What is the “Goal System,” Anyway?
In this course, you will have the opportunity to decide what final mark you would like to achieve on each assignment by deciding how much of the assignment you want to attempt. As this is something that you are probably not used to doing, this short document has been created to help explain the concept. This system will help you to set a goal and then take the responsibility to reach it.
You will be able to decide how much work you want to do, with the expectation that a higher mark will require you to do more work. This system will apply ONLY to assignments while tests will be evaluated in the traditional way. When you begin each assignment you can decide up front the amount of work that you feel you can comfortably handle. Keep in mind, however, that while you can limit the amount of work you have to do, you also limit the highest mark that you can achieve in the course. The great news is that this system will help prevent students from feeling overwhelmed by the workload. You will be able to focus on the parts that you choose to do and you will also do a good job on those parts. In other words, you know your own limitations and this system will allow you to focus on the parts of assignments that you are required to complete and not worry about the rest. In general, successive questions on an assignment will become more difficult.
Let’s look at a hypothetical assignment. Imagine an assignment which has 10 questions included with it (the assignment can be found on pages 2 and 3 of this document). For a variety of reasons, you might decide that for this assignment you want to complete only the first seven questions. This means that you must complete these questions completely and correctly and the maximum grade you can earn on the assignment is 70%.
There are some very important requirements to keep in mind when considering the mark that you want to work toward:
1. Each assignment you hand in will be evaluated on an “all-or-nothing” basis. This means that everything you do, as stated earlier, must be complete and it must be correct.
2. After you submit an assignment it will be graded and handed back to you. You will have a period of 3 or 4 days to make any corrections necessary. Once your corrections have been made, you must come in person to discuss the corrections to demonstrate that you understand the correct answer. For example, if you completed all 7 questions but got one of them wrong, you can correct that one answer and resubmit the assignment. Mr. Gallant will be available every morning from 8:10 to 8:40 as well as between classes if you need help with any part of any assignment, even before it has been submitted. If, after making your correction(s) and meeting with Mr. Gallant, you still have not answered everything correctly, a mark of zero will remain for this assignment because you did not complete the work you agreed to complete. That is worth saying again. If you do not answer all questions that you attempt completely and correctly, you will get a mark of zero for that assignment. To avoid earning a mark of zero you must repeat this process until everything has been completed correctly. Remember that incomplete and incorrect work is unacceptable when you’ve agreed to achieve a specific mark. It is also important to emphasize that there is no reason to ever get a zero. Getting a zero would mean that you chose to not come in for help with the part(s) of the assignment that you were struggling with.
3. Late assignments will be accepted with a penalty of 30% up to one day late. Assignments submitted more than one day late will not be accepted. If a student is absent on the day an assignment is due, s/he may submit it on the day s/he returns to school if a valid, written excuse is provided.
**SAMPLE LAB ACTIVITY**
Diffusion Through Membranes
Cell membranes are selectively-permeable by nature and as such, exert some control over substances passing through them into and out of cells. In the presence of a concentration gradient, substances will diffuse from an area of high concentration to one of low concentration across a selectively permeable membrane. Water, too, will diffuse through membranes in a process called osmosis. The net movement of water is from an area of high [H2O] (i.e., low [solute]) to one of low [H2O] (i.e., high [solute]).
In this experiment you will measure diffusion of small molecules through dialysis tubing, a selectively permeable membrane. Small solute molecules and water molecules can move freely through a selectively permeable membrane, but larger molecules will pass through more slowly, or perhaps not at all. In medicine, the movement of a solute through a selectively permeable membrane is called dialysis. The size of the minute pores in the dialysis tubing determines which substances can pass through the membrane.
By detecting the presence of particular molecules on each side of the dialysis tubing, we can determine which molecules passed through the tubing and which did not. Starch molecules react with iodine to form a dark blue compound. The presence of glucose can be tested with Benedict's solution or Clinitest tablets. If glucose is present, the mixture will turn a series of shades of green. The appearance of a yellow or brown compound means the glucose is rather concentrated (check the package for concentration ranges). The presence of starch will be tested with Lugol's solution, (Iodine Potassium-Iodide or IKI). For the Lugol test, a dark blue color is a positive result.
A. Osmosis
Procedure
1. Obtain a 10 cm piece of 2.5-cm dialysis tubing that has been soaking in water. Twist one end of the tubing and fold it over, then tie off that end with string to form a bag. To open the other end of the bag, rub the end between your thumb and forefinger until the sides separate.
2. Pour molasses solution into the tube until it is about half full.
3. Twist the top of the tube and tie it securely. Be sure to leave a gap of about 1 cm between the top of the liquid and the thread. Try to squeeze out as much air as possible before tying the bag.
4. Rinse the outside of the tube with water to remove any molasses which may have contaminated it.
5. Place the tube in a 300 or 400 mL beaker and add enough water to just cover it. Label the beaker ‘A’ and make sure the names of you and your partner are on it.
6. Let stand overnight and record observations in the morning. Note that you might see a faint yellow color in the water in this beaker. This is natural pigments in the molasses and not the molasses itself.
B. Diffusion
Procedure
1. Prepare another tube as in procedure A but pour starch solution in the tube.
2. Tie and rinse the tube.
3. Place the tube in a beaker of water and label it ‘B’ and make sure the names of you and your partner are on it.
4. Add iodine solution to the water slowly until the water is a faint yellow color.
5. Let stand 20 min and record observations.
6. Prepare a similar setup except put glucose solution in the tube and do not add iodine solution. Be sure to rinse the tube before putting it in the beaker of water. Label this beaker ‘C’ and make sure the names of you and your partner are on it. Let stand 20 min.
7. Pour about 5 mL of water from beaker ‘C’ into a test tube and add half of a Clinitest tablet. Do not shake the test tube. Record the color about 15 s after the tablet stops bubbling.
Thought-provoking Questions (at least, that’s the idea)
1. a) Describe the test results which show the presence of starch.
b) Can the starch molecules pass through a dialysis membrane? Which results support this conclusion?
2. a) Describe the test result that shows the presence of glucose.
b) Can glucose molecules pass through the dialysis membrane? Which results support this conclusion?
3. Is the membrane 100% selective? Explain.
4. Describe and account for any changes that occurred in beaker ‘A.’ Be sure to specify the direction of movement for each molecule.
5. Describe and account for any changes that occurred in beaker ‘B.’ Be sure to specify the direction of movement for each molecule.
6. Describe and account for any changes that occurred in beaker ‘C.’ Be sure to specify the direction of movement for each molecule.
7. For each of the following questions, explain your answers. Base your answer on your results.
a) Which molecules pass through the membrane with ease?
b) What molecules pass through the membrane slowly?
c) What molecules were unable to pass through the membrane?
8. a) Why was the membrane rinsed off after being filled and tied?
b) Why was a 300 mL beaker with the minimum amount of water used instead of a larger beaker with, say, 500 mL of water?
9. Suppose that a tube filled with a 5% molasses solution was placed in a beaker filled with a 10% molasses solution. What would happen? Why?
10. A single starch molecule may have thousands of atoms, a glucose molecule has 24, and the ions of dissolved salt are the size of single atoms.
a) Using your knowledge of diffusion across selectively permeable membranes, explain the observations of this experiment.
b) Why is the chemical digestion of starch necessary?
c) Does this investigation show that starch molecules cannot move across living membranes? Explain.