
As surrounding light bulbs from other participants
were switched on and off during trials, the specimen
would be exposed to different light intensity during
the period. Those with more light energy from
surrounding sources would result in higher
transpiration rate.
While observing the water level in potometers,
varying points of view by the human eye would have
caused inaccurate reporting of actual values
indicated by the tube.
Potential Improvement
The trials should be done at a confined
space with no other light sources contacting
the plant. This allows a cause-and-effect
relationship between light source distance
and transpiration rate.
The potometer should always be placed on
a flat surface and the observation of water
level should be conducted at eye level for a
fixed angle of viewing.
Systematic Errors are factors associated with faulty experimental designs that causes consistent errors in reflecting the
true value of the experiment.
Table 9) Systematic errors present in the experiment.
Systematic Error
Potometer damage
Significance
Due to the damage of the potometer, water constantly dripped
out of the apparatus and hastened the decrease in water level,
which creates inaccurate results by a constant margin
Potential Improvement
The experiment should be
repeated multiple times using
another potometer.
Conclusion
The practical aimed to investigate the effects of different distances between the plant and the light source
(20,40,60,80cm) on the transpiration of Callistemon by measuring the rate of transpiration (mL 10min -1) using a
potometer. The hypothesized result suggested as the distance between the light source and the plant increases, the
amount of water taken by the plant would decrease, lowering rate of transpiration. The results have shown a substantial
decrease in the rate of transpiration as the distance between the light source and the plant increases, supporting the
hypothesis and concluding that the amount of light energy received significantly affects the rate of transpiration in
Callistemon. However, the results have demonstrated moderate validity and low precision through the high scatter of
results and series of systematic errors. Moreover, random errors and a low sample size contributed to the diminishment
of reliability, hence limiting the conclusion to the specimen used only. To improve the quality of results, the practical
should be conducted repeatedly with more trials and using various apparatus throughout, which would aid in identifying
errors and enhance the accuracy of findings.
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