Good Purpose Case Study Example

Part Two: Conduct an Experiment

The purpose of this lab is to determine the effect of light intensity on photosynthesis. This will be accomplished by measuring the number of oxygen bubbles produced by a piece of algae in one hour under light bulbs with different watt ratings.

Introduction

Photosynthesis and cellular respiration are two mirror-image processes that plants undergo to convert water and carbon dioxide into glucose and oxygen, and vice versa. Research has shown that increased light intensity only increases the rate of photosynthesis up to a certain point; after a maximum intensity is achieved, plants undergo no more increase in photosynthesis (Biggs, Edison, Eastin, Brown, Maranville, & Clegg, 1971). This means that the relationship of photosynthesis and respiration is continuous but nonlinear.

Hypothesis

The rate of oxygen bubble production will increase non-linearly with the increasing wattage of the light source.
Methods
The procedure used involved placing a piece of algae in water and placing a light bulb over the algae. The wattage of the bulb was increased from 0 watts to 25 watts, 50 watts, and 100 watts. The number of oxygen bubbles produced by the algae in one hour was measured for each bulb. The experiment was conducted three times for each bulb, and then the number of bubbles produced was averaged over the three trials.

Results

Discussion and Analysis
Figure One: the average number of bubbles produced per hour for bulbs of watt ratings 0W, 25W, 50W, and 100W.
The prediction made in the hypothesis bore out in the results of this experiment. The rate of increase in production of bubbles increased between 25W and 50W, but decreased between 50W and 100W. The measurements confirm the hypothesis.

Answers to discussion questions:

What effect does the intensity of light have on the rate of photosynthesis?
The rate of photosynthesis increases with the increasing watt rating of the light bulb up until around 50 watts, beyond which, the amount of photosynthesis nearly reaches equilibrium.

Is it possible to examine the relationship between photosynthesis and respiration under controlled experimental conditions?

Yes, one may examine this relationship using the scientific method. Using the scientific method, you can measure the uptake of carbon dioxide (photosynthesis) and compare it to the production of oxygen (respiration) and see how the rate of these processes compare.

Works Cited

Biggs, W. W., Edison, A. R., Eastin, J. D., Brown, K. W., Maranville, J. W., & Clegg, M. D. (1971). Photosynthesis light sensor and meter. Ecology, 52(1), 125–131.