|Stephen G. Saupe - Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; (320) 363-2782; firstname.lastname@example.org|
Gink & Go Bake Bread
Setting: Gink and Go are in the kitchen preparing to bake some bread.
|Go:||I can't wait to make some bread. What ingredients do we need?|
|Gink:||The recipe says we need some flour, water, and salt.|
|Go:||Check. What else?|
|Gink:||Yeast. Do we have any?|
|Go:||Got it. I just bought a pack of active dry yeast at the grocery store. Isn’t it amazing?|
|Gink:||Duh, what’s amazing?|
|Go:||The yeast. I was just thinking about our anhydrobiosis discussion in Saupe’s bio class.|
|Gink:||(sigh loudly) Can’t you ever do anything without thinking about Saupe’s stupid class? Anhydro – who?|
|Go:||Anhydrobiosis. Don’t you remember that Saupe said it refers to organisms like yeast that can withstand periodic drying. One minute they can be happily going about their business, and the next they are sitting in a foil package, dry as a bone, in an inactive metabolic state.|
|Gink:||Just add water and they spring back to life. It’s as if they were resurrected from the dead. Just like magic.|
|Go:||Yeah. Anhydrobiosis is a great adaptation that lets these organisms live in aquatic environments that periodically dry up. What’s really amazing is that organisms can withstand extremes of cold, heat and even radiation, in the anhydrobiotic state.|
|Gink:||That is pretty cool. It would be much easier to withstand Saupe’s bio class if I could dry myself down before each one and then rehydrate myself after it’s over.|
|Go:||Get real. Most organisms can’t revive after they’ve been dried because as their cells dry down the cell and organelle membranes come into contact and essentially glue themselves together.|
|Gink:||Well, if my cells were to dry down and irreversibly react so I couldn’t revive, then how does yeast do it?|
|Go:||As yeast cells start to dry down they produce sugars, like trehalose, that act like a cushioning. It prevents the membranes from chemically-reacting with one another. Once they rehydrate, the sugar dissolves, and the organism springs back to life.|
|Gink:||Holy Methuselah. Yeast cells are basically immortal.|
|Go:||Well, not quite. But they can survive in the dry state for many years. In fact some water bears collected from dried herbarium specimens were revived after more than 100 years.|
|Gink:||What are water bears? Are they those dumb-looking things that lumbered along in the video clip that Saupe showed us?|
|Go:||Right. They’re also called tardigrades and are microscopic animals that occupy their own phylum. You know, lot’s of other organisms exhibit anhydrobiosis including nematodes, rotifers, some mosses and ferns, and even some mushrooms can do it.|
|Gink:||Give me that yeast so I can rehydrate it to make our bread. You know, since Saupe’s lectures are so dry, do you think if I threw some water at him he would finally show a little life in our class?|
What is anhydrobiosis?
Name some organisms capable of anhydrobiosis.
Why did this process evolve? What is the evolutionary/ecological advantage of this ability?
Why are some organisms able to revive after drying but most others are not? Explain the mechanism for anhydrobiosis.
Trehalose is the sugar that acts as the 'protectant' in yeast cells. Do you think this sugar is chemically more similar to glucose or sucrose? Explain.
Draw the expected line on the graph below. Explain the rationale for your diagram.
Blood has a very short shelf-life. How might anhydrobiosis provide a mechanism to improve storage. Describe an experiment to test your hypothesis.
Are anhydrobiotic organisms alive or dead when dry?
Check out the quotes below. How do they relate to this dialog? Do you agree?
"Life is nothing but a physical phenomenon” (Lamarck, 1820)
“Only when the structure is damaged or destroyed does the organism pass from the state of anabiosis…to that of death” D.Keilin (1959)
“Life is nothing more, nothing less than the arrangement of certain molecules” (B. Rensberger, Science 80, Nov)
Last updated: February 01, 2010 � Copyright by SG Saupe