Define the term cell respiration.

Explain the mechanics of inhalation in the human lungs.

Describe the production of ATP from glucose by the aerobic system.

cell respiration is the controlled release of energy in the form of ATP <from organic compounds in cells>✔

Breathing in:
external intercostal muscles contract
OR
rib cage moves upwards and outwards✔

diaphragm flattens / contracts✔

thoracic cavity volume increases/lungs increase in size/capacity✔

thoracic cavity pressure decreases ‹therefore air rushes in›
OR
air rushes in from high pressure to low pressure/inhalation continues as long as the pressure difference exists / air flows from an area of higher pressure to an area of lower pressure✔

additional muscles can also be involved such as the trapezius, sternocleidomastoid / scalene / pectoralis minor / back muscles✔

the aerobic energy system / aerobic glycolysis involves three processes: glycolysis, Krebs cycle, electron transport chain✔

glycolysis takes place in the cell cytoplasm / outside the mitochondria✔

Krebs cycle and electron transport chain takes place in mitochondria✔

the aerobic energy system can produce ATP from all the main food groups of our diet✔

it involves the production of ATP with oxygen✔

in the presence of oxygen, pyruvate is processed by the Krebs cycle which liberates electrons that are passed through the electron transport chain producing energy ‹ATP›✔

the oxidative system of energy production can generate up to 38 molecules of ATP from one molecule of glucose✔

Glucose oxidation:
during glycolysis glucose is firstly phosphorylated which uses up 2ATP✔

glucose is split into two pyruvate molecules during glycolysis, <which regenerates 4ATP>✔

glycolysis generates a net production of 2ATP✔

during aerobic production of ATP pyruvate is converted to acetyl CoA which enters the Krebs cycle / which generates 2 ATP✔

CO₂ and hydrogen ions are released from the Krebs cycle✔

hydrogen ions are carried to the electron transport chain where energy and water are produced / which produces 34 ATP✔

Many pupils repeated the definition found within the guide, however many pupils referred to aerobic respiration and regularly missed its key function which is to produce ATP.

Most pupils gained 2 marks by identifying the diaphragm contracting and the lungs expanding. However, many pupils were limited by identifying the intercostal muscles rather than the specific external intercostal muscle. A few pupils discussed exhalation rather than inhalation. Many pupils discussed gaseous exchange and the pathway of air flow and misunderstood the requirements of the question to discuss the mechanics of the action.

Few students achieved full marks for this question. Many pupils demonstrated confusion between the site of the Krebs cycle and electron transport chain. Very few pupils were able to identify that glycolysis is the first stage of the aerobic system and that it breaks down glucose into two pyruvate molecules.