Chapter 3 - The Chemistry of Life


Chapter 3 – The Chemistry of Life (Revision Notes)




3.1 Chemical elements and water


3.1.1 State that the most frequently occuring chemical elements in living things are carbon, hydrogen, oxygen and nitrogen.


- the most frequently chemical elements that are occuring in living organisms are:

            - Carbon – 19%

            - Hydrogen – 10%

            - Oxygen – 65%

            - Nitrogen – 3%

- they are used in the molecular structures of all carbohydrates, proteins, lipids and nucleic acids


3.1.2 State that a variety of other elements are needed by living organisms, including sulphur, calcium, phosphorus, iron and sodium.


- living organisms contain more than 20 other element which are also present, but far less common

            - Sulphur – 0.25%

            - Calcium – 1.5%

            - Phosphorus – 1%

            - Iron - 0.7%

            - Sodium - 0.15%


3.1.3 State one role for each of the elements mentioned in 3.1.2.


-       Sulphur – found in certain amino acids (cysteine and methionine), needed for the synthesis of two amino acids, allows proteins to form disulphide bonds


-       Calcium – co-factor in some enzymes, can be found in bones and teeth, involved in neurotransmitter release in synapses


-       Phosphorus – phosphate groups in ATP, part of DNA molecules, component of nucleic acids and cell membranes


-       Iron –  found in cytochromes and haemoglobin (animals), allowing oxygen transport (aerobic cell respiration)


-       Sodium –  involved in the generation of nerve impulses in neurons, raises the solute concentration which causes water to enter by osmosis, in membrane function




3.1.4 Draw and label diagram showing the structure of water molecules to show their polarity and hydrogen bond formation.



- water (H2O) is made up of two hydrogen atoms covalently bound to an oxygen atom

                  → involves sharing of electrons but they are NOT shared equally

                  → oxygen atom, having more protons, attracts the electons more strongly (oxygen has higher electronegativity)

                  → the oxygen atom becomes slightly negative and the hydrogen atoms become slightly positive


      - hydrogen bonding

                  → covalently bonded molecule that have a slight potential charge are usually POLAR

                  → the charged regions of the water molecule can attract polar or charged compounda

                  → water molecules associate through weak hydrogen bonds




3.1.5 Outline the thermal, cohesive and solven properties of water.


-       Thermal properties high specific heat capacity (the measure of energy require to raise the temperature of 1g of substance by 1°C) – water can absorb or give off a great deal of heat without changing temperature greatly

-       high heat of vaporization – water absorbs a great deal of heat when it vaporizes (the amount of energy absorbed per gram as it changes from liquid to a gas/vapour) – cooling mechanism


-       these properties


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