State one role for each of the elements mentioned in 3.1.2
Sulphur (S): Found in certain amino acids (cysteine and methionine), allowing proteins to form disulphide bonds, needed for the synthesis of 2 amino acids
Calcium (Ca): Found in bones and teeth, also involved in neurotransmitter release in synapses
Phosphorus (P): Component of nucleic acids and cell membranes
Iron (Fe): Found in hemoglobin (animals), allowing for oxygen transport
Sodium (Na): Involved in the generation of nerve impulses in neurons
Outline the thermal, cohesive and solvent properties of water
Thermal Properties
Water has a high specific heat capacity (the measure of energy required to raise the temperature of 1 g of substance by 1°C)
Water has a high heat of vaporisation (amount of energy absorbed per gram as it changes from a liquid to a gas / vapour)
Water has a high heat of fusion (amount of energy required to be lost to change 1 g of liquid to 1 g of solid at 0°C)
These properties occur as a result of the extensive hydrogen bonding between water molecules - this allows water to absorb considerable amounts of energy with little change in form (H-bonds need to be broken first)
Cohesive Properties
Water molecules are strongly cohesive (they tend to stick to one another)
Water molecules will also tend to stick to other molecules that are charged or polar (adhesion)
These properties occur as a result of the polarity of a water molecule and its ability to form hydrogen bonds with appropriate molecules
Solvent Properties
Water can dissolve many organic and inorganic substances that contain electronegative atoms (such as fluorine, oxygen and nitrogen)
This occurs because the polar attraction of large quantities of water molecules can sufficiently weaken intramolecular forces (such as ionic bonds) and result in the dissociation of the atoms
Other Properties
Water is transparent, allowing light to pass through it (important for photosynthesis)
Water expands when frozen, becoming less dense / lighter (important for life on earth - oceans don't freeze)
Explain the relationship between the properties of water and its use in living organisms as a coolant, medium for metabolic reactions and transport medium
Coolant
Both plants and animals use the evaporation of water from the surfaces of their bodies to facilitate cooling (sweating and panting in animals, transpiration from leaves in plants)
Water can be used to carry heat to cooler places in our bodies (countercurrent exchange of thermal energy)
Medium for Metabolic Reactions
Water can dissolve many organic and inorganic substances to facilitate chemical reactions
Water can also absorb thermal energy released as a by-product of many chemical reactions
Transport Medium
The forces of attraction between water molecules help facilitate the transport of water up the xylem of plants
Water is an effective transport medium for dissolved substances (in plants, minerals from the soil and sugars from the leaves can be transported in water through the xylem and phloem respectively; while in animals, water in the blood is used to transport oxygen, glucose and urea)
Surface Tension
The force of attraction between water molecules makes water sufficiently dense for some smaller organisms to move along its surface
Distinguish between organic and inorganic compounds
Organic compounds are compounds containing carbon that are found in living things - except hydrogen carbonates (HCO3-), carbonates (CO32-) and oxides of carbon (CO, CO2)
Inorganic compounds are all other compounds (there are less different inorganic compounds than organic compounds)
(a) Define monomer and polymer and give example of each
A monomer is a molecule that is able to bond in long chains. (i.e.) glucose
A polymer is a long chain composed of many repeating subunits. (many monomers) (i.e.) polyethylene, sucrose
(b) Explain the processes of dehydration synthesis (condensation) and hydrolysis
Dehydration