2.2 Water Flashcards
what is the bonding in water like? discuss charges and bonding within and between molecules
water is a covalent bond between 2 Hs and 1 O, however the share of electrons is unequal so the nucleus of the O is more attractive to the electrons than the nucleus of the Hs. This makes the H partially positive and the O partially negative.
This is called a polar covalent bond.
because the water molecules are bent and not linear the two H form one pole and the O forms a seperate pole
water molecules only have a slight charge so there is not that much attraction to other particles however there is enough to have a significant effect
the attraction between the seperate molecules is a hydrogen bond, or more precisely and intermolecular force. this is the force when one polar molecules is attracted to a slightly negative atom of another polar molecules
explain the cohesive property of water
cohesion is the binding together of two molecules of the same type i.e. two water molecules
this cohesion or sticking together due to hydrogen bonds is useful as it means water can be transported in plants through the xylem at low pressure. (high tensile strength)
this only works because water is not seperated by suction forces
results in a high surface tension which provides habitat to e.g. pond skaters
explain the adhesive property of water
hydrogen bonds can form between water and other polar molecules causign water to stick or adhere to them.
e.g. water adheres to cellulose molecules in cell walls which is useful as if water evaporates adhesive forces cause water to be drawn out of nearest xylem vessle to keep the walls moist to absorb CO2 for photosynthesis
explaint the thermal properties of water
water is a liquid for most temps (between 0 - 100 degrees) so in most habitats
high specific heat capacity
due to large number of hydrogen bonds you need a lot of energy to change temp of water. This makes water relatively stable compared to land or air so a thermally stable habitat for aquatic life
high latent heat of vaporization
i.e. you need a lot of heat to cause it to vaporize
good evaporant coolant
evaporation has a cooling effect as you take heat with you, water is a good evaporation coolant in e.g. sweat, transpiration
explain the solvent properties of water
The polar nature of water means it forms shells around charged and polar molecules. This prevents them from clumping and keeps them in solution.
Water forms hydrogen bonds with polar molecules as it has both a partially negative & positive pole both ions dissolve.
cytoplasm is a complex mixture of dissolved substances needed for metabolism.
water is a universal solvent
importance of ice and water
ice is less dense than water so will float on water due to the hydrogen bonds expanding and repelling in a crystalline lattice
less to habitat above ice, helps reduce overcooling in water and means it floats so wildlife in ponds do not freeze to death
importance of transparency of water
allows sunlight through which is needed for photosynthesis in aquatic plants in ponds and in the eyes for animals
what is hydrophobic and hydrophilic?
hydrophilic are water loving molecules that either dissolve in water ( polar molecules e.g. glucose or chloride ions) and substances that water adheres to (e.g. cellulose)
hydrophobic are substances that are insoluble in water but can dissolve in other solvents e.g aectone (e.g. all lipids)
if you have two non polar molecules in a lipid they behave as though they are attracted to each other. This is hydrophobic interaction. If they are together more bonds can form between the water molecules as the water molecules are more attracted to eachother than to the non polar molecules.
therefore non polar molecules in water tend to form larger and larger groups
comparing water and methane’s properties
methane is a waste product in anaerobic respiration in e.g. METHANOGENIC PROKARYOTES who live in swmps and places where oxygen is lacking e.g. guts of animals (sheep, cattle) or waste dumps
they are encouraged to produce methane in anaerobic digesters for fuel.
methane is
- non polar
- no hydrogen bonds
therefore oxygen has
- higher specific heat capacity
- higher latent heat of vaporization
- higher melting point
- higher boiling point
cooling the body with sweat
sweat is secreted by sweat glands into narrow glands and is then carried onto skin where it spreads out and evaporatied
works because water has
- high latent heat of vaporization
solutes in the sweat e.g. ions remain on skin so it tastes salty
it is controlled by hypothamlamus which monitors blood temp and recieves sensory input from temp receptors in skin. It can stimulate sweat production of up to 2 liters per hour.
when adrenaline is released we also sweat even if cold in anticipation of intense activity resulting in overheating.
other methods of cooling e.g. panting and transpiration also rely on heat loss through evaporation.
what and how does the blood plasma transport things?
sodium chloride - freely soluble in water as made of ions
amino acids - have n/p charges so soluble, however depending on R group some are philic and some phobic but all are soluble enough to be carried in the plasma
glucose - polar so can be dissolved in blood plasma
oxygen - non polar and very low solubility, water easily becomes saturated, as temp increases water solubility decreases so less oxygen. Far too little dissolved to supply cells withO2 so we use haemoglobin which has binding sites for O2
fat molecues
- non polar, insoluble,larger than O2
- carried in lipoprotein complexes
- these have phospholipids which are hydrophilic on outside in monolayer and fats and hydrophobic hydrocarbons on the inside
cholesterol
- non-polar
- hydrophobic except small hydrophilic region at one end
- transported with fatso in lipoprotein complexes in the phospholipid monolayer with hydrophilic region facing outwards
