The Light Intensity On The Essay Example
The Light Intensity On The Essay Example

The Light Intensity On The Essay Example

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Abstract Duckweed is a small aquatic plant that is able to grow rapidly, making it the ideal specimen for our experiment.

It is hypothesized that altering the amount of light received by duckweed will alter its photosynthetic rate. It is predicted that lower light intensity will lower the rate of growth in duckweed. Two treatment groups were covered with a screen in order to reduce light intensity. Both groups were kept under a controlled light source for fourteen days and plant counts were taken at regular intervals. The ravg for the experimental group was 0.1613 and the range for the control group was 0. 047. The results indicated that our predictions were correct; duckweed that received less light exhibited a lower rate of growth. For those interested in harvesting duckweed, future studies can focus on determining the amount of light needed for optimal gr


owth. Introduction Plants are able to convert light energy into chemical energy through the process of photosynthesis (Campbell & Reese, 2005).

This process is dependent on both abiotic and biotic factors. Since plants are autotrophs, the most vital are abiotic factors such as light, temperature, wind, water, and atmospheric gases (Campbell & Reese, 2005). The plant of interest in this study is Lemna minor. Duckweed is a small aquatic watering plant that inhabits freshwater environments and exists in clusters of 3-4 leaves that are approximately 2-4 mm in size (Galt et al, 2005). Duckweed was chosen for this experiment because it can be manipulated easily within a laboratory setting.

This experiment was designed to test the hypothesis that altering the amount of light received by the Duckweed will alter its photosynthetic rate. Plants that receive

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more light are predicted to exhibit a higher rate of per capita growth because light is a necessity to carry out the process of photosynthesis. Plants that receive more light are also predicted to reach their carrying capacity sooner because of their increased rate of growth. The carrying capacity is defined as the maximum number of individuals that can sustain life given the limited resources of the environment (Campbell & Reese, 2005). Materials and Methods In this experiment, four plastic cups were used.

These plastic cups represented two control groups and two treatment groups. These four cups were filled with 200 ml of a culture growth medium consisting of a 0. 75 gram•liter-1 concentration of Stern’s Miracle-Gro 15-30-15 Plant Nutrients in distilled water. Added to each of the cups were approximately 20 duckweed individuals as the initial population. The fill line was also marked in order to accurately refill the cups with the culture medium as plant uptake and evaporation occurred. The two treatment groups were covered by screens with approximately 1 mm-sized hole.

The screens served as a filter that would lower the light received by the treatment groups without interfering with gas exchange. Two groups were not covered by screens in order to serve as controls. These four cups were then placed under Chroma-50 full-spectrum fluorescent lamps and kept at a constant light intensity of 54. 16 micromole of photons/square meter/second measured with the Li-Cor ML250 Quantum Light Meter. The photoperiod was 12 hours for each day. The cups were kept under the light for fourteen days, with data recorded on days 0, 5,7,11, and 13.

Data recorded on these days included the population count, root

length, cluster size, and leaf size. Once the data was recorded, it was analyzed for the per capita growth rate using the equation: r = (1/t) ln (Nt/N0)In this equation, r is the intrinsic rate of growth. Nt represents the number of plants counted at time t, N0 represents the initial number of individuals within the population, and t represents the time (in days, for our experiment). Results The data obtained from the experiment included the population count for both the treatment and control groups over a period of fourteen days.

The ravg for experimental groups 1 and 2 was 0. 1613 and 0. 1798. The ravg for control groups 1 and 2 was 0. 2047 and 0.

1959. The average population on day 13 for the treatment group was 172. 5 individuals and 307 individuals for the control group.Our results show that the group which received less light had a lower population count and exhibited a lower overall per capita growth rate.

The average population count for duckweed in the treatment groups was lower than that in the control groups for each day data was recorded (Table 1). By day fourteen, the average population size of the control group reached 307 individuals, nearly twice that of the treatment group (Table 1). Table I: Population count for duckweed in the presence/absence of a screen over a period of fourteen days DayAverage population count of Duckweed n the absence of a screenAverage population count of Duckweed in the presence of a screen 020. 519. 5 55345 78565 11185. 5138 13307172.

5 Using the experimental data, we calculated the per capita population growth rate of Lemna minor using the equation r

= 1/t•ln(Nt/N0). The results showed that duckweed grown in the presence of a screen exhibited a lower per capita growth rate than duckweed grown in the absence of a screen (Table 2). Table II: Calculated per-capita population growth rate (r) values for each group over a fourteen day period. All values measured in day-1 Day Duckweed grown in the absence of screen (1) Duckweed grown in the bsence of screen (2)Duckweed grown in the presence of a screen (1)Duckweed grown in the presence of a screen (2) 00000 50. 19490.

18520. 15380. 1792 70. 21490. 19110. 15180.

1888 110. 20370. 19680. 17550. 1801 130.

20540. 21070. 16390. 1711 ravg0.

20470. 19590. 16130. 1798 Figure 1 is a representation of the data recorded in Table 1, plotting the average population size versus time (in days).

The results in Figure 1 illustrate that the population size of duckweed exposed to light with a screen was much smaller than that of duckweed exposed to light without a screen throughout the fourteen day period.Figure 1: Average population of duckweed when exposed to light in the presence/absence of a screen over a 14 day period The duckweed was also observed qualitatively for overall health. Those in the control group had larger clusters and longer roots than those in the treatment group. Also, the leaf color of the treatment group was a yellow/green while the leaf color of the control group was bright green. Discussion The purpose of this experiment was to test our hypothesis, which stated that varying levels of light would alter the photosynthetic rate of duckweed.We predicted that lowering light intensity would decrease the rate of growth in duckweed.

Based on the results of

this experiment, this hypothesis was proven correct. The results show that the average population size and the growth rate of duckweed in the treatment groups were lower than that of the control groups. The second prediction stated that duckweed exposed to more light will reach carrying capacity sooner. Conclusions were not reached on the second prediction because the experiment ended before carrying capacity was reached.The data collected, however, does suggest that the carrying capacity will be reached sooner by the groups that receive more light. These results were achieved because light is a crucial abiotic factor in the growth of plants.

When the amount of light a plant receives is altered, the rate of growth is also altered due to the change in photosynthetic rate. It is evident through the small discrepancies in data within the treatment and control groups that experimental errors. One experimental error is the negligence on our part of refilling the treatment and control cups with the growth medium throughout the course of the experiment.As the water level went down, the growth medium should have been added to the fill line for all four cups in order to maintain this variable. Since light is a crucial factor to the growth of duckweed and other plants, future studies should be directed at finding the optimal amount of light for plant growth. This could have resounding benefits, allowing researchers and green-thumbs alike to grow plants more quickly and effectively.

Literature Cited 1) Brun, F. G. , Olive, I. , Perez-Llorens, J.

L. , and J. J. Vergara.

2007. Effects of Light and BiomassPartitioning on Growth, Photosynthesis and Carbohydrate Content of the Seagrass Zostera noltii Hornem. Journal of

Experimental Marine Biology and Ecology. Vol.

345(2): 90-100. 2) Campbell, N. A. , & Reese, J. B.

2005. “Population Ecology”. Biology. 7th Edition.

San Francisco, Pearson Education Inc. , 1143-1147 pp. 3) Galt, C. , D. Huckaby, T.

Stanton, P. Baker. 2005. “Ecology”. Laboratory Manual for Biological Sciences II.

6th Edition. CSULB Bookstore, Long Beach, 105-110 pp. 4) Nedbal, L. and U.

Rascher. 2006. Dynamics of Photosynthesis in Fluctuating Light. Current Opinion in Plant Biology.

Vol. 9(6): 671-678.

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