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#passive transport

5 public questions tagged with this topic.

Basics of Cell Biology

Which of the following types of transport requires ATP?

Membrane transport classification depends on thermodynamics and mechanism. Simple diffusion of lipophilic gases O2, CO2, steroids occurs directly through hydrocarbon core partitioning driven solely by concentration gradient without protein. Facilitated diffusion via channels like aquaporins and carriers like GLUT1 enhances polar solute permeation down gradient, increasing rate and specificity, still entropy-driven, saturable, no ATP hydrolysis. Osmosis is water movement across semipermeable membrane toward solute, also passive. Active transport moves substrates against electrochemical potentia

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 11: Active Transport Requires ATP.

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Membrane Transportation

Which of the following processes does not require ATP?

Membrane transport energetics divide conceptually into active requiring cellular energy input and passive driven solely by existing electrochemical gradients toward equilibrium. Primary active transport directly couples exergonic ATP hydrolysis to ion movement against gradient: Na+/K+ ATPase phosphorylates aspartate forming E1P E2P cycle extruding three sodium importing two potassium, V-type proton pumps rotate c-ring acidifying lysosomes using ATP, ABC transporters dimerize nucleotide binding domains consuming ATP to expel drugs and lipids. Secondary active cotransporters such as SGLT1 sodium

Ref: Lodish et al., Molecular Cell Biology, Chapter 11: Classification of Transport - ATP Requirement.

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Membrane Transportation

Which of the following is not a property of facilitated diffusion?

Facilitated diffusion encompasses carrier and channel mediated passive movement strictly down electrochemical gradient sharing discriminating features versus simple diffusion and active transport. Transport is obligately mediated by integral proteins with defined binding sites or selectivity filters conferring high specificity for instance GLUT1 preferring D-glucose over L-glucose tenfold and aquaporin excluding ions while passing water at billion per second via NPA motif. It is saturable because limited carriers or channels create Vmax plateau when all sites occupied enabling competitive inhi

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 11: Properties of Facilitated Diffusion.

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Membrane Transportation

Which membrane transport process is energy-independent?

Transport classification distinguishes energy-dependent versus independent processes based on need for free energy beyond ambient thermal energy and existing gradients. Simplest criterion examines whether net flux can occur spontaneously down electrochemical potential or requires coupling to external energy store. Simple diffusion of hydrophobic molecules like steroid hormones and non-polar gases occurs directly across lipid without protein and without ATP, driven by entropy. Facilitated diffusion remains energy-independent but overcomes barrier for polar solutes using integral membrane protei

Ref: Lodish et al., Molecular Cell Biology, 8th ed., Chapter 11: Energy-Independent Transport – Facilitated Diffusion.

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