1.2: Preparing for the Experiment
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In this experiment, you will be investigating the effects of different nutrient deficiencies. To do this, you will first need to do some background research on the role of different essential nutrients within the plant. Use your background research to develop a question about plant nutrition.
Examples of questions
What is the effect of nutrient deficiency on vertical growth?
What effect did nutrient deficiency have on the biomass?
How does nutrient deficiency differentially affect roots vs. shoots?
Feel free to be creative with your questions!
Next, you’ll need to form a hypothesis about how plants grown in the absence of a particular nutrient will respond. A hypothesis should be a statement that predicts some influence of the independent variable on the dependent variable. Because it includes the dependent variable, your hypothesis should include measurable terms. For example, “plant health” is not measurable, but plant height and biomass are.
Your statement or prediction concerning nutrient deficiency in Brassica rapa is based on what you know about plants, on your observations, from literature we have in lab, or from information you can glean from the internet, books, nursery fertilizer boxes, etc. If the data you collect does not support your hypothesis, it is okay. In fact, that is often the case in science. We are using science to test your hypothesis, not to prove it right. Here is a brief checklist I like to use when making a hypothesis:
- It is a statement, not a question
- It does NOT use the phrase "I think..."
- It makes a prediction
- It is falsifiable (it is possible to collect data that proves it incorrect)
- It includes terms that I can measure
- It is specific enough that someone else could read it and know the parameters of the experiment
Next, you will need to decide what data (evidence) you will need to collect to test your hypothesis. Review the description of the experimental design on the following page to get some ideas.
During each lab meeting your group will measure/observe at least 5 plant characteristics and record them. These data will then be included in your final written report. Be sure that your data collecting is consistent. Terms like small or large mean very little. However, smaller or larger compared with the control (complete fertilizer) may tell us something about the treatments you are using. Below are some examples of variables you might choose to measure, but do not feel restricted to this list.
Some characteristics that can be observed in comparison with the control and without the use of measuring instruments are basically qualitative:
- Leaf size – use terms like smaller, larger, same size, thicker, thinner
- Leaf appearance – terms might include darker, lighter, rougher, smoother, more hairy
- Leaf number – more, fewer, similar
- Height – taller, shorter
- Form – bushier, more elongated, more squat
- Speed of maturity – faster, slower, similar
- Disease Symptoms/Abnormalities – chlorate (yellowing), pale, spotted, blotched, wilted, curling, rotting, crinkled
Some characteristics that require measuring are basically quantitative:
- Leaf size
- Plant Height
- Leaf length
- Amount of fertilizer added/used
- Number of leaves
- Number of flowers
- Final biomass
You can take pictures to aid in cataloguing your results.
Analysis of results
We will discuss in class a few ways to analyze your results. Often obtaining averages for collected data and comparing to the control is an effective method.
If you have any questions, bring them up in class—you are probably not the only one! We will spend some time during each of the following labs making observations and discussing what we see.