water Flashcards
1
Q
how do hydrogen bonds form between water molecules?
A
- water is a polar molecule: oxygen is more electronegative than hydrogen so attracts electron density in covalent bond more strongly
- O is δ- (slightly negative) and H is δ+ (slightly positive)
- there are inter-molecular forces of attraction between a lone pair on O δ- of one molecule and H δ+ on an adjacent molecule, forming a hydrogen bond
2
Q
state 7 biologically important properties of water
A
- high surface tension
- cohesion between molecules
- incompressible
- reaches maximum density at 4°C
- metabolite / solvent for chemical reactions in the body
- high specific heat capacity
- high latent heat of vapourisation
3
Q
why is the incompressible nature of water important for organisms?
A
- provides turgidity to plant cells
- provides hydrostatic skeletonfor some small animals e.g. earthworms
4
Q
explain why ice floats on water. why is this important for organisms?
A
- ice is less dense than water because H-bonds hold molecules in fixed positions further away from each other
- this insulates water in arctic climates so aquatic organisms can survive - water therefore acts as a habitat
5
Q
why is the high surface tension of water important for organisms?
A
- it slows water loss due to transpiration in plants
- water rises unusually high in narrow tubes, lowering demand on root pressure
- some insects can skim across the surface of the water
6
Q
why is water an important solvent for organisms? give an example
A
- it is a polar universal solvent that transports charged particles involved in intra- and extracellular reactions
- e.g. PO4^3- for DNA synthesis
7
Q
why is the high specific heat capacity and latent heat of vapourisation of water important for organisms?
A
- acts as a temperature buffer which enables endotherms to resist fluctuations in core temperature to maintain optimum enzyme activity
- cooling effect when water evaporates from skin surface as sweat / from mouth when panting
