All organisms take in and also release carbon compounds. Draw a labelled diagram of the carbon cycle.

Describe how the rate of photosynthesis can be measured.

Explain the mechanism of ventilation in humans.

CO₂ in atmosphere/air;
plants/producers linked to carbon in air/CO₂ with arrow labeled photosynthesis;
plants/consumers linked to animals/consumers with arrow labeled feeding;
plants/producers and animals/consumers linked to carbon in air/CO₂ with arrow labeled (cell) respiration;
plants/producers and animals/consumers linked to decomposers/bacteria/fungi with arrow labeled death;
decomposers/bacteria/fungi linked to carbon in air/CO₂ with arrow labeled (cell) respiration;
plants/producers connected to carbon in air/CO₂ with arrow labeled combustion/forest fire;
decomposers/bacteria/fungi linked to fossil fuels/coal/oil/natural gas with arrow labeled (partial) decomposition;
fossil fuels/coal/oil/gas linked to carbon in air/CO₂ with arrow labeled
combustion;         

Award marking points only if arrows point in correct direction.

correct equation for photosynthesis in words or symbols;
measure production of oxygen;
example of method to measure oxygen production;
(eg count bubbles from water plant/collect oxygen data per unit of time using electronic sensors/probes)
measure uptake of CO₂;
example of method; (eg method of measuring (aquatic) pH changes/shift per unit time)
measure increase in biomass;
example of method; (eg sample (dry) mass of crop before and after timed period)

not possible to measure water uptake since water is transpired/used in turgidity/many chemical processes;
another valid method if concept of rate (measurements per time) is included;

air enters/exits lungs through trachea, bronchi and bronchioles;
during inspiration/inhalation external intercostal muscles contract;
causing ribs to move upwards/outwards;
during inspiration diaphragm contracts/flattens;
causes increase in volume of thorax/lungs;
decrease in pressure allows air to enter (passively);
during expiration internal intercostal muscles contract/external intercostal muscles relax;
causing ribs to move down/in;
diaphragm relaxes/returns to original domed position;
abdominal muscles contract to push diaphragm up;
causes decrease in volume of thorax/lungs;
increase in pressure forces air out of lungs;
Award [5 max] for inhalation or exhalation only.

(Plus up to [2] for quality)

Many candidates spent considerable time drawing beautiful trees, rabbits, and factories but labels on the arrows that connected the various components of the carbon cycle. Some candidates never showed CO₂/carbon in the air.

Many candidates could name production of O₂, uptake of CO₂, and an increase in biomass as methods to measure the rate of photosynthesis. This meant an easy three marks. Gaining marks beyond that became very difficult. The primary reason was that when candidates gave details about the method, they failed to mention rate, as in a unit of time for the measurement e.g. bubbles of O₂ released per minute. The equation for photosynthesis was rarely given by any candidate.

The mechanism of ventilation in humans was generally explained well. Some accounts were flawed when specific intercostals muscles contracting or relaxing were not identified. More serious problems occurred when candidates mixed up ventilation with gas exchange at the level of alveoli or dwelled on cell respiration.