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Related Concept Videos

Diffusion01:12

Diffusion

191.1K
Diffusion is the passive movement of substances down their concentration gradients—requiring no expenditure of cellular energy. Substances, such as molecules or ions, diffuse from an area of high concentration to an area of low concentration in the cytosol or across membranes. Eventually, the concentration will even out, with the substance moving randomly but causing no net change in concentration. Such a state is called dynamic equilibrium, which is essential for maintaining overall...
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Centrifugation01:05

Centrifugation

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Centrifugation is a separation technique based on differences in density or size. It is commonly used to separate solids from aqueous interferents. During centrifugation, the sample is placed in centrifugation tubes and spun at high angular velocity, which allows centrifugal force to act differentially on the different densities or masses of the components. After spinning, the supernatant liquid is decanted. Depending on the specific application, either the pellet or the supernatant is retained...
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Active Transport01:14

Active Transport

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Active transport is a critical biological process that allows cells to move solutes against an electrochemical gradient. This process requires direct energy input and is characterized by its selectivity, saturability, and susceptibility to competitive inhibition.
Primary active transporters, like Na+, K+ and -ATPase, directly utilize ATP to move ions across the membrane. These transporters play significant roles in various physiological processes. For instance, Na+, K+ and -ATPase maintain...
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Protein Diffusion in the Membrane01:24

Protein Diffusion in the Membrane

4.3K
Proteins show rotational as well as lateral diffusion across the membrane. The lateral diffusion of proteins was confirmed through the cell fusion experiment where mouse and human cells were fused, resulting in hybrid cells. When the human and mouse cells fused, the specific membrane proteins on human and mouse cells were marked with the red and green-fluorescent markers, respectively. Initially, the red and green fluorescence was located on the respective hemisphere of the cell. As time...
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Mechanism of Ciliary Motion01:05

Mechanism of Ciliary Motion

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The ciliary structures were first seen in 1647 by Antonie Leeuwenhoek while observing the protozoans. In lower organisms, these appendages are responsible for cell movement, while in higher organisms, these appendages help in the movement of the extracellular fluids within the body cavities.
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Passive Diffusion: Overview and Kinetics01:17

Passive Diffusion: Overview and Kinetics

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Passive diffusion is a critical process that allows small lipophilic drugs to cross the cell membrane along a concentration gradient. This mechanism's efficiency depends on four primary factors: the membrane's surface area, the drug's lipid-water partition coefficient, the concentration gradient, and the membrane's thickness.
When administered orally, drugs establish a substantial concentration gradient between the gastrointestinal (GI) lumen and the bloodstream, expediting...
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Related Experiment Video

Updated: Jun 22, 2025

Measurement of Cellular Chemotaxis with ECIS/Taxis
11:37

Measurement of Cellular Chemotaxis with ECIS/Taxis

Published on: April 1, 2012

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Densitaxis: Active particle motion in density gradients.

Vaseem A Shaik1, Gwynn J Elfring1

  • 1Department of Mechanical Engineering, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.

Proceedings of the National Academy of Sciences of the United States of America
|June 27, 2024
PubMed
Summary
This summary is machine-generated.

Active particles exhibit taxis in fluid density gradients. "Puller" swimmers align parallel to gradients, while "pusher" swimmers orient perpendicular, demonstrating novel densitaxis behaviors.

Keywords:
active matterbiophysicsfluid dynamicsmicroswimmerstaxis

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Related Experiment Videos

Last Updated: Jun 22, 2025

Measurement of Cellular Chemotaxis with ECIS/Taxis
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Area of Science:

  • Fluid dynamics
  • Biophysics
  • Active matter physics

Background:

  • Organisms navigate complex environments, often encountering fluids with varying densities.
  • Understanding self-propelled particle behavior in stratified fluids is crucial for ecological and biotechnological applications.

Purpose of the Study:

  • To investigate the dynamics of active particles in fluid density gradients.
  • To provide theoretical evidence for taxis induced by density gradients, termed densitaxis.

Main Methods:

  • Theoretical analysis of a force- and torque-free spherical squirmer model.
  • Calculation of particle reorientation dynamics in response to density stratification.

Main Results:

  • Density gradients induce reorientation in active particles.
  • Swimmer orientation depends on their propulsion mechanism (swimming gait).
  • Puller-type swimmers align parallel to density gradients, exhibiting densitaxis.
  • Pusher-type swimmers align normal to density gradients.

Conclusions:

  • Density gradients significantly influence the motion and orientation of active particles.
  • Densitaxis offers a mechanism for understanding biological organism movement in stratified environments.
  • Modulating density gradients can be a strategy for controlling active particle suspensions.