Monday, April 27, 2009

Yeast Cell Monday

Now that I've got a live sourdough starter residing in my refrigerator, I have to remember to feed it once a week. And since that process involves removing some of the old starter, I'm going to try to bake with it, rather than just toss it out. Last week's waffles were not universally loved. (For some, "tangy" and "waffles" apparently don't go together.) So I will try some more bread, which was much more popular. In fact, I could see how it could become addicting.

Anyway, the yeast posts the kids put together left out a look at yeast cells. So here they are. Yeast cells are jelly-bean shaped. At the top left is an electron microscope photo of yeast cells dividing from Science Image in Australia. The diagram at right is from a bread baking webpage.

These two photos were taken with our microscope at 400X magnification. To the left is a digitally-enhanced photo of storeboughten baker's yeast. If you click on it, you can see it large enough to pick out the nuclei in some of the cells. To the right is the wild sourdough yeast we captured in our kitchen.

Why yeast cells are interesting, from the Howard Hughes Medical Institute:
Key findings about human genes have come from studying the humble, blob-like cells of baker's or brewer's yeast, which one researcher calls, shockingly, our relatives. In 1996, yeast became the first eukaryote (an organism whose genetic material is enclosed in a cell nucleus) to have its entire genome sequenced. Ever since, it has remained at the forefront of research on genetics. Almost everything we know about the cell-division cycle, for instance, comes from experiments with yeast, and many new methods of analyzing genes were first tried out in yeast.
Some more resources on yeast cells:

The University of Sidney in Australia's website on fungi.

Thursday, April 23, 2009


Not quite sure what these guys are doing, but it does look interesting:

DIYbio is an organization that aims to help make biology a worthwhile pursuit for citizen scientists, amateur biologists, and DIY biological engineers who value openness and safety. This will require mechanisms for amateurs to increase their knowledge and skills, access to a community of experts, the development of a code of ethics, responsible oversight, and leadership on issues that are unique to doing biology outside of traditional professional settings.
There's a lot more info at their Wiki. They're based in Cambridge, MA, but have local cells (so to speak) around the world. Check them out!

Wednesday, April 22, 2009

What is ATP?

Today's episode of Unseen Life on Earth talked about ATP, but somehow I didn't catch what ATP was. The video above offers a quick explanation using cereal. You can also check out:

ATP and Energy Storage from Biology in Motion - a cartoon mini-lecture

Tuesday, April 21, 2009

What is a cell?

I've been trying to find some resources that explain the basics of cell biology, including explaining what all those little organelles are. So far most of the sites I've found seem designed for reviewing material that's already been covered. So I'm making a list here of some sites that we can check out. Hopefully some will turn out to be useful. I'll add more as I find them, and list them in the sidebar as well.

Basics of Cell Structure:

Cells from Enchanted Learning. (This is a website aimed at elementary students that I used a lot when my kids were younger. Still good for really basic information on lots of topics.) Includes directions for making a model of a cell from Jello and candies.

Plant cell pitch-penny game: From Ellen McHenry, for elementary-age kids

Cell (biology) from Wikipedia

The Virtual Cell Webpage: There is an "online text" written in simple language for rank beginners, and a 3D animated cell to explore.

Cell Ultrastructure from BiologyMad. Also clearly written. To find it, click on AS Biology, then Microscopy, Cells, Diffusion & Membranes, then scroll down to Cell Ultrastructure.

What is a Cell? from the National Center for Biotechnology Information

Inside the Cell, an interactive online publication from National Institute of General Medical Sciences (also available as PDF)

A Tour of the Cell from the National Science Foundation. The illustrations here are somewhat clearer than some of the others.

More Advanced:

Unseen Life on Earth: We've started watching this online 12-part video series, based on a PBS special

Inside a Cell from the University of Utah

Photos and Videos:

The Biobus is a mobile educational lab in NYC. Their website has videos of crawling goldfish cells. (Maybe we can try that with some of our goldfish!)

Virtual Cell Animation Collection

The Inner Life of a Cell (3D Animation, no narration - look for link in article about how the video was made)

Thanks, Lorna!

Monday, April 20, 2009

Capturing wild yeast to make sourdough bread

The yeast starter The finished loaves

Last week, we were trying out a yeast experiment that didn't work out in time for the post, but this week we have successfully finished the project: making sourdough bread using home-grown yeast.

Growing Yeast (Or "Starter")
Source: Recipe Zaar

1/2 cup unsweetened pineapple juice
1/2 cup whole wheat flour
1 cup unbleached all-purpose flour
2 cups water

DAY ONE: Mix 2 Tablespoons flour and 2 Tablespoons pineapple juice. Stir well, cover and let sit for 24 hours at room temperature.

DAY TWO: Add 2 Tablespoons flour and 2 Tablespoons pineapple juice. Stir well, cover and let sit another 24 hours at room temperature. We started to see bubbles.

DAY THREE: Add 2 Tablespoons flour and 2 Tablespoons pineapple juice. Stir well and let sit 24 hours at room temperature.

DAY FOUR: Stir mixture and measure out 1/4 cup--discard the rest. To the 1/4 cup, stir in 1/4 cup flour and 1/4 cup water. Let sit 24 hours at room temperature.

REPEAT Day Four until mixture expands to double its size and smells yeasty.

The starter being poured into a bowl

Updated: Kathy's Foolproof (!) Whole Wheat Sourdough Recipe
To make a loaf for supper, I make the sponge the night before, make the dough after breakfast, shape the loaf after lunch and turn on the oven to bake the bread (no preheating) about 35 minutes before I need to start making supper. Then I use the hot oven for whatever I'm making that night.

3 cups of sponge (proofed starter)
1 cup whole wheat flour
2 cups white flour (less or more as needed)
4 teaspoons of sugar
2 teaspoons of salt
1 tablespoon of olive oil
  1. To make the sponge, add one cup water and one cup whole wheat flour to starter in large bowl. Let sit out overnight (or at least 2 hours). If you use a glass bowl, you can check that it is bubbly all the way through.
  2. Measure out the sponge for the bread into a large mixing bowl. Take the leftover starter and add one cup water and one cup flour. Mix, cover, and return to the refrigerator.
  3. Take the sponge for the bread and add the sugar and salt. Mix well, then knead in the flour a half-cup at a time. Knead in enough flour to make a good, flexible bread dough. The dough should stretch, not tear, when you fold it.
  4. Pour oil into bowl. Put dough in bowl and turn until covered in oil. Let rise, loosely covered, in a warm place (like an oven heated for 1-2 minutes) for ~3 hours, or until doubled.
  5. Place dough on baking tray. Gently knead and shape into a loaf. Make three gashes across the top. Let rise again, loosely covered, 2-3 hours.
  6. Remove covering on loaf. Sprinkle with water. (This makes the crust crispy.) Turn oven on to 425 degrees F. (No preheating needed.) Bake about 35 minutes, or until brown and fragrant. Loaf should sound "hollow" when tapped on bottom.
NOTE: If you don't use your refrigerated starter in about a week you will need to feed it. Remove one cup of starter (you can use it for waffles!), add one half cup each water and flour, mix, and return to fridge for a week. Continue indefinitely.

ALSO NOTE: The liquid that sometimes separates out is called hootch, and smells like it! Just stir it back in.

The two loaves made on our second try. (Ready to go into the oven.)

Some links we used:

Breadtopia video
Microbiologist Debra Wink's sourdough experiment
Sourdough use and maintenance tips from King Arthur flour
Sourdough basics by S. John Ross

Tuesday, April 14, 2009

Root Beer

This week for chemistry, we decided to make root beer (To learn about yeast.) We used the yeast to carbonate the soda, and we more or less followed the instructions on this site
We actually made two bottles using different methods. Here are the two methods we used:

The flavoring syrup

Bottle #1

For this one, we took all the ingredients in the original instructions, but we dissolved the sugar on the stove until it was a syrup, than we mixed the rest of the ingredients (plus a packet of Maltodextrin To make it thicker) into the syrup, and poured the syrup into the bottle along with about a liter of water.

The flavoring being poured into the bottle

Bottle #2
For this bottle we pretty much followed the instructions on the website. Also, we didn't add any Maltodextrin.

A glass of the finished project

Planting Science

Planting Science is a resource for teachers which includes two, free, online units you can also use at home, "The Wonder of Seeds" for grades 7-12 and "The Power of Sunlight" for grades 9-12. They not only include experiments, but information on things like Investigating Plants Safely, Thinking and Working Like a Scientist, and Making Meaningful Graphs.

This site was recommended by a homeschooler, but a quick glance at it makes me think it needs some translation from "biology teacher speak" into regular people language. However, it could give you good ideas for experiments, and you can always Google to find a more novice-friendly version or explanation of what's going on.

Monday, April 6, 2009

Yeast Experiments, Part 1

Yeast Week - Home Brewing

We have been doing a few yeast experiments this week, some of which are still in the process of being completed. The major part of this week was making our own root beer, which will be covered in another post. Here we have two small experiments that we did as well.

Testing Yeast Experiment.

Before we tried the root beer experiments, we found that the yeast we were going to use (it was champagne yeast from a kit) had expired in 2006, so the first thing we did was to test to see if it was still good with this experiment.


Small glass measuring cup
Candy thermometer
Measuring spoons
1 package Champagne yeast (1 package yeast = 2 1/4 teaspoons)

1. Pour 1/4 cup water into a small glass measuring cup for liquids. Heat in microwave 20 seconds on high. Stir. Measure temperature. Water should be between 100 and 105 degrees F. If too cool, heat for 10 seconds. If too hot, add some cool water.

2. Add ½ teaspoon yeast and a pinch of sugar. Stir and let sit for 5 to 10 minutes, until the sugar and yeast dissolve. If a foamy layer forms on the surface, the yeast is still active.

3. If still active, seal the package and put in refrigerator for later. If not, throw it out.

The result was that the champagne yeast was too old to be used. We tested this along with regular baker's yeast and decided to use that instead.

Champagne yeast on the left, baker's on the right.

Watching yeast ferment

This experiment was just for fun. It has a neat effect which was very cool to see.


2 empty soda bottles, washed no tops
2 latex balloons
2 rubber bands
glass measuring cup, 1-cup capacity
measuring spoons
water, room temperature

1. In each bottle put 2 teaspoons yeast, 1 teaspoon sugar and 1 cup water.

2. In one soda bottle, add 2 tablespoons flour. Mark this bottle.

3. Secure a balloon on top of each soda bottle with a rubber band.

The balloon on the left is the one without flour, the green one has the flour in it.

-FoodSub - Yeast Types:
-Red Star Brand Yeast:

Sunday, April 5, 2009

Biology Online

Here's a site I found today when I needed information on photosynthesis for a book I'm working on:

Biology Online is the number one website for biology content and information on the web. The site aims to educate and promote awareness of all things biology, offering free and easy access to information in the biological sciences.

Created in 2001, the site provides a wealth of information in the diverse field of biology offering a forum for discussion, an editable-dictionary with thousands of terms, links to external resources, tutorials, articles and a biology book catalogue with user reviews.