A Level Biology : Module 1 - Biological Molecules

Question 1

Notes about water

Answer 1

• Medium in which metabolic reactions take place within cells
• Habitat
• Covalently bonded H and O atoms
• Oxygen is weakly negative, hydrogen is weakly positive
• Water is a POLAR molecule (dipole)
• Has HYDROGEN BONDS

Question 2

What are Hydrogen Bonds?

Answer 2

• Formed between WATER MOLECULES
• Because of the polarity of water molecules, hydrogen bonds form between the oppositely charged regions of adjacent water molecules

Question 3

Properties of Hydrogen bonds?

Answer 3

• They are weak, but when in large numbers can be form a strong structure
• These bonds contribute to water’s vital properties

Question 4

Properties of Water

Answer 4

• Excellent Solvent
• High specific heat capacity
• High specific latent heat of vaporisation
• High surface tension / Cohesion
• Less dense when a solid
• Acts as a reagent
• Habitat
• Transport medium
• Coolant

Question 5

Water as a solvent

Answer 5

• It is a polar molecule
• So ions, such as NaCl and other covalently bonded polar substances will DISSOLVE in water
• Allows chemical reactions to occur within cells (because dissolved solutes are more chemically reactive when free to move around)
• Metabolites can be transported efficiently (except non-polar hydrophobic molecules)

Question 6

High specific heat capacity in water

Answer 6

• The amount of thermal energy required to increase the temperature of 1kg of the substance by 1 degrees celsius
• 4200 J/KG°C
• Lots of energy is required to break these hydrogen bonds between water molecules, and lots to build them. Hence temperature of water does not fluctuate greatly
• Suitable habitat due to its ability to maintain a constant temperature without fluctuation (it can absorb a lot of heat and temp wont vary much), which is vital in maintaining temperatures optimal for enzyme activity
• Water in the blood plasma is vital for transferring heat from the body to it
• Blood plasma passes through more active and warmer regions of the body, and heat energy is absorbed but temp remains fairly constant, thus regulates constant body temperature

Question 7

Latent heat of vaporisation in water

Answer 7

• To change state from liquid to gas, a large amount of energy is required to break the hydrogen bonds and evaporate
• This is an advantage to organisms because lots of energy is required to evaporate only a little bit of water
• This provides a cooling effect, eg. Transpiration from leaves or evaporation from skin

Question 8

Water’s cohesive and adhesive properties

Answer 8

• HYDROGEN BONDS CAUSE THESE PROPERTIES
• Allows columns of water to move through xylem in plants, and through blood vessels in animals
• Enables surface tension when air meets water (hydrogen bonds occur between top layer of water molecules, forming a film, on which pond skippers can float)
• Water can hydrogen bond to other molecules such as CELLULOSE, which is ADHESION.
• This can enable water to move up xylem due to transpiration

Question 9

Direct role of water being a solvent in organisms

Answer 9

• Transport medium
• Allows chemical reactions to occur

(DUE TO POLARITYT OF WATER)

Question 10

Direct role of water having a high specific heat capacity

Answer 10

• Habitat
• Maintenance of optimal temperature

(due to hydrogen bonds)

Question 11

Direct role of water having a high specific latent heat

Answer 11

• Coolant

(due to hydrogen bonds)