Chapter 2.4

Question 1

Water Molecules: structure and attraction

Answer 1

—-The oxygen atom attracts the electrons more strongly than the hydrogen atoms, resulting in a weak negatively charged region on the oxygen atom (δ–) and a weak positively charged region on the hydrogen atoms(δ+), this also results in the asymmetrical shape

• This separation of charge due to the electrons in the covalent bonds being unevenly shared is called a dipole. When a molecule has one end that is negatively charged and one end that is positively charged it is also a polar molecule
• Water is a polar molecule

Question 2

water def

Answer 2

• Water is composed of atoms of hydrogen and oxygen. One atom of oxygen combines with two atoms of hydrogen by sharing electrons (covalent bonding)
• The polarity of water molecules allows hydrogen bonds to form between adjacent water molecules

Question 3

Hydrogen bonds contribute to the many properties water molecules have that make them so important to living organisms:

Answer 3

• An excellent solvent – many substances can dissolve in water
• A relatively high specific heat capacity
• A relatively high latent heat of vaporisation
• Water is less dense when a solid
• Water has high surface tension and cohesion
• It acts as a reagent

Question 4

Hydrogen bonds

Answer 4

form between water molecules

—-As a result of the polarity of water hydrogen bonds form between the positive and negatively charged regions of adjacent water molecules -Hydrogen bonds are weak, when there are few, so they are constantly breaking and reforming. However when there are large numbers present they form a strong structure

Question 5

Water Molecules: In Living Organisms

Answer 5

• Water has many essential roles in living organisms due to its properties:
• The polarity of water molecules
• The presence and number of hydrogen bonds between water molecules

Question 6

Solvent

Answer 6

-As water is a polar molecule many ions (e.g. sodium chloride) and covalently bonded polar substances (e.g. glucose) will dissolve in it

—-This allows chemical reactions to occur within cells (as the dissolved solutes are more chemically reactive when they are free to move about)

—-Metabolites can be transported efficiently (except non-polar molecules which are hydrophobic)

Question 7

High specific heat capacity

Answer 7

• The specific heat capacity of a substance is the amount of thermal energy required to raise the temperature of 1kg of that substance by 1°C. Water’s specific heat capacity is 4200 J/kg°C
• The high specific heat capacity is due to the many hydrogen bonds present in water.
• It takes a lot of thermal energy to break these bonds and a lot of energy to build them, thus the temperature of water does not fluctuate greatly

Question 8

The advantage for having high specific heat capacity in living organisms is that it

Answer 8

• Provides suitable habitats
• Allows for constant temperatures within bodies and cells to be maintained (this ensures enzymes have the optimal temperatures)
• This is because a large increase in energy is needed to increase the temperature of water

Question 9

Latent heat of vaporisation

Answer 9

• In order to change state (from liquid to gas) a large amount of thermal energy must be absorbed by water to break the hydrogen bonds and evaporate
• This is an advantage for living organisms as only a little water is required to evaporate for the organism to lose a great amount of heat
• This provides a cooling effect for living organisms, for example the transpiration from leaves or evaporation of water in sweat on the skin

Question 10

Properties of water & its role in living organisms table

Answer 10