Water Flashcards
What does a low water activity mean?
That water molecules are “tied up” with other molecules so not available.
What is Water Use Efficiency?
Carbon Dioxide assimilated per unit of water transpired.
Which plants have high WUE?
CAM plants. Some plants close stomata, and store carbon dioxide overnight as malate.
Is water polar?
Yes, as there is an uneven distribution of charge, and so interactions occur with other polar molecules.
Oxygen is negative. Hydrogen is positive.
Can form weak hydrogen bonds.
How many bonds are formed in ice?
Bonds are formed with 4 other molecules.
Can also occur in water, however breaks down into a dynamic network. Bonds with 3 other molecules.
Consequence of many hydrogen bonds?
High melting point
High boiling point
High latent heat of evaporation
How does water stabilise ions?
Through hydration, if water has access to charge.
What is conformational flexibility?
Change in the shape of a macromolecule, often induced by the environment. Usually dynamic and flexible.
What is a condensation reaction?
Dehydration reaction. Removes water and requires energy input.
Why is hydrolysis more likely than condensation?
Doesn’t require energy. Add water to split molecules.
How can the diffusion of water through membranes be controlled?
Adjust composition either side of the membrane.
Rigid cell wall stops rapid influx.
Periodically remove water.
What is the hydrophobic effect?
The observed tendency of non-polar substances to aggregate in aqueous solution and exclude water molecules.
Maximises hydrogen bonding between molecules of water and minimises the area of contact between water and non-polar molecules.
Which are the three types of water insoluble material that are biologically important?
Biominerals - inorganic compounds that have exceeded their solubility product and precipitated.
Macromolecules - as well as associations of macromolecules with polar groups to interact effectively with water.
Lipids - low molecular weight compounds, such as fatty acids and phospholipids. Largely non-polar structures that permit very few interactions with water.
Example of a biomineral?
Calcium phosphate - used in shells, bones and teeth.
Magnesium carbonate - used in reef corals.
Silica - used in sponges.
Common routes to biomineralisation?
Crystal growth/precipitation within an intracellular vesicle.
-Spicules in Acantharia.
Precipitation within an intracellular or extracellular protein or polysaccharide matrix.
-Bone. Calcium phosphate precipitated in an extracelllular collagen matrix.
