Excerpts from Photosynthesis Introduction Sections

Good Excerpts

Note that while none of these quotes would stand alone as a good Introduction, a number of these ideas combined together might do quite nicely.

Background Theory (more detail in Literature Review) — Why is this important?

♦ Plants are, directly or indirectly, the food of the world, and photosynthesis is where it all starts. Photosynthesis makes food for the plant, and the plant is food for us. . . Therefore, this study was undertaken to determine what color or colors of light best promote photosynthesis.

♦ Photosynthesis is the chemical process in which plants convert light energy into chemical energy. Chloroplasts, located within each cell of the leaf, absorb light and use it to convert a combination of carbon dioxide and water into glucose, producing a byproduct of gaseous oxygen. In order to complete this process efficiently, the plant’s chloroplasts contain chlorophyll and other pigments that absorb different wavelengths of light. These other pigments exist so that the plant can absorb the wavelengths of light that chlorophyll A can’t. The pigments that aid in photosynthesis are carotenes and xanthophylls, and two types of chlorophyll: chlorophyll A and chlorophyll B (author, year).

♦ Photosynthesis is the process by which plants use light energy to convert carbon dioxide (CO2) and water (H2O) into sugar (C6H12O6) (author, year).

♦ Plants are able to use carbon dioxide and water to produce glucose, used for food, oxygen, which is released, and water. Plants are only able to complete this process by using energy from the sun or other sources of light (author, year).

♦ Because carotenes and xanthophylls are different colors, they are capable of capturing energy from a light source that chlorophyll A or B cannot and transferring that energy to the chlorophyll causing photosynthesis to take place (author, year).

♦ Photosynthesis involves pigments inside a leaf that enable the plant to capture, transform, and store solar energy (author, year).

♦ Xanthophylls, carotenes, and chlorophyll B can harness other wavelengths of the sun’s energy that the chlorophyll A can use during photosynthesis (author, year).

♦ Photosynthesis is known to make oxygen by carbon fixation (author, year).

Observation, Question, Hypothesis, Prediction — the Scientific Method

♦ Why must light be present for a plant to perform photosynthesis? What parts of the plant react or use the energy of light to carry out the process of photosynthesis? Can different colors (wavelengths) of light have different effects on a plant? Questions like this can be answered by finding out what pigments are in a plant, what colors or wavelengths the different pigments absorb, and in which colors of light a plant will best perform photosynthesis.

♦ Light energy must be absorbed for photosynthesis to occur. Since light exists in colors, some colors could be more effective than others in driving photosynthesis. There could be more than one pigment available for use in photosynthesis. Plants could possibly make different pigments to absorb a variety of the colors of light.

♦ The green coloration of a spinach leaf suggests that the leaf reflects light around 525 to 550 nm.

♦ Which color(s) are better for photosynthesis? It is thought that absorption peaks should correlate with maximum photosynthesis. Because chlorophyll A and B look green, they should not be absorbing or using green light. Thus, green light should be the least useful or the least involved in photosynthesis. It is thought that red or blue light should be more useful in photosynthesis.

Goals/Objectives for the Study — What will be accomplished?

♦ A study was undertaken to ascertain whether any relationship exists between colors of light available to and absorbed by the different pigments in a plant and the photosynthetic rate in that plant.

♦ . . . to study how effective different wavelengths are in driving photosynthesis in order to gain a better understanding of how this process works in the chloroplast.

♦ The objectives of this study were a) to discover what pigments are present in plant leaves and to isolate these pigments, b) to determine absorption spectra for each of the pigments found, noting maximum and minimum absorbances, c) to discover any relationship that may exist between color(s) of light available to and/or absorbed by a plant and the rate of photosynthesis by that plant as evidenced by oxygen evolution, and d) to then compare the absorption spectra for the known pigments with the rates of photosynthesis in different colors of light to determine which wavelength(s) of light are the most useful for photosynthesis and/or which of the plant pigments are involved in photosynthesis.

♦ . . . to discover what pigments vital to the photosynthesis process were present in plant leaves. . .

What will be done? (more detail in Methods and Materials) — How will this be accomplished?

♦ Pigments were extracted from leaves and were separated to see which pigments were present. The light absorbances of the isolated pigments at various wavelengths were measured to obtain an absorbance spectrum for each pigment. Plants were then placed into pigmented solutions to . . .

♦ The pigments in a spinach leaf were separated to be tested individually. The absorbance spectra of the pigments were obtained, noting the minimum and maximum absorbance for each pigment. Sprigs of Elodea were placed into various colored solutions to discover any relationships that may exist between the colors of light available to a plant and the rate of photosynthesis in those colors, as evidenced by oxygen evolution.

♦ The effects of color of available light on photosynthesis in plants like Elodea can be tested by placing specimens of the plant into solutions containing food coloring. The production of oxygen by each specimen can be measured as an indication of the rate of photosynthesis in each color.

Application to Daily Life — Sometimes used as a “wrap-up” to nicely end the Introduction.

♦ Many people would be interested in this type of research so that they could better run greenhouses or even vegetable gardens. More efficient photosynthesis might make business better or give more vegetables, more quickly, in the garden.

♦ This research will enable a better understanding of how light may best be used to benefit plants by showing which colors of light are best absorbed by the pigments involved in photosynthesis.

♦ This experiment is important because the results may be used to further the farming and agricultural industry, thereby producing more food and healthier crops to feed the world.

♦ Photosynthesis is needed for other life forms to thrive, for not only does this process produce the glucose needed for energy and a starting point for other molecules, but also the oxygen essential for cellular respiration (author, year).

Grammar — Remember:

Here’s one from the re-write that’s fairly good. (I did slightly edit a couple of grammatical errors.)

It is common knowledge that plants require light to grow. What may not be common knowledge, however, is the color of light in which plants flourish. It has been reported that the blue/violet light absorbed by plants is responsible for foliage growth. Plants grown only in blue light are compact with lush, dark-green leaves but few flowers. Red and far-red light affects the growth processes in various plant parts. Incandescent light is good in the red range while fluorescent light tends to be better in the blue range (Carter, 1997).

While the relationship between the various colors of visible light and plant growth will not be tested in this experiment, the relationship between the various colors of visible light and the rate of photosynthesis will be explored.

By first identifying the various pigments contained in a spinach leaf, it will be possible to determine that each pigment is absorbing a different wavelength of light. Each pigment will be examined with a spectrophotometer to determine its absorption spectrum, thus confirming its identity. Absorbance readings at various wavelengths will be obtained for each pigment, noting the maxima and minima for each.

Any relationship that may exist between colors of light available to and/or absorbed by the plant and the rate of photosynthesis by the plant will be explored through measurement of oxygen evolution by plants exposed to various colors of light. These data will then be compared to the absorption spectra for the known pigments. The rates of photosynthesis in different colors of light will determine which wavelengths of light are the most useful for photosynthesis.


Not So Good Excerpts (including some grammatical problems)

Thou shalt not begin an Introduction in any of these ways:

♦ In this study, we collected Elodea from our classroom aquarium. This was done to see if any relationship exists between colors of light absorbed by the plant. [and ???]

Don’t make grandiose claims like “This study was undertaken. . .

[Note that to say “A greater or better understanding was gained,” is OK.]
but don’t undersell yourself, either:

and/or . . .

♦ . . . plants can absorb all the spectrums of light to . . . [should be “spectra”]

♦ The elodea. . . [should be “Elodea”]

♦ In order to find the different pigments in spinach, we needed to . . . [use passive voice]

♦ . . . the absorption spectra determines. . . [use “spectrum determines” or “spectra determine”]

♦ absorbency, absorbencies. . . [use “absorbance” or “absorbances”]

♦ . . . through different spectra’s of light. . . [use “spectra” — There’s no such thing as an “of light” that belongs to several spectra.]

♦ . . . between the different colors of light that was made available to. . . [use “colors were”]

♦ thus allowing the leaves to absorb sunlight and storing it. . . [use parallel construction — either “absorbing and storing” or “absorb and store”]

♦ . . . any relationship which may exist between colors of light available to a plant. [and ???]. . . [Relationships always occur between one thing AND another.]

♦ . . . a spectra for each pigment. . . [use “spectrum”]

♦ The plant Elodea was used for this purpose at different wavelengths. . . [the prepositional phrase “at different wavelengths” does not modify “purpose”]

♦ In this study, the pigment in plant leaves was separated from each other. . . [use “pigments were separated from each other”]

♦ Photosynthesis is the conversion of light energy stored in glucose. . . [use “conversion of light energy to chemical energy which is stored in glucose”]

♦ . . . maximum and minimum absorbances was noted. . . [use x and y were. . ]


Copyright © 1998 by J. Stein Carter. All rights reserved.
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