Nutrition
(1.1) David is a 15 year old boy, he is very active and participates in a lot of sporting activities. David needs to ensure he has a balanced diet and for this to occur he will require an intake of various nutrients via both diet and fluids. If David does not consume a balanced diet he will become unhealthy or may acquire various deficiencies. Without nutrition David would eventually die. Nutrients will allow Davids body to function properly - to move, grow, respire,reproduce, excrete and for his senses (irritability) to work.

The need for movement is to ensure Davids muscles and joints work and do in fact move properly, his muscles will be able to contract and detract and this will enable his joints to move.
Davids growth is not just limited to his height and/or weight, he also need the cells within his body to divide, accumulate and expand appropriately. Muscles, bones and vital organs will continue to grow as he does.
Respiration will play an important part of Davids life, this will mainly be a subconscious process that he may take for granted, until possibly, a lack of nutrients cause his breathing to become troubled. Nutrients are required for respiration so that food that he has ingested can be converted into energy in the form of glucose. Glucose mixed with oxygen is what he will inhale via his breathing therefore exhaling carbon dioxide and water.

Food + Oxygen ⇒⇒⇒ Carbon Dioxide + Water

Glucose + Oxygen ⇒⇒⇒ Carbon Dioxide + Water

C₆H₁₂O₆ + 6O₂ ⇒⇒⇒