Monday, September 13, 2010

Designing an Experiment

Today students had a pop quiz on the reading assigned for homework as well as the controls and variables material they learned last week.

After the quiz, we looked at the blog (see post below) to look back at what was required to properly complete the homework. Many students then realized that they did not follow the directions properly, especially where they needed to have five test groups and five samples. In this one instance, that's actually OK, as it is a helpful teaching tool to understand what it means to follow directions and have a strong experimental design.

We worked as a class to come up with the following set up.

Hypothesis: If seeds are placed in various concentrations of NaCl then there will be variation in the rate of growth.

Independent Variable: [NaCl]

Dependent Variable: change in mass of seed

Set up:Figure 1: The red dots represent seeds, which were placed in the center of a 9cm Petri Dish (in F block, a 5.2cm Petri dish was suggested).

Group 1: The control group. 20ml of distilled water is added to the petri dish.

Experimental Groups (* the salt concentrations were different in each class * make sure you write the correct concentration for your class).

Group 2:
Group 3:
Group 4:
Group 5:

Homework, due tomorrow, 2 parts:

PART 1: Complete the rest of the experimental set up. Important questions to think about are:
* What will your light source be? How close will the plants be to the light? How can do make sure all the plants receive equal light?

* How often will you collect data?

* Water evaporates. What will you do to compensate for this?

PART 2: Make a data table that you could use to record your data from this experiment. You do not need to create data, just make the table.

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