Combined Science Revision
- Air is cooled to -78°C.
- Water and carbon dioxide are removed as solids.
- The remaining air is further cooled by a process of rapid compression and expansion until it reaches a temperature of -200°C.
- At this temperature all gases are liquids except for rare gases.
- The liquefied gases are pumped into the the fractionating tower an the temperature allowed to rise gradually.
- Nitrogen which has a boiling point of -196°C turns to gas and is collected.
- Oxygen which has a boiling point of -183°C is collected as a liquid from the bottom of the tower.
(ii) Breast milk:
- is not contaminated
- is at a suitable temperature
- contains antibodies which defend the baby against disease
(b) The child is injected with weakened or dead pathogens. White blood cells produce antibodies to fight the pathogens. After recovery, the body keeps the antibodies to fight future infections.
- lack of moisture
- lack of oxygen
- unsuitable temperature
(a)(i) Efficiency = (MA ÷ VR)× 100
= (50 ÷ 100)× 100
(ii) Some of the energy:
- is lost in overcoming friction.
- is used against the weight of the moving parts.
(b)(i) Pressure is the force per unit area.
- cannot be easily compressed
- transmits presure equally in all directions
- reduces friction of the pistons
- prevents rusting of the hydraulic jack components.
- White blood cells – antibody production and engulfing pathogens.
- Platelets – blood clotting.
- Red blood cells – transporting oxygen.
(b) Artificial and natural immunity.
(a) Highest – 1300 to 1500 hrs
Lowest – 0300 to 0500 hrs and 0500 to 0700 hrs
Highest → This is caused by increased light and heat and reduced humidity; all of which increase the evaporation of water from the leaves.
Lowest → water loss is reduced as the temperature drops, light intensity drops and humidity increase because the rate at which water evaporates from the leaves is low under these conditions.
(b) Plants are adapted for water loss in the following ways:
- fewer stomata on the surface of the leaf
- presence of hairs o the surface of the leaf
- reduced leaf size
(a) Iron pyrites (iron sulphide) is roasted in air to produce sulphur dioxide. Sulphur dioxide is then oxidised to sulphur trioxide at 450°C, 1 atom using vanadium (v) oxide as a catalyst.
(b) Sulphur trioxide is absorbed in concentrated sulphuric acid to produce oleum. Sulphur trioxide is is not directly added to water because the heat of reaction would produce a mist of sulphuric acid that is difficult to condense. Oleum is then diluted with water to obtain more concentrated sulphuric acid.