Water Flashcards
Describe the structure of a water molecule
A Water molecule consists of two Hydrogen atoms covalently bonded to an Oxygen atom. Because oxygen is more electronegative than hydrogen, it has a greater pull on the shared electrons. This that the oxygen atom is slightly negative (δ-) (because of the closer electrons), and hydrogen is slightly positive (δ+). Water is therefore called a Polar Molecule.
Name the bond that can link two water molecules together.
A hydrogen bond
Explain what a hydrogen bond is, which types of atoms it can join together and where they occur in biology.
A hydrogen bond is the weak attractive force between molecules or parts of molecules that are polar. They are constantly breaking and reforming.
Define the term ‘polar’
Where there is an uneven distribution of charge across a molecule, with regions of δ-and δ+.
Explain why water is a polar molecule
In a covalent bond, electrons are not always shared equally between the atoms. Oxygen is more electronegative that Hydrogen, so it attracts electrons more strongly. This means the electrons spend more time closer to oxygen, so oxygen has a slightly negative charge.
Define the term ‘electronegativity’
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.
***Define the term ‘dipole’
Permanent dipole molecules are classified as polar.
What is the biological significance of the high specific heat capacity of water?
A lot of energy needed to heat water up meaning bodies of water remain at constant temperatures so are stable environments for organisms to live
What is the biological significance of the freezing of water?
Ice is less dense than water as more hydrogen bonds form at lower temperatures, holding the water in a fixed lattice. This means ice floats and provides an insulating layer on the top of water bodies, enabling living things to move and survive underneath.
What is the biological significance of the high specific latent heat capacity of water?
A lot of energy is needed to break the hydrogen bonds in water and cause it to evaporate, making it ideal when animals sweat for using up heat energy
What is the biological significance of the cohesion of water molecules?
- production of surface tension allows insects to walk on water
- water molecules stick together, and adhesion means they stick to the walls of the xylem so in transpiration water can move against gravity up the xylem
What is the biological significance of the fact that water is a solvent?
- water can act as a medium for chemical reactions
- water can transport dissolved substances into and out of cells
What is the biological significance of the reactivity of water?
Can take place in many reactions including hydrolysis and photosynthesis
Define the term ‘hydrophilic’
Molecules forming ionic or a hydrogen bond with the water molecule are said to be hydrophilic.
Define the term ‘hydrophobic’
Nonpolar molecules that repel the water molecules are said to be hydrophobic.
