a1.1 water Flashcards
why does life depend on water?
- the first cells originated in water
- water is a solvent, allowing it to dissolve and transport molecules around the body
- water is a metabolite, meaning it’s involved in chemical reactions in cells
- water is a temperature buffer in bodies and ecosystems
- water maintains biological structures
why is water a polar molecule?
although water as a whole is electrically neutral, the sharing of electrons is uneven between the oxygen and hydrogen atoms. the oxygen atoms attracts the electrons more strongly than the hydrogen atoms, resulting in a delta negatively charged region on the oxygen atom and a delta positively charged region on the hydrogen atom
why do water molecules form hydrogen bonds?
a hydrogen bond is an attraction between two polar molecules. hydrogen bonds form between the positive and negatively charged regions of adjacent water molecules
define cohesion
cohesion is the attraction of water molecules to each other by hydrogen bonding
how does cohesion cause the effect of surface tension?
the surface of water acts as a elastic membrane because water molecules are more attracted to other water molecules than the air. for an object to break the surface, many hydrogen bonds must be broken - this causes some objects to float. living organisms, such as pondskaters, use the surface of the water as their habitat
how does cohesion allow the transport of water in the xylem?
there are continuous columns of water in the xylem. each column of water is under tension and is pulled upwards when water evaporates in the leaf. this is because the hydrogen bonds between water molecules can withstand a lot of tension and can be pulled up without breaking
define adhesion
adhesion is the hydrogen bonds that form between water and the surface of a solid composed of polar molecules. this causes the water to stick to the surface of the solid
what is capillary action?
capillary action is liquid flow through a narrow space from the combined effects of cohesion, adhesion and surface tension.
what are the solvent properties of water?
water is polar and so any polar substances will dissociate and dissolve in water - they are hydrophilic. once dissolved in solution, substances are more chemically reactive and remain in solution. non-polar substances are immiscible with water and will be repelled by polar molecules - these are hydrophobic
why are the solvent properties of water important for life?
the solvent properties of water are vital for allowing enzyme controlled chemical reactions to occur in the cytoplasm. these reactions are collectively known as the metabolism
why are water’s SHC and LH important?
water has a very high SHC which means it takes a lot of energy to increase the temperature of water - this means it is thermally stable
water has a very high LH of vaporisation. this means it takes a lot of heat energy to evaporate - this makes it a good cooling mechanism
why is water’s buoyancy important?
buoyancy is an upwards force exerted by the fluid it is immersed in. living organisms have an overall density close to that of water making it easier to use it as a habitat (not much energy is needed to float)
why is water’s viscosity important?
viscosity is due to internal friction caused when one part of the fluid moves relative to another part. water has higher viscosity when compared to organic solvents due to hydrogen bonds. solutes increase viscosity even more
why is water’s thermal conductivity important?
thermal conductivity is the rate at which heat passes through a material. water has a relatively high thermal conductivity. as a consequence, aquatic organisms are more at risk of heat loss
how did water originate on earth?
the most accepted theory is that large asteroids collided with earth at a higher frequency during the first hundred million years of earth’s formation. these delivered water to the planet
