Do purple/red leaves photosynthesise at the same rate as green leaves?

DECONSTRUCTION | Considerations | Justifications (Benefits)(Limitations) Method of testings the rate of photosynthesis

According to research prior factors such as light intensity, temperature and CO 2
What is Photosynthesis? Factors that affect photosynthesis (rate): Plants require sufficient amount of concentration must be controlled.
Photosynthesis is the biochemical process done to generate metabolic energy by converting light light intensity, CO2 and optimal temperatures for an optimal rate of Measuring O2 production (Science, n.d.):
energy (sunlight) into chemical energy (glucose) (NGS, 2022). Carbon dioxide (CO 2) and water (H2O) photosynthesis. If these factors are limited/uncontrolled the leaves will not be
Procedure: Preparing two clear cups with 300 ml of water mixed with 1/8 tsp of baking
are converted into glucose as a storage of energy, and oxygen as a waste product (Cooper, 2000). able to undergo ideal photosynthesis hence, yielding imprecise and unreliable
soda and one drop of dish soap. The baking soda, which is sodium bicarbonate,
results.
Stages of photosynthesis: As the light intensity increases, ample amount of light energy is provided for provides the leaves CO2 to photosynthesise. This factor is controlled as 1/8 tsp must
what organelles are involved? Photosynthesis occurs in the Chloroplasts of plant cells. This organelle the process of light dependent reaction to occur within the chloroplast, be added to the solution. The dish soap breaks down molecules on the surface of the
is enclosed by a double membrane and a membranous plastid system that includes the grana, stroma, therefore increasing the rate of photosynthesis (Benckiser, 2021). To obtain leaf so that the CO2 can easily enter the leaf ensuring that the leaves are provided
lamella and thylakoids (ScienceDirect, n.d.). The first stage of photosynthesis is known as Light high accuracy and precision, the different coloured leaves must be provided sufficient amounts to optimally photosynthesise. As the experiment is held in water It
dependent reactions, as the reaction must occur under the presence of light energy, this reaction equal amounts of light intensity from a consistent source. Extending the can potentially be adjusted to a specific temperature that is ideal for both leaves to
occurs in the thylakoid membrane (Khan Academy, 2016). Chlorophyll and other pigments reside in the duration of light exposure, leaves have more time to absorb light energy and optimally photosynthesis. With a hole puncher, 10 disks are cut out from each (red
thylakoid membrane. These pigments provide the colours to leaves. It is a key part in the light convert it into chemical energy, resulting in increased overall photosynthetic and green) coloured leaf – to make sure all leaves have the same surface area, and
dependent reactions as it allows plants to absorb energy from light (at different wavelengths) (National activity (Aggie, n.d.). Specific wavelengths and adjustable intensity (light results are reliable and valid. A syringe is used is to create a vacuum, that eliminated
Geographic, 2022). When energy is absorbed, the electrons are transferred along a thylakoid chain, quality) of synthetic lighting allow for exact control over lighting conditions. This any air within the leaf disks air pockets and replace it with the solution (baking soda)
where the chlorophyll alters it to a lower energy state, where it is harnessed to make ATP (Sudhakar, control allows researchers to systematically control light parameters, facilitating in the syringe. Without the air pockets, the leaf disks will sink to the bottom of the
2019). Light independent (Calvin cycle) reactions are the second stage of photosynthesis which occurs precise testing of photosynthetic rates of different leave colours (Darko et al., syringe. The disks and solution then go back in the cup (that the solution was
in the stroma of the chloroplast (Ha, 2020). Enzymes in the stroma work alongside ATP to breakdown 2014). If sunlight (natural lighting) were to be used for this experiment, it must originally derived from). The cup is placed on top of a light source (LED)- controlled
CO2 and H2O molecule in a metabolic reaction to form glucose (form of energy) (Jingjing Han, 2022). be done during the mid-day to obtain proper results. According to light intensity, the chloroplasts within the leaf disks will start to photosynthesize. As a
investigations conducted at Obihiro University, it was discovered that the net result, tiny bubbles of oxygen on top or underneath the leaf disks. As the leaf disks
photosynthetic rate (the saturation points for light intensity), under natural
How do leaves get their colour? accumulate more oxygen gas, they will eventually float to the top. Recording Results:
sunlight intensity, reached a maximum at mid-morning (around 10:00am), and
Within green leafed plants, there is a high concentration of chlorophyll. Chlorophyll pigments absorb With the help of a timer, every two minutes, the no. of leaf disks reaching a floating
then showed midday depression (Koyama, 2014). The midday depression was
blue and red wavelengths and therefore reflects green colour (USDA, 2023). While chlorophyll is found possibly cause by the increased temperature as the day proceeds. If the
state must be counted. This timer and recording system must continue until all the leaf
in all plant, the concentration may vary and compensated with other pigments such as Carotenoids temperature is too high, the enzymes operating light- independent reactions disks in both leaves reach a floating state. – By having a set mark as to when
(yellow and orange) and Anthocyanins (Harvard Forest, 2018). Chlorophyll reacts more sensitively to start to denature, reducing the rate of photosynthesis and stopping the reaction recording time recording should start and when it should finish generated valid and
strong light intensity compared to carotenoids and Anthocyanins (Grover, n.d.). As function of completely (BBC, 2023). As the temperature increases to an optimum degree, accurate results. Water may not allow the light to reach the leaf disks at the bottom of
chlorophyll requires sunlight and warm temperatures, when these factors are not provided to an the number of successful collisions also increase, therefore the rate of the cup. Therefore, limiting the intensity of the light and reducing the rate of
optimal extent, the genes involved in anthocyanin synthesis, and transport are significantly expressed photosynthesis surges (Canvin, 1969). To control temperature a water bath or photosynthesis, extending the procedure for longer and yielding inaccurate results
(Ahammed, 2023). Anthocyanins reflect red and purple colours and are usually found in plants that are controlled heated light can be used. The optimal temperature for with high scatter.
exposed to very strong light intensities or reside in low temperature habitats (service, 2024). Measuring the absorption of CO2 molecules:
photosynthesis ranges between 20- 40C but different plants have varied
Different species and specific colour leaves: (examples) Procedure: Seal the top of an empty bottle with a CO 2 sensor and allow it to
optimal temperature due to the habitat in which it was grown (Cornic, 2021). To
reduce the range and achieve an optimal temperature, that will enable different
record data for 1 minute – The initial CO2 concentration is recorded (results have
Coleus Redhead and Electric lime coleus: Solenostemon scutellarioides (Coleus), are coloured leaves to photosynthesise at an ideal rate, plants that are from the
tropical plant species with a large variety of colour foliage (including green and red/purple) an origin point). This allows results to accurately be interpreted with high validity
same habitat and species should be used. E.g. Cordyline, are a subtropical
(Elsner, 2022). These plants perform best in direct sun limited to morning hours and require as the sensors can detect changes in concentration better. After one minute,
plant species that have a variety of coloured leaves, prefer temperatures
time in shaded areas (Greg, n.d.). The optimal temperature of Coleus plants is between place 5 red leaves (roughly the same size) facing downward seal the bottle with
between 18- 24C, due to the cooler environment that they are adapted too
20C - 35C (Illinois, n.d.). As the plants are of the same species, they are likely to possess the CO2 sensor same size leaves will produce accurate and precise results as
(Studioplant, n.d.). Hence, resulting in accurate and precise results. CO2 along
similar leaf structure and size (therefore higher accuracy and precision as the leaves will the amount of pigment (chloroplast) will generally be the same. By facing
with H2O is a key reactant needed for plants to produce energy and conduct
have similar surface areas). The plants would also have similar secondary metabolites downwards, the side that usually photosynthesise on is exposed to the light pad
photosynthesis (nature, 2014). Limited CO2 concentration would directly reduce
(Toppr Ask, n.d.). these plants are very accessible. genetic predisposition would vary better. Recording Results: The bottle is placed under a light pad and record
the effect of other factors on the photosynthesis reaction (Reckitt, 2021). An
Oklahoma state university study was conducted on the effects of CO2
results every 2 minutes for a 10-minute duration. Conduct this procedure 5 time
between both plants causing low precision. Heavenly Bamboo (Nandina Domestica): with supplementation, on other factors affecting photosynthesis (light
an optimal temperature between 15-38C, this shrub requires full sun condition (high light for red and green leaves. the controlled recording produces high accuracy and
&temperature). the results displayed, additional CO2 increased the light
validity in results as the duration of 10 mins provides sufficient time to record the
intensities) but can easily adapt to low light conditions (Gardenia.net, 2019). Easy access intensity required to obtain the light saturation point, thus increasing the rate of
photosynthetic reaction. The light pad provides a controlled light intensity for
photosynthesis. Additionally, the optimum temperature for maximum
to red and green leaves as the plant produces both colours all year round. The genetic plants to optimally photosynthesise. The temperature given off from the light pad
photosynthesis was dependent on the availability of CO2, The higher the
composition as well as Genetic predisposition will be the same therefore results will have may vary for each trial and may be too high for the leaves to photosynthesise as
amount of available CO2, the higher the optimum temperature requirement of
greater precision. Completely green or red leaves may be difficult as majority of the plant’s the enzyme would denature. The production of O2 within the bottle will eventually
plants (okstate.edu, 2023). To ensure elevated concentration of CO 2, the
leaves are multicoloured. eliminate the concentration CO2 therefore the rate of photosynthesis will be
experiment can be conducted in a solution containing CO2 producing
molecules, such as hydrogen carbonate or baking soda in a water solution
reduced much quicker than expected for both leaves.
Justification for design: The following justification made were due to convenience and suitability for a school environment and which would lead to accurate and precise results.
The Type of plant used to represent red and green leaves are Solenostemon scutellarioides (Coleus): Coleus Redhead (red) and Electric lime coleus (green). This was the best option, as it brought diverse colour leaves while allowing the true rate of photosynthesis in green
(chlorophyll) and red (Anthocyanins + chlorophyll) leaves to be tested without overlap of other pigments such as carotenoids (found in plants changing colour throughout season). CR & ELC as they remain the same colour all year round  high concentration of only Anthocyanins +
chlorophyll. Leaves will be ethically taken from these plants and using specifically a 6mm hole puncher 10 leaf disks for red and green leaves will be cut out (6mm- smaller surface area  faster rate of reaction) (BBC, 2021). There will be a total of 5 trials for green leaves and red
leaves. increased no. trial  low scatter and indication of random errors  high precision and reliability. To test the rate of photosynthesis and answer the question “Purple/red leaves photosynthesis at the same rate as green leaves?” results will be obtained from the practical by
measuring the O2 production of the leaf disks. By using a timer, the number of floating leaf disks for both cups will be recorded every 2 minutes for a 10-minute duration (both red and green should have reached a floating state during this time due to the oxygen produced through
photosynthesis). Therefore, making the colour of the leaf disk (red or green) the independent variable and the overall time takes (rate- minutes) for all the red leaf disks to reach a floating state (the amount of oxygen produced by the disk) compared to green leaf disks. As the
repeatedly mentioned factors such as light intensity and CO2 play a big role in photosynthesis rates, therefore, these factors much be controlled. Light intensity will be controlled by utilising a photosynthesis promoting LED light pad [refer to figure 1 below] with other light source being
completely blocked allowing the LED pad to be the only source of light. The LED pad contains different qualities and wavelengths of light  both pigments can absorb sufficient amount of light through their preferred wavelength (Anthocyanins -blue, green + chlorophyll – violet,
orange) (Harvard Forest, n.d.) (Rubio, 2015). CO2 will be elevated and controlled by adding exactly 1/8 tsp of baking soda to the experiment solution that will provide the leaf disks the CO2 required. While temperature is a factor greatly influencing the rate of reaction, the solution will
not have an altered/controlled temperature as the optimal temperatures for ELC and CR is 20-35C which is the general temperate of room temperature water anyhow (Illinois, n.d.). alteration in water temperature would mean fluctuation and more safety required  it was decided not
to control temperature.
DESIGN: Assessing the rate at which red and green Solenostemon scutellarioides photosynthesise

Aim: To investigate the effect of red (Coleus Redhead -CR) and green (Electric lime coleus -ELC) Solenostemon scutellarioides
Figure 1:
photosynthesis leaves on the rate of photosynthesis; By recording the time (minutes) taken for the different coloured leaf disks to reach a
promoting LED light floating state.
pad. contains red, blue Hypothesis: ELC leaves will have a greater rate of photosynthesis, as the leaf disks will reach a floating state faster (min)
and orange wavelength compared to red Solenostemon scutellarioides. This is due to the high concentration of chlorophyll within ELC leaves that can
that allow various easily absorb light energy unlike CR that have Anthocyanins pigments limiting light energy from reaching the chlorophyll.
pigment to absorb light Independent Variable: Different breed and coloured Solenostemon scutellarioides leaf disks (CR – red) and (ELC - green).
and conduct Dependent Variable: Rate of photosynthesis – the amount of time (min) taken for the CR and ELC leaf disks to rise in the cup
photosynthesis (Darko, (due to the O2 produced via photosynthesis).
Factors Held Constant:
Factor Method for holding factor constant Impact on results (mins taken for all leaves to reach a floating state) if not controlled and
ethical considerations
Light source and A photosynthesis promoting LED light Results will showcase many outliers and low accuracy. Various light sources and random
intensity pad [refer to figure 1 in left column] placement of plastic cups will cause disproportionate light quality and intensities
must be the only light sources utilised. (chromaviso, n.d.). Weather conditions causing natural light to fluctuate. This reduction in
Windows and ceiling lights must be light availability can inhibit photosynthetic activity as plants may not obtain enough energy
closed. For every trial, the clear plastic to perform photosynthesis at an optimal rate (Reckitt, 2021). Low accuracy and precision
may be displayed if this factor is not controlled.
cups (in which the experiment will
Leaf disks will not photosynthesise properly (produce O2 bubbles  no buoyancy for
occur) must be placed directly in the
leaves to float) (Science, n.d.).
middle of the pad to retain optimal light
The plastic cups can be washed and reused again.
intensity.
CO2 concentration Within each trial, exactly 1/8 tsp of If not controlled, some trial’s solution will be concentrated while other would be diluted.
baking soda (from the same source – This way the leaf disks are provided uneven CO 2 amounts, producing high scatter while
to keep strength of baking soda lowering the precision and reliability. Due to inconsistent mixing, the baking soda may not
constant) must be added to 300 ml of be activated  no reaction will occur, and results will be invalid.
water in each clear plastic cup. The A baking soda, soap, and water solution is not chemically harmful to the environment and
solution must be mixed thoroughly until can be disposed easily. The minimal amounts of product being used ensures no wastage.
homogeneous.

Leaf disk size and Use a 6mm hole puncher to cut 10 leaf Different surface areas would have varied amounts of chlorophyll (Borsuk and Bredesen,
amount. Source of disk of CR and ELC leaves. Do this 2019). The rate of reaction will vary, and high systematic errors will cause the observed
sample immediately CR leaf disks will be values to be skewed causing low accuracy. The small hole puncher size means only a
obtained from one CR plant for every small no. of leaves are used. the remaining leaves after leaf disks are cut out should be
trial. The same will be done for ELC placed in compost. Leaf disks would arrive at inconsistent rates and the general time take
leaf disks. prior each trial. for all leaf disks to reach floating state will vary significantly producing high scatter and
unreliable results. Many plants are not being used creating waste and no harm is done to
plants.
Orientation of leaf After the leaf disk are placed into the The procedure would not be valid or reliable as the disks are not all retaining proper light
disks in solution solution (Once the vacuum procedure intensity therefore results will have high scatter and produce inaccurate results.
has occurred), using a tweezer the
disk’s adaxial surface (section where
chloroplasts is most concentrated -
darker red/green) must be orientated to
the bottom of the cup facing the LED
pad (Exploratorium, 2019).
Method of recording The amount leaf disks reached a Low precision and reliability would be seen in results that were not controlled or have a
results floating state is recorded every 2 systematic method of recording.
minutes.

Factors That Cannot Be Controlled:

Factor Why factor cannot be held constant Effect on results

Genetic Since the plants were not monitored or grown by the The light intensity, water supply and CO2 concentration may extensively
predisposition experimenters (due to extensive amount of time high/low for some of the leaf disks. Major systematic errors could be caused
and plant required). Factors such as the genetic predisposition and due to this uncertainty such as consistently higher amount of time could be
conditions up brining are unclear. Genetically ELC may have taken for ELC leaf disks to reach a floating state compared to CR leak disks.
smaller air pockets less CO2 is absorbed; or CR have  The results will display significantly low amounts of accuracy and validity
altered mechanism of absorbing light due to its up and the hypothesis (constructed with accurate findings) will be invalidly
bringing (Theeuwen et al., 2022). proven wrong.
Strength of Factors such as the age and strength of the product Random errors may occur as some trials may have higher concentrations of
baking soda cannot be accurately known. Due to the environment in unreactive baking soda. This causes outliers and scatter in the results 
which the baking soda was place in. Certain sections of
 substance might have oxidised and is now unreactive reducing the precision and reliability of the results.
(Portal, n.d.).

Safety Assessment

Potential hazard Prevention Control measures

Slipping and falling due to water spillage while Potential breakage of equipment. As the light in Spilled water must immediately be wiped and
transporting TPC filled with water. the environment is very minimal it may be hard to cleaned from the floor and a “wet floor” sign to
see where you are going. To prevent this, perform alert others must be place until the area is dry.
Potential breakage of equipment. Breakage of all steps of the method on one station to reduce Clean area, use first aid kit to aid any injures.
LED light. movement across the laboratory. Safety gear: Report to student services if injures is severe.
glasses, coat and gloves must be worn prior to
starting the experiment. Experiment must be done
under instructor supervisions. Working First aid
must also be present.

Control Group: Control group (:

In this control group, the “controlled” variables such as light intensity and CO2 are
Materials / Apparatus (justification of material along with method) (: not added. This is done to determine which changes or outcomes are due to the
2 Transparent plastic cups (2TPC) errors as opposed to a controlled variable (bndixon3, 2022). Method 
Baking soda (BS)
 Collect the 2 TPC and 300MC and go to the tap. Using the 300MC, pour
Mixing spoon 300ml of tap water into each TPC. Safely (be cautious of spills) Return to
300 ml Measuring cup (300 MC) station with equipment.
Normal tap Water (TW)  Retrieve 1 big leaf from the ELC and CR plants (take these leaves back to you
1/8 teaspoon station). Carefully cut 10 leaf disks from the large ELC leaf with the 6mm hole
Dish soap puncher.
Photosynthesis promoting LED pad (LED pad)  Place the 2 TPC of water 1 with the green leaves and 1 with red leaves in a
6 mm Single-hole puncher dark environment
1 CR Plant / 5 Big CR leaves  Start a timer for 10 minutes. At the end every 2 minute, record the number of
1 ELC Plant / 5 Big ELC leaves floating leaf disks for both cups in the data table below (also record the
Plastic syringe, 10-mL (without the needle) quantity of oxygen bubbles at every 2 minutes).
Aluminium foil  Briefly swirl (using the mixing spoon) the disks to prevent them from getting
Timer stuck to the bottom or sides of the cup.
Tweezers  Continue this step for the 10-minute duration (all leaf disks should remain at
Camera (optional – to record photosynthesis reaction) the bottom of the TPC).

Method
Advise to conduct practical with a partner (In step 7, aluminium is used to preserve the leaf disks in the dark until the other plant’s leaf disks solution is prepared.
This delay could cause the preserved leaf disks to retain more amounts of CO2. A systematic error could possibly occur, as one coloured leaf disks could
consistently display erroneously faster rates of photosynthesis (leaf disk reaching a floating state (min)). To eliminate this and reduce time from each trial, it is
highly recommended to conduct with a partner.) (:
Method Justification
1 (With a partner) Collect material: a Photosynthesis  Assumptions such as prices and accessibility of this product are accounted for as it can
promoting LED pad (LED pad), baking soda (BS), 1/8 easily be acquired from online stores such as eBay or amazon within a price range of
measuring tsp, dish soap, 2 Transparent plastic cups of $15 – $30 (eBay, n.d). the “Photosynthesis promotion” via a LED light concept is also
the same size (and structure) (TPC), a 300 ml found in other technologies e.g. lamps or coloured films that could places on regular
measuring cup (300MC), Plastic syringe - 10mL without light [refer to appendix 1].
the needle, 6 mm Single-hole puncher Aluminium foil,
 An LED pad was specifically chosen as it could delivered the most concentrated quality
timer, mixing spoon, tweezers and camera.
of light that would ensure the leaf disks obtaining sufficient amount of light energy
2 Find a workspace with a plug point and place all material
down on the station. Set up the LED pad by placing the through their preferred wavelength (Anthocyanins -blue, green + chlorophyll – violet,
attachment plug of the LED pad into the plug point and orange) (Harvard Forest, n.d.) (Rubio, 2015). Other alternatives e.g. natural lighting or
switch on. laboratory lighting was not choses due to varied and weak light intensities [refer to
3 Collect the 2 TPC and 300MC and go to the tap. Using deconstruct justification above references included].
the 300MC, pour 300ml of tap water into each TPC.  After the experiment is completed, the light pad can be installed as a hanging lamp
Safely (be cautious of spills) Return to station with helping plants within the vicinity to grow better.
equipment. Prepare the baking soda solution by filling  All material is moved to station prior to experiment as it reduce amount of movement
the cups with 300 (mL) room-temperature waters. Then around lab  reducing risk of injuries later in the dark and more time efficient.
add about 1/8 (tsp.) of BS to the water and use the  Switching the LED pad on is the first step of the method as it allows the light to generate
mixing spoon until the baking soda has dissolved. Then, heat that can be used to promote photosynthesis (Canvin, 1969).
add one drop of dish soap to the baking soda solution
 As the practical is conducted among a group of people, a common station where
and gently stir using the mixing spoon until it has
dissolved.
material such as water and the ELC and CR plants can reside is vital. For the plants,
4 Retrieve 1 big leaf from the ELC and CR plants (take this manner allows the leaves to retain nutrients from its plant source  when time for
these leaves back to you station). Carefully cut 10 leaf experiment, the required number of leaves (dense in nutrients) can be extracted from
disks from the large ELC leaf with the 6mm hole the plant and easily perform photosynthesis within the controlled variables.
puncher.  Opposed to this, by collection the leaves prior and keeping them away until experiment
5 Using the syringe, Remove the plunger from the syringe time; would mean the leaves would already start to deteriorate and the rate of
and place 10 leaf disks into the syringe. Place the photosynthesis and transpiration will reduce (Salute, 2019).
plunger back into the syringe and push it down until only  This way the leaves of the plant are not being wasted and accurate and precise results
a small volume of air is left in the syringe. Be careful not
 to crush the leaf disks. are being obtained.
6 Suck up a small volume of the baking soda solution into  Steps 3 and 4 are the only step in the method that require the experimenters to move
the syringe with the leaf disks. Close the opening of from their station. The safety is put to question as moving around with water may lead to
the syringe with a finger and draw back on the plunger to accidental spills and injuries. To prevent this from happening exterior lights will be kept
create a vacuum. Hold the vacuum for 10–15 seconds on until solution are made so experiments can properly see. The aluminium foil will
and swirl the leaf disks to suspend them in the solution. prevent exterior sources of light from getting in.
Release the plunger and remove your finger from the
 The ratio of 300 ml water and 1/8 of baking soda is applied as it is a consistent method
syringe opening to release the vacuum. Observe the leaf
disks. if all the leaf disks have not sunk to the bottom of controlling the amount of CO 2 provided to the leaf disk for optimal photosynthesis
of the solution, hold the vacuum for 10–15 seconds and (okstate.edu, 2023). The optimal pH for photosynthesis in plants is 7 (neutral), the 300
swirl the leaf disks. ml water and 1/8 of baking soda ratio was chosen as it can neutralise any acidity given
7 Remove the plunger from the syringe and pour all 10 off by water or leaves as photosynthesis occurs (Banas, 2017) (Waiākea, n.d.).
leaf disks and the solution into the TPC the solution was  The 6mm hole puncher allows for a consistent surface area to be experimented with.
initially retrieved from Cover the cup with aluminium foil The small surface area will allow faster rate of photosynthesis to occur as the light
so no light can get in the top. You want to keep the leaf intensity and CO2 can enter and encompass the leaf disks faster (science buddies, n.d.).
disks in the dark until your other cup is ready. By having 10 leaf disks for ELC and CR leaves improves the estimate precision leading
8 Repeat steps 4–7 for CR leaf and use the solution in the to more reliable results.
other TPC. Partner…  Utilising the full leaf was not considered as obtaining similar sized leaves from one plant
9 Once step 8 is complete, shut all window blinds and for 5 trials was not practical; Would have led to a lot of wastage and imprecise results
switch off any lights within the lab so that the LED pad with high scatter.
may be the only source of light.  The dish soap and syringe are two extra but vital steps that contribute to more precise
10 Remove the aluminium foil from the ELC leaf disk TPC and accurate results. The dish soap breaks down molecules on the surface of the leaf.
and place both TPC (CR and ELC) in the middle of the
The syringe’s vacuum eliminates any air within the leaf disks air pockets and replace it
LED pad.
with the solution (baking soda) in the syringe. Both steps are done so that the CO 2 can
11 Start a timer for 10 minutes. At the end every 2 minute,
easily enter the leaf ensuring that the leaves are provided sufficient amounts to
record the number of floating leaf disks for both cups in
the data table below (also record the quantity of oxygen optimally photosynthesise.
bubbles at every 2 minutes).  The exterior light source being completely blocked allowing the LED pad to be the only
Briefly swirl (using the mixing spoon) the disks to source of light.
prevent them from getting stuck to the bottom or sides of  The set duration of 10 min and consistent conservation of leaf disks behaviour (O 2
the cup. Continue this step for the 10-minute duration surrounding the disk) every 2 minutes allows trends and patterns to be identified and
(all leaf disks should have reached a floating state by accurate conclusion to be drawn. The 5 trials will allow any potential scatter caused by
this time) random errors even out and reliable results to be obtained.
12 Once data is recorded for the 10 minutes, dispose of
the leaf disks. Rince the TPC thoroughly and repeat
steps 3-11 again for another 4 more trials.

Results
In the results table below, prepare a data table with three columns. Column 1 is the time, in minutes (min). In columns 2 and 3 you will record the results of your
leaf disk assay—the laboratory procedure you are using to investigate photosynthesis—both with baking soda and without baking soda
** ideally the trial should not take more that 10 min to complete (Exploratorium, 2019).
If one trial takes more than 10 min to complete there is a potential random error causing it. If this occur continually, there is a systematic error.
Table 1: CONTROL GROUP: Record the number of ELC leaf disks reaching a floating state every 2 minutes during a 10-minute trial -
Trials No. of green leaf disks reached floating state
0 min 2 min 4 min 6 min 8 min 10 min
ELC leaf
disks
CR leaf
disks

Table 2: Record the number of ELC leaf disks reaching a floating state every 2 minutes during a 10-minute trial.
Trials No. of green leaf disks reached floating state
0 min 2 min 4 min 6 min 8 min 10 min
1
2
3
4
5
6
7
Average

Table 3: Record the number of CR leaf disks reaching a floating state every 2 minutes during a 10-minute trial.
Trials No. of red leaf disks reached floating state
0 min 2 min 4 min 6 min 8 min 10 min
1
2
3
4
5
6
7
Average
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appendix:

Appendix 2: photosynthesis Appendix 3: photosynthesis

Appendix 1: photosynthesis promoting
promoting lamp (Big W, n.d) promoting light sheets (Fruugo, n.d)
light pad (eBay, n.d)
 Oxygen levels released from red and green Nandina
domestica leaves in the process of photosynthesis
Introduction:
Photosynthesis is the biochemical process converting light energy (sunlight) into chemical energy (glucose) (NGS, 2022). Carbon dioxide (CO 2)
and water (H2O) are converted into glucose (C 6H12O6) as a storage of energy, and O 2 as a waste product (Cooper, 2000). Photosynthesis occurs
in the Chloroplasts of plant cells. This organelle is enclosed by a double membrane and a membranous plastid system that includes the grana,
stroma, lamella and thylakoids (ScienceDirect, n.d.). Chlorophyll and other pigments reside in the thylakoid membrane and allows plants to
absorb energy from light (at different wavelengths) (National Geographic, 2022). While chlorophyll is the pigment giving leaves its green colour
other plant leaves such as red cabbage has higher concentrations of Anthocyanin pigments that reflect red and purple colours in leaves (Ren,
2019). While the concentration of these pigments, cause leaves to be different colours, weather the rate of photosynthesis for red and green
leaves is similar or different is unknown. To test this question, Nandina domestical is a shrub producing both red and green leaves all year long
will be used (Gardenia, 2019).

The rate of photosynthesis is majorly affected by factors such as light intensity, CO2 concentration and temperature. As the light intensity
increases, ample amount of light energy is provided for the process of light dependent reaction to occur within the chloroplast, therefore
increasing the rate of photosynthesis (Benckiser, 2021). Similarly, If the temperature is too high, the enzymes operating light- independent
reactions start to denature, reducing the rate of photosynthesis and stopping the reaction completely (BBC, 2023). CO2 along with H2O is a key
reactant needed for plants to produce energy and conduct photosynthesis (nature, 2014). Limited CO2 concentration would directly reduce the
effect of other factors on the photosynthesis reaction (Reckitt, 2021). Therefore, to test the rate of photosynthesis properly within red and green
nandina domestica leaves, sufficient amounts of light intensity, CO2 and optimal temperatures is required for an optimal rate of photosynthesis.
If these factors are limited/uncontrolled the leaves will not be able to undergo ideal photosynthesis hence, yielding imprecise and unreliable
results. The Rate of photosynthesis will be tested by amount of O2 produced (ppt) measured via a Vernier O2 sensor.

Aim:
To investigate the effect of red and green coloured Nandina domestica leaves on the rate of photosynthesis from the amount of oxygen
produced (ppt).

Hypothesis:
Green leaves will have a greater rate of photosynthesis as it will produce a greater amount of O2 compared to red leaves over 10 min, this is due
to the high concentration of chlorophyll within green leaves that will conduct photosynthesis.
Variables:
Independent variable:
Different coloured (Green and Red) Nandina domestica leaves.
Dependent variable:
The amount of oxygen (ppt) produced by the red and green leaves in a 10-minute trial (10 leaves each).
Factors held constant:
Factor Method for holding factors constant Effect on results (if not held constant)
Light intensity Light pad generating consistent amount Low accuracy will be identified as many outliers as possible and
and quality of light will be used. leaves inconsistent/unpredicted behaviour pattern will be identified within
will be placed within a clear and results yielding invalid results. As the different leaves would be
colourless plastic bottle directly atop of exposed to varied and limited light intensities and amounts casing
light pad (in direct light exposure). varied rate of photosynthesis (Wimalasekera, 2019).
No. of leaves, size A general size will be set prior to leaf If sizes and no. leaves were not consistent throughout trials, high
and surface area of selection. This ensured the selected scatter would be observed due to the random increases of O 2
leaves leaves had similar amounts of chlorophyll production by larger sized leaves or larger no. of leaves (Vera, 2024).
while the genetic predisposition would be the results would also be invalid and display low accuracy as the
similar. Each trial will use 10 leaves. results with high scatter and outliers would not match the true value of
the experiment.
Vernier oxygen Same vernier oxygen sensor will be used Results would hold many random and systematic errors due to the
sensor and Set for each trial. inconsistent method of testing leading to imprecise results that are far
timings (prior and from the true value and invalid. Inconsistent timing would produce high
during data collection) scatter in results as some leaves are given more time to
photosynthesise compared to others. Therefore, results lack precision
and reliability.

Uncontrolled Factors:
Factor Why factor cannot be controlled Effect on results
Oxygen escaping Due to random errors such as incorrect Results may not have high accuracy as the
placement of Vernier oxygen sensor on the sensor may not have recorded the true
bottle. Additionally, the quality of the sensor
 causes many opportunities for oxygen amount of O2 (ppt) produced by the leaves.
(produced via photosynthesis) to escape and The results would also lack precision and
not be recorded. reliability as the random errors would yield
varied results that cannot be obtained
repeatedly.

Genetic predisposition Genetic information of the plant e.g. Different amounts of chlorophyll in the
amounts of chloroplast/chlorophyll and leaves would yield different rates of
nutrition conditions specific to the subject
photosynthesis  different oxygen. The
Nandina Domestica plant is unknown as it
was not grown or monitored prior genetic predispositions specific to this plant
experiment. causes results with low accuracy and
reliability as the results cannot only be
obtained with these plants and cannot be
applied to other species (Wang, 2018).

Safety:

Potential hazard Prevention Control measures

Allergies or insect harm while collecting leaves Potential breakage of equipment. Perform all Student must report to SSO immediately where
steps of the method on one station to reduce protocols for such hazards must be listed and
movement across the laboratory. Safety gear: followed
Potential breakage of equipment. Breakage of glasses, coat and gloves must be worn prior to Clean area, use first aid kit to aid any injures.
LED light or sensor. starting the experiment. Experiment must be done Report to student services if injures is severe.
under instructor supervisions. Working First aid
must also be present.

Materials

Fresh Nandina Domestica leaves – green & red

Venier O2 gas sensor
Computer
Graphical Analysis app
Bio-chamber
Light pad

Method:
1. 5 fresh red, green Nandina Domestica leaves of similar size were collected.
2. Graphical Analysis was launched and connected to the O2 gas sensor on computer.
3. Set up the data-collection mode:
a. Mode was clicked to open Data Collection Settings.

b. Rate was changed to 15 samples/min and End Collection to 15 min. “Done” was clicked.
c. unit were changed to ppt by clicking the O2 meter and choosing ppt as the Units.
4. one Nandina Domestica leaf was placed inside the bio-chamber and inserted into the O2 gas sensor into the top. It was ensured that the
bio-chamber was completely sealed from the atmosphere.
the bio-chamber was then placed on the light pad.

5. The sensor was kept equilibrating for five minutes prior. After data collection commenced and was collected for 10 minutes.

6. Data was saved and steps 4-6 were repeated.

7. When data collection was finished, the rate of photosynthesis was determined.
Results:
Control group Results (no light):

0mins 2mins 4mins 6mins 8mins 10mins

GREEN 190.4 189.7 189.8 190.1 190.1 190.1
RED 190.5 190.6 190.6 190.6 190.5 190.5

Raw data tables of amount oxygen produced by green and red Nandina Domestica leaves during 10-minute trials:
Table 2: The amount of oxygen produced by green Nandina Domestica leaves every 2 minutes during a 10-minute trial.
Trials Oxygen (ppt)
0 min 2 min 4 min 6 min 8 min 10 min
1 183.83 184.5 184.86 185 184.98 184.91
2 192.63 192.71 192.01 191.90 191.81 190.20
3 193.70 193.90 194.00 194.10 194.20 194.20
4 191.9 192.3 192.4 192.4 192.3 192.3
5 184.24 184.42 184.29 184.42 184.24 184.13
6 187.10 187.13 187.08 186.92 186.74 186.46
7 191.17 191.23 191.25 191.21 191.17 191.12
Average 189.2 189.4 189.4 189.4 189.3 189.0

Table 3: The amount of oxygen produced by red Nandina Domestica leaves every 2 minutes during a 10-minute trial.
Trials Oxygen (ppt)
0 min 2 min 4 min 6 min 8 min 10 min
1 185.61 185.78 185.94 185.98 185.96 185.88
2 165.73 165.84 165.86 165.77 165.88 165.69
3 192.40 193.10 193.50 193.60 193.50 193.40
4 215.34 215.34 215.36 215.38 215.40 215.41
5 182.13 182.57 183.02 183.11 183.13 183.11
6 185.11 185.16 185.60 185.39 185.20 185.07
7 190.55 190.69 190.70 190.65 190.54 190.42
Average 188.1 188.1 188.4 188.6 188.6 188.5

Graph1: Average rate of oxygen produced by different coloured Nandina Domestica leaves:

The Effect of Leaf Colour on The Average Rate of Oxygen

Produced

189.4 189.4 189.4 189.4

189.3
Average oxygen produced (ppt)

189.2 189.2

189 189

188.8

188.6
188.5 188.5 188.5
188.4 188.4
188.3
188.2
188.1
188
0 min 2 min 4 min 6min 8 min 10 min

Time (minutes)

green leaves Average Linear (green leaves Average)

red leaves Average Linear (red leaves Average)
Discussion:
[Refer to graph 4] Over the 10-minute experiment, the average O2 produced by green leaves was seen to progressively decrease, producing a
negative linear correlation. Conversely, a positive linear correlation was displayed for the increased production of O2 by red leaves. Hence,
supporting the hypothesis that green leaves will have a greater rate of photosynthesis as it will produce a greater amount of O2 compared to red
leaves over 10 min. At 0-minutes, red leaves stood at 188.1 ppt of O2 while green leaves started at 189.2 ppt. Naturally, both leaves exhibited an
initial increase of O2 production with red leave demonstrating a steeper and much longer increase compared to green between the 0–4-minute
mark. The data subsequently started to plateau (at 188.5 ppt between 4-8 minutes and green at 189.4 ppt between 2-6 min respectively)
indicating the deceleration of the reaction. Green leaves exhibited a large decreasing slope amid 6-10 minutes going from 189.3ppt to 189.0ppt
with a difference of 0.4ppt, while red leaves displayed a decrease of 0.1ppt starting later at 8 minutes.

Accuracy and validity [refer to graph 1]:

The greater concentration of chlorophyll (plastid helping with photosynthesis) present in green leaves suggests that green leaves would perform
a higher rate of photosynthesis compared to coloured leaves (Takashima, 2009). This theory is supported as green leaves produced a much
higher amount of O2 compared to the red leaves. While red started off at 188.1 ppt, green leaves had a much higher starting point at 189.2ppt.

The plateau demonstrated by both coloured leaves in Graph 1, indicates the end point of the reaction. The rate of photosynthesis will only
increase until it is limited by another factor; thus, causing the rate of photosynthesis to decelerate, reaching endpoint (Benckiser, 2021). These
results illustrate high accuracy and validity as it is supported by the biological theory. As the leaves photosynthesise and produce O2 within the
bottle, the concentration of CO2 will eventually be insufficient to support a higher rate of photosynthesis, and factors such as increasing light
intensity will have no effect, causing the rate to plateaus. Light independent reactions are catalysed by enzymes, as the enzymes approach their
optimum temperature, the overall rate of photosynthesis increases. As the enzymes reach a temperature higher that the optimum, the rate it
begins to decrease, as enzymes are denatured, until it stops (BBC, 2023). This would affect the Light independent reactions and limit the
amount of oxygen produced making temperature a potential limiting factor. Temperature for optimal photosynthesis is 25- 35C. As the
experiment was conducted during winter, this could have instigated the reaction to plateau as the environmental temperatures are lower than
the optimal conditions (Yamasaki, 2002). By placing the leaves in a controlled environment with optimum temperatures, the leaves could have
shown possible increases in average O2 production while possibly eluding the early plateau and decrease, though potential systematic error
may have resulted in the decrease for both leaves from 6-10 min.

In daylight, plants are both respiring and photosynthesising, so oxygen and carbon dioxide are diffusing in and out of the leaves as reactants
and products of photosynthesis and respiration reactions (RHS, 2024). The data again displays high accuracy as decreasing slope displayed by
both leaves could be the leaves undergoing aerobic respiration and utilising the O2 (ppt) in the bottle produced via photosynthesis. Additionally,
the hypothesis is proven as green leaves had a faster rate of photosynthesis, therefore, started to aerobically respire earlier.

The validity of the results was significantly lowered as liming factors such as temperature (gradual heating of light pad, exterior temperatures of
lab) and CO2 concentration (reduced as O2 was produced) were not properly held constant and leaf surface area differed throughout trials
causing different coordinate values across trials and displayed varied photosynthetic rates.

Precision and reliability:

The Data demonstrate an Overall trend of increasing O2 production (ppt) as time increases High scatter within raw data values, evident at 0min
oxygen (ppt)165 and 215 (50ppt difference) demonstrates low reliability and therefore precision. As different sized Nandina domestica leaves
were utilised each trial, this therefore saw varying oxygen concentration results. To justify this, trial 2 may have had smaller leaves, resulting in
less chloroplast and hence, reduced rate of photosynthesis, this therefore sees higher starting oxygen values compared to trial 4 which had 215
ppt. this could possibly be due to the random error of oxygen escaping the chamber, therefore decreasing the oxygen levels that were produce
by the leaves. Oppositely, Green leaves demonstrated a high rate of precision with each trial following the average behaviour of photosynthesis
and remaining in a range between 9.87 difference. Green leaves displayed concordant values as trial remained within the 180-190 range
indicating less scatter between results/or the data. Concordant values demonstrate high precision within results, indicating greater/high
reliability. Although trial 3 of green nandina domestica leaves, defied the general performance of other trials as instead of decreasing around 8
min mark it remain in plateau state at 194.20ppt (tough this brings minute scatter within results this increases accuracy as ideally the rate of O2
production should have merely plateaued and not decreased).

Evaluation:
Potential Random Errors:
The various surface area to volume ratio/ size of the leaves may have been a random error that produced inconsistency within results. Smaller
leaves typically have a larger surface area-to-volume ratio, which could contribute to faster rates of photosynthesis per unit area due to
increased light exposure and efficient gas exchange (Socratic, n.d.). Because the trials used different sized leaves, the results were not
consistent, which resulted in a significant scatter and range within trials 2-4 of red Nandina Domestica leaves. Furthermore, changes in
chlorophyll concentration or pigmentation levels among leaves can skew results, affecting their unique photosynthetic capacity regardless of
size. Random errors in leaf placement could have caused variations in light exposure, effecting photosynthetic activity. This would imply that
parts of the leaves, particularly those that were larger in size, placed within the container were restricted from the light due to leaf overlap. As a
result, some trials, such trial three of green nandina domestica, took longer to plateau because the leaves did not receive enough light exposure
to initiate photosynthesis at the appropriate rate. By having an ideal size for the leaves or using a tool such as a hole puncher can significantly
reduce the various surface area and overlap of leaves, therefore more precise and reliable results with less scatter and range. More trials would
also be beneficial as random errors causing scatter would be balanced out, increasing the precising and reliability of results more.
Potential Systematic errors:
The intensity of the light pad along with the thickness of the plastic bottle may have affected the intensity of light the leaves were exposed to.
This systematic error generates a constant bias across the experiment, since the plants' photosynthetic results continuously underperforms
due to lack of optimal light intensities. Due to this the true value of results cannot be drawn limiting the validity of results severely. The method of
testing may have reduced validity further as placement of the O2 sensor as well as quality of the product may have been poor. Hence, results
that are invalid and lack in accuracy.

Limitations and conclusion:

The results of this experiment displayed high accuracy as the green leaves had a higher rate of photosynthesis compared to red leaves. The
initial increase and later plateau demonstrated by both leaves displayed an accurate presentation of the photosynthesis reaction with limiting
factors (most likely CO2) causing the plateau for both leaves. The accuracy was then increased by green leaves as a negative correlation was
produced due to the green leaves aerobically respiring and utilising the O2 produced via photosynthesis. The validity of the results was reduced
as limiting factors such as CO2 and temperature were not controlled and varied throughout results. Many random errors (different size leaves
across trials and overlap inside testing bottle) were detected within the raw data and produced great amounts of scatter in trials 2-4 of red
leaves, hence, lowering the precision and reliability of the results. Thought the results held high accuracy, factors such as CO2 concentration,
varied temperatures and genetic predispositions limit the application of these results on other trials. The CO2 absorption or glucose productions
by red and green nandina domestica leaves could have also been measured alongside the O2 production (ppt) during the photosynthesis
reaction. This manner would allow the rate of photosynthesis of red and green leaves to be better understood and any errors or abnormal
patterns to be clearly identified and validated for by other results of the reaction. Different plants or a greater no. of Nandina domestica plants
must be tested on to gain more precise and reliable results.

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