Human Physiology: Membrane transport and resting potential — Diffusion and Osmosis
How molecules and water move passively across cell membranes, and why it matters for lungs, blood and brain.
Human Physiology · 23 questions
Try 3 questions
1. What drives simple diffusion across a membrane?
- Attraction toward the cell nucleus
- ATP spent by membrane pumps
- Random motion down a concentration gradient
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Answer: Random motion down a concentration gradient
Molecules move randomly, so more of them cross from the crowded side than from the sparse side, with no energy input from the cell.
2. Which substance crosses the lipid bilayer most easily by simple diffusion?
- Oxygen
- Sodium ions
- Glucose
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Answer: Oxygen
Small, nonpolar molecules like O2 dissolve in the lipid core; glucose is too polar and large, and ions are blocked by their charge.
3. Why can steroid hormones like cortisol enter cells without a channel or carrier?
- They are large protein molecules
- They carry an electric charge
- They are lipid-soluble
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Answer: They are lipid-soluble
Steroids are built from cholesterol, so they dissolve in the membrane and diffuse straight through to receptors inside the cell.
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