real science for today's homeschooler

Yeast – Examining Living Cells

Yeast - Examining Living Cells

Yeast . . . it turns grapes into wine . . . it makes bread rise . . . but did you know it’s actually a living one-celled fungus? Yeast provides a safe way for children to observe a few of the life processes of living cells.

1. Living Cells Need Water – Add dry yeast to very warm water to activate them. Explain to children that the yeast must have water in order to carry out life processes. They are able to survive in a dormant state without water, but they won’t become active and grow until they have water.

2. Living Cells Need Food – Put some of the hydrated yeast culture in two small containers (preferably clear). Add sugar to one of the containers, but not to the other. Let children observe the differences they see over time. Does “feeding” the yeast cells make them more active?

3. Living Cells Produce Waste – The yeast culture with sugar will give off noticeable amounts of carbon dioxide gas in the form of bubbles. Explain to children that the cells are getting rid of waste just like they do . . . by “breathing” out carbon dioxide gas.

4. Living Cells Reproduce – If a microscope is available make a slide from a drop of the yeast culture with sugar. Look carefully and you may find a cell that is undergoing “budding.” Budding is the way yeast cells reproduce. First they double all the material inside the cell that’s needed to keep it alive. Then they separate out one set of the material and pinch it off in a little pocket on the side of the cell. The new pocket will eventually pop off and form a new yeast cell! Children enjoy seeing the “baby” yeast cells. 🙂

Extension – Make bread or another pastry that requires yeast to make it rise. Ask children to use what they have learned about the yeast cells to explain what is happening inside the dough. (The yeast is eating the sugar and using the water in the dough to grow. As it grows it produces waste in the form of carbon dioxide gas. The gas bubbles are what makes the bread rise. As the yeast reproduces, more and more yeast cells can produce more and more gas bubbles and the dough gets bigger and bigger!)

Share this on...Email this to someoneTweet about this on TwitterShare on Facebook

Separating a Mixture

Separating a Mixture

A mixture contains two or more substances that are not chemically combined. Each substance retains its original properties, and can be separated by physical means. Challenge your student to design a method to separate a mixture into its separate components.

First, you’ll need to make the mixture that will be separated. A suggestion would be to mix salt, sand, pebbles, and iron filings. Home improvement stores sell “play sand” which works well for many science experiments, and you can order iron filings from the internet. The base of your mixture should be sand, then add the other substances in slightly smaller quantities.

Here are the steps of the experiment:

1. Have your child observe the mixture and guess the substances from which it is made.

2. Explain the scientific definition of a mixture and give your child a sample of each of the individual substances in the mixture.

3. Ask your child to brainstorm the physical properties of each of the individual substances. (If they don’t come up with these on their own, lead them to include that salt dissolves in water, pebbles are much larger than the other ingredients, and iron is magnetic.)

4. Ask your child to brainstorm how the physical properties of the substances could be used to separate each from the mixture. Depending on the age of the child, you may or may not have to help with this step. You can also lead them to experiment with the individual substances by seeing which will dissolve in water and which are attracted to a magnet, etc.

5. Once your child has developed a plan to separate the mixture, help them carry it out. Here are a few suggestions to successfully separate the four ingredients:

PEBBLES – Separate the pebbles either by picking them out individually with tweezers or fingers, or by straining them out. A colander or a piece of window screen works well as a strainer.

IRON FILINGS – The small iron fragments can easily be pulled from the mixture with a magnet. To keep the magnet clean, put it inside a plastic baggie. After you have collected the iron filings on the outside of the bag, pull the magnet away from the plastic and the filings will be released.

SALT – Pour the mixture into a container of water and stir well until the salt has had time to dissolve completely. Pour off the water. To demonstrate that the procedure worked, evaporate the water to reveal the salt left behind.

SAND – Once the other three ingredients have been removed, the (wet) sand will be left behind.

6. Emphasis that your child has proven that the original material was a mixture because the individual parts were separated by physical means.

Share this on...Email this to someoneTweet about this on TwitterShare on Facebook

Take the Pluto Survey!

Take the Pluto Survey!

We all remember learning the nine planets of the solar system when we were in school. And just like that, there were only eight! Poor Pluto! In 2006 the IAU (International Astronomical Union) demoted Pluto to nothing more than a “dwarf planet” when another rocky body, similar to Pluto, was discovered beyond Neptune.

But, on September 18 Harvard University hosted a debate about the controversial classification of Pluto and it seems quite a case was made to reinstate Pluto back to its former planet status. Although you may have heard rumors that Pluto is now a planet again, the debate was informal and no official decision has been made. The IAU meets again in Honolulu, Hawaii in August, 2015 and no official change will be made before then, at the earliest. Still, the Harvard debate has stirred up quite a bit of emotions concerning Pluto!

I was very surprised to find that my students have very strong opinions concerning the fate of Pluto, with some believing it should be reinstated as the ninth planet of our solar system and some not. Which got me thinking . . . what a great topic to get kids involved in current events in science! So, I want to challenge you to get your kids involved. Encourage them to do some research on the pros and cons of classifying Pluto as a planet and come to their own decision. Once they have, please have them share their opinion through this one question survey. I’ll share the results of the survey when it looks like a clear winner has emerged! (The survey is completely anonymous and no information is collected other than the answer to the one survey question!)

Share this on...Email this to someoneTweet about this on TwitterShare on Facebook