Water Transport

What makes water a useful substance?

• it is a solvent

• most biological reactions take place in it

• it can transport substances - good at this due to its depolarisation nature

• water is cohesive

Structure of water molecules?

• one oxygen and two hydrogen molecules - (covalent)

• the oxygen is slightly negative (delta negative) and the hydrogen is slightly positive (delta positive)

• water is a dipolar molecule

• these slightly charged molecules are attracted to the opposite charge of other water molecules - causes hydrogen bonding

Why is water cohesive?

• cohesion = attraction between molecules of the same type

• water is cohesive as it is dipolar

• helps water flow and makes it good at transporting substances

Why is water a good solvent?

• water is dipolar and so they can be attracted to ions

• when water molecules completely surround an ion, the ion dissolves

What are mass transport systems?

They are used to carry raw materials from specialised exchange organs and remove metabolic waste

• e.g the circulatory system

Why do multicellular organisms require mass transport systems?

• cannot rely on simple diffusion as they have a lower SA:V (distance is too large)

• the system is used to provide raw materials for aerobic respiration (glucose and CO2) so that the organism can respire and get energy