Flashcards in The Biological Importance of Water Deck (34)
Define the term 'Polar'
The uneven distribution of charge resulting in atoms within a molecule to have opposing charges (one having a partial negative charge, another having a partial positive charge).
i.e. A polar covalent bond is when electrons (negatively charged) have been shared unevenly between atoms.
Define the term 'Dipole'
A molecule that has both positive and negative charges due to an uneven distribution of charges.
Define the term 'Electronegativity'
Electronegativity is the measure of the tendency of an atom to attract bonding pairs of electrons. Some atoms have a much stronger electronegativity than others.
Give examples of some atoms with a strong electronegativity.
Oxygen, Flourine, Nitrogen
Explain what a hydrogen bond is, which types of atoms it can join together and where they occur in biology.
- A weak type of chemical bond (but collectively they are very strong)
- Occurs between a hydrogen atom and another strongly electronegative atom of a polar covalent bond in the same or another molecule.
- In water, the slightly negative oxygen atoms are attracted to the slightly positive hydrogen atoms in another molecule.
Explain why water is a polar molecule.
A water molecule is formed by covalent bonds (the sharing of electrons) betweeen hydrogen and oxyen atoms. Because oxygen is more strongly electronegative than hydrogen it has a greater pull on the shared electrons than the hydrogen, resulting in an uneven distribution of charges.
This causes a partial negative charge on oxygen (due to the closeness of the electrons) and a partial positive charge on hydrogen, therefore it is a polar molecule. (Water forms polar covalent bonds)
Gives some roles that water plays in life.
- Medium for transport
- Medium for chemical reactions
- Temperature control
- Reproduction (bringing the male and female gametes together for fertilisation)
- A reactant
- A solvent
Describe the structure of a water molecule.
A water molecule consists of two hydrogen atoms and one oxygen atom. They are bonded by polar covalent bonds.
What is the bond that links two water molecules together?
A hydrogen bond.
Draw two water molecules and label the bond that links them together.
Draw and look up in text book.
Explain why water is a polar molecule.
Water is a polar molecule because oxygen is more strongly electronegative than hydrogen, so it has a greater pull on the shared electrons. This results in oxygen having a slightly negative charge and hydrogen having a slightly positive charge, therefore, it is polar.
Explain how the polar nature of water makes it's freezing point 0 and it's boiling point 100.
Because water is polar, hydrogen bonds form between the molecules. Collectively, these bonds require a lot of energy to break and separate the water molecules. This means that water has a high boiling.
Explain the biological significance of water's freezing and boiling point.
Because water's boiling point is 100 degrees it stays as a liquid at most envrionmental temperatures, and so provides a stable aquatic environment and medium for chemical reactions.
Explain how the polar nature of water gives it a high specific heat capacity.
Hydrogen bonds give water a high specific heat capacity. The hydrogen bonds between the water molecules can absorb a lot of energy so it takes a lot of energy to heat water up.
What is high specific heat capacity?
The energy needed to raise the temperature of one gram of a substance by 1 degrees celsius.
Explain the biological signifcance in having a high specific heat capacity.
Water temperature remains fairly stable, reducing fluctuations in organisms and environments. Cells and aquatic environments slow to freeze.
Explain how the polar nature of water gives it a high latent heat of vaporisation.
Water is polar, so it has hydrogen bonds between molecules. It takes a lot of energy to break the hydrogen bonds between water molecules because hydrogen bonds absorb a lot of energy, so a lot of energy is used up when trying to evaporate water.
What is the biological significance of water having a high latent heat of vaporisation?
It is effective as a coolant, through sweating because a large amount energy is expended in evaporating sweat from the surface of our skin. This also happens in panting and transpiration.
Explain how the polar nature of water means that it has a lower density when a solid.
Water molecules are held further apart in ice than in liquid water because each water molecule forms four hydrogen bonds to other water molecules making a lattice shaper. This means that ice takes up a greater volume with the same mass, and so it is less dense.
When is water at its highest density?
At 4 degrees Celsius.
What is the biological significance of water being less dense as a solid?
Because ice floats water freezes on the surface first, this forms an insulating layer over the rest of the water meaning that water under the ice does not freeze. This means that the aquatic environment of organisms does not freeze over completely.
Explain how the polar nature of water makes it a good solvent for other ionic and polar molecules.
The polar nature of water means that one side of the water molecule is delta positive and one side is delta negative. They attract to ionic and polar compounds because the delta negative side attracts to the positive ion in the compound (e.g. Oxygen is attracted the negative Na+ in NaCL) and delta positive side is attracted to the negative ion in the compound (e.g hydrogen is attracted to CL-). The individual charged ions are pulled away from the compound and are surround by water molecules to form a hydration sphere, so the compound is dissolved.
Explain the biological significance of water being a good solvent for polar and ionic compounds.
Enables transport of substances in solution (i.e. in the human circulatory system and in the vascular bundles of plants). Oxygen and other essential nutrients can dissolve in water in aquatic environments.
When something is hydrophilic, it can interact with water. It will readily dissolve or absorb water.
When something is hydrophobic, it repels water. It is insoluable in water.
Explain how the polar nature of water makes it cohesive.
Cohesion is the attraction of molecules of the same type. Water molcules are very cohesive because they have the attraction of hydrogen bonds between them (due to them being polar)
Explain the biological significance of water being cohesive?
Creates water collumn of transpiration stream, through the xylem of a plant. Creates a surface on which small organisms can live. The shape of rain drops.
Explain how the polar nature of water makes it adhesive.
Adhesion is when water adheres non- water molecules surfaces. This is because it forms hydrogen bonds to other polar molecules.
What is the biological significance of water being adhesive?
It allows capillary action, which is when water rises up narrow tubes because it has adhered to the surfaces of them. For example, when water rises up the xylem of a plant and through air spaces between particles in the soil.