Introduction to Membrane Transport quiz #3 Flashcards
Introduction to Membrane Transport quiz #3
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Which types of molecules can freely diffuse across biological membranes without protein facilitation?
Small, uncharged, and nonpolar (hydrophobic) molecules, such as oxygen and carbon dioxide, can freely diffuse across membranes. What is the difference between passive and active transport across membranes?
Passive transport does not require energy and moves molecules down their concentration gradient, while active transport requires energy to move molecules against their concentration gradient. Give an example of a molecule that can freely diffuse across a membrane and explain why.
Oxygen (O2) can freely diffuse across membranes because it is small, uncharged, and nonpolar. How do polar or hydrophilic molecules typically cross biological membranes?
Polar or hydrophilic molecules usually require protein facilitation, such as channels or transporters, to cross membranes. What is exocytosis and why is it important?
Exocytosis is the process by which cells expel large molecules or particles by fusing vesicles with the membrane, important for removing waste and secreting substances. What features prevent ions like sodium (Na+) from freely crossing the membrane?
Ions like sodium are charged and hydrophilic, which prevents them from passing through the hydrophobic core of the membrane without protein facilitation. What is meant by the term 'semi-permeable' in relation to membranes?
'Semi-permeable' means the membrane is partially penetrable, allowing some molecules to pass while blocking others. What is the role of transport proteins in membrane transport?
Transport proteins facilitate the movement of molecules that cannot freely cross the membrane, such as ions and polar molecules. Why do nonpolar molecules cross membranes more easily than polar molecules?
Nonpolar molecules cross more easily because they are compatible with the hydrophobic interior of the lipid bilayer. Name a process that allows cells to take in large particles and briefly describe it.
Phagocytosis is a process where cells engulf large particles or microorganisms by wrapping the membrane around them. Why do macromolecules like proteins and nucleic acids require special transport mechanisms to cross membranes?
Macromolecules are too large to pass through the membrane directly and require bulk transport processes like endocytosis or exocytosis. How does the charge of a molecule influence its ability to cross the membrane?
Charged molecules are repelled by the hydrophobic core of the membrane and cannot cross without protein facilitation. Summarize the main factors that determine whether a molecule can freely cross a biological membrane.
A molecule's size, charge, and polarity determine its ability to freely cross a membrane; small, uncharged, nonpolar molecules cross easily, while large, charged, or polar molecules do not.