biology lab

Photosynthesis and Cellular Respiration

Photosynthesis and respiration are reactions that complement each other in the environment. In reality, they are the same reactions, but they occur in reverse. During photosynthesis, carbon dioxide and water yield glucose and oxygen. Through the respiration process, glucose and oxygen yield carbon dioxide and water. They work well because living organisms supply plants with carbon dioxide, which undergoes photosynthesis and produces glucose, and these plants and bacteria give out oxygen, which all living organisms need for respiration.

Photosynthesis and respiration can be illustrated as follows:

Because these processes cannot be observed by the naked eye, it is difficult for many individuals to conceptualize. To fully appreciate this fundamental relationship, it is important to have an understanding of the living body as a chemical substance, to have basic knowledge about the chemical elements that compose the living body, and to appreciate that gas (CO2) is the source of the plant's body. These complementary systems allow for the existence of animals, which need the oxygen (O2) that is produced by the plants during photosynthesis.

The relationship between cellular respiration and photosynthesis is continuous. During photosynthesis, glucose is produced from converted sunlight energy by plants. In general, the more light, the faster the rate of photosynthesis. However, research many years ago demonstrated that increased light intensity only increased the rate of photosynthesis up to a certain point. Therefore, the relationship of photosynthesis and cellular respiration is nonlinear (Biggs, Edison, Eastin, Brown, Maranville, & Clegg, 1971).

Question: What effect does the intensity of light (photosynthesis) have on the rate of cellular respiration (measured as the number of oxygen bubbles)?

Model Answer

The relationship between cellular respiration and photosynthesis is continuous. During photosynthesis, glucose is produced from converted sunlight energy by plants. In general, the more light, the faster the rate of photosynthesis. However, research many years ago demonstrated that increased light intensity only increased the rate of photosynthesis up to a certain point. Therefore, the relationship of photosynthesis and cellular respiration is nonlinear (Biggs, Edison, Eastin, Brown, Maranville, & Clegg, 1971).

Scientific Method

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. What is the scientific method? The scientific method is a way to probe into science by asking questions in a systematic way, which generates a hypothesis with the ultimate goal of improving the understanding of the problem.

The following are the steps of the scientific method:

• Background and observation

• Generate a hypothesis

• Conduct an experiment based on the hypothesis

• Data analysis and results

• Share your conclusions with the scientific community

Question: Is it possible to examine the relationship between photosynthesis and cellular respiration under controlled experimental conditions? Explain your response in detail.

Model Answer

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

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:

References

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.

Cousins, A. B., Johnson, M., & Leakey, A. D. (2014). Photosynthesis and the environment. Photosynthesis Research, 119(1–2), 1–2.

Gnaiger, E., Steinlechner-Maran, R., Mendez, G., Eberl, T., & Margreiter, R. (1995). Control of mitochondrial and cellular respiration by oxygen. Journal of Bioenergetics and Biomembranes, 27(6), 583–596.

Ocean Explorer. (2013). Chemosynthesis vs. photosynthesis. Retrieved from the National Oceanic and Atmospheric Administration Web site: http://oceanexplorer.noaa.gov/edu/learning/5_chemosynthesis/activities/chemovsphoto.html

Science & Plants for Schools. (n.d.). Measuring the rate of photosynthesis. Retrieved from the Science & Plants Web site: http://www.saps.org.uk/secondary/teaching-resources/157-measuring-the-rate-of-photosynthesis