Water activity Flashcards
What are mechanosensitive channels?
○Mechanosensitive channels are used in hypotonic habitats to decrease cytoplasmic osmotic concentration (Willey, et al., 2011, pp.173-175).
○They open in response to PM stretching, due to increased hydrostatic pressure and swelling of cell, allowing solutes to leave cell (Willey, et al., 2011, pp.173-175).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Define water activity and briefly describe how it can be determined.
○Water activity is a quantitative measure of the amount of water that is available in a habitat (Willey, et al., 2011, pp.173-175).
○It can be determined by dividing a solutions vapour pressure by the vapour pressure of pure water (Willey, et al., 2011, pp.173-175).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
What is plasmolysis?
○Plasmolysis is when the PM shrinks away from the cell wall when the cell is in a hypertonic solution, caused by flow of water out of cell (Willey, et al., 2011, pp.173-175).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
What are compatible solutes?
○Compatible solutes are chemicals which are stored at high concentrations without affecting metabolism or growth (Willey, et al., 2011, pp.173-175).
○Compatible solutes are used to ensure the microbes cytoplasmic osmotic concentration is slightly above the osmotic concentration of habitat (Willey, et al., 2011, pp.173-175).
○They do this to keep their PM pressed firmly against the cell wall, and to prevent dehydration of cell (Willey et al., 2011, pp.173-175).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Why is it difficult for microorganisms to grow at low Aw values?
○It can be difficult to grow at low Aw values because to keep water in cells they must ensure their internal solute concentration is high, which requires extra energy and effort (Willey, et al., 2011, pp.173-175).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
Why does Halobacterium require sodium and potassium ions?
○Halobacterium are archaea which are extreme halophiles, microbes adapted to a hypertonic, saline environment (Willey, et al, 2011, pp.173-175).
○They need high amounts of potassium and chloride ions to ensure they remain hypertonic to their habitat, to ensure water doesn’t flow out of cells (Willey, et al., 2011, pp.173-175).
○Furthermore, high potassium levels are also needed for stability and activity of their enzymes, ribosomes and transport proteins (Willey, et al., 2011, pp.173-175).
○They also need sodium ions as it stabilises PM and cell wall (Willey, et al., 2011, pp.173-175).
References: Willey, J.M., Sherwood, L.M., Woolverton, C.J. (2011) Prescott’s Microbiology. 8th edn. New York: McGraw-Hill.
