Carol Giles [Collins HS] Molds
Objective: To introduce students to the fungi kingdom by creating a mold zoo (a version of this lab can also be found in the SMILE archives).
Carol gave each of us slices of ordinary white bread. We used each slice as a swab to wipe at various places in the classroom and environs (to see what mold spores we would pick up). After swabbing, each slice was sprinkled lightly with water and placed inside a sealable sandwich bag and taken home to incubate. As a control Carol had us each take a piece of bread, not swab anything with it, and spray it with a bleach solution; each control slice was sealed inside its own sealable bag.
The swabbed slices will pick up various mold spores which are so tiny that we cannot see them with our naked eyes. But after ~1-3 weeks (the time will vary from experiment to experiment) each spore will multiply, using the bread as a food source, into a “colony” with huge numbers of identical cells. The colonies will be easy to see and will grow in size as time goes by. The number of different types of spores picked up on a single swabbed slice of bread will be reflected in the different types of colonies on the bread (they will differ by color, texture, etc.); this “survey” can be extended to all the colonies on all the bread slices swabbed by the entire class.
The control slices should confirm that what grew on the swabbed slices was, in fact, due to spores picked up during the swabbing, and not to spores originally on the bread.
Because we had only one presenter today, we had a long discussion of various topics in biology and chemistry. Ken Schug pointed out that the bleach used in the control experiment (above) kills cells by oxidizing various essential biological molecules, so that they no longer function properly.
Chris Etapa asked about the elodea experiment in which this alga is placed in a test tube containing water in the dark and the light. In the light bubbles of oxygen are given off during photosynthesis and in the dark respiration releases carbon dioxide, which can cause a precipitate if the elodea is placed in “lime water” (the Ca++ ion in lime water forms a calcium carbonate precipitate in this experiment). Chris said that she was having a hard time getting a precipitate with the lime water in the dark; Ed Scanlon suggested using a pH indicator instead, which might be more sensitive (the carbon dioxide given off during respiration in the dark will acidify the medium).
Barb Lorde asked about why her house plant is dripping water. It is in a humid room, and the “transpiration” of water from the roots, through the xylem vessels all the way to the leaves, continuously brings water from the roots and it must go somewhere after it gets to the leaves. Normally the water is given off as vapor, but presumably in Barb’s humid kitchen, it is given off as a liquid.
We had a long and interesting discussion about stem cells, in humans, other animals, and plants. In the course of this discussion we used our wireless internet connection to find out that human children can regenerate fingertips up to the age of about six years!! We also discussed a bit about how the sequence of DNA is determined (for example, in the human genome project).
|Nov 23||Brenda Daniel|
|Dec 14||- ? -|
Notes prepared by Benjamin Stark.