Study guides › B/B › Biology
Membranes & Transport
The plasma membrane decides what enters and leaves a cell. You will learn membrane structure, predict which transport route a molecule uses, apply osmosis and tonicity, calculate equilibrium potentials, and describe vesicular traffic and receptor signaling.
Study this chapter in PrepMed (free)
What this chapter covers
- The Fluid Mosaic Model. Membrane composition explains permeability, fluidity, and how proteins sit in the bilayer. Expect questions on cholesterol and temperature.
- Passive Transport & Osmosis. Passive transport needs no energy. Tonicity questions ask you to predict which way water moves and what happens to cell volume.
- Active Transport. Cells use ATP directly or indirectly to build gradients. Know the Na⁺/K⁺ pump numbers and how secondary transporters borrow its energy.
- Membrane Potential & the Nernst Equation. Resting potential is a calculation topic: know ion concentrations, the Nernst equation, and which ion dominates at rest.
- Vesicular Transport & Membrane Receptors. Large cargo and signals cross the membrane by vesicles and receptors. Know the three forms of endocytosis and the three receptor classes.
Key points to know
- Phospholipids are amphipathic: polar head, nonpolar tails
- Unsaturated and short tails raise fluidity; saturated and long tails lower it
- Passive transport goes down the gradient and uses no ATP
- Carrier-mediated transport saturates (Vmax); simple diffusion is linear
- Primary active transport: ATP directly, against the gradient
- Na⁺/K⁺ ATPase: 3 Na⁺ out, 2 K⁺ in per ATP; electrogenic
- Nernst: E = (61.5/z) log([out]/[in]) at 37 °C
- Resting potential ≈ −70 mV, near E_K because of K⁺ leak channels
Try a practice question
Which molecule is most likely to cross a phospholipid bilayer by simple diffusion?
- Na⁺
- Glucose
- Steroid hormone
- Glutamate anion
Show the answer
C. Steroid hormones are small and nonpolar, so they dissolve in the hydrophobic core. Ions and polar or charged molecules need channels or transporters.
Common questions
What does this chapter cover?
Membranes & Transport covers The Fluid Mosaic Model, Passive Transport & Osmosis, Active Transport, Membrane Potential & the Nernst Equation, Vesicular Transport & Membrane Receptors.
What should I know first?
Phospholipids are amphipathic: polar head, nonpolar tails Unsaturated and short tails raise fluidity; saturated and long tails lower it Passive transport goes down the gradient and uses no ATP
24 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.