2: Water and Life Flashcards
State 4 unusual but very useful types of properties of water.
- cohesive
- adhesive
- thermal
- solvent
How can the 4 ‘unusual but useful’ types of properties of water be explained? What is this a good example of?
- using the theories of dipolarity and hydrogen bonding
- theories being used to explain natural phenomena
Explain the ‘cohesive’ properties of water in terms of hydrogen bonding and dipolarity. Give an example of a benefit to living organisms this property provides.
Explanation:
- water molecules cohere because of hydrogen bonds that form between them
Example:
- strong pulling forces exerted to suck columns of water up to the tops of the tallest trees in tubes called xylem vessels. These columns rarely break
Explain the ‘adhesive’ properties of water in terms of hydrogen bonding and dipolarity. Give an example of a benefit to living organisms this property provides.
Explanation:
- dipolarity of water molecules makes them adhere to surfaces that are polar and therefore hydrophilic
Example:
- adhesive forces between water and cellulose in cell walls in the leaf
- cause water to be drawn out of xylem vessels, keeping the cell walls moist and able to act as a gas exchange surface
Explain the ‘thermal’ properties of water in terms of hydrogen bonding and dipolarity. Give an example of a benefit to living organisms this property provides.
Explanation:
- due to hydrogen bonding, water has high melting and boiling points, high latent heat of vaporization and high specific heat capacity
Example:
- thermal properties cause water to be liquid in most habitats on earth = suitable for living organisms
- high specific heat capacity makes its temp change slowly so it is a stable habitat
- high heat of vaporization makes it an effective coolant in leaves or in sweat
Explain the ‘solvent’ properties of water in terms of hydrogen bonding and dipolarity. Give an example of a benefit to living organisms this property provides.
Explanation:
- many substances dissolve in water due to its polarity, including those composed of ions or polar molecules
Example:
- most chemical reactions take place with all of the substances involved in the reaction dissolved in water, so water is the medium for metabolic reactions
What happens in a condensation reaction?
two molecules are joined together to form a larger molecule plus a molecule of water
What sort of reactions are anabolic reactions?
condensation reactions
What is a dimer?
a pair of monomers - single sub-units - bonded together
What is a polymer composed of?
a long chain of monomers
What would you call two amino acids joined together?
a dipeptide
What sort of reaction joins two amino acids together?
a condensation reaction
What would a long chain of amino acids be called?
a polypeptide
What bond links amino acids together?
a peptide bond
Draw a condensation reaction between two amino acids. (p19)
-
Name three macromolecules that are built through condensation reactions.
- proteins
- carbohydrates
- lipids
What is the basic sub-unit of carbohydrates?
monosaccharides
What would a condensation reaction between two monosaccharides form?
a disaccharide + H2O
What does a long chain of monosaccharides form?
a polysaccharide
What are glycerides made from?
fatty acids and glycerol
What is the maximum number of fatty acids that can be added to glycerol? What does this form?
3 - a triglyceride + 3 water molecules
What happens in a hydrolysis reaction?
a large molecule is broken down into a smaller molecule
What is used up in a hydrolysis reaction?
water
How is water used in a hydrolysis reaction?
- -H and -OH split (hence lysis = splitting)
2. -H and -OH needed to make new bonds after a bond in the macromolecule has been broken
Give 3 examples of hydrolysis reactions.
- polypeptides + H2O –> dipeptides or amino acids
- polysaccharides + H2O –> disaccharides or monosaccharides
- glycerides +H2O –> fatty acids + glycerol
