Chapter 4

Question 1

What is so special about the molecule water, and why are its specific characteristics so important for life on earth

Answer 1

• High specific heat (amt of heat required to raise temp of unit mass by 1 C) due to hydrogen bonding = temperature changes in aquatic systems are buffered compared to terrestrial systems
• Increasing density from 0 to 4 C -> protects water bodies from freezing solid. As ice is less dense than water, ice cover is made during frozen periods - this ice cover acts as insulation, protecting deeper water body. During summer, less dense, warmer water floats on cooler water = insulation
• Salinity-density relationship: water increased in density with increased salt concentrations - high salinity water sinks to bottom of water body
• Greater density of water makes aquatic organisms relatively buoyant against gravitational pull - exert less energy
• Higher viscosity means slower passive sinking e.g. planktonic algae sink slower at lower temp

Question 2

Why do lakes not freeze solid during winter?

Answer 2

Increasing density from 0 to 4 C -> protects water bodies from freezing solid. As ice is less dense than water, ice cover is made during frozen periods - this ice cover acts as insulation, protecting deeper water body.