Discussion.

``Each cell in the muscles needed more oxygen when doing more work because of increased cellular respiration within the cell. Each cell also required glucose which is part of cellular respiration. Two substances produced during cellular respiration are carbon dioxide and water.
For the cells to function, it requires inputs (sugar, O2) it also requires outputs (H2O, CO2).

Blood is the transport system for oxygen, glucose, carbon dioxide and part of the water. Blood is made up of three different cells, the red blood cells, the white blood cells, and the platelets, it is also made up of a watery liquid called plasma.

Oxygen in the blood is carried by a system of tubules made-up ofarteries, arterioles, and capillaries. Oxygen diffuses from the high concentration in the arterial capillaries into the area of low concentration in the cell. Oxygen attaches itself to the erythrocytes that are red blood cells. Erythrocytes contain hemoglobin which isa molecule that contains an iron atom. Oxygen binds itself to that iron atom.

Carbon dioxide diffuses from the high concentration in the cells intothe area of low concentration in capillaries around the cell. The capillaries carry the blood rich in carbon dioxide to the venulesand then to the veins. The veins carry the carbon dioxide to the upper and lower vena cavathat lead into the right atrium, then down to the right ventricle, into the lungs then to the left atrium. It then leads to the left ventricle, to the cells.

Receptors, such as the one in the aorta, detect the rise in carbon dioxide in the body as the blood leaves the left ventricle. The carbon dioxide receptor examines the level of carbon dioxide in the blood. The receptor sends a signal to respiratory centre in response to an increase or decrease in the levels of carbon dioxide. The respiratory centre is located in the medulla oblongata at the base of the brain.

The respiratory centre, which is part of the central nervous system and part of the autonomous nervous system, sends a signal to the muscles involved with respiration such as the intercostal muscles in the ribcage and the diaphragm to work faster if the levels of carbon dioxide have increased. These signals occur very quickly. During the intense activity level the abdominal muscles were also activated by the respiratory system.

As the muscles around the lungs contract, they enlarge the area around the lungs. The enlarged area around the lungs decreases the pressure in the lungs. The pressure outside the body is greater at that point than in the lungs so air from the outside is forced into the lungs by the difference in pressure. As the muscles relax and return to their original positions, the higher pressure on the lungs forces air from the lungs into the air.

The lungs are comprised of two main sections. The left and the right lungs. Air from the outside enters through the veins. The veins then carry it in the blood back to the heart. This continues with the same procedure.

The results in the experiment indicate that both respiration and pulse increased with higher activity levels. The mean results support the hypothesis. The range in the results can be explained by different levels of strenuous activities, some requiring more oxygen, and by different levels of fitness among the subjects.``