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If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked. Membrane transport is essential for cellular life. As cells proceed through their life cycle, a vast amount of exchange is necessary to maintain function. Transport may involve the incorporation of biological molecules and the discharge of waste products that are necessary for normal
function.1 Membrane transport refers to the movement of particles (solute) across or through a membranous
barrier.2 These membranous barriers, in the case of the cell for example, consist of a phospholipid bilayer. The phospholipids orient themselves in such a way so that the hydrophilic (polar) heads are nearest the extracellular and intracellular mediums, and the hydrophobic
(non-polar) tails align between the two hydrophilic head groups. Membrane transport is dependent upon the permeability of the membrane, transmembrane solute concentration, and the size and charge of the solute.2 Solute particles can traverse the membrane via three
mechanisms: passive, facilitated, and active transport.1 Some of these transport mechanisms require the input of energy and use of a transmembrane protein, whereas other mechanisms do not incorporate secondary
molecules.3 Passive transport is the simplest method of transport and
is dependent upon the concentration gradient, and the size and charge of the solute.2 In passive transport, small uncharged solute particles diffuse across the membrane until both sides of the membrane have reached an equilibrium that is similar in concentration. The
direction of solute travel is indicative of the concentration of that particular particle on each side of the membrane. Figure 1. Passive diffusion of O2 and CO2 across a membrane over time 1-3. Based on the thermodynamics of the system, particles will move from an area of high concentration to an area of low concentration in order to increase the entropy of the cell. Additionally, this particle movement will occur spontaneously as the free energy (Gibbs free energy; ∆G) of the system is negative.4 Where:
What types of molecules can passively diffuse through a cell membrane?Thus, gases (such as O2 and CO2), hydrophobic molecules (such as benzene), and small polar but uncharged molecules (such as H2O and ethanol) are able to diffuse across the plasma membrane. Other biological molecules, however, are unable to dissolve in the hydrophobic interior of the phospholipid bilayer.
Which kind of substance pass through membrane by passive diffusion?The correct option is (d) hydrophilic substances. Cellular membranes are often composed of a phospholipid bilayer. Because of this, lipid-soluble substances can diffuse passively through a membrane.
What are 3 examples of passive transport?There are three main types of passive transport: Simple diffusion – movement of small or lipophilic molecules (e.g. O2, CO2, etc.) Osmosis – movement of water molecules (dependent on solute concentrations) Facilitated diffusion – movement of large or charged molecules via membrane proteins (e.g. ions, sucrose, etc.)
What substances enter the cell through passive transport?Passive osmosis and diffusion
Some substances (small molecules, ions) such as carbon dioxide (CO2) and oxygen (O2), can move across the plasma membrane by diffusion, which is a passive transport process.
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