1.7 Water

Question 1

How does hydrogen bonding occurs between water molecules?

Answer 1

• Water is a polar molecule (oxygen molecule has a partial negative charge; hydrogen atoms have a partial positive charge)
• Slightly negatively charged oxygen atoms attract slightly positively charged hydrogen atoms of other water molecules

Question 2

List the properties of water that are important in biology?

Answer 2

• High specific heat capacity
• High latent heat of evaporation
• Cohesive
• Solvent
• Metabolie

Question 3

Why does water have high specific heat capacity and why is it important in biology?

Answer 3

• Polar so many H bonds form between water molecules - these allow water to absorb a relatively large amount of heat energy before its temperature change
• Good habitat for aquatic organisms eg/ lakes as temperature more stable than land
• Organisms mostly made of water so helps maintain a constant internal body temperature - important as temperature affects enzyme activity

Question 4

Why does water have high latent heat of vapourisation and why is it important in biology?

Answer 4

• Polar so many H bonds form between water molecules - these can absorb a lot of energy before breaking, when water evaporates
• Evaporation of small amount of water is an efficient cooling mechanism
• Helping organisms maintain a constant body temperature

Question 5

Why does water have cohesion and why is it important in biology?

Answer 5

• Polar so many H bonds form between water molecules - so water molecules tend to stick together
• Column of water doesn’t break when pulled up narrow tube eg/ xylem
• Produces surface tension at an air-water surface so invertebrates can walk on water eg/ pond skates

Question 6

How is water a solvent and why is it important in biology?

Answer 6

• Polar (has a slightly positive and negative ends)
• Can separate (dissolve) ionic compounds eg/ NaCl as positive end attached to negative ion (Cl-) and negative end attracted to positive ion (Na+)
• Can dissolve other substances eg/ inorganic ions, enzymes, urea, etc
• Acts as a medium for metabolic reactions (which can happen in water)
• Acts as a transport medium eg/ in xylem to transport nitrates which are needed to make amino acids