Impact of Light on the Growth Rate of Lentils

Impact of Light on the Growth Rate of Lentils

 Abstract

Light is required for the plant to grow. It supports the growth from germination to photosynthesis and flowering of the plant.  The different concepts light, namely the light intensity, direction, quality, and amount, can be managed to optimize the rate of growth of the plant. Photosynthesis is the process by which the plant makes food and occurs when sunlight breakdown the carbon (IV) oxide absorbed the plant into sugars and releases oxygen as the by-product.  In this study, lentils were placed in two separate transparent glass jars; one was placed in a well-lit room while the other was placed under the shade outside.  Their growth was closely monitored, the width between the splits of the seeds measured, and the color of lentils in each jar noted.  The seedling grew inside germinated faster than the seedling placed outside because it received blue-red light that promoted germination. In contrast, that outside received the far-red light that slowed down the germination. Further, the sprout of the seedling placed grew continued to grow by the 5^th day while the shoot of lentil inside stopped. The lentil outside accessed sunlight and, through photosynthesis, produced food that promoted its growth while the lentil inside had no access to sunlight and, thus, could not produce food stunting its growth 

INTRODUCTION

Plant growth occurs through cell growth and cell differentiation. During the growth, the cell enlarges. Cell differentiation occurs when new cell types arise from precursor cells and become independent cells increasing the number of cells. The cell growth occurs in the meristems contributing to germination. Germination is the process through which a seedling develops a shoot and a root.  The process depends on oxygen, the right temperature, and water to occur. A study that was done by Elnaggar et al. revealed that germination for plants placed outside in the light was higher at a higher temperature than at lower while in the germination of plants placed in the dark, the reverse was true (2018).  From the study, it is clear that light is not a condition that has to exist for the germination of seeds to occur. However, its existence may influence the rate of germination of the plant by increasing or decreasing it. Taylor et al. did a study in which they exposed germinating seeds to different light (2004). The research indicated that the germination rate was increased by red and white light and slower in the far-red light. The study also showed that darkness decreased the rate of germination.  Taylor et al. indicated that the quality and intensity of the light for the plants grown in darkness reduced the rate of germination of the plant (2004).  The study showed that plants grown in the shade use the far-red wavelength of light for germinating.

According to Purbey, Singh, and Pongener, light is the essential optimization of plant growth (2019). Every concept that plant growth entails responds to light from germination, flowering, and ripening of fruits. Within the light environment, light provides plants with the energy needed for the growth of the plant and also gives it information. Light passes information to the plant through three concepts; the quantity, quality, direction, and periodicity. The amount of light represents its intensity and radiant energy reaching the plant. Different habitats have different intensities of light, which affects plant growth differently. Purbey et al. declared that the quantity of light reaching the plant might be improved by aspects such as pruning, employing training systems, and arranging the tree in a specific way (2019).  Shading or screening are means used by the farmers to control the light quantity, mainly when temperatures are extremely high.Further, the quality of the light shows its color and wavelength, whereas direction provides light with a spatial concept (Purbey et al., 2019). In the research to analyze the effect of light quality on the growth of the plant, Song et al. show that the most significant growth of the etiolated plant exists in the red spectrum (2017). The research also claimed that phototropism is the maximum at the red wavelength. Etiolated plants are those that grow in the shade resulting in smaller leaves, weak stems, and longer internodes. Additionally, the periodicity of light shows how much light varies in a particular habitat.  The concepts mentioned above affect the growth of branches, sizes of leaves, and their orientation as well as the length of the internodes. Further, with the help of the photosystems, plants absorb a specific wavelength of light and transform the light into biochemical energy (Song et al., 2017). The plants respond by psychological processes, such as the growth of the plant.  The importance of light to the plant is evident during photomorphogenesis. Photomorphogenesis is a process whereby changes occur in the development of the plant as a result of alteration in the light environment.

Photosynthesis is the process by which the plant produces food. During photosynthesis, the plant fixes carbon (IV) oxide, which depends on the light quantity reaching the canopy of the plant. The study by Purbey et al., also shows that the light intensity also affects the carbon exchange rate (2019). The less the amount of light reaching the leaf of the plant, the lower the carbon exchange rate.  During photosynthesis, light is converted into chemical energy.  The part of the plant that receives the light is the chlorophyll and carotenoids.  A study by Guasch and Sabater on different biofilms; one calcerous stream from a plant placed outside and the other silicious stream from a shaded plant indicated that there was a low photosynthesis efficiency and higher light saturation and chlorophyll/carotenoids ration in the first film (1995). The study stated further that the plant in the shade adapted by having higher photosynthesis efficiency while the light intensity was lower as well as the chlorophyll/carotenoids ratio. It is therefore clear that photosynthesis is a necessary process and, plants have to adapt effectively to maximize it, which in turn maximizes the growth rate of the plant.  During the photosynthesis process, light breaks down carbon (IV) oxide into sugars and releases oxygen as the by-product of the process (Guasch and Sabater, (1995). The photosynthetic process occurs in the mesophyll of the leaf, particularly in the chloroplasts. Inside the chloroplasts is chlorophyll, which absorbs the specific wavelengths of sunlight.  The first part of photosynthesis depends on light and, as mentioned above, involves absorption of sunlight and storing it in the form of chemical energy within the granum. The second part does not depend on light and involves the electrons from the first step providing energy that enables formations of sugars from carbon (IV) oxide.   According to Amoozgar, Mohammadi and Sabzalian, LEDs lights can be used to improve the photosynthetic rate (2017). In the study, Amoozgar et al. treated the plants with different amounts of LED lights and, compared with those grown under the greenhouse and discovered that the later plants grew faster than the former (2017).  Plants adapt differently under different lights. Those plants that grow in the shade will tend to produce chlorophyll b, while those that grow in the sun tend to produce chlorophyll a. The two distinct types of chlorophyll absorb light at different wavelengths and use them for photosynthesis.

Research Question

What is the effect of light on the germination rate of the seed?

What is the effect of light on the growth rate of the seedling?

Hypothesis

1. Light increases the rate of germination.
2. The presence of sunlight increases the rate of growth of the seedling.

METHOD

Materials

• Two identical transparent glass jars
• 2 cups full of water
• Two cheesecloth covers
• Two lentils seeds

Light Conditions

The first jar was placed inside a well-lit room but away from the sun while the second jar was placed outside under a shade. Further, the temperature environment over the five days was approximately 82-85 degrees Fahrenheit.

Procedure

The study used orange lentils. The lentils were placed in similar jars and filled with approximately one cup of water. A cheesecloth cover was then added at the top.  The study first left the seeds to soak for 12 hours. Afterward, the water was drained, and the seeds were rinsed.  The study was done at room temperature throughout 5days. Each day, the study involved cleaning and flowing water from the seeds. The research ensured that rinsing and soaking were done at the same time each day. The study carefully examined the germination of the seed, from the cracking of the seeds to the sprouting of the shoot. The research examined then and measured the width of the split of the seeds in the two jars.  The study also observed the color of the seeds and recorded any of the color changes.  The research also examined and measured the lengths of the sprouts. The lengths were recorded.

RESULTS

One the first day of the study, the study noted that the lentils had started to split in both the jars. Further, the study observed that the color of the lentils was similar in both the jars.  The water in the jars had become cloudy, but it was drained.  The only distinction that the study noted was that there was a slight difference in the temperature of the water in the jars with the jar outside being slightly warmer. On day 2 of the study¸, it was noted that lentils were no longer bright yellow. It was observed that both the lentils had split. The lentils on the inside had divided by 3cm while the lentils on the outside had split by 2cm. It was therefore clear that the lentils on the inside had split more than the lentil on the outside. On the third day of the study, it was seen that the length between the split was still 3cm for the lentils inside and 2cm for the lentil outside. The study noticed that the shade of orange of both the lentils was similar as they were the previous day. It was observed that the lentils had begun to sprout. The length of the sprouts on the inside was approximately 0.5 inches, while the length of the shoot on the outside was at least 0.25 inches.  The study observed that the color of the lentils was maintained as well as the width of the splits.  On the fifth day of the study, it was seen that the sprout inside did not grow anymore while the shoots outside continued to grow and reached the same height as that inside (0.5 inches).  The sprouts were the same height by the end of the fifth day.

Figure One: The Growth of the lentils in the two days throughout 5days.

DISCUSSION

The germination rate of the lentils growing inside was faster than that outside because of the quality of light that they received.  The quality of light affects the rate of germination of seeds. The lentil growing outside under the shade used far-red light, which does not stimulate germination; thus, it was slower.  The lentil growing inside in the well-lit room accessed the blue-red light; thus, the rate of germination was faster.  The lentils in the jars are sensitive to light; therefore, accessing the blue-red light promoted the growth of those inside the well-lit room.  The seeds all germinated at room temperature, proving that germination is slower under lower Red: Far-red ratio.  During the first few days of germination, the seed did not need the sun but depended on the water, oxygen, and ample temperature available within the jar. Since all these factors were constant, the quality of the light reaching the seeds determines their germination rate.  Further, as the germination of the lentil inside the room reached day 4 and 5, it stagnated because sprouting required sunlight for photosynthesis, which was unavailable in the house.  Through photosynthesis, plants, make food, and develop.  Sunlight is not only essential for photosynthesis to take but also increases its speed.  The lentil outside under the shade continued to grow in day four and day five because it adapted to the low light reaching it and produced chlorophyll b. The chlorophyll b absorbed the limited sunlight and produced food through photosynthesis. As noted early, photosynthesis is effective when there is low sunlight.  As a result, the lentil outside continued to grow.  The study proved the first hypothesis wrong because light does not increase the rate of germination. Instead, the quality of the light influences germination with red-blue stimulating growth while the far-red light slows germination. The study proved the second hypothesis right because the presence of sunlight indeed promoted the growth of the lentils placed outside.

CONCLUSION

In summary, plant growth occurs through cell differentiation and growth, which in turn results in the germination of the plant.  Light may not be a condition necessary for germination to take place, but its quality influences the rate of germination.  Additionally, the blue and red light increase the rate of germination while the far-red light slows down the rate of germination.  Light has four concepts that may affect the rate photosynthesis, which are the intensity, the amount, the variation, and the direction of the light. In the experiment, the germination of the lentil inside was faster than outside due to the quality of light that they received. The growth of the lentil outside continued while that of the lentil inside stopped because sunlight is a necessary condition for photosynthesis. Since the lentil inside did not access sunlight, it could no longer make its food through photosynthesis; thus, its growth became stunted.

References

Amoozgar, A., Mohammadi, A., & Sabzalian, M. (2017). Impact of light-emitting diode irradiation on photosynthesis, phytochemical composition, and mineral element content of lettuce cv. Grizzly. Photosynthetica, 55(1), 85–95. https://doi-org.sbcc.idm.oclc.org/10.1007/s11099-016-0216-8

Elnaggar, A., El-Keblawy, A., Mosa, K. A., & Soliman, S. (2018). Drought tolerance during germination depends on light and temperature of incubation in Salsola imbricata, a desert shrub of Arabian deserts. Flora, 249, 156–163. https://doi-org.sbcc.idm.oclc.org/10.1016/j.flora.2018.11.001

Guasch, H., & Sabater, S. (1995). Seasonal Variations in Photosynthesis-Irradiance Responses by Biofilms in Mediterranean Streams. Journal of Phycology, 31(5), 727–735. https://doi-org.sbcc.idm.oclc.org/10.1111/j.0022-3646.1995.00727.x

Purbey, S. K., Singh, S. K., & Pongener, A. (2019). Management of Light for Quality Production of Litchi. International Journal of Bio-Resource & Stress Management, 10(5), 529–538. https://doi-org.sbcc.idm.oclc.org/10.23910/IJBSM/2019.10.5.2034

Song Jinxiu, Meng Qingwu, Du Weifen, & He Dongxian. (2017). Effects of light quality on growth and development of cucumber seedlings in controlled environment. International Journal of Agricultural & Biological Engineering, 10(3), 312–318. https://doi-org.sbcc.idm.oclc.org/10.3965/j.ijabe.20171003.2299

Taylor, I. N., Peters, N. C. B., Adkins, S. W., & Walker, S. R. (2004). Germination response of Phalaris paradoxa L. seed to different light qualities. Weed Research, 44(4), 254–264. https://doi-org.sbcc.idm.oclc.org/10.1111/j.1365-3180.2004.00397.x