Aim:
To observe the effect of light intensity (lux) on the rate at which a plant photosynthesises.
Hypothesis:
If the amount of light upon a plant is increased, then the plant will photosynthesise at a greater rate.
Introduction:
I chose to conduct this experiment to determine the most effective lighting for growing plants, which I hope to incorporate this information into growing vegetables in the most effective way at home. When searching for how to measure the photosynthesis rates of a plant, the bubble counting method was one which frequently appeared and was highly recommended, leading me to choose this as the method of measurement for the experiment. Pennywort was chosen as the aquatic plant as it can be found in shallow water, so light is a major element of how well it photosynthesises. The temperature of the plant was going to vary with the different lux outputs, however the idea of either a bath of water for the plant or a water “barrier” to prevent this was recommended. The water “barrier” was easier and more accessible so I chose to regulate and control the temperature of the plant and it’s surrounding environment using this option.
Risk Assessment:
Hazard Risk Mitigation
Lamp Hot lamp burning someone Take care when handling the lamp and avoid as much as possible.
Water Spilled water causing someone to slip or fall Be cautionary around the water and clean up any spills immediately with a dry cloth.
Experimental Design and Procedure:
In this experiment, the variables taken into consideration are
Independent: Light on plant
Dependent: Bubbles produced
Controlled:
– Temperature of water and plant
– Type of plant
– Time taken for experiment
– Size of plant
– Light source
Materials:
– GroLux Lamp [for lux output]
– Pennywort [for photosynthesis]
– 250mL container [to hold the plant in so that the conditions for each experiment are the same]
– Paper clip [to use as weight for plant]
– Lux meter [to measure the lux output of the lamp]
– Thermometer [measure the temperature of the water around the plant to ensure a valid test]
– 1000mL container [holding water to act as a temperature barrier/control]
– Timer [measurement of time the experiment takes]
– Mineral water [surrounding the plant for a constant environment]
Set up:
1) Fill the 250mL beaker with mineral water and place it near the lamp.
2) Fill the 1000mL beaker with water (can be tap water) and place it between the lamp and the 250mL beaker to act as a heat filter.
Procedure:
1) One 5cm stem of the Pennywort was cut off and submerged in the 250mL beaker with the cut part of the plant facing upwards. A paperclip was used to ensure that the plant remained submerged throughout the entire experiment.
2) The thermometer was used to check that the temperature was constant.
3) A few minutes passed for the initial surge of bubbles to stop before the measurement began, as the carbon dioxide and water will bubble at the beginning of this experiment.
4) The lux output of the lamp in its positions as measured and recorded.
5) A five minute timer began and the quantity of bubbles that were created by the plant was counted and recorded.
6) This experiment was repeated multiple times, with the lux output (distance from the plant) of the lamp changing in order that a trend might become apparent. The controlled experiment was conducted (and repeated) with an absence of light, as to give a set of results that the remaining data could be compared to.
Results:
Data to be collected:
– Amount of bubbles generated within the time frame of 5 minutes
Table:
Lux Output
(lx) Bubbles Formed (O2/min)
Test 1 Test 2 Test 3 Average
0 0 0 0 0
2000 25.0 23.0 22.0 23.3
4000 27.0 28.0 24.0 26.3
6000 29.0 26.0 27.0 27.3
8000 25.0 31.0 30.0 28.7
10000 32.0 30.0 32.0 31.3
12000 31.0 35.0 33.0 33.0
14000 36.0 34.0 37.0 35.7
16000 39.0 37.0 38.0 38.0
18000 42.0 43.0 45.0 43.0
20000 46.0 49.0 48.0 47.7
22000 50.0 52.0 48.0 50.0
24000 53.0 54.0 51.0 52.7
Graph:
Discussion:
The increase in average amount of bubbles, from 0 bubbles with a lux output of 0, to 52.7 bubbles with a lux output of 24000 lx, is an indicator that increase of lux output was proportional to the amount of bubbles formed within the five minute time limit.
This is due to the fact that in the photosynthesis process carbon dioxide and water are processed by the plant to create glucose and oxygen, influenced by the amount of light that reaches the plant. Therefore, the rate of photosynthesis should, and did, increase along with the bubbles of oxygen that were formed.
The accuracy, validity, and reliability of the experiment were of a high standard, and couldn’t be improved by much. The only options that could be considered in improving the experiment could be more variety in lux outputs for a greater reliability.
Accuracy:
Accuracy was maintained through the experiment by using a high quality lux meter for measuring the lux output of the GroLux lamp, which is designed to assist in the growth of plants. A timer was used in the experiment, rather than relying on a human to count the length of time that the experiment was conducted for. The quantities of water were measured using a measuring cylinder to allow for a high level of accuracy in this experiment.
Reliability:
The reliability will be ensured through the repetition of this experiment. Each amount of lux output will be tested on the plant 3 times, in the same controlled conditions. A wide range of lux outputs were examined in this experiment in order that the reliability of the experiment was as accurate as possible. In this experiment, the reliability was quite high, and could only be improved by more repetitions of the experiment in order to further prove the trend shown.
Validity:
The inclusion of the 1000mL container filled with water acting as a temperature “filter/barrier” maintains a constant environment for the plant, allowing the experiment to be highly valid. As the equipment used in this experiment was created by a major company, the quality of the product is guaranteed, leading to a more valid test than if the equipment was created in a domestic situation. By using an aquatic plant and a lamp designed for plant growth, the experiment retains validity due to the equipment being specialised for this use.
Conclusion:
As predicted in the hypothesis, the increase of lux output causes an increase in bubbles formed within five minutes by the Pennywort (aquatic plant).
Photographs:
Bibliography :
Saps.org.uk. (2018). Measuring the rate of photosynthesis. [online] Available at: http://www.saps.org.uk/secondary/teaching-resources/157-measuring-the-rate-of-photosynthesis [Accessed 22 Jun. 2018].
BiologyWise. (2018). Photosynthesis in Aquatic Plants. [online] Available at: https://biologywise.com/photosynthesis-in-aquatic-plants [Accessed 23 Jun. 2018].
Slawson (2018). Risk assessment template media. [online] Slideshare.net. Available at: https://www.slideshare.net/mobile/KhemSlawson/risk-assessment-template-media-10512123 [Accessed 28 Sep. 2018].