Flashcards in Unit 2: Biological Molecules Deck (21):
What type of bond holds water molecules together?
Hydrogen bonds, which gives water some very important properties
What are hydrogen bonds?
Weak forces of attraction that form between molecules or between parts of a larger molecule. E.g. in water there is an attraction between the oxygen atom and each of the hydrogen atoms
Why can hydrogen bonding occur between water molecules?
Water molecules are polar, which means there is an uneven distribution of charge. Oxygen atoms attract electrons more strongly than hydrogen atoms.
What do hydrogen bonds cause?
Properties of water
Between 0 and 100 degrees celsius, water molecules are held together loosely but can move past each other and water remains a liquid. In order to evaporate, H-bonds must be broken to allow the formation of a gas.
Why does ice float on water?
At lower temperatures, the molecules have less kinetic energy and move about less, meaning more H-bonds can form and at 0 degrees celsius enough would have formed to hold water molecules in a stationary position - rigid lattice, which holds molecules further apart, therefore it is less dense and floats
Water Properties: Thermal Stability
High specific heat capacity (a lot of heat needed to warm it up and therefore has a fairly consistent temperature, which is essential for life)
Water Properties: Freezing
Less dense than water so it floats, which insulates the water and prevents it fully freezing therefore living things can survive below the ice
Water Properties: Evaporation
A lot of energy is needed to cause evaporation, which is used to cool the surface of living organisms
Water Properties: Cohesion
The attraction of water molecules produces surface tension, which creates a habitat on the surface and continuous columns of water to be pulled up the xylem
Water Properties: Solvent
As water molecules are polar, water can dissolve a wide range of substances
Water Properties: Reactant
Water can be used in a wide range of reactions from hydrolysis to photosynthesis
Water Properties: Incompressibility
Water cannot be compressed into a smaller volume which means it can be pressurised and pumped in transport systems or used for support in hydrostatic skeletons
Single, small molecules
Long chains of repeated units (repeated monomers)
Monosaccharides and Polysaccharides
Amino Acids and Polypeptides
Nucleic Acids (M&P)
Nucleotides and DNA/RNA
Making bonds, H2O produced
Breaking bonds, uses H2O