Water

What metabolic reactions does water help in?

Metabolite in:

-condensation and hydrolysis reactions

-chemical reactions in aqueous medium

-chemical reactions in aqueous medium

-raw material in photosynthesis

What property of water means substances dissolve in it? Which substances?

a solvent - which dissolves:

• gases (o2 and co2)

• wastes (ammonia and urea)

• inorganic ions and hydrophilic molecules (ATP, amino acids, monosaccharides)

• enzymes whose reactions occur in solution

  
  

How does water help with temp control?

• it has a high latent heat of vaporisation so a lot of body heat and energy is used to vaporise water - carries heat away + cools surface

What are other properties of water?

1) not easily compressed – provides support

2) transparent – aquatic plants can photosynthesise

3) molecules are very cohesive - (stick together) which helps water transport in plants

How does structure of water cause polarity? How does polarity cause water to stick together?

1)

• Consists of one atom of oxygen joined to two atoms of hydrogen by shared electrons

• because the shared negative hydrogen electrons are pulled towards the oxygen atom, the other side of each hydrogen is left with a slight positive charge

• whilst the unshared negative electrons on oxygen atom give it a slight negative charge

• this difference in charge of atoms makes water polar (partial negative charge on left, partial positive charge on right)

2) Weak hydrogen bonds form between a positively charged hydrogen atom on one water molecule and a negatively charged oxygen atom on another water molecule (attract eachother)

Property and explain

1) Important metabolite – hydrolysis requires a water molecule to break a bond, condensation releases a molecule of water as a new bond is formed

Property and explain

2) Good solvent – because water is polar the positively charged end of water molecule is attracted to negative ion, negatively charged end of water is attracted to positive ion, meaning ions get surrounded by water molecules (dissolve)

property and explain

3)High latent heat of vaporisation – water vaporises when the hydrogen bonds holding water molecules together break – this means it requires a lot of energy to evaporate 1 gram of water – effective for cooling animals as body heat is used in water evaporation

property and explain

4) Specific heat capacity-

• hydrogen bonds stick water together, requiring more energy to break them – lot of energy used to break these bonds (high boiling point) so there is less heat energy available to increase the temp of water (takes a lot of energy to heat up 1 gram) so give water a high specific heat capacity

• due to this water acts as a buffer (can resist changes in temp) so provides a temp-stable habitat for organisms – the water inside organisms is stable and so buffers them against sudden temp changes, maintaining constant internal body temp

property and explain

cohesion + surface tension:

• water molecules are cohesive (attracted to each other so stick together) due to their polarity – large cohesive forces allow it to be pulled in a column up the xylem tissues

• cohesion means water has high surface tension when in contact with air – molecules pulled back into body of water rather than escaping – this means the surface acts like a skin (strong enough to support pond skaters)