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Created by tiasabs over 6 years ago


Topic 2.2 Water of IB Biology Chapter 2 Molecular Biology

Resource summary

  1. Hydrogen bonding in water
    1. H2O molecules polar and linked by hydrogen bonds
      1. covalent bond 2H, O
        1. H partial positive; O partial negative
          1. bent; poles are 2H and O
            1. positive and negative ions attract and form ionic bonds
              1. water - partial charge; less attraction, hydrogen bond
                1. intermolecular force rather than bond
                  1. slightly positive pole weakly attracted to slightly negative pole
                  2. Properties of water
                    1. Cohesive properties
                      1. binding of two molecules of the same type
                        1. due to hydrogen bonding
                          1. useful for water transport in plants
                            1. xylem sucks up water at low pressure
                            2. Adhesive properties
                              1. hydrogen bonds between water and other polar molecules
                                1. useful in leaves
                                  1. water adheres to cellulose in cell wall
                                    1. water absorbed from nearest xylem in case of evaporation from leaf via air network spaces to keep walls moist for CO2 absorption
                                    2. Thermal properties
                                      1. High specific heat capacity
                                        1. H bonds restrict motion so high heat required to break them
                                          1. relatively large amount of energy needed
                                            1. thermally stable habitat
                                            2. High latent heat of vaporisation
                                              1. lots of energy needed for evaporation to break H bonds
                                                1. Good evaporative coolant
                                                2. High boiling point
                                                  1. 100 degrees Celsius for same reason
                                                3. Solvent properties
                                                  1. polarity prevents molecules from clumping
                                                    1. dissolves molecules
                                                      1. cytoplasm - complex mixture of dissolved substances
                                                    2. Hydrophilic and hydrophobic
                                                      1. hyrophilic = water loving
                                                        1. substances that dissolve in water like glucose, sodium and chloride ions
                                                          1. substances that water adheres to such as cellulose
                                                          2. hydrophobic = water "fearing"
                                                            1. insoluble in water
                                                              1. non polar and no charge
                                                                1. all lipids such as fats and oils
                                                                2. forces that cause non polar substances to form groups = hydrophobic interactions
                                                                3. Comparing water and methane
                                                                  1. methane = waste product of anaerobic respiration where oxygen is lacking by certain prokar.
                                                                    1. methanogenic prokar. live in swamps, wetlands, animal guts, waste dumps
                                                                      1. methane fuel & greenhouse gas
                                                                        1. both small molecules linked by single covalent bonds
                                                                          1. water polar, forms H bonds methane non polar, cannot form H bonds
                                                                          2. Cooling the body with sweat
                                                                            1. sweat carried via narrow ducts to skin surface where spread out and released
                                                                              1. heat on skin used to evaporate sweat and cool blood
                                                                                1. solutes in sweat left on skin
                                                                                  1. controlled by hypothalmus in brain
                                                                                  2. Transport in blood plasma
                                                                                    1. Sodium chloride
                                                                                      1. amino acids
                                                                                        1. Glucose
                                                                                          1. Oxygen
                                                                                            1. Fat molecules
                                                                                              1. Cholestrol
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