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#diffusion

12 public questions tagged with this topic.

Induction Morphogen -ll

Which signaling type involves diffusion of molecules to nearby cells?

Paracrine signaling involves secretion of soluble ligands that diffuse locally through extracellular matrix to affect neighboring cells within several cell diameters. Ligands like FGF, Hedgehog, BMP and EGF bind cognate receptor tyrosine kinases or serine-threonine kinases activating MAPK or Smad cascades. Concentration declines with distance, enabling gradient formation and threshold responses. Juxtacrine requires direct membrane contact via Notch-Delta, autocrine targets same producing cell, synaptic is specialized neuronal transmission via neurotransmitters. Paracrine underlies embryonic in

Ref: Alberts, Molecular Biology of the Cell, 6th ed., Chapter 15: Paracrine Signaling Mechanisms.

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Membrane Transportation

Which of the following is not an example of facilitated diffusion?

Facilitated diffusion denotes protein mediated passive transport operating down electrochemical gradient, characterized by saturation kinetics and competitive inhibition but lacking ATP hydrolysis. Several protein families exemplify it. GLUT uniporters possess twelve transmembrane helices organized into two bundles that alternate between outward open and inward open via rocker switch, transporting glucose along blood tissue gradients. Ion channels such as voltage gated sodium and potassium channels form aqueous pores with selectivity filters containing carbonyl oxygens and charged rings permit

Ref: Cooper, The Cell, 8th ed., Chapter: Facilitated Diffusion vs Active Transport - Na+/K+ ATPase Distinction.

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Membrane Transportation

Which of the following conditions describes osmotic pressure?

Osmotic pressure is a colligative property describing tendency of water to move across semipermeable membranes that allow solvent but restrict solute permeation. When compartment containing dilute solution is separated from concentrated solution, water chemical potential is higher where solute activity is lower. Spontaneous diffusion drives water toward higher solute until chemical potentials equalize, causing volume increase and hydrostatic pressure rise on concentrated side. The additional hydrostatic pressure required to stop net influx and hold volumes constant at equilibrium defines osmot

Ref: Alberts et al., Molecular Biology of the Cell, Chapter 11: Osmotic Pressure Definition and van't Hoff Equation.

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Membrane Transportation

Which of the following best defines Fick’s law of diffusion?

Fick's laws provide quantitative framework for diffusion in solutions and across biological membranes integrating concentration, distance and membrane properties. First law states net diffusive flux J, amount per area per time, is proportional to concentration difference divided by distance, expressed mathematically as J equals minus D diffusion coefficient times dC/dx concentration gradient, where negative sign denotes direction from high to low. D depends on temperature increasing Brownian motion, solute Stokes radius inversely via Stokes-Einstein relation, viscosity of medium and partition

Ref: Berg et al., Biochemistry, 9th ed., Chapter 11: Fick's Law of Diffusion and Concentration Gradient.

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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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Membrane Transportation

Which of the following statements about osmosis is incorrect?

Osmosis describes net water movement across selectively permeable membrane driven by difference in solute concentration and water chemical potential, not by ATP. Plasma membranes and artificial phospholipid bilayers act as semi-permeable barriers allowing water to partition and diffuse but restricting most solute diffusion due to polarity. Water molecules move randomly but statistically from compartment with lower osmolarity, higher water mole fraction and higher chemical potential, to compartment with higher solute concentration, lower water potential, until hydrostatic pressure compensates o

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 11: Osmosis and Water Movement.

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Membrane Transportation

Which of the following statements about membrane transport is true?

Plasma membrane selectively controls solute entry through distinct physico-chemical mechanisms dictated by molecular properties. Small non-polar gases such as O2, CO2, N2 and NO partition readily into hydrophobic core and cross by simple diffusion governed by Fick's law, without assistance, explaining lung alveolar exchange and mitochondrial oxygen supply. However many essential nutrients are hydrophilic or charged and face high energetic barrier. Facilitated diffusion provides protein-assisted route down concentration gradient without direct energy coupling, accelerating equilibration thousan

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 11: Membrane Transport – Facilitated Diffusion Principles.

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Cell Communication

Which junction permits rapid diffusion of small molecules? (June 2018)

Gap junctions, is consistent with established principles of cell signaling, receptor pharmacology and cellular regulation. Experimental measurements of binding parameters, genetic loss-of-function studies and pharmacological interventions all converge on the same interpretation. Related options address neighboring concepts but do not satisfy the precise criterion stated in the question.

Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)

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BASICS of PLANT+PYQS

At cellular level, the most dominant mode of transport for small molecules is:

That points to B: Diffusion. Compared with the other options, Diffusion is the one that correctly describes the BASICS of PLANT concept. The wrong ones are A) Active transport; C) Mass flow; D) Endocytosis. If you’re stuck, eliminate anything that contradicts a basic fact you already know for this topic.

Ref: Best CSIR NET Plant Physiology books: Master Unit 6 with Taiz & Zeiger and Salisbury & Ross. Crack Part C experimental questions with top textbooks.

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