The Effect Of Sodium Chloride On Yeast Cells

Quantitative task preparation 


Water Potential

Water potential is a measure of the concentration of water molecules that are able to diffuse. 

Unit - kPa

  • Water moves from a high water potential to a low water potential, down a water potential gradient
  • Osmosis - movement of water molecules by diffusion, from a high water potential to a low water potential, across a partially permeable membrane
  • Movement of water molecules will occur until the water potential is the same on both sides of the membrane. 
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Cells in solution of high water potential

  • partially permeable membrane 
  • the cell is in a solution with a water potential higher than the cell content 
  • water molecules will move down the water potential gradient, into the cell, by osmosis
  • from a higher water potential to a lower water potential  
  • the cell will swell 
  • animal cell - burst (haemolyse
  • plant cell - the cell wall prevents the cell from getting any larger; osmosis stops at this point (turgid)
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Cells in solution of low water potential

Placing the cell in a concentrated salt/sugar solution - i.e. water potential is lower than the cell content.

  • water will diffuse out of the cell down the water potential gradient by osmosis, from a higher water potential to a lower potential 
  • the cell will shrink 
  • animal cell - cell contents will shrink and shrivel up
  • plant cell - cytoplasm and vacuole will shrink as they lose water (crenated) and the cell surface membrane will pull away from the cell wall (plasmolysis
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Alcoholic Fermentation

Under ANAEROBIC conditions in yeast cells 

  • pyruvate loses a CO2 molecule - DECARBOXYLATED
  • becomes ethanal
  • enzyme - pyruvate decarboxylase
  • ethanal accepts hydrogen atoms from reduced NAD
  • reduced to ethanol
  • enzyme - ethanol dehydrogenase 
  • NAD is reoxidised - can accept more hydrogen atoms from glucose during glycolysis 

** rate of growth in yeast cells is faster in aerobic respiration

  • yeast produces CO2
  • CO2 reacts with water to form carbonic acid, lowering pH
  • denatures the proteins within the yeast cell (enzymes, Na/K pumps)  
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Rana Rashid


Thank you for this , this really helped me with my isa and my homework.

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