A 1.1 WATER

• What mass of the cell is made up of water?

  70% - 95%
• How fundamental is water?

  so fundamental that astronomers look for signs of water on other planets and moons as possible indicators of extra-terrestrial life
• What is water composed of?

  one atom of oxygen is covalently bonded to 2 atoms of hydrogen
• is water neutral or charged?

  as a whole it is neutral
• describe the bonding in a water molecule?

  The oxygen atom attracts the electrons more strongly than the hydrogen atoms, resulting in a weak negatively charged region on the oxygen atom (δ-) and a weak positively charged region on the hydrogen atoms(δ+),
• dipole meaning

  separation of charge due to the electrons in the covalent bonds being unevenly shared
• What is a polar molecule?

  a molecule in which the charges are unevenly distributed
• is water polar?

  yes water is polar
• Where do hydrogen bonds form?

  Between the slight positive charge of hydrogen and slight negative charge of oxygen in different water molecules
• What are hydrogen bonds?

  weak bonds that constantly break and reform - more like an intermolecular force than bond
• What is cohesion?

  Attraction between molecules of the same substance - water has cohesion due to hydrogen bonds
• what do hydrogen bonds allow?

  allow for strong cohesion between molecules
• where is cohesion useful?

  narrow xylem tubes can draw up water to the top of plants without breaking the water column
• what does cohesion create?

  surface tension which allows insects (pond skaters) to move across the surface of water
• What is adhesion?

  An attraction between molecules of different substances
• what does adhesion enable?

  water to move up the xylem during transpiration
• where is adhesion useful?

  in xylem vessels when they become air-filled, adhesion between water and the xylem wall help refill the vessel
• Hydrophobic meaning

  water hating - more attracted to other hydrophobic substances
• Hydrophilic


  water loving - chemically attracted to water
• what molecules are generally hydrophilic?

  polar molecules and molecules with a positive or negative charge
• what molecules are generally hydrophobic?

  non-polar molecules with no positive or negative charge
• why is water generally described as a universal solvent?

  because most biological molecules are hydrophilic and can be dissolved - however not all can be thus, water solvent properties allow it to be used as a medium for metabolism & transport
• what does solubility enable?

  metabolism as chemical reactions can occur as they can move around the solvent
• what is the thermal properties of water?

  water requires a great deal of energy to break the hydrogen bonds between the water molecules
• what is the specific heat capacity of water?

  4200 J/KgC
• what hypothesis has scientists come up with to state how water came to earth

  asteroid hypothesis
• why could earth not have water when it was formed

  as conditions were too hot for water vapour to condense into liquids
• what are the oldest group of asteroids in the solar system called

  carbonaceous chondrites
• what do the carbonaceous chondrites contain

  hydrogen isotopes similar to those found in seawater
• name the 2 asteroids with similar hydrogen isotopes to earths water

  carbonaceous chondrites and eucrite achondrites
• how would the meteorites have caused water to be dispensed onto earth

  during impact, water vapour would have been released and trapped by earths gravity as temperatures would have allowed the condensation to from liquid water
• What is the Goldilocks zone?

  an area that is not too hot and not too cold
• What is water in biological terms

  the medium of life
• what does 'water as a medium of life' mean

  first cells originate in water and water remains the medium in which most processes in life originate from
• what has the abundance of water over billions of years allowed?

  allowed life to evolve as water is the medium for life
• what happened during the formation of the first cells

  small volume of water became enclosed in a membrane thus allowing substances to be dissolved in it & allowing chemical reactions to occur
• why is water in a liquid state more useful

  allows molecules to move around and interact thus allowing the processes of life to happen
• what happens between the positively and negatively charged particles

  attract each other to form ionic bonds
• why are hydrogen bonds useful

  although they are a weak intermolecular force, water molecules are small, thus there are many of them, allowing them to give water unique properties
• What are the unique properties of water?

  ability to dissolve many substances, cohesion and adhesion, ability to absorb a relatively large amount of energy as heat, the ability to cool surfaces through evaporation, and the low density of ice