It is not uncommon for scientists to encounter a problem that cannot be explained.

It is not uncommon for scientists to encounter a problem that cannot be explained. As a result, scientists use another fundamental process that is referred to as the scientific method. During photosynthesis, carbon dioxide and water yield glucose and oxygen. The products of cellular respiration are carbon dioxide and water, which is made from one molecule of glucose and oxygen. (Cousins, Johnson, & Leakey, 2014). Because these processes cannot be observed by the naked eye, it is difficult for many individuals to conceptualize them. Experiments like the one conducted in this course allow for the use of common tools to observe changes in cellular respiration indexed as “bubbles and different light source intensity (various watts of light) to observe what happens in nature” (Gnaiger, Steinlechner-Maran, Mendez, & Margreiter, 1995). These complementary systems allow for the existence of animals, which need the oxygen (O2) that is produced by the plants during photosynthesis. It is possible to examine the relationship between photosynthesis and cellular respiration under controlled experimental conditions.

The Experiment

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Objectives

• You will establish a better understanding of photosynthesis and cellular respiration.
• You must apply the scientific method to solve (or understand) a problem.
• You will virtually design and conduct controlled experimentation.
• Collect, analyze, and draw conclusions from your observed experiment.

Laboratory Materials and Methods

You will need your laboratory journal (worksheet provided) to record your steps and observations.

Problem

• How does the concentration of sunlight relate to the rate of photosynthesis in the seaweed?
• What are the different methods of measuring the rate of photosynthesis?

The following methods can be used to calculate the rate of photosynthesis (Science & Plants for Schools, n.d.):

• Measuring the uptake of CO₂
• Measuring the production of O₂
• Measuring the production of carbohydrates
• Measuring the increase in dry mass

Process and Outcomes

You will measure the production of O₂ in your experiment. Oxygen can be measured by counting the bubbles evolved from seaweed to measure the amount of gas evolved over a period of time. For this experiment, you will be counting the number of bubbles originating from the seaweed at one-hour intervals.

You can then investigate the amount of gas produced by four different light intensities (0, 25, 75, and 100 watts). Each of these different light intensities will be measured 3 times.

The following table shows the outcomes of the experiment:

Table 1: Rate of Photosynthesis Measured by the Number of Oxygen Bubbles

1 hr. Intervals