Sunday, January 31, 2010

Egg Experiment for Biology

My oldest is studying Apologia's Exploring Creation With Biology this year. Many of the experiments so far have been microscopic, hence no photos. I didn't realize this experiment was on a macro level, so I only got a picture of the last step.

Anyway, the first step of this experiment consisted of soaking a raw egg in vinegar. This dissolves the shell while leaving the semipermeable membrane intact. Osmosis allowed water from the vinegar solution to pass through, swelling the egg.

In the next step, the egg is now soaked in corn syrup. Now, osmosis causes water from the egg to move out of the membrane, which causes the egg to shrink and dimple.

In the final step, the egg in soaked in distilled water. Once again, the water passes into the egg through the membrane, causing the egg to again swell.


At this stage, the egg looked and felt like a bouncy ball, and the yolk was barely visible. The membrane was tougher than at the beginning of the experiment, but was still breakable.

There was another experiment on diffusion, so we could see the difference between osmosis and diffusion. We didn't get any pictures of the other experiment.

Saturday, January 23, 2010

Water Bears

My two youngest have been studying science using Swimming Creatures of the Fifth Day for the past two years. Last week we studied a very unique microscopic creature - tardigrades, otherwise known as Water Bears. Today I came across a video of them:




Aren't they cute?

Thursday, January 14, 2010

To Grade or Not to Grade?

That is the question over at Turned Loose.

Rebecca asks:

My fellow homeschooling moms, what do you do? Grade everything? Assess based on effort? Other?

That is an excellent question. Of course when you have a high schooler (my oldest is in 9th grade this year), you need to come up with a grading scheme for your transcript. This is pretty simple with some subjects - our math and Spanish programs grade automatically. But, with many other subjects, its not so easy. How much do you weight tests vs. worksheets? How do you grade oral discussions? What percentage do you give to writing assignments?

This is one of the reasons I really love Tapestry of Grace. They have come up with some very excellent grading rubrics that help you grade all those intangibles like participation in discussions. This is an excellent way to assess comprehension of the more complicated subjects.

For students in the lower grades, I actually do not grade. I don't believe that grading work is useful other than to puff up or pull down a young spirit. It doesn't teach anything.

Instead, I sit down with my children and review the work with them. When they've made a mistake, I work over the problem with them orally, trying to lead them to the correct answer. We then correct the work together (always with the homeschool mom's trusty red pen!) and end with both of us having a greater understanding of their strengths and weaknesses. Eventually they learn to review their work more critically, to double check their answers, and to ask questions more readily.

I believe this results in a much better outcome for both of us than simply handing them back a graded paper.

What do you do?