Photosynthesis processes and mechanisms

Photosynthesis Lab

This experiment was carried out in order to develop and understanding and appreciation of photosynthesis, the mechanism on which almost all of the internal energy needs of living organisms depends, and to measure the rate of photosynthesis and some of the factors influencing this rate. Segments of spinach leaf were placed in conditions that caused them to undergo photosynthesis in a controlled and observable environment, enabling the observation of the process and of influences upon the rate of reaction occurring within the spinach leaf in light of environmental changes. Specifically, this experiment measured the proximity of the spinach leaf segments to their light source and its impact on the rate of photosynthesis, with the initial assumption that the closer the leaf segments were to this light source, the faster the photosynthesis would occur. The experiment showed that the reverse was actually the case, and when the spinach leaf segments were moved closer to the light source the rate of photosynthesis was approximately 50% longer. Possible reasons for this result and methods for further experimentation are discussed.

Introduction

Though human beings most if not all of the animal kingdom consists of heterotrophs -- organisms that must eat things (typically other organisms) in order to survive -- almost all life is ultimately dependent on the work of autotrophs -- organisms that use sunlight and/or other environmental (that is, inorganic) sources (Kent, 2000). The most common form of autotrophy is photosynthesis, the process by which most plants convert sunlight into usable energy stored in the form of carbohydrates (Kent, 2000). Through a series of complex chemical steps, incoming sunlight is first converted to chemical energy, and then in a second reaction that is not itself light-dependent this chemical energy is used to create a carbohydrate -- a simple sugar -- which contains energy in the form of certain molecular bonds that can be broken to release this energy (Kent, 2000; Dalton, 2012). Photosynthesizing plants make up the foundational level of any food chain; organisms higher on the chain must eat these plants and/or other organisms that have themselves eaten these plants in order to obtain the energy they need, and in this way the process of photosynthesis is vital to almost all life on the planet (Kent, 2000; Dalton, 2012).

This research set out to determine how the distance between plant matter and the light source it is using affects the rate of photosynthesis it achieves, utilizing a controlled environment in which spinach leaf segments are exposed to light and the chemical changes they undergo as a result of photosynthesis is indirectly measured. By keeping all other variables in the experiment consistent across two trials but by adjusting the space between the light source and the spinach leaf segments, the impact that this distance has on photosynthesis rates can be demonstrated. It is hypothesized that the closer the spinach leaf segments are to the light source the faster the photosynthesis reaction will happen, as more of the energy from the light source ought to reach the spinach leaf segments rather than being reflected or spreading into the environment surrounding the spinach leaf segments.

Materials and Methods

Procedure is found on pages 258 to 259 in Biology I: Molecular and Cells Laboratory Manual (Dalton, 2012).

Results

"1" represents the first trial, with an average time-to-surface of 282.4 seconds at a distance of seven centimeters from the light source.

"2" represents the second trial, with an average time-to-surface of 422.9 seconds at a distance of four centimeters from the light source.

Conclusion

An autotroph is an organism that uses sunlight and/or other inorganic features of its environment to create/convert the energy it needs in order to survive, such as most plants including the spinach that was used in this experiment (Kent, 2000; Dalton, 2012). A heterotroph, on the other hand, is an organism that needs to consume other organisms in order to meet its internal energy needs; humans are one obvious example of autotrophs, as is almost every member (perhaps every member) of the animal kingdom (Kent, 2000; Dalton, 2012). In autotrophs that photosynthesize, such as the spinach used in the experiment, the photosynthesis occurs in spherical cytoplasmic organelles called chloroplasts located in the cells of the plant an typically especially abundant in the leaves -- broad, flat structures meant to catch a great deal (proportionally speaking) of sunlight (Kent, 2000; Dalton, 2012). The general reaction that occurs in photosynthesis is the taking in of sunlight, which is converted into chemical energy and is used -- along with the raw materials of six molecules of carbon dioxide and twelve molecules of water to produce one molecule of sugar and six molecules of oxygen gas:

sunlight + 6CO2 + 12H2O = C6H12O6 + 6O2 (Dalton, 2012).