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The transport of oxygen from air in the alveoli of the lungs to the cytoplasm of respiring muscle cells.

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Introduction

Biology Synoptic Essay The transport of oxygen from air in the alveoli of the lungs to the cytoplasm of respiring muscle cells Alveoli are the gas exchange sites of the body; one of the gases, oxygen, enters the body via the mouth and nostrils. Breathing involves the increase and decrease of air pressure in the lungs, which is relative to that of the air. A fall in air pressure in the lungs causes breathing in (inspiration), and a rise in pressure in the lungs causes breathing out (expiration). Because of the thorax volume increasing (therefore air pressure inside thorax is below atmospheric pressure), air flows in, down the trachea and into the alveoli. Once in the alveoli, the oxygen dissolves, because of the moist wall lining, and then diffuses across the wall and into the blood stream.

Middle

soon as O2 has diffused from the alveolus to the blood, the blood moves onwards and more deoxygenated blood becomes present as a continuous process. The blood is however moving quite slowly in these capillary beds, in order to ensure that as much gas exchange as possible occurs. Now that the oxygen is in the plasma, it passes into the red blood cells (through diffusion again) where it binds to haemoglobin. Haemoglobin is a globular protein, the haem group is important in transporting oxygen. The tertiary structure of haemoglobin gives it a distinctive shape and this allows the oxygen molecules to bind onto its active site, as it has a complementary shape to the site. Therefore, another molecule would not be able to bind to that specific active site on the haemoglobin molecule, as it would not have the right shape.

Conclusion

the double circulation of the heart). The oxygen in the being sent to the muscle tissue breaks from the haemoglobin and diffuses into the cells of the muscle tissue. This is because they need oxygen to respire more as the body is undergoing exercise. For the oxygen to get into the cell it must pass through the cells membrane, which consists of a phospholipids bilayer (two layers of phospholipids). Phospholipids have a head that is hydrophilic (i.e. mixes with water) and a tail that is hydrophobic (i.e. does not mix with water), because of this the head is on the outside of the layer and the tail is on the inside. Diffusion of a small molecule like oxygen requires no added energy; it diffuses freely across the cell's plasma membrane and into the cytoplasm of the respiring muscle cell. Alana Russell Page 1 16/05/2007

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