Water

Question 1

Why are water molecules polar?

Answer 1

• oxygen has a greater affinity for electrons (more electromagnetic)
• this makes oxygen slightly negative and hydrogen slightly positive
• this creates different charged regions, which makes water polar

Question 2

What does dipolar mean?

Answer 2

• has two charged regions

Question 3

What makes water a stable structure?

Answer 3

• the numerous hydrogen bonds despite singular bonds only having a weak attraction/bond.

Question 4

Why does water have such a high boiling point?

Answer 4

• hydrogen bonds needs to be broken, which uses a lot of energy.

Question 5

Why is water ‘cohesive’ and what is the biological significance?

Answer 5

• cohesive due to the hydrogen bonds
• significant as it provides surface tensions that can be used for a habitat e.g. pond skaters
• cohesion also allows within a column of water the column doesn’t break when molecules are pulled up
• e.g. this allows xylem in transpiration to pull up water

Question 6

What is specific heat capacity and what is its biological significance?

Answer 6

• water absorbs/loses a relatively large amount of heat before temperature changes
• stops body temperature fluctuating too much and so enzymes don’t denature

Question 7

What is latent heat of vaporisation and what is its biological significance?

Answer 7

• water absorbs a large amount of energy before it turns into water vapour
• heat taken to vaporise sweat simultaneously cools you down, which stops enzymes denaturing also
• works in plants too

Question 8

Why does water act as a solvent for so many solutes? What is the biological significance?

Answer 8

• charges of the hydrogen and oxygen become attracted to the other polar molecules and separates the ions
• allows transport and high % of water increases metabolism
• polar molecules will dissolve in water but non-polar molecules won’t

Question 9

What are hydrophilic substances?

Answer 9

• substances that dissolve in water as they become part of water’s hydrogen bonded structure

Question 10

What are hydrophobic substances?

Answer 10

• substances don’t dissolve in water as they can’t become part of water’s hydrogen bonded structure

Question 11

How does the density of water facilitate life?

Answer 11

• life can be buoyant/float so organisms survive and can preserve energy
• ice has a lesser density than water making it float, so polar bears can hunt for example
• ice insulates the water beneath stopping the temperature fluctuating so aquatic life can survive

Question 12

Suggest, with reasons which properties of water make it such an important component of blood

Answer 12

• liquid so can transport substances
• acts as polar solvent
• allows chemical reactions
• biological molecules polar
• ions are charged
• relatively resistant to temp change as coolant

Question 13

Describe ways in which the physical properties of water allow organisms to survive over a range of temperatures

Answer 13

• SHC, body thermally stable, enzymes won’t denature
• latent heat of vaporisation, takes lots of heat to evaporate sweat cooling the body down, so enzymes won’t denature
• ice less dense than water so floats
• ice insulates
• solvent, reactions can happen, transport medium
• cohesion/adhesion, transpiration stream
• surface tension
• transparent, underwater photosynthesis
• high density, buoyant