Left to right: Celithemis amanda, a dragonfly; DNA; human karyotype; palmetto
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Intro/Chapter 1 - Some Biology Basics
Chapter 2 - Chemistry and Chemical Bonds
Chapter 3 - Water
Chapter 4 - molecules with carbon backbones
Chapter 5 - biological macromolecules
Chapter 6 - Cells
Chapter 7 - Membranes and how to get through them
Chapter 8 - Energy and Enzymes
Chapter 9 - Cellular Respiration
Chapter 10 - Photosynthesis
Chapter 12 - Cell Cycle and Cell division
Chapter 13 - Asexual and Sexual Reproduction UPDATED OCT 31
Chapter 14 - Mendelian Genetics
Chapters 14-15 Beyond Mendel
Chapter 16 - DNA
Chapter 17 - From DNA to Protein
Answers to Transcription-translation worksheet (MS Word document)
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Q: I have a question for you about cellulose. Since cows can digest cellulose because of their stomach systems, if you eat cow, do we intake any of that broken down cellulose. If so, I didn't think that humans could digest it. How does this work?
A: Actually it's the bacteria in the cow's stomachs that digest the cellulose. In this case "digest" doesn't just mean "absorb" - it means enzymatically cleaving apart the cellulose into the component glucose monomers. So the bacteria changes the cellulose to glucose, the cows absorb the glucose and use it to power their cells, and when we eat the cow, even the glucose is long gone, but the cow's cells have used the energy from the glucose to make more "cow" molecules, sugars and proteins and such.
Did you follow that?
If so, here's one more wrinkle - very likely the bacteria, once they've converted cellulose to glucose, don't just release the glucose for the cows to absorb. The bacteria themselves would ferment the glucose for energy, and the cows would absorb some other molecules that the bacteria discard. Any way you look at it, the cellulose never makes it out of the cow's stomach and into the cow's bloodstream. But the atoms that made it up probably do, and the energy contained in the cellulose definitely powers the cow.
Q: Hello! I have two questions concerning chapter 8: on membranes. As I was reading, I was wondering when concerning active transport -- the sodium-potassium pump, are there any other 'pumps' or is this just a very special important form of active transport. Is it the only one that has specific steps involved? i.e.- special pumps that involve the transfer exhange of certain elements such as Na and K...
A:Pretty much all active transport can be thought of as a "pump," so the Na-K pump is just one example. There are similar ATP-powered protein pumps that move other substances across the membrane. And each would have several steps involved - binding with the substrate, removal of a phosphate group from ATP for energy, moving the substrate across the membrane, and release of the phosphate group. So what you saw is pretty typical.
Not all of those pumps exchange *two* kinds of substrate. Many only move one substrate across the membrane.