Photoselective Films


1.0 Plants have little option but to function in the environment that they are found in. For photosynthetic organisms, it has been necessary for them to develop mechanisms to sense their light environment and to adjust their form and metabolism to optimise their performance (Willis and McElwain, 2002). Since light environments alter, these organisms have also developed the ability to continuously adjust their function to current conditions; this process is known as photomorphogensis (Beerling, 2008). Plants and their ancestors have adapted themselves over millions, if not billions of years, to use light as a source of their primary energy (Lane, 2003). This project has investigated the details of their energy source by splitting the luminescence they utilise and to grow a model species under three of the fundamental wavelengths. There has been little research carried out on the effects of excluding different wavelengths on photoautotrophs however, this project has increased knowledge of frequencies by secondary research and by applying this research to the test.

1.1 From the research, conclusions were drawn to reveal why these frequencies are acquired by photoautotrophs and what their impacts are. Afterwards a methodology was developed to carry out the experiments to get the results. The experiments occurred over a 9 week period at The University of York. There were 3 test groups with 3 trials that were designed to test the hypotheses. The 3 test groups included: blue, green and red light with white light as the independent variable.

1.2 The results were recorded onto tables and processed through the discussion to either prove or disprove the three hypotheses stated. In the discussion, the results were cross referenced with the research to obtain more precise conclusions and to provide an explanation on why the outcome might have occurred. Conclusions have been drawn, invalid hypotheses rejected and explanations summarised with recommendations for improvements for future research and investigations based on this subject.


2.0 This project aimed to prove the hypotheses and to find out what processes are involved in photosynthesis, photorespiration and how light frequencies influence these processes. The fundamental aim of the experiment was to investigate the effects of light wavelengths on photosynthesis and what would occur if certain wavebands were removed. There are 4 principle hypotheses that will be investigated in this study:

  1. H1 height will alter when grown under photoselective films.

  2. H0 height will not alter when grown under photoselective films.

  3. H1 when grown under photoselective films leaf span will modify.

  4. H0 when grown under photoselective films leaf span will not modify.

  5. H1 root length will alter under photoselective films.

  6. H0 root length will not alter under photoselective films.

  7. H1 dry weight will alter under photoselective films.

  8. H0 dry weight will not alter under photoselective films.


3.0 The aim of this investigation was to review the processes involved in photosynthesis and how different light frequencies influenced the means of these processes. This study aimed to determine what would occur if the wavebands were split, by utilising secondary research to form a valid experiment.


3.1 Kamen (1963) describes photosynthesis as: ‘A process in which electromagnetic energy is converted to chemical energy that can be utilised for various biosynthetic processes.’ Plants require photons, CO2, and H2O to produce sugar and carbohydrates (Dawkins, 2010; Capon, 2010). Below is the equation to demonstrate photosynthesis:

6CO2 + 6H2O → (Photons & Chlorophyll) C6H12O6 + 6O2

Light-dependent reactions occur in the thylakoid membranes (reaction centres) of the chloroplasts and utilise photons to synthesize ATP and NADPH (Smil, 2006; Leegood, 1998).

3.2 The process commences with photosystem II (250-400 pigment molecules) when a chlorophyll molecule gains sufficient energy from the adjacent pigment, which enables photolysis of H2O to occur (breaking of hydrogen and oxygen) (Mauseth, 2008). This process produces O2 which is expelled and electrons and protons (H+) which are utilised. This occurs in the granum of the chloroplast or the ‘stacks of thylakoids’ (Emerson et al, 1957; Dawkins, 2006). Chitnis (1996) states that the H+ are then translocated through the cytochrome which energises and excites H+ to the second stage of light-dependent reactions which is shown in the following stages:

Photosystem II (P680) → Plastoquinone → Cytochrome b6 → Cytochrome f → Plastocyanin → Photosystem I (P700)

3.3 Photosystem I activates electrons for transfer to the Fd and finally to NADP+, where the protons from water splitting are exhausted to create NADPH+ H+ (Allaby, 2006; Harrison, 2008). To demonstrate the ability to liberate oxygen from water, Chitnis (1996) formulated the following:

The positively charged P800 exerts a strong pull on the H20 molecule, splitting it into H+ and OH- ions. It requires CI- and Mn2+ ions to act as a catalysis:

4H20 → (Mn2+, CI-) → 4 (OH-) + 4H+

OH donates its electron to oxidise P680:

4(OH-) → 4e- → 4OH

OH radical obtained forms H20 and liberates oxygen:

4(OH) → H20 → 4H+ → 4e- → 02

Donation of H+ ion from the formation of NADPH is utilised for the Calvin-Benson Cycle (Beerling, 2008). Below is a summary of the differences between the photosystems.

Table of photosystems

Table 1 Photosystem comparison

(Source: Reddy et al, 2004)

3.4 The end products are transferred to the light-independent reactions, these reactions occur in the stroma found within the chloroplast between the grana and thylakoid. C02 is delivered to the stroma where they are reduced to ATP and combined with H+ to power the Calvin-Benson Cycle (B.B.C., 2011; Kratz, 2011; Devlin, 2007). This process converts ATP into the carbohydrates needed to power the photoautotrophs. The key enzyme of the cycle is RuBisCO. This enzyme fixes C02 to ATP by complex redox reactions to gain the carbohydrates, lipids and proteins which are required for development (Hall and Rao, 1999; Singleton, 2004). Kratz (2011) expressed the following equation for this process:

3CO2 + 6NADPH + 5H2O + 9ATP → glyceraldehyde-3-phosphates (G3P) + 2H+ + 6NADP+ + 9ADP + 8Pi

3.5 Plants convert photons into chemical energy with a photosynthetic efficiency between 3-6%, however photosynthesis varies with the frequency of light and intensity temperature and proportions of C02, which can vary between 0.1 – 0.8% in the atmosphere (Blankenship, 2001; Akutagawa and Ozaki, 2011; Franklin et al, 2005). Photosynthetic systems store 469 kilojoules of energy and in some cases up to 502 kilojoules. This process is more productive when both photosystems are balanced in their uptake of light. By comparison, solar panels convert photons into electrical energy at an efficiency of 6 - 20% (Blankenship, 2001). This table puts the reactions of photosynthesis into a timescale.

Timeline of photosysthesis

Table 2 Time of Photosynthesis

(Source: Taylor et al, 2009)

Research review

3.61 Research conducted by Shumin and Rajapakse (2000) explored the effects of different concentrations of far-red light utilising 3 photoselective films. 3 concentrations of far-red light were set up using a sample of 3 Dendranthemax grandifora cultivars, 20 ‘Bright Golden Anne’, 20 ‘Iriden’ and 20 ‘Yellow Snowdon’. In addition, 5 of the cultivars utilised were propagated beneath non-photoselective films for the control. The photoselective films were held in place by utilising P.V.C. piping with 2 fans to ensure continuous airflow. Plants were asexually reproduced and left to grow in nominal light conditions for a week. The cultivars were placed under the enviro-boxes for a month in a controlled glasshouse.

3.62 The study discovered the greater the concentration of far-red, the greater the reduction in height of the plants. Internodal growth was reduced by up to 35% in specimens under the higher concentration, this also decreased leaf area and dry weight (Shumin and Rajapakse, 2000). However there was a 25% reduction in light received by the specimens as the films absorbed parts of the spectrum (Graham, 2008).

3.63 A possible problem with their methodology was that a glasshouse is difficult to maintain to a constant environment due to external influences such as sunlight. Sunlight levels can easily fluctuate within a glasshouse due to the ‘greenhouse effect’ (Ingram et al, 2008). As light enters the glasshouse 50% is captured, thus increasing temperature. Glasshouses heavily rely on the external environment which can be unpredictable (Preece and Wilson, 1993). Unpredictability is a major hazard in an experiment, as variables need to be controlled to arrive at a precise conclusion.

3.64 Shumin and Rajapakse (2000) used asexual reproduction in their experiments, which has the major advantage of producing uniform specimens; subsequently leading to copies of successful individuals. Conversely if one of the copies contracted a disease or pest the others would equally be susceptible, which could result in specimens getting damaged or killed (Crops, 2009). If plants were to be reproduced sexually this would not occur as they contain different genes resulting in different susceptibilities and resistances (Beck, 2010). On the other hand, it could affect the outcome of the experiment as plants would not be uniform.

3.65 Peat is widely used for the production of plants albeit containing varying amounts of nutrition. This could have affected the outcome on their tests as one group may have received more nutrition than another. Furthermore, the above research had only 1 trial. This could have affected the outcome as it would have decreased the viability of the experiment as 1 trial’s result could have consequently produced an outliner result (Ashfield, 2008).

3.71 Wilson and Rajapakse (2001) compiled a study using photoselective films to investigate alternatives to using chemical growth retardants. They utilised 3 plants each of 3 species of Salvia (S. x ‘Indigo’, S. longispicata and S. splendens) which were purchased as plug plants. There were 3 groups which included a control that were set up using P.V.C. piping, far-red and red photoselective films and a non-photoselective film. The substrate used was a 20/80 mixture of osmocote and soiless-media. There was a fan at the bottom of the enviro-boxes with a small incision at the top to release the resulting air. The specimens were grown in these boxes for 6 weeks. After this period an additional 2 trials occurred. The minimum temperature recorded was 17°c followed by the maximum temperature of 35°c.

3.72 This research revealed that when grown under far-red the compactness, yield and greenness of the plants had increased. When grown under red film, plants showed no significant difference. Flowering and leaf area under both films was unaffected. Nevertheless the dry weight of the plants had increased under the far-red film.

3.73 A disadvantage of using enviro-boxes is that it reduces airflow. When airflow is restricted humidity increases which leads to an increased risk of diseases such as Botrytis (Harrison, 2008). The author of this study has tried to rectify this issue by inserting a fan at the bottom of the boxes and making an incision at the top. However this could have resulted in unwanted light entering the enviro-boxes as escaping air pushes the incision apart. One issue which was not addressed in this study was the sample size. Can 9 plants with 1 trial represent the population? This may have affected the validity of the study as there were not enough trials to gain an average as suggested by Greenhaun (1996). A possible solution may have been to increase the number of plants used within each group and to complete 2 further trials, this would have increased test validity.

3.74 There was a large differential between the minimum and maximum temperatures in this experiment. Plants respond to different temperatures which may have influenced their growth rates; inevitably decreasing the reliability of the tests (Sambamurty, 2005). A more controlled environment such as a growth cabinet could have ensured more variables were controlled.

3.81 A comprehensive study comparing 6 flowering species was led by Cerny et al (2003), to explore the effects of far-red and red light on plant development. The experiment occurred in an open polythene glasshouse using 3 groups. To construct the enviro-boxes P.V.C. piping was utilised with the films attached. This was followed by the control which had a non-photoselective film. 40 plants were grown under the enviro-boxes for 3 months from January to March. Light level readings were recorded every 5 minutes once a week using a spectro-radiometer. The following genera were used: Zinnia, Dendranthema, Cosmos, Petunia, Rosa and Antihrrum.

3.82 Of the genera utilised there was no significant difference in height when Antihrrum and Rosa were grown under far-red. The Zinnia, Dendranthema, Cosmos and Rosa had a considerable reduction in flowering. On the contrary, Antihrrum and Petunia had an insignificant delay in flowering (Cerny et al, 2003). All genera which when grown under far-red, had a noticeable increase in compaction. Red had no significant impact upon the growth or flowering of the specimens.

3.83 To ensure that all the groups were receiving the same conditions a non-photoselective film was utilised for the control. Although the film does not filter out specific wavebands, it ensures that variables such as humidity, temperature and light are kept constant (Horticultural Development Council, 2010). 240 plants were employed for this study which increases the outcome’s precision. Conversely there was only 1 trial completed but with increased numbers of specimens 1 trial may have been enough.

3.84 The study occurred from January to March in the southern hemisphere. During this period heavy rainfall and turbulent weather systems are widespread (Lane, 2006). This could have affected plant growth due to the polythene glasshouse being open to weather conditions. In addition specimens were measured by all the contributors, which could have resulted in inconsistencies as people measured in different ways (Rouncefield and Holmes, 1989). This could have been resolved by one person being responsible for measuring, which would have reduced the likelihood of systematic errors.

3.91 In 2008 a study was launched to overcome the problem of elongation when commercial crops were shaded during the summer. Cummings et al (2008) employed 3 groups to explore possible solutions to this problem: 20 plants were to be grown under neutral shading, 20 under blue shading, 20 under red shading and 20 un-shaded as a control. Pisum sativum were grown from seed and placed directly into each of the trial conditions. 2 seeds were planted in each pot to act as a support in the event of one not developing. Incandescent lights were used to supplement the light levels as the experiment had occurred during Spring and Autumn in a controlled-glasshouse. Light level readings were recorded using a spectro-radiometer once a week at mid-day.

3.92 Cummings (2008) revealed that when grown under blue shading, height would be significantly reduced and yield increased; whereas when grown under red shading plants would increase their height and reduce their yield. Additionally his study discovered that when plants had a reduction in height a delay in flowering occurred.

3.93 The experiment carried out considered a key confounding variable. What would occur if one of the seeds did not develop? It was decided to plant 2 seeds in each pot. This reduced the likelihood of seeds not developing which may have resulted in the collapse of the experiment (Grimaldi, 2005). Incandescent lights were used in the experiment to supplement lighting due to the season the test had occurred. Although this may appear to benefit the experiment it may have created a bias. Incandescent bulbs are well known to emit long-wave radiation (Reddy et al, 2004). This could have enhanced the red shading as red light is located on the longer frequencies on the electromagnetic spectrum. However fluorescent bulbs emit most of the spectrum and thus would have been better to use for this type of experiment (Ingram et al, 2008).

3.94 Placing the spectro-radiometer in one place once a week may not represent the light levels of the location as they can frequently fluctuate at different times of the day (Leegood and Lea, 1998). To achieve a good representation the spectro-radiometer could have been placed in several areas to gain a mean result. This would have increased the validity of the readings as the entire area would have been taken into consideration.

3.10 It is apparent from all the research which has been reviewed, that adequate controls need to be in place to ensure this investigation can draw precise conclusions. To ensure environmental specifications are met a growth cabinet with overhead fluorescent lights has been used, as growing specimens in a glasshouse would increase the amount of confounding variables (Blankenship, 2001). Furthermore this would protect against variation in the wavebands being received by the plants. To increase the validity of this experiment, 3 separate trials have been completed to gain a more precise outcome. Plants have been grown sexually which would increase disease resistance within the majority of the plants. 2 seeds had been planted per pot so it could protect against seed development failure as suggested by Cummings et al (2008). See appendix 2 for details on photoselective films.


4.0 This study aims to determine the effects of segmented wavelengths on plant growth by measuring leaf span, height, dry weight and root length. Specimens were grown in a Snijder growth chamber. Prior to the experiment the growth cabinet at the biology department at the University of York was programmed and left to run for 2 weeks to ensure that environmental specifications were being followed. Illumination was provided from above to spread the light equally and to stimulate upright growth, see appendix 3 for specifications.

4.1 36 x 7.6cm sized pots were filled with 50/50 mixture of sand and terragreen and 2 seeds of Lycopersicum esculentum ‘Money Maker’ were sown in and then watered. In each group, 9 Lycopersicum were grown for 3 weeks, 36 for each trial and 108 overall. As reinforcement, 2 seeds were planted in each container reducing further confounding variables. When 2 seeds had developed 1 was withdrawn. 9 plant pots were placed in 4 drip proof trays. Each tray was placed in one of the 4 enviro-boxes. 1 with red, 1 with blue, 1 with green and 1 non-photoselective film, see appendix 3 for trial design. Subjects were then placed into the Snijder growth cabinet 37cms away from the source of light to ensure maximum illumination output which was effectively reduced by the filters.

4.2 Lycopersicum had been germinated under white light for 1 week until the first true hypocotyls developed and then they were placed into the enviro-boxes. During the time the specimens were grown, temperature and light readings were collected to monitor environmental specifications (Valiela, 2010).

4.3 There were 3 trials to gain an accurate outcome (Field and Hole, 2003). Each trial consisted of 3 groups, to test specific wavelengths: red, blue, green and white which act as a control variable (Abbott, 2010. Pers. Comm. Mr Colin Abbott chief technician of biology at The University of York). Refer below for the trial layout.

Study layout

Table 3 Trial Layout

4.4 Specimens were irrigated when required and supplemented with Phostrogen multi-purpose fertiliser to enrich the inert substrate to retain the health of the plants. The application has been uniform throughout the trials at 4.5 grams per 4 litres, refer below for details.

Table of nutrient make up

Table 4 Nutrient Makeup

(Source: Royal Horticultural Society, 2010)

4.5 Once a week, specimens had their height and leaf-span measured inside the growth cabinet to ensure environmental constancy within the experiment. After each trial specimens were measured from stem base to apical meristem and from stem base to root-meristem, photographed, root architecture documented and biomass readings recorded (Montgomery et al, 2010).

4.6 To gain dry weight, specimens were removed from the substrate and briefly washed. Plants were then blotted to remove any free surface moisture. Specimens were placed into a drying oven at 100°C for 48 hours. Plants were left to cool for 3 hours and weighed on a scale which measures in milligrams (Reed et al, 2007). This trial process was repeated twice during subsequent weeks.


5.0 From the descriptive statistics that were analysed it was found that when grown under blue light Lycopersicum grew on average 0.1cm taller. When grown under red light, specimens had reduced height by 3mm. Specimens grew 0.94cm taller when propagated under green light as demonstrated in the table.

Table 5 Growth rates above substrate (cm) (n4=27)

Below is a chart illustrating the differences in height.

Figure of leaf span

Figure 1 Plant heights (cm) (n4=27)

Two inferential analyses were then completed. The Anderson-Darling test provided a P-value of 0.010 signifying normal distribution. The Levene’s test showed a P-value of 0.148 which demonstrated equal variance. A One-way ANOVA test was then completed to investigate if there was a significant difference between the groups. The test result was:

One-way ANOVA: F= 1.20, P 0.310 (N4=27)

This demonstrates no significant difference within the heights.

5.1 Specimens which developed under blue light had an increase of 1.41cm in leaf span. However there was no significant difference when grown under red and green light. When cultivated under green light specimens grew 0.38cm taller and under red light they grew 0.53cm taller as illustrated in the table below.

Leaf span growth rates

Table 6 Leaf span development rates (cm) (n4= 27)

Below is a chart demonstrating the differences in leaf span.

Difference in leaf span

Figure 2 Differences in leaf span (cm) (n4=27)

The Anderson-Darling test indicated a P-value of 0.015 demonstrating normal distribution. The Levene’s test showed a P-value of 0.026 which demonstrated equal variance. A One-way ANOVA test was then completed to investigate if there was a significant difference between the groups. The test result was:

One-way ANOVA: F= 1.24, P 0.294 (N4=27)

This signifies no significant difference in the leaf area.

5.2 This study has revealed that when cultivated under blue light the roots grew up to 1.82cm longer when compared to the control. In contrast when grown under red light the root length decreased by 0.66cm. There was however a difference when cultivated under green light which decreased by 5.02cm as demonstrated below.

Root enlongation rates

Figure 3 Differences in root lengths (cm) (n4= 27)

5.3 The Anderson-Darling test provided a P-value of 0.012 signifying normal distribution. The Levene’s test showed a P-value of <0.001 which demonstrated unequal variance. A One-way ANOVA test was then completed to investigate if there was a significant difference between the groups. The test result was:

One-way ANOVA: F= 22.54, P <0.001(N4=27)

This determines a significant difference in root elongation.

5.4 A post-hoc test was then required to identify differences between the groups. It revealed that there was a significant difference in root elongation between the green and the other groups (P=<0.05) and between the blue and the control (P=<0.05). However, there was no significant difference between control and red and blue and red (P=>0.05). This demonstrates that green and blue photoselective films impact upon the growth of Lycopersicum roots, this is shown as below:

Individual 95% CIs For Mean

Based on Pooled StDev

Level N Mean StDev --------+---------+---------+--------

Blue 27 6.411 2.301 (---*---)

Control 27 8.274 3.051 (---*---)

Green 27 3.259 0.860 (---*---)

Red 27 7.619 1.541 (---*---)


Pooled StDev = 2.105 4.0 6.0 8.0

The post-hoc test can be reported as:

T Statistic = 3.69 x √ (4.43/27) = 1.49.

5.5 From the biomass readings that were recorded plants that were grown under blue light saw a 0.89g decrease in dry weight, under green light specimens saw a 1.16g decrease in dry weight and finally under red light plants saw a 0.37g decrease in dry weight.

Dry weight of tomato plants

Table 7 Dry weight of Lycopersicum (g) (n4= 27)

The chart below illustrates the differences in dry weight.

Dry weight of specimens

Figure 4 Dry weight of specimens (g) (n4= 27)

5.6 The Anderson-Darling test presented a P-value of 0.020 indicating normal distribution. The Levene’s test showed a P-value of 0.600 which demonstrated equal variance. A One-way ANOVA test was then completed to investigate if there was a significant difference between the groups. The test result was:

One-way ANOVA: F= 2.31, P 0.152 (N4=27)

This signifies no significant difference in the dry weights of the plants.

Refer to appendix 4 for raw data.

Refer to appendix 5 for observation log, photographic evidence and seed development chart.

5.7 The following charts are comparing the overall results for each of the readings to clearly demonstrate differences in growth patterns for each of the groups.

Comparison of study readings

Figure 5 Comparison of readings recorded (cm/g) (n4= 108)

The chart below represents the percentage differential in growth for all the readings that were taken. Note that all specimens grown under coloured light had more variable growth when compared to the control.

Percentage differential in growth rate of plants

Figure 6 The percentage differential in growth (%) (n4= 108)


6.0 There was no significant difference found in the height of plants when grown under photoselective films. When further investigated, there was a slight increase in the height of plants when under green. The P-Value (P=0.310) establishes that there was no significant difference and from this, the H0 can be accepted. This may be because red light is within the P.A.R. that plants exploit for their development. This result was supported by Wilson and Rajapakse’s (2001) and Cerny et al (2003) as they all conclusively revealed that height was unaffected by red or blue photoselective materials. Red is absorbed by plants and is known to promote flowering and budding but not to increase the growth (Wolken, 1995). To affect development red light needs to be absorbed in conjunction with blue, which encourages leafy growth and development (Zelitch, 1972).

6.1 It was revealed that the leaf span was unaffected when grown under photoselective films. The largest differential was identified when propagated under blue light demonstrating a slight increase; refer to page 24, table 6. Blue is within the P.A.R. range and can encourage plants to increase their leaf surface area. Phytochromes react to high levels of blue to aid in collecting other parts of the spectrum used in development. However, from the P-value (P=0.294) the H0 can be accepted. In contrast, Cummings et al (2008) discovered that plant height and leaf span were significantly reduced when propagated under blue. One major difference between this study and Cummings et al (2008) was the light source that was utilised. Cummings et al (2008) employed incandescent bulbs which emitted long-wave radiation otherwise recognised as red light, which may have helped to decrease leaf surface area.

6.2 When investigated there was a significant difference in root enlargement when grown under green and blue light (P=<0.05). Red photoselective film however did not have any effect on root development; refer to page 25, figure 3. From this result the H1 can be accepted. Shumin and Rajapakse (2000) indicated that red light does not impact upon root expansion supporting one of the outcomes of this study. This research has revealed that blue light decreased root length by 22.6% and green by 60.6%. This is as a result of green light absorbing the red and blue sub-wavebands of the spectrum, thus decreasing the P.A.R. which plants need to grow in (J.H.S.B., 2010). Blue light is known to manipulate the root shoot ratio as the energy transfer channels are sensitive to this radiation. As blue light decreases so does the efficiency of photosynthesis (Devlin, 2007). This reduces root length from the lower amounts of energy available resulting in dehydration.

6.3 From a horticultural point of view the results indicate that blue and green photoselective films may increase the compaction of the plants, from the shortening of roots. Thus improving the quality of certain types of plants such as bedding. As an illustration of this, 198mol/m2 was emitted from the light source within the growth cabinet. When the photoselective films filtered out the wavebands, it altered the frequency of the criteria needed (Exploratorium Education, 2010). This could also reduce the long-term costs for a nursery, as films have been proven to remove the need for chemical growth retardants, as proved by Wilson and Rajapakse (2001).

6.4 In relation to dry weight it was revealed that there was no significant difference. Each of the groups lay within the confidence intervals by 98.7% and had a P-value of 0.152. From the evidence the H0 will be accepted. Cerny et al (2003) also discovered that dry weight was unaltered by means of the blue and red photoselective films. A possible explanation was uncovered by Wilson and Rajapakse (2001) who discovered that the mass stayed continuous when plants were grown under separate wavelengths. Conversely when plants were grown fully under red and blue light, mass should increase as it enhances the P.A.R. plants utilised for photosynthesis (Lawlor, 2000).

6.5 The experiment conducted occurred over a 9 week period. The plants were grown under the films for 2 weeks for each of the trials. This period may have not been adequate for plant development. To ensure a more valid result, plants could have been grown under their films for longer. A ruler was used to measure the differences in height, span and root length. However, accuracy could not be guaranteed as the substrate was uneven and some plants had to be straightened. To overcome this issue the researcher could have used a digital photographic analysis program which could have precisely measured a plant’s height, up to four decimal places (N.S.A.C., 2011).

6.6 Other research conducted used P.V.C. piping to erect their enviro-boxes. This experiment chose to use cardboard boxes, not only from an economical point of view but because they were bio-degradable, which meant they could easily be recycled. Conversely, using cardboard has the disadvantage of decreasing film surface area, due to its being thicker than P.V.C. If more funds were available P.V.C. piping would have been chosen. Another model plant species which may have been used for this experiment was Arabidopsis thaliana which has a more rapid germination rate by 57%, when compared to Lycopersicum (Bleecker, 2005). This increase in germination could have increased the efficiency of the experiment. In addition Arabidopsis spp. had a shorter life cycle, which would have resulted in a complete life cycle under the films which may have increased the validity of this study.

6.7 The experiment occurred within a growth chamber to ensure the reliability and validity of this experiment. The input of water and nutrients were precisely monitored and maintained. Input of light and temperature although closely monitored were not precisely controlled as they could vary by 5% due to the nature of radiation (R.H.S., 2008). The humidity was difficult to control, as humidity levels increased after watering and decreased when the cabinet door was opened.

6.8 More research is required to further explain the effects observed in this study on green light. Why did the plants continue growing under green light, when green light does not contain any P.A.R? Another unanswered question was the lack of difference in dry weight. Plants growing under different wavelengths should have different masses, as there was a significant difference in root development when under blue and green. It may be that plants could survive in green light growth for a short period by using their starch reserve to supplement their energy creation (Wilson et al, 2010). A possible hypothesis for the lack of difference in the dry weights could be due to the balancing of growth rates. For instance, when grown under red light the height may increase and roots may decrease, thus balancing the total mass of the plants.

6.9 To conclude there was no significant difference in plant height, dry weight and leaf span, however, this study revealed that there was a significant difference in root growth in green and blue light.


7.0 Photoselective films have been utilised to investigate the different effects on Lycopersicum development using 4 methods of measurement: plant height, leaf span, dry weight and root elongation. From the research it is clear that blue and green photoselective films reduce root development and that more research is required to develop the understanding of how photoselective films interact with plant height, span and dry weight. Under blue light Lycopersicum root lengths decreased by 22.6% and under green light root lengths decreased by 60.6%. However under red light root lengths decreased by 7.9% resulting in no significant difference. This research suggests that horticulturists could utilise these films to decrease root length thus to increase the compaction of their produce, especially within the bedding plant industry.

7.1 One of the shortcomings of this experiment was the length of time that specimens spent under the photoselective films. Specimens were grown for 2 weeks under these filters due to the cost of using the growth cabinet. This may not have been enough time to gain a significant difference in height, span and biomass. Furthermore, the enviro-boxes used were made out of cardboard to reduce expenditure. As cardboard is weaker when compared to P.V.C. piping it requires a larger surface area to hold up the structure. This increase in surface area could have reduced the light received by the plants.

7.2 More research is required to explain the differentiation observed when grown under green light. As previously discussed plants require P.A.R. to generate energy for development. However green light does not contain any wavebands of P.A.R., so the logical question would be why did they survive? Additionally more studies are required to understand the effects of red light and how it can be utilised for commercial purposes. A study similar to Wilson and Rajapakse (2001) revealed no significant difference when specimens had been grown under red light. In addition there is little research available on the effect of red light and this could be an area for future research.


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µm – Micrometres

03 – Three oxygen atoms

0H – Hydrogen peroxide

2C – Two carbon atoms

ADP - Adenosine Diphosphate

APG - Phosphoglyceric acid

ATP - Adenosine triphosphate

b6 - Cytochrome

C – Carbon

C02 – Carbon Dioxide

C3 – Three carbon fixation pathway

C4 – Four carbon fixation pathway

C6H12O6 – Glucose

Cal – Calorie

CAM - Crassulacean acid metabolism

CH – Chemical symbol for carbohydrates

CI – Chlorine

DNA - Deoxyriboneucleic acid

e – Electronic

Fd - Ferredoxin

Fe – Iron

G - Gram

G3P - Glyceraldehyde-3-phosphates

H+ - Hydrogen Ion

H0 - Null hypothesis

H1 - Hypothesis

H2O – Chemical symbol for water

Kcal – Kilocalorie

Kj - Kilojoules

M - Metre

Mg – Magnesium

Mm – millimetres

Mn – Manganese

Mol - Micromole

NADP - Nicotinamide adenine dinucleotide phosphate

NADPH - Nicotinamide adenosine dinucleotide phosphate

Nm – Nanometres

O – Oxygen

OAA – Oxaloacetate

P700 - Photosystem I

P800 - Photosystem II

PAR – Photosynthetically Active Radiation

PEP - Phosphoenolpyruvate carboxylase

Pfr- Far-red light receptors

PGA - Phosphoglycolate

Pi – Generally term used for phosphates

Ppm – Parts per million

Pr –Red-light receptors

PVC - Polyvinyl chloride

RuBisCO - Ribulose-1, 5-bisphosphate carboxylase oxygenase

RuBP - Ribulose 1, 5-bisphosphate

UV – Ultraviolet radiation

UV-A - Long wave ultraviolet radiation