Leaf Disc Experiment to research Rate of Photosynthesis

In this experiment, the result of light intensity on rate of photosynthesis was investigated by recording the time taken for the leaf discs to float at the surface of sodium hydrogen carbonate solution in the beaker. This technique is more accurate than to immerse a plant and then count the number of bubbles produced each and every minute. It is because it is simpler to observe the leaf discs that happen to be bigger than the bubbles and there is also no need to count the number of bubbles produced at the same time which most probably lose the concentrate to record an accurate time.

Sodium hydrogen bicarbonate was used in this experiment to provide carbon dioxide to the pineapple leaf discs to perform photosynthesis. This does not have a high attentiveness of skin tightening and dissolved in it however the amount is enough for the aquatic plants to endure. Hence, by using sodium hydrogen bicarbonate will increase the concentration of skin tightening and available for plant life to produce sugar and air thus, increasing the rate of photosynthesis. That is important so that the time taken for the leaf discs to float on the surface will never be too long also to get a clearer consequence as well.

The leaf discs sink when put into the bicarbonate solution. This is because the bicarbonate solution infiltrates the environment areas of the leaf discs triggering the overall denseness to increase. That is why the leaf discs sink. Alternatively, when the leaf discs were remaining in the beaker under the light fixture, we had detected that the leaf discs little by little rise up to surface. The real reason for this is, when photosynthesis occur, air will be released in to the interior of the leaf leading to the buoyancy to change. Hence, the leaf discs rise to the top. However, at a times, the leaf discs kitchen sink again. This happened as respiration process that occurs at the same time, consumed oxygen, thus it removed the oxygen from mid-air spaces thereby, triggering the bicarbonate treatment for complete the spaces again. This therefore, ends up with the sinking of the leaf discs again. Since both processes took place at the same time, we can say that the result obtained is the net rate of photosynthesis.

Now, to analyse further, when the experiment used white light, the graph produced has a lesser rate of photosynthesis in comparison to that of the other colors such as red and blue light. It is because chlorophyll will only absorb light with a certain wavelength. Since, white light has various colors which range from violet to red, thus, not absolutely all light will be absorb, thus, the source of light will never be fully utilised to execute the photosynthesis process. However, if red light can be used, the graph will have an increased rate of photosynthesis as red light has the highest percentage absorbance by the chlorophyll substances. Alternatively, if the green light is used, a graph with lower rate of photosynthesis will be produced as green light gets the lowest percentage absorbance by the chlorophyll substances. This green light in the white light is the light that's not utilized by the chlorophyll making the rate of photosynthesis of the leaf discs is leaner than other leaf discs under other colors of light.

After all the results were obtained, graphs were plotted by using all the data. From graph 8. 21, we can easily see that as the distance of the light of light fixture to the bottom of the beaker raises, the speed of photosynthesis lowers. This is because of the higher light strength when the distance of the light bulb to the bottom of the beaker is shorter. We can see it obviously at the desk 8. 24. This happened because higher light depth provides higher photon energy to excite electrons of the chlorophyll. Therefore, when this happens, there will be higher amount of energy in the form of ATP to make a higher amount of sugar and air. Thus, we can conclude that the rate of photosynthesis is higher at the bigger light power. These described well on the action of graph 8. 22 which we can say that the graph shows rate of photosynthesis is straight perpendicular to the light strength.

The graph 8. 22 was plotted to show the relationship of light strength on the rate of photosynthesis. This graph is used to aid the graph 8. 21 produced earlier so that the effect obtained can be state to have a high certainty which is proven to be right. Plus, from the graph 8. 22, we can see that the bigger the light intensity, the higher the pace of photosynthesis which is compliment to the idea. This means that both graphs support the theory of light strength as you the factors that impacting the speed of photosynthesis whereby any reduction in distance or increase in light intensity, may cause to an increase on the pace of photosynthesis.


Hence, predicated on the debate above, we can conclude that in any increase of the distance of the light bulb to the base of the beaker may cause in the decrease of light depth. Then, with the increase of light power will cause in the reduction in the time used for the leaf discs to float on the top of solution which represents the increase of the speed of photosynthesis. Hence, hypothesis is accepted.

Limitations and Recommendations


The leaf discs possessed problems in sinking. It is because liquid of soap was not added into the bicarbonate solution.

Add few drops of liquid of cleaning soap in to the bicarbonate solution so the soap will wets the hydrophobic surface of the leaf discs thus allowing the answer to infiltrate to air spaces easier.

The stopwatch did not started immediately after the beaker was put under the light. Thus, enough time taken noted is shorter than it should be.

Start the stopwatch simultaneously with the placement of the beaker under the light fixture. It is advisable to utilize a teammates whereby one settle the beaker placement and a different one start the stopwatch.

The size of the leaf discs is not constant. That is due to the challenges to punch out the leaf discs by by using a blunt cork borer.


Use a sharper cork borer to punch out more consistence size of leaf discs. This will help to produce a higher quality results.

Parallex error took place while calculating 20ml of sodium bicarbonate. This causes the concentration of skin tightening and for every distance aren't constant. Thus influencing the results reliability.

Make sure the eye are positioned immediately perpendicular to the size of measuring cylinder. This will help to reduce parallex problem of the quantity readings.

Table 8. 25 Constraints While Carrying out the Test and Recommendations to boost the Results Obtain in the Future

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