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Examination How Different Coloured Rays of Light Affect Photosynthesis

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Examination of How Different Colours of Light Affect The Rate of Photosynthesis INTRODUCTION Plants are an essential part of the food chain required by all living things to survive. The growing world population and subsequent alteration to the natural environment has placed increased pressure on available plant resources. This is particularly evident in the area of agriculture, where optimum crop productivity is important to meet the increased demand for food by the growing world population.

Plants are autotrophic, which means they make their own food, sustaining life without needing to consume other organisms1.

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They do this through the process of photosynthesis. This is where light energy from the sun (or other radiant source) is trapped by green plants and transformed into chemical energy. All photosynthetic organisms contain chlorophyll, a green pigment found in plant chloroplasts. There are three types of chlorophyll pigment – a, b and carotenoids. Chlorophyll a is the pigment primarily responsible for the process of photosynthesis.

It is green as a result of reflecting green light rays.

Light energy is captured by chlorophyll and used to form ATP molecules, which are in turn used as an energy source by plants in a chemical reaction with combines carbon dioxide and water to produce glucose and oxygen. 2 The equation which describes the process of photosynthesis is: Carbon dioxide + water light energy > glucose + water + oxygen Chlorophyll Light energy is essential for photosynthesis to occur and this is usually provided in the form of sunlight. All light, including sunlight, is a collection of wavelengths.

The visible light spectrum contains wavelengths which vary in intensity from around 350nm (nanometres) to 750nm (Figure 1). Chlorophyll reflects green light (so leaves appear green) and absorb more blue and red light 4 . Figure 1: Wavelengths on the Visible Light Spectrum (Source Britannica. com) The rate at which photosynthesis occurs is influenced by the wavelength of light. The shorter a light wavelength, the more energy it has and the higher the rate of photosynthesis. That is, light energy is absorbed most effectively at shorter wavelengths. So, red light has more energy than green light5.

Knowing optimum light conditions to maximise photosynthesis (and therefore plant growth rate) could be considered useful information, especially to those involved in agriculture. HYPOTHESIS Plants require photosynthesis to produce food energy. If lightwaves at higher intensity result in a higher rate of photosynthesis, then plants grown under red will have a faster growth rate than plants grown under other colours in the visible light spectrum. EXPERIMENT DESIGN An experiment was designed to investigate the effect of different coloured lights on the growth rate of bean plants.

The plants were grown under blue, red, yellow and green lights in controlled conditions over a period of time. A control experiment was established by growing plants under identical conditions using unfiltered (white) light. The height of each plant was measured periodically and the results tabulated and analysed. Independent variables affecting the experiment included: •Colour of light (wavelength) Dependent variables affecting the experiment included: •Growth rate of plant Controlled variables affecting the experiment included: •Starting height of plants •Size and type of container Soil type and volume •Water •Duration of light applied •How deep and far apart planted Uncontrollable variables affecting the experiment included: •Temperature The group of plants growing under each colour light, plus the control group, were individually measured on a regular basis and the average plant height of each group was calculated. The rate of growth was analysed by calculating the change in growth of each group of plants under the different lights and comparing these results. MATERIALS AND EQUIPMENT 20 x bean plants 10 x plant pots, (same size) 5 x cardboard boxes (same size)

Stanley knife Cellophane – red, green, blue, yellow, clear 5 x microscope lamps Adhesive Tape Ruler showing millimetres and centimetres Potting mix Sticky labels Marker pen Pad and pen for recording results Gloves Face mask METHOD 1. Collect all materials and equipment. 2. Cut a square hole, 20cm x 15cm, in the top of each cardboard box. 3. Cut a square of each colour cellophane slightly larger than the hole. 4. Tape a cellophane square over the hole in each box, giving one box each with red, green, blue, yellow and clear cellophane. 5. Fill each pot with potting mix to the same level. 6.

Plant 2 bean plants in each pot, ensuring all are planted to the same depth and the same distance apart from each other. 7. Allocate two pots per box. 8. Number each plant per box from one to 4 and label pots accordingly. 9. Measure each of the plants from where it emerges from the soil to the top of the plant and record this data on a table. 10. Place pots inside each box, giving five boxes with two plants each. 11. Position boxes in room away from direct sunlight. 12. For each box, place a microscope lamp directed through the cellophane towards the pots inside. 13. Turn on each lamp. 14.

Each science lesson, record the height of each plant from where it emerges from the soil to its highest point and record data. 15. At the end of the data collection period, analyse results and report. RISK ASSESSMENT Potting mix is known in some circumstances to be a carrier of the legionella bacteria. To protect against possible infection, gloves and face masks should be worn when handling potting mix. RESULTS The daily data recorded in the log book is attached as Appendix 1. The average height was calculated for the group of plants under each of the light conditions and this information appears in Table 1 below.

Table 1: Daily Average Plant Height per Colour (expressed in centimetres) Day1Day 2Day 3Day 4Day 9Day 11Day 12 Red9. 6310. 131112. 3813. 2513. 513. 5 Blue10. 510. 7311. 511. 751212. 312. 4 Orange1010. 8811. 512. 5313. 8814. 5315 Green14. 815. 5515. 8816. 116. 7517. 317. 45 Control9. 1310. 3810. 7512. 215. 7516. 8817. 88 All plant groups showed an increase in average height throughout the period of the experiment, however results were affected by individual plants within each colour group which did not thrive as well as others under the same conditions.

The actual average growth of each colour group is shown in Table 2 below. Table 2: Average Overall Growth per Colour (expressed in centimetres) Light ColourAverage Height Day 1 Average Height Day 12Total Average Increase (cm) Red9. 63 13. 53. 87 Blue10. 5 12. 41. 9 Orange10 155 Green14. 8 17. 452. 65 Control9. 13 17. 888. 75 The plants grown under the control (or white) light displayed the greatest growth rate, followed in turn by plants grown under the orange, red, blue and green lights. The increase in plant size from the start to the end of the experiment period for each light colour is shown in Graph 1 below.

Graph 1: Average Percentage Increase in Plant Size Per Colour Group DISCUSSION The results of the experiment do not support the hypothesis that plants grown under red light will have a faster growth rate than plants grown under other colours in the visible light spectrum. According to the data and analysis, plants grown in the control group (white light) recorded the greatest increase in growth, followed by plants under orange light. Although orange light is close to red light in the colour spectrum, the plants grown in the control group under white light significantly outperformed all others.

Various factors may have influenced the accuracy of the results obtained. The rate of photosynthesis is dependent on the supply of light, carbon dioxide water, temperature and other variables like the amount of chlorophyll in individual plants. At any time, the rate can be limited by a short supply of any of these elements. The average height of plants in each group at the beginning of the experiment also varied. Variation in the amount of growth in individual plants within each colour group may indicate that plants photosynthesise (and therefore grow) at different rates depending on their stage of development.

Another factor which may have influenced growth rate is whether the delicate roots were damaged when the plants were being placed in the potting mix. Another consideration is the effectiveness of coloured cellophane to produce the light colour required to test the hypothesis. A more effective method would be to use actual coloured light filters. It would be worthwhile repeating the experiment with greater emphasis on ensuring that controlled variables are as uniform as possible. Excluding all incidental light so that the plants only received light from the chosen colour source would also improve the accuracy of the results.

CONCLUSION Plants require light for photosynthesis. Research indicates that plants photosynthesise at a higher rate when grown under more intense wavelengths, that is, under red light (measured at 650-700nm). The results of this experiment did not support the hypothesis that the growth rate of the bean seedlings would be higher when the seedlings were exposed to red light. The experiment could be repeated with more accuracy with controlled variables, using light filters rather than cellophane and by excluding all incidental light from the experimental plants to obtain more accurate data.

References 1. http:www. ehow. com/about_4598110_why-do-plants-need-sunlight. html (10. 8. 09). 2. Biology, A Contextual Approach, pp192-194. 3. http:www. bio. net/bionet/mm/photosyn/1998-May/001477. html (09. 8. 09) 4. http://photoscience. la. asu. edu/photosyn/education/learn. html (10. 8. 09) 5. http://ww. rsc. org/education/teachers/learnnet/cfb/photosynthesis. htm (11. 8. 09) Bibliography http://www. bio. net/bionet/mm/photosyn/1998-May/001477. html, Chan, G, How does colour of light affect photosynthesis? , 25 May 1998. Accessed 10. . 09 http://www. colorado. edu/eeb/courses/1230jbasey/abstracts%202008/36. htm, Light Wavelength. Accessed 10. 8. 09 http://www. dnr. sc. gov/ael/personals/pjpb/lecture/lecture. html, Accessed 11. 8. 09. http://www. ehow. com/about_4598110_why-do-plants-need-sunlight. html. Reed, A. Why do Plants need Sunlight? Accessed 11. 8. 09 http://www. madsci. org/posts/archives/2000-04/954889693. Bt. r. html, Accessed 10. 8. 09. http://media-2. web. britannica. com/eb-media/30/27030-004-293E0372. jpg, Visible Light Spectrum. Accessed 10. 8. 09 ttp://photoscience. la. asu. edu/photosyn/education/learn. html, Effect of Certain Wavelengths of Light on Growth of Plants. Accessed 11. 8. 09 http://www. rsc. org/education/teachers/learnnet/cfb/photosynthesis. htm, Importance of Wavelength of light on rate of Photosynthesis. Accessed 9. 8. 09 Spenceley, M et al. Biology A Contextual Approach. 2004. Heinemann, Harcourt Education, Port Melbourne. http://www. usc. edu/CSSF/History/2004/Projects/J1616. pdf http://wiki. answers. com/Q/Do_plants_grow_faster_under_certain_colors_of_light

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Examination How Different Coloured Rays of Light Affect Photosynthesis. (2018, Jan 29). Retrieved from https://graduateway.com/examination-how-different-coloured-rays-of-light-affect-photosynthesis/

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