Biology/bio
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Question
Can all molecules diffuse through all cell membranes?
The answer is no--the ability of a molecule to diffuse through a cell membrane (or any membrane) depends on factors including size of the molecule, charge, polarity, size of the openings in the membrane, and the composition of the membrane. A straightforward example of is the inability of small ions to diffuse directly through cell membranes. Small ions--sodium, calcium, etc.--have charges that make them unable to cross phospholipid membranes, even though they are quite small relative to the membrane. They must move through ion channels instead.
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Answers by Expert:
John Locke
Expertise
I will answer all biology-related questions through the undergraduate level. I will explain unclear concepts and suggest approaches to solving problems, but would prefer not to completely solve homework problems for you. If you are completely stumped on homework, tell me what you already know and I will help you as much as possible. Please do not ask me for ideas on school research projects; part of research is determining a suitable area of investigation, and that's not a task that should be completed by someone else. Please don't simply send me your homework for solutions. If you are having difficulty after you have started an analysis, I will be happy to direct your thinking; in particular, I would prefer to not simply solve pedigrees for students, but I will be happy to assist in solving pedigrees that you have already started. If you don't understand how to analyze a pedigree, I'd highly recommend watching this video, in which a biology professor explains the basic concepts of pedigree analysis: http://www.youtube.com/watch?v=HbIHjsn5cHo
Experience
I have a BS in Bioengineering with a concentration in Chemical Engineering (which included a heavy focus on biology), and have taught biology, biochemistry, and related subjects for some time now.
Education/Credentials
BS Bioengineering, Penn State University
MCAT/DAT/OAT Instructor
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