Biology Lab Report. Does light intensity affect the rate of photosynthesis?

  turn from deep red to purple

Constant                    : the apparatus settings, the volume of sodium bicarbonate

  Solution (5 cc), the length of pond weed (5 cm)

Apparatus:

7 boiling tubes, 7 rubber stopper, 1 black paper, capillary tube, lamp

Materials:

Pond weed, fresh sodium bicarbonate indicator

Method:

1. CO2 was blown into some fresh bicarbonate indicator until it turns to red, which used for experiment.
2. The test tubes are set up like in the diagram 1 and placed at varying distances from the light source. For the control experiment, put in a dark place with no light.
3. The time taken for bicarbonate indicator in each test tube to turn from deep red to purple is taken and recorded.  

Data Collection

Data Processing

Rate of photosynthesis can be calculated using formula as below:

Number of bubbles released

20 minutes

Using the information from the table above, we can plot a graph of rate of photosynthesis against light. (see attachment)

Conclusion

The rate of photosynthesis is directly proportional to light intensity

Evaluation:

From doing this experiment, some flaws that have altered the experiments result has been detected.

1. The length of the pondweed is insufficient. Therefore, the amount of oxygen released is not sufficient.
2. The time allocated for the experiment to be done is not sufficient. The amount of oxygen released is not sufficient to change the colour of the sodium bicarbonate indicator.
3. The volume of the indicator used is too high making the change of colour difficult because there are more mole per cc that is needed to be reacted
4. There is other source of light at the place of the experiment making the variable is questionable.

To improve this experiment, some action must be done to make the experiment a lot more accurate the next time it is done:

1. The length of the pondweed must be increased but it must have almost the same amount of leaf to ensure that it is one of the fixed variables. The amount of oxygen released will alternately increased therefore the experiments results will be much faster and the data can be taken in time
2. The time for doing the experiment should be increased so that there is enough time for the weed to released enough oxygen that will turn the indicator from deep red to purple.
3. The volume of the indicator should be decreased so that the colour changes of the indicator will be faster. The concentration of the indicator should also be reduced so that the colour changes would be faster due to the fact that the mole of the indicator is lesser than usual
4. The experiment should be done in a very dark place where there are no source of light because the present of other light source will alter the experiment’s results