respiration

During digestion, the carbohydrates we eat, such as starch, are broken down by enzymes into glucose. This is absorbed into the blood from the small intestine. Glucose travels around the body in the blood plasma. When we breathe in, oxygen from the air diffuses into the blood from the alveoli in the lungs. Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration. The oxygen combines with a chemical called haemoglobin found in the red blood cells and travels around the body.