Bioprocessing Procedure

• Bioprocessing with immobilised cells is carried out in a bioreactor.
• The gel beads, with the immobilised cells, are held in suspension in the nutrient medium.
• The bioreactor is sterile – other types of micro-organisms would have a major negative impact.
• Temperature, pH, substrate and product concentration and waste level are checked constantly.
• The product can be produced by continuous flow or batch processing.
• Industrial fermentation of alcohol is often carried out with yeast cells immobilised in jel beads.
• A yeast suspension is mixed with a sodium alginate solution.
• Drops of the mixture are allowed to harden in calcium chloride solution.
• Small gel beads with live, trapped yeast are formed.
• Nutrients can diffuse through the gel to the live yeast.
• Fermentation product will diffuse from the yeast into the liquid medium.

Advantages of Immobilised Cells

• Easier purification of the product as the separation of the cell beads is not a problem.
• Easy to recover and recycle the cells– more economical process..
• The cells remain functional for much longer as it is a gentler process.

Mandatory Activity

Prepare and Show the Production of Alcohol by Yeast.

• Boil water for 15 minutes: removes all the dissolved oxygen.
• Almost fill two flasks with the deoxygenated water.
• Allow them to cool to 25°C in the sealed flasks.
• Sealed to prevent re-oxygenation.
• Dissolve glucose in each flask.
• Measure the density (specific gravity) of each solution using a hydrometer and record.
• Add live yeast to one — the experiment.
• No yeast in the other — the control.
• Place a thin layer of oil on the top of the water in each.
• The oil keeps the water out of contact with the air and prevents reoxygenation
• Insert a ‘fermentation lock’ into each.
• The fermentaton lock allows waste carbon dioxide to escape without the entry of air.
• Maintain the temperature at 25°C in a water bath or on a heating tray.
• After a week test each flask density and for alcohol using orange acidified potassium dichromate.
• Results:
  Control: no change in density and no alcohol (no colour change)
  Experiment: the density of the solution has decreased and colour change from orange to green
• Conclusion
  Yeast fermentation produces alcohol.

Movement Through Cell Membranes – Diffusion, Osmosis, Turgor

Diffusion

Diffusion is the net passive movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration.

Diffusion stops when the concentration is the same in all regions.

Some major examples of diffusion in biology:

• Gas exchange at the alveoli — oxygen from air to blood, carbon dioxide from blood to air.
• Gas exchange for photosynthesis — carbon dioxide from air to leaf, oxygen from leaf to air.
• Gas exchange for respiration — oxygen from blood to tissue cells, carbon dioxide in opposite direction.
• Transfer of transmitter substance — acetylcholine from presynaptic to postsynaptic membrane at a synapse.
• Osmosis — diffusion of water through a semipermeable membrane.

High Diffusion Rate: short distance, high temperature, big concentration difference and a low density medium.

Osmosis

Osmosis is a special example of diffusion. It is the diffusion of water through a semipermeable membrane from a more dilute solution to a more concentrated solution.

Note: diffusion and osmosis are passive, i.e. energy from ATP is not used.

A semipermeable membrane is a barrier that permits the passage of some substances but not others; it allows the passage of the solvent molecules but not some of the larger solute molecules.

Cell membranes are described as selectively permeable because not only do they allow the passage of water but also allow the passage of certain solutes. The presence of particular solutes stimulates the membrane to open specific channels or trigger active transport mechanisms to allow the passage of those chemicals across the membrane.

Дата добавления: 2015-11-14