Lab Report on Photosynthesis



Writing Assignment

Biology 212

Winter 2006

Scientific writing

One of the objectives of the laboratory experience this term is to develop your writing skills. In science, writing is an important means of communication. A scientific paper usually includes the following parts: a title (statement of the question or problem), an abstract (short summary of the paper), an introduction (background and significance of the research, including any hypotheses and predictions), a materials and methods section (report of exactly what you did), a results section (presentation of data), a discussion section (interpretation and discussion of results), and references (books and periodicals cited in the introduction or discussion sections).

Assignment

Write a lab report on your experiment investigating the effect of moist and dry conditions on optimum interplant distance that maximizes areal yield (yield per square meter of field surface). The report should be typed with double-spaced text, 12 pt font and pages numbered with the following components.

Title

The title should be as short as possible and as long as necessary to communicate to the reader the question being answered in the paper.

(Additional resource )

Introduction

This section gives the background and rationale for your research question. In other words, it places your research in context. This introduction section includes your research question, hypothesis, and prediction. The background and rationale information should be no more than 1-1.5 pages. You must give credit for any information that you gain from other sources and present in your report by citing the reference. Two references are required.

(Additional resource )

Methods

Give a brief description of your experimental design (1 paragraph), which includes your independent and dependent variables.

Results

This section, which is the central section of a scientific paper, has two components: (1) text describing your results (1-2 paragraphs) and (2) a figure (graph) summarizing your data. The figure (graph) needs to have a complete title. Cite your figure in the text portion of your report. Do not interpret your results in this section. Review pages 14-18 in your lab manual for tips on presenting and analyzing results. Use the guidelines in the handout attached to your in-lab assignment to prepare your graphs.

Discussion

(Additional resource )

In this section, you will analyze and interpret the results of your experiment. Use the following guidelines from your lab manual Appendix A: “Simply restating the results is not interpretation. The Discussion must provide a context for understanding the significance of the results. Explain why you observed these results and how these results contribute to our knowledge. Your results will support or confirm your hypothesis or will negate, refute or contradict your hypothesis but the word “prove” is not appropriate in scientific writing. If you results do not support your hypothesis, you must still state why you think this occurred. Support your ideas from other work (book, lectures or outside reading of scientific literature). State your conclusions in this section.

“Complete your Introduction and Results sections before you begin writing the Discussion. The figures and tables in the Results section will be particularly important as you begin to think about your discussion. The graphs allow you to visualize the effects that the independent variables had on the dependent variables in your experiment. Studying these data will be one of the first steps in interpreting your results. As you study the information in the introduction section and your data in the Results section, write down relationships and integrate these relationships into a rough draft of your discussion.

“The following steps may be helpful as you begin to outline your discussion and before you write the narrative:

• Restate your question, hypothesis, and prediction.

• Write down the specific data, including results of statistical tests.

• State whether your results did or did not confirm your prediction and support or negate your hypothesis.

• Write down what you know about the biology involved in your experiment. How do your results fit in with what you know? What is the significance of your results?

• How do your results support or conflict with previous work? Include references to this work.

• Clearly state your conclusions.

• You are now ready to write the narrative for the Discussion. Integrate all of the above information into several simple, clear, concise paragraphs. Discuss the results; do no simply restate the data. Refer to other work to support your ideas”.

References You must give credit to any information that you gain from other sources and that you present in your report. At least two references are required. See resources below for guidelines on citing references. References need to be listed in alphabetical order by author’s last name.

No references from the Internet will be accepted for this assignment unless from an on-line peer reviewed scientific journal.

How to decide what information must be referenced



How to write a successful summary without plagiarizing





How to cite references





Additional Resources

The Biology web site, , has information on resources for writing and library research.

General information on writing a scientific report

Appendix A Scientific Writing in your lab manual.

Evaluation form included with this assignment sheet.

Be sure to talk with your Lab Instructor if you have any questions.

Due Date

Your Lab Instructor will assign the due date. The grade on late reports will decrease 5% per day.

Format

Evaluation

Your lab report will be evaluated on the content (4 points) and the effectiveness of your communication, including text and figures (5 points). See the attached page for a sample evaluation form.

Evaluation of Lab Report on Seedling

Biology 212

Winter 2006

|CONTENT |COMMENTS |

|Title | |

|Introduction | |

| Background and rationale | |

| Research question | |

| Hypothesis | |

| Prediction | |

|Methods | |

| Description of experimental design | |

| Procedures | |

|Results | |

| Table or figure (graph) | |

| Text describing results | |

|Discussion | |

|COMMUNICATION | |

|Writing | |

| Grammar, spelling, punctuation, capitalization | |

| Sentence construction | |

| Paragraph structure: sentences in logical order supporting | |

|one main idea in each paragraph | |

| Organization of paragraphs | |

| Conciseness and clarity of writing | |

|References | |

|Required number | |

|Listed in Reference section | |

|Cited in text | |

|Figure (graph) | |

|Each title tells a complete story | |

|Organization of report | |

|Headings and subheadings included | |

|Double-space text | |

|Pages Numbered | |

Summary from Lab

Spacing Plants for Optimal Yield

The distance between plants greatly affects their areal yield (their final biomass per square meter of field surface). If plants are too close, intense competition for light and water causes them to grow poorly or die, and areal yield from a field of these crowded plants will be low. If the plants are too far apart, individual plants will grow well, but there will be so few plants per square meter that yield will be low. There is an intermediate distance between plants at which yield per square meter is maximized. The interplant distance that produces the greatest rate of areal photosynthesis (mg C per m2 per day), and thus the largest areal yield, is influenced by several factors, such as temperature extremes, light intensities and water availability.

Research Question

How would the optimum interplant distance that maximizes areal yield (yield per square meter of field surface) change with moist and dry conditions?

Hypothesis [Write a hypothesis based on the research question on your worksheet. Remember your hypothesis should be a biological explanation for how you think the optimum interplant distances would change with moist and dry conditions. ]

Prediction [Write a hypothesis based on the hypothesis on your worksheet]

If the hypothesis is true, then the results of the computer model should give the following results:

If the hypothesis is not true, then the results of the computer model should give the following results:

Results and Discussion

You will report the results and write a discussion of your results for your Writing Assignment. The instructions for your writing assignment will be provided in a separate handout. To help you interpret your results for your Writing Assignment, answer the following questions on your worksheet.

• Why do plants starve and die at very close interplant distances?

• Why do the leaf area index and soil water depletion change with increasing in interplant distance?

• For your data what is the leaf area index at which plants are first able to realize positive net photosynthesis?

• How does net photosynthesis for individual plants change as interplant distance increases?

• Does individual plant photosynthesis reach a maximum value? Why?

• Which interplant distance gives the greatest net photosynthesis per square meter for your data? Why does areal net photosynthesis decrease once this optimum interplant distance is exceeded?

Glossary

Allocation The assignment of photosynthate to the growth of roots, stem height, stem thickness, or leaves.

Areal photosynthesis Net photosynthesis per unit area (in Seedling, mg C/m2/day).

Fixed carbon Carbon that has been incorporated into sugar by photosynthesis.

Leaf-area index (LAI) The ratio of total leaf area to underlying soil area. When leaf-area index exceeds one, leaves must be shading one another. High LAIs mean both severe shading and serious water loss through transpiration.

Net photosynthesis Carbon fixed by photosynthesis minus carbon consumed by respiration. Net photosynthesis is positive when photosynthetic production exceeds the requirements of respiration and negative when respiration outstrips photosynthetic productivity. Net photosynthesis must be positive for growth to occur. Negative net photosynthesis (due to shading, water stress, or old leaves) will cause death by starvation.

Net photosynthesis per square meter (m2) Net photosynthesis per plant multiplied by the number of plants per square meter.

Net photosynthesis per plant A measurement equal to photosynthesis (carbon fixed into carbon compounds) minus respiration (carbon used up by oxidation). If the result is positive, the plant has photosynthate (carbon products produced by photosynthesis), to devote to growth after satisfying its respiratory costs. If it is negative, the plant is starving and not growing.

Number of plants per square meter (plants/ m2) A measurement computed from the distance between plants.

Percent of water demand satisfied The percentage of the plant’s water needs that can be met by the uptake of water from the soil.

Percent of the maximum net photosynthetic rate This rate would be 100% if all leaves were new, if there was no lack of water, and if there was no shading.

Photosynthate The sugars made by photosynthesis.

Photosynthetic rate The rate of carbon fixation expressed as a percentage of the maximum rate that would occur under optimum conditions of full sunlight, optimum temperature (25ºC), abundant water, and all leaves new and unshaded.

Relative humidity The amount of water in the air expressed as a percentage of the maximum amount of water that air of this temperature could hold. Low relative humidities greatly increase water loss through transpiration.

Respiration The consumption of sugars and other organic molecules in the process of metabolism. Every cell in a plant requires photosynthate merely to stay alive. If respiration requires more photosynthate than photosynthesis can produce, net photosynthesis is negative and the plant must use its food reserves

Soil water depletion The decrease of soil water (in milligrams per cubic centimeter of soil: mg/cc) that has occurred due to the uptake of water by plants.

Stomata The microscopic openings on the underside of a leaf through which the leaf absorbs CO2 from the air and loses water. During water stress, these openings close and photosynthesis stops.

Transpiration Evaporation of water through the stomata of leaves.

Water demand The percentage of its water needs that a plant is currently satisfying by water uptake from the soil. A water demand reading of less than 100% indicates water stress.

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