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Questions and Answers
The resting membrane potential (RMP) is typically around ______ mV.
-70
The Na+/K+ pump uses ______ to function.
ATP
The Na+/K+ pump exports ______ sodium ions out of the cell.
3
Simultaneously, the pump imports ______ potassium ions into the cell.
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Water crosses the membrane primarily through channels called ______.
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Water movement occurs due to ______, which is the passive movement from low to high concentration.
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Osmolarity is defined as the amount of ______ dissolved in one litre of water.
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For example, one mole of glucose in one litre of water is equivalent to ______ osmolar.
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An osmotic gradient affects the movement of water from a region of low ______ to a region of high osmolarity.
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The difference in osmolarity helps predict which way the ______ will flow across a membrane.
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Osmolarity is the amount of solute dissolved in 1 litre of ______
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1 mole of NaCl in 1 litre of water equals ______ Osmolar
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One mole of solute depresses the freezing point of water by ______˚C
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The osmolarity of plasma is approximately ______ mOsm
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ICF and ECF refer to ______ and extracellular fluid, respectively.
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Osmolarity is measured by the depression of ______ point.
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Plasma contains Na+ at a concentration of ______ mM.
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The membrane of red blood cells contains ______ that facilitate water movement.
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No net movement of water occurs between ICF and ECF because osmolarity is the ______ in both.
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The osmotic fragility of red blood cells is measured against ICF osmolarity of ______ mOsm.
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Glucose must leave the intestine and enter ______, crossing lipid membranes and interstitial space.
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Transport involves molecules crossing cell ______.
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Cells have a resting membrane potential (RMP) of ______ mV.
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Substances move from a high concentration to a low concentration along a ______ gradient.
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The ______ is a selectively-permeable barrier that regulates the entry and exit of substances in cells.
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Molecules, ions, and gases must cross multiple ______ membranes inside cells.
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Passive transport does not require ______ to move substances across membranes.
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In transport, the ______ of a substance determines if it can cross a membrane.
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In a solution of 280 mOsm, there is no osmotic gradient, meaning the solutions are __________.
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In a 140 mM NaCl solution, the RBC maintains its normal size and __________.
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When placed in pure water, osmolarity is greater __________ the cell.
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In pure water, the RBC explodes due to the influx of __________.
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When RBCs are placed in sea water, osmolarity is greater __________ the cell.
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In sea water, the RBC implodes and __________ its function.
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The RBC membrane contains __________ to facilitate water movement.
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Osmosis occurs when the cell membrane is __________ to water.
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Water moves __________ down its concentration gradient.
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Osmosis is essentially the same as __________.
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RBC are placed in a solution of 280 mM ______; the urea solution is referred to as being isosmotic.
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If the solute CANNOT cross the cell membrane, the solution is also ______.
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Cells have a Resting Membrane ______ of -70 mV.
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When RBCs are exposed to a solution with a permeable solute, they may ______ due to osmotic pressure.
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There is a rare disease in which ______ transporters are absent from RBC, making them resistant to lysis.
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Study Notes
Circulation and Transport
- Glucose moves from the intestine to blood using circulation and transport across cell membranes.
- Glucose crosses 4 cell membranes to enter the bloodstream and another 3 to enter a muscle cell
Challenge of transport inside cells
- Multiple intracellular membranes, such as mitochondrial membranes, nuclear membranes, and sarcoplasmic reticulum, require molecules to cross them
### Cell membranes: a selectively-permeable barrier
- Two main factors determine if a substance crosses a cell membrane: permeability and electrochemical gradient.
- Permeability refers to whether the membrane will allow the substance to pass through.
- Electrochemical gradient refers to the “force” on the substance to cross the membrane, considering both chemical and electrical forces.
Electrochemical gradient
- Substances move from high concentration to low concentration due to a chemical gradient.
- Cells have a resting membrane potential (RMP) of -70 mV.
- Fick’s law and Na+/K+ pump explain the RMP.
- Na+/K+ pump actively transports 3 Na+ ions out of the cell and 2 K+ ions into the cell using ATP.
- This pump is electrogenic, as it exports more positive charge, contributing to the negative RMP.
Transport across cell membranes
- Water moves across the cell membrane by osmosis, which depends on the permeability of the membrane and the osmotic gradient.
- Aquaporins are water channels that facilitate water movement.
- Water moves from regions of low osmolarity to regions of high osmolarity.
Osmolarity
- Osmolarity is the concentration of solute dissolved in 1 liter of water.
- 1 mole of glucose in 1 liter of water equals 1 Osmolar (1 Osm).
- 1 mole of NaCl in 1 liter of water equals 2 Osmolar (2 Osm) because NaCl dissociates into two osmotically active ions.
- Freezing point depression can be used to measure the osmolarity of biological fluids.
ICF and ECF solute compositions
- Although the solute compositions of intracellular fluid (ICF) and extracellular fluid (ECF) differ, there is no net movement of water between them because the overall osmolarity is the same in both.
Osmotic fragility of Red Blood Cells
- Red blood cells (RBCs) have aquaporins that allow water to move across their membranes.
- RBCs maintain their normal size and shape when in a solution with the same osmolarity as their ICF.
- RBCs can lyse (explode) in pure water because of the high osmotic gradient, causing water to rush into the cell.
- RBCs can implode in a hypertonic solution with higher osmolarity than ICF, because water rushes out of the cell.
### Osmotic vs. Isotonic
- A solution that is isosmotic to the ICF of the cell, but the solute CAN cross the cell membrane, is NOT isotonic.
- If a solution is isosmotic to the ICF of the cell, and the solute CANNOT cross the cell membrane, the solution is also isotonic.
Summary
- Cells maintain a negative resting membrane potential (RMP) due to the action of the Na+/K+ pump.
- Water moves across the cell membrane by osmosis, following the osmotic gradient.
- Red blood cells are particularly susceptible to changes in osmolarity, illustrating the importance of maintaining osmotic balance.
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Description
Test your knowledge on the transport mechanisms of glucose and the challenges involved in crossing multiple cell membranes. Explore concepts related to selectively-permeable barriers, permeability, and electrochemical gradients critical for cell function.
