Internal Assessment: Planning Lab
Due: Wednesday March 20, 2013
Water pollution and Lemna growth
Investigate the growth of duckweed (Lemna) over time, given different conditions. Possible suggestions are: water type or a pollutant common in water bodies—oil, heavy metals, pesticides and fertilizers.
Planning Rubric
Links to example IAs:
http://essia.wikispaces.com/file/view/Sample%201.pdf/244518345/Sample%201.pdf
http://essia.wikispaces.com/file/view/Sample%209.pdf/244519229/Sample%209.pdf
Links for information about duckweed:
http://www.mobot.org/jwcross/duckweed/duckweed.htm
http://www.extension.iastate.edu/Publications/SP99.pdf
http://www.fcps.edu/islandcreekes/ecology/duckweed.htm
PLANNING
Variables are factors that may affect the outcome of your experiment. They are measurable factors, not pieces of equipment. Do not use the word “Amount”. It is not specific enough – terms like mass or volume are better.
Independent variable: This is the variable that you manipulate – you choose the values to investigate.
Dependent variable: This is the variable that changes in response to changes in the independent variable. It is what you are measuring or trying to find out.
Controlled variables: These are other factors that may also affect the dependent variable. They need to be kept constant in order to ensure a fair test.
Uncontrolled variables: Usually climate factos tht you try to keep the same for each sample.
Decide what to investigateStart with the variables!
1. Decide what you want to find out about – this is your dependent variable.
2. Brainstorm (and list) all the possible variables that could influence your dependent variable.
3. Choose ONE to be your independent variable.
4. All the others will be your controlled variables.
1. Write an Aim/Problem/Research Question
A good format is “To determine how [the independent variable] affects [the dependent variable] in [the context of your experiment].”
e.g. To determine how acid rain affects the germination in common beans
e.g. To find the effect of age and gender on the perception of global warming of Ugandans.
1. To achieve a “2” on Aspect 1 you need to state a focused research question. To do this you should:Briefly state what you are trying to find out.
2. Include both the independent and dependent variables.
3. Specify the scope of your experiment by stating the context of your investigation.
1. It is unlikely that your experiment will allow you to draw a conclusion that applies to all situations.
2. Therefore you need to state the conditions under which your experiment is operating e.g. the species being studied (scientific name), gender, age group, location etc
2. Identify the variables
Make sure you have read the information on variables (textbox in Step 1).
In order to achieve a “2” for Aspect 1 you must:
Example for Step 3f.
Controlled variable
Temperature at which reaction occurs
Duration (time) of the reaction
Method to control the variable
The test tubes in which the reaction occurs will be placed in a water bath set to 40°C for the duration of the reaction.
The reaction will be allowed to proceed for 300 seconds. This will be timed using a stopwatch (±0.1seconds).
1. State the independent. State the levels of the independent variable that will be tested (see step 5a for more information).
2. State the dependent variable.
3. State how the dependent variable will be measured (if it can’t be measured directly).
4. List several controlled variables.
Aspect 2 requires that you explain the method you will use to control each of the (controlled) variables.
5. Give brief (but specific) explanation of how you will control (keep at a constant value) each variable. Including this in the variables section ensures that you have considered each of the controlled variables. However, it should ultimately appear in the method.
6. If a variable cannot be controlled, state this. Then describe how you will try to minimize any change and/or how you will monitor the variable. See Appendix 1 for uncertainties to consider.
3. List the equipment (apparatus and materials) needed
Choosing appropriate equipment will allow you to achieve a “2” for Aspect 2.
Make sure that your equipment list includes all of the following:
1. All of the equipment and materials needed for the experiment (after writing you method read through it and check of the items used as you go on your equipment list)
2. Numbers of items (e.g. 2 petri dishes)
3. Volumes and concentrations of any solutions needed (e.g. 300ml of 0.5M hydrochloric acid)
4. Precision (and range if appropriate) of all measuring instruments. How precise do you need to be in your measurements?
5. Sizes of beakers or other items (e.g. 250ml beaker, 10cm length of dialysis tubing)
Number of Values
If you are looking for a correlation, at least 5 different values are needed (the more the better).
If you are comparing two different situations, 3 values will be sufficient.
4. Plan and write a method/procedure
Planning a Method
Aspect 3 of Planning assesses your ability to collect sufficient relevant data. The following considerations are important to ensure that you collect enough data and that the data will help to answer your Aim-
Range of Values
You may need to do some research to help you decide.
e.g. if testing acidic rain solutions then you would want to test values around 5.6pH. If you are investigating chemical spills in you might want lower pH values
1. What values of the independent variable should you test?How many values should you test? Decide how many values will be needed to show any trend or pattern. Plan for an ideal situation – worry about time constraints later. Usually 5.
2. What is an appropriate range of values?
1. How will you measure your independent and dependent variables?
1. Can you measure it directly (raw data) or do you need measure other values (raw data) and use them to calculate values (processed data) for your independent variable?
Number of Trials
All systems, because of their complexity and normal variability, require replicate observations and multiple samples of material. Remember that a minimum of 5 values is needed for calculating means and standard deviations. Other statistical tests have other requirements e.g. Spearman’s Rank requires at least 30 values.
2. What measuring instruments will be best to use? Do you know how to use them?What level of precision is required in your measurements?
3. What units will you use to record your measurements?
2. How may trials or replicates need to be carried out?
1. Consider how you are going to process your data
2. Now go back and double check that you have collected enough of the right types of measurements. Plan for an ideal situation – worry about time constraints later.
3. Will any calibration of equipment need to be carried out to avoid any errors and uncertainties in taking measurements? How will this be done?
Write the Procedure
A clear, easy to follow method is necessary to achieve a “2” on Aspects 2 and 3.
Think about method you have seen and what information you like to have! Someone (who has not done the experiment before) should be able to follow your procedure and obtain similar results.
The following features contribute to writing a good method.
1. The method can be written as instructions like a recipe
2. Do not begin with “Gather all of the materials” … it is kind of a given that you will do this!!
3. Use numbered steps (rather than paragraphs).
4. Use a diagram if possible to show how to set up any equipment. Then you can say “Set up the equipment as shown in the diagram”. This would save you writing a lot of words.
5. Specify what will be measured (and the units to be used)
Include details of how you will measure values