Chapter 2: The importance of water Flashcards
Structure of water
-consists of 2 hydrogen atoms and one oxygen atom joined by shared electrons (covalent bonds)
-shared negative hydrogen electrons are pulled towards the oxygen atom and the other side of the hydrogen atom is left with a slight negative charge
-unshared negative electrons on the oxygen atom gives it a slight negative charge, makes water molecule polar. Hydrogen bonds form as a result of dipoles formed by electronegativity.
What are hydrogen bonds?
-Hydrogen bonds (dipole-dipole interaction) are weaker than covalent bonds
-they add strength to a molecule
-weak intermolecular forces
e.g in water the oxygen atom attracts the electrons more and so the oxygen atom becomes more electronegative and is said to have a slight negative charge whereas the hydrogen atoms become slightly short of electrons and become slightly electropositive.
Properties of water: high specific heat capacity
-hydrogen bonds between the water molecules absorb high level of energy
-important in keeping aquatic habitats thermally stable
-important in stabilising internal body temperature as the environment changes
Transparent
-allows light to pass through which is important for light dependent stage of photosynthesis
High heat of latent evaporation
LHE=Energy required to break hydrogen bonds between water molecules
-important in thermoregulation of mammals: cooling by sweating, panting
-evaporation of water removes heat from the surface of skin/tongue
High cohesion between water molecules
Cohesion=attraction between dipoles of adjacent water molecules forming hydrogen bonds
-important in transpiration stream: long continuous columns of water form in xylem vessels
-important in transporting and circulating molecules e.g plasma, translocation
-provides supportive role: hydrostatic skeleton (earthworm), turgor pressure (plants), amniotic fluid (supports and protects foetus), supports aquatic organisms
-enables motility of aquatic organisms as they thrust against it=forward motion
Universal solvent
-carries polar molecules and ions
-ions and ionic molecules are surrounded by water molecules so they dissolve
-important in transporting ions, proteins
-important in removing waste e.g urea in urine
-important in allowing chemical reactions to take place inside cells e.g hydrolysis of macromolecules (proteins and lipids), respiration, protein synthesis
-metabolic functions: reactant in photosynthesis, hydrolysis reactions and medium for all biochemical reactions
Low density when solid
-water freezes at 0 degrees
-water molecules are held further apart as each water needs to form 4 hydrogen bonds with different molecules as the hydrogen bonds form a lattice
-density decreases when it freezes as it floats on surface of water in liquid state
-important as insulates water beneath the ice
-forms surface which acts as habitats for some organisms e.g polar bear
-changes in density produce circulation currents in large bodies of water so aids nutrient cycling
Adhesive and cohesive properties
-adhesion: hydrogen bonding between water and the lining of the xylem, cellulose in cell walls of xylem, hydrophilic parts of lignin
-adhesion acts as a lubricant, reduces friction e.g formation of pleural fluid (minimises friction between lungs and ribcage), mucus (to allow passage of faeces from large intestine to rectum and out of anus), synovial fluid (reduces friction and resistance in joints)
-cohesion: allows continuous, unbroken column of water molecules in xylem (enabling transpiration stream)
Molecular motility
-weak hydrogen bonds means water molecules can move easily relative to each other
-allows osmosis to occur
