1.7 Water Flashcards
What percentage of tissues is water in plants and mammals?
Plants= 90%
Mammals= 60-70%
What is the molecule water made up out of?
Two hydrogen atoms covalently bonded to one oxygen atom.
What is this symbol and what does it mean?
Delta symbol = slight charge ; either slightly positive or slightly negative
(due to uneven even distribution of electrons)
Where are hydrogen bonds found?
Water, and other other biological compounds ( carbohydrates and proteins)
Describe why the electrons in water are not shared evenly between the hydrogen and oxygen atom
The larger oxygen atom pulls the electron closer towards it and becomes slightly negatively charged, whereas the smaller hydrogen atom becomes slightly positively charged. These slight charges attract one another and form a weak interaction called the hydrogen bond. These are continually broken and reformed.
Hydrogen bonds individually are […..] interactions. Many hydrogen bonds are [……..] interactions.
Hydrogen bonds individually are weak interactions. Many hydrogen bonds are stronger interactions.
What kind of molecule is water?
Polar molecule = has an uneven distribution of charge
Name all 9 properties of water
- Metabolite
- High latent heat of vaporisation
- Liquid with relatively high boiling point
- Low density of ice
- High specific heat capacity
- Cohesion
- Solvent
- Transport medium
- Transparent
What is the biological importance of water being a metabolite?
A metabolite is a molecule that takes part in a metabolic reaction (condensation and hydrolysis reactions) e.g photosynthesis or splitting disaccharides to monosaccharides by hydrolysis reactions
Why does water have a high latent heat of vaporisation?
The evaporation of water requires a lot of energy to break the hydrogen bonds. When water evaporates from a surface it ‘removes’ the heat and has a cooling effect
E.g sweating and transpiration
Why does water having a relatively high boiling point?
The continual making and breaking of hydrogen bonds in water means that it is a liquid not a gas and it is difficult for water molecules to escape the liquid which means that the boiling point is much higher than other similar sized molecules
Why does water have a low density of ice?
As water is cooled the molecules slow down (less kinetic energy), more hydrogen bonds form holding the water molecules to form a crystalline structure which is less dense than liquid water. This means that Ice floats on water and insulates the organisms that live beneath it
Why does water have a high specific heat capacity?
The hydrogen bonds in water prevent the movement of the water molecules so relatively large amounts of energy are required to increase the temperature of the water. Water therefore has a high specific heat capacity; buffering changes in temperature. This means that large bodies of water are thermostable - marine life is dependant on thermostability to survive
think how on a hot day in England you go to the beach and the sea is still cold
Why does cohesion occur in water and what is its biological importance?
- Hydrogen bonds cause water molecules to stick together. This results in surface tension at the surface of the water (can allow organisms e.g pond skaters to ‘walk on water’).
- Water can be transported up the xylem in the transpiration stream as cohesion between water molecules makes long thin columns of water difficult to break
- produces surface tension where water meets air
Why is water a really good solvent?
The polarity of the water makes it a good solvent - any polar molecules like ions will dissolve well in water. The negative ions will be attracted to the positive end of the water molecule and the positive ions to the negative end. Water molecules tend to cluster around any charged parts of solute molecules. Allows metabolic reactions (e.g photosynthesis and respiration) to take place in solution in the cytoplasm.
