Water And Inorganic Ions

Question 1

Where are inorganic ions found?

Answer 1

• in organisms where they occur in solution in the cytoplasm of the cells and in bodily fluids as well as a part of larger molecules

Question 2

What are the features of inorganic ions in the body?

Answer 2

• can be in concentrations ranging from very high to very low
• they perform a range of functions
• function of an ions is related to its structure

Question 3

Iron ions

Answer 3

• found in haemoglobin
• role in transport of oxygen

Question 4

Phosphate ions in DNA

Answer 4

• structural role in DNA
• store energy in ATP molecules

Question 5

Hydrogen ions

Answer 5

• determine pH of solution
• and so the functioning of enzymes

Question 6

Sodium ions

Answer 6

• transport of glucose and amino acid across plasma membranes

Question 7

What is the structure of a water molecule?

Answer 7

• no overall charge - oxygen has a slight -ve charge and hydrogen has a slight +ve charge
• has both +ve and -ve poles and is dipolar

Question 8

Hydrogen bonding in water

Answer 8

• +ve pole of one molecule attracts the -ve pole of another water molecule
• attractive force between 2 water molecules is called hydrogen bonding
• each fairly weak, together they form important forces, causing water molecules to stick together - giving unusual properties (cohesion - attraction between like molecules)
• each molecule can form 4 hydrogen bonds with other water molecules

Question 9

Specific heat capacity of water

Answer 9

• molecules stick together and so more energy required to separate them than if there were no hydrogen bonds
• bpt is higher than expected (would be gas otherwise - no life on Earth)
• more energy needed to heat specific mass of water and so high specific heat capacity
• acts as a buffer against sudden temperature variations (stabilises aquatic environment)

Question 10

Latent heat of vaporisation

Answer 10

• due to H bonding, more energy needed to evaporate 1 mole of water
• this energy is latent heat of vaporisation
• evaporation of water, e.g. sweat in mammals is very effective at cooling as body heat used to evaporate water

Question 11

Cohesion and surface tension

Answer 11

• tendency of molecules to stick together is known as cohesion
• H bonding so water has large cohesive forces (can be pulled through a tube such as xylem in plants)
• when molecules meet air, they are pulled back to body of water - this force is surface tension and means small organisms can stand on it

Question 12

Importance of water in living organisms

Answer 12

Water in metabolism
- hydrolyse complex molecules e.g. proteins to amino acids
- chemical reactions take place in aqueous medium
- raw material in photosynthesis
Water as solvent
- dissolves other substances readily
- gases e.g. CO2 and oxygen
- waste e.g. ammonia and urea
- enzymes (reactions aq)
- inorganic ions and hydrophilic molecules e.g. ATP and amino acids

Question 13

Other features of water

Answer 13

• evaporation cools organisms and allows them to control temperature
• not easily compressed and gives support e.g. hydrostatic exoskeleton of earthworm and turgor pressure in herbaceous plants
• transparent so aquatic plants can photosynthesise and light rays can penetrate jelly-like fluid in eye and reach the retina

Question 14

Adhesion vs cohesion

Answer 14

• cohesion = attraction between like molecules
• adhesion = attraction between unlike molecules