IGCSE Biology : U2 : Respiration

Respiration is the release of energy from organic food molecules. Energy is used in movement, reproduction, staying warm, hunting and excretion. 


ATP or adenosine triphosphate is a fundamental molecule used as primary energy source in organism. 

  1. Muscle Contraction - energy needed for muscle fibres to slide past each other during muscle contraction

  2. Active Transport - the active transport of molecules and ions across cell membranes.

  3. Cell division and growth - Used during meiosis and mitosis and for repair

  4. Biosynthesis reactions - Creating complex molecules from simpler ones 

  5. Metabolic processes - providing activation energy for chemical reaction necessary for life.

  6. Nerve impulse propagation - supporting the transmitting of nerve impulse.

  7. Maintenance and repair - repair and maintenance of cells and tissue ensuring the proper functioning longevity of cellular components.


Aerobic Respiration : 


Oxygen + Glucose - Carbon dioxide + Water + ATP

6O^2+C^6H^12O^6- 6CO^2 + 6H^2O +ATP


Aerobic respiration takes place in the mitochondria. 


1 Glucose -> 38 ATP



Anaerobic Respiration : 


Anaerobic respiration is when there is a lack of oxygen or no oxygen. It occurs when the blood cannot reach the muscles fast enough to supply them with the required oxygen. It is not very efficient and produces little ATP. The lactic acid is left and it breaks down your muscles which hurts. This is removed aerobically (Requiring oxygen). EVen after the intense physical activity has finished the person will still breath heavily drawing as much oxygen into the lungs as possible.


Glucose - Lactic Acid + ATP 


1 Glucose -> 2 ATP


Oxygen refers to the amount of oxygen that the body needs to completely oxidise the lactic acid that has built up in the body and therefore help it to recover and strenuous exercise .


What happens in the muscles when you exercise at a high intensity ? 

Anaerobic respiration will take place because not enough oxygen is being supplied and less ATP is produced aerobically  and produces lactic acid in your muscles. The lactic acid breaks down your muscles and needs to be removed aerobically. Otherwise it will kill your muscles.