Biological Molecules Flashcards
Describe water.
Water is a polar molecule – the oxygen atoms are slightly negative and the hydrogen atoms are slightly positive. Hydrogen bonds form between adjacent water molecules.
What are properties of water?
Liquid at room temperature, low density when solid, good solvent, cohesion/surface tension, high specific heat capacity, high latent heat of vaporisation
Why is water a liquid at room temperature?
As the water molecules move, they continually are making/breaking hydrogen bonds. The hydrogen bonding also makes it more difficult for them to escape and become a gas. Water has a low viscosity, despite its hydrogen bonds.
Why is water being a liquid at room temperature important for living organisms?
Provides habitats for living things in rivers/lakes/seas. Provides an effective transport medium – i.e. blood. Provides a medium for chemical reactions. Forms a major component of the tissue of living organisms.
Why does water have a low density, when solid?
When water goes to freezing point, due to its polar nature, the water molecules align themselves in a structure. This structure is less dense than that of liquid water.
Why is water, having a low density when solid, important for living organisms?
Provides a habitat for organisms that live on the floating ice. Aquatic organisms also live in a stable environment – the ice does not sink, so the sea will not freeze over. Bodies of water (with organisms) are insulated against the extreme cold as a layer of ice reduces the rate of heat loss.
Why is water a good solvent?
A good solvent for many substances found in living things – i.e. ionic solutes (NaCl)/covalent solutes (glucose). Water is polar – the positive/negative parts are attracted to the positive/negative parts of the solute. The water molecules cluster around these parts of the solute molecule/ion, which helps separate them and keep them apart. They are now dissolved and the solution is formed.
Why is water being a good solvent important for living organisms?
Molecules can be transported around living things, having been dissolved in water first. Molecules/ions can react together in water – i.e. cytoplasm.
Why does water have a high specific heat capacity?
Water requires a lot of energy to increase its temperature and therefore, break its hydrogen bonds. This means water does not change temperature, very easily.
Why is water having a high specific heat capacity important for living organisms?
Aquatic organisms need a stable environment in which to live. Organisms need a stable temperature in order that, enzymes do not denature and reactions can happen properly.
Why does water have a high latent heat of vaporisation?
When water evaporates, the latent heat of vaporisation (heat energy), helps the molecules break from each other to become a gas. The molecules are held together by hydrogen bonds so lots of energy is needs for a water molecule to evaporate.
Why is water having a high latent heat of vaporisation important?
Water can act as a coolant – for mammals are cooled when sweat evaporates from the skin / plants are cooled when water evaporates from mesophyll cells (in leaf).
Why does water have cohesion and surface tension?
Water molecules show cohesion – the hydrogen bonds between them, pull them together – even on the surface of water. The surface of the water contracts (molecules are being pulled inwards), giving the surface the ability to resist force that is applied to it – surface tension.
Why is water having cohesion and surface tension important for living organisms?
Surface tension allows small insects to water on water. Transpiration (plants) – transportation in the xylem.
