To investigate the effect of the distance from the light source of Hydrilla verticillata on the rate of photosynthesis
Alternative Hypothesis: –There is a significant effect of the distance from the light source of Hydrilla verticillata on the rate of photosynthesis. Null Hypothesis: –There is no significant effect of the distance from the light source of Hydrilla verticillata on the rate of photosynthesis.
(6) 15 cm Hydrilla verticillata (3) 150 mL of water (1) 1000 mL beaker (3) 250 mL beaker Light bulb (present in the laboratory) Ruler Scissors Timer Container with water Match
Independent Variables –Light intensity –Distance from the light source (bulb and sunlight) –Sunlight Dependent Variables –Rate of photosynthesis (Number of bubbles) –Range of flame in the match stick Controlled Variables –Light bulb –Volume of water –Length of Hydrilla verticillata
1.The needed materials were prepared. 2. Six (6) 15 cm Hydrilla verticillata were cut with the use of scissors in the container with water to prevent from drying up. 3.Three beakers were filled by 150mL of water and two Hydrilla verticillata each, respectively.
4. The beakers were then positioned on their respective places: –Control set-up was placed outside of the laboratory for it to be lighted with sunlight.
–Set-up A was placed 10cm away from the light bulb uplifted by a 1000mL beaker. (A ruler was used to measure the distance.)
–Setup B was placed 25cm away from the light source which is the light bulb inside the laboratory. (A ruler was used to measure the distance.)
5. The 6 Hydrilla verticillata were allowed to equilibrate for 3 minutes so that it can give enough time for the plants to adapt to the new environment to have a stable rate of photosynthesis. 6.After the time set for the adaptation of the plants, the setups were then timed simultaneously for 20 minutes. 7.The number of bubbles that appeared were recorded. 8.Lastly, the setups were illuminated with match sticks to differentiate the abundance of oxygen present in each beaker.
The students used the distance from the light source as the focus of the experiment to identify which setup has the greater and lesser rate of photosynthesis whether the one that is nearer, farther or the one that is kept under normal condition. To determine the rate of photosynthesis, they count the number of bubbles that appeared. The presence of bubbles in the water represents the exchange of oxygen (by- product) and carbon dioxide (needed gas in the process). They also lighted a match in the beaker to visually know and compare the presence of oxygen in each beaker.
NUMBER OF MINUTES NUMBER OF BUBBLES Control SetupSetup ASetup B 1 – 5077 5 – 10151 10 – 150523 15 – 200801 TOTAL114412
Based on the tabulated data, it can be clearly observed that the three setups have different number of bubbles in a certain time although Setups A and B have equal number at first but later on, the first one has drastically increased in the number of bubbles in the succeeding minutes. Setup A had the greatest number of bubble formation (144) followed by Setup B (12) and Control Set-up (1), respectively.
Due to the students’ exemplary curiosity level, they lighted a match stick inside the beaker to identify which set-up has the most number of oxygen. They linked this action to the concept they learned in Chemistry, in which Oxygen is an element necessary for combustion. They thought that if the beaker will have the greatest range of flame; oxygen is abundant in it and the Hydrilla verticillata contained in that beaker has the fastest rate of photosynthesis.
With respect to the lighting of the match, Setup A visually had the biggest flame, followed by Setup B and Control setup, respectively. The number of bubbles and the range of flame produced the same rank and order with regards to the rate of photosynthesis: Setup A, Setup B and Control setup, correspondingly.
From the given data, the students learned that it is the light intensity that caused Setup A to have the fastest rate of photosynthesis and slowest rate as for the control setup. As stated by Bareja (2011), the nearer the distance of the plant from the light source, the brighter light it will have which means a stronger light intensity. It is the reason why Setup A had the most number of bubbles since it is the one closest to the light source (10cm away from the bulb).
According to Manaker(1981), an increase in the intensity of light will result to an increase in the rate of photosynthesis and will likewise reduce the number of hours that the plant must receive every day. And so, they can produce more food, release much oxygen and absorb more carbon dioxide. However, weak light intensities tend to reduce plant growth, development and yield because low amount of solar energy restricts the rate of photosynthesis (Vergara 1978).
The students inferred that Hydrilla verticillata under nearer distance from the light source will have stronger light intensity resulting to faster rate of photosynthesis in contrast to those that are far from the light source. Therefore, the alternative hypothesis is accepted and the null one is rejected. Indeed, there is a significant effect of the distance from the light source of Hydrilla verticillata on the rate of photosynthesis.