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Water and inorganic ions: the properties life depends on questions
Why a water molecule is polar and how hydrogen bonds form between molecules. The properties that follow: solvent, high specific heat capacity, high latent heat of vaporisation, cohesion and surface tension, and ice being less dense than water. The roles of hydrogen, iron, sodium, phosphate, calcium and nitrate ions.
8 original questions · 25 marks · the water and inorganic ions: the properties life depends on notes · Biological molecules, water and inorganic ions
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State two properties of water that result from hydrogen bonding between its molecules, and state one biological consequence of each.
Mark scheme
- B1 any one property: high specific heat capacity, high latent heat of vaporisation, cohesion and high surface tension, or ice being less dense than liquid water
- B1 a consequence of that property, for example that the temperature of a cell or a habitat changes slowly
- B1 a second property from the same list
- B1 a consequence of the second property, for example that evaporation of sweat removes a large amount of heat
Describe how a hydrogen bond forms between two water molecules.
Mark scheme
- B1 the oxygen atom attracts the shared electrons of each covalent bond more strongly than the hydrogen atoms do, so the oxygen is slightly negative and the hydrogens are slightly positive
- B1 the molecule is therefore polar
- B1 a slightly positive hydrogen atom of one molecule is attracted to the slightly negative oxygen atom of a neighbouring molecule, and that attraction is the hydrogen bond
Explain why the temperature of a large lake changes more slowly during a hot day than the temperature of the air above it.
Mark scheme
- B1 water has a high specific heat capacity, so a large amount of energy is needed to raise the temperature of a given mass of it
- B1 much of the energy absorbed goes into breaking hydrogen bonds between the water molecules rather than into increasing their kinetic energy
- B1 so the temperature of the lake rises slowly, and organisms living in it are not exposed to rapid changes in temperature
Explain how sweating cools a mammal, and explain why only a small volume of sweat is needed to remove a large amount of heat.
In winter a pond freezes at the surface while the water below stays liquid. Suggest how this is explained by the structure of ice, and suggest what it means for the animals living in the pond.
Explain why sodium chloride dissolves readily in water but a triglyceride does not.
Give the role of iron(II) ions, phosphate ions and calcium ions in a named structure or process.
A crop grown in soil low in nitrate has pale leaves and grows poorly. Explain why a shortage of nitrate ions has these effects.
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