Essay
Biological cycles essay
A cycle is a biological pathway or process in which the end product of one cycle becomes the starting point for the next. Write an essay about cycles in biology.
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A cycle is a biological pathway or process in which the end product of one cycle becomes thestarting point for the next. Write an essay bout cycles in biology.
Cycles play a massive part in biology. In humans, the cardiac cycle is essential for maintaining life,
using oxygen from the mechanism of breathing to sustain aerobic respiration. This, in turn,
producing ATP from ADP and Pi, allowing phosphate to be incorporated into an organism biomass,
providing a starting point/product for the phosphorous cycle.
Oxygen is present in many biological cycles; aerobic respiration, photosynthesis and the mechanism
of breathing in humans. In order to receive the oxygen needed for aerobic respiration, humans must
take in oxygen from the air. This is done through the mechanism of breathing. Breathing is an active
process, requiring muscle contraction and relaxation to occur. For inspiration to occur, the external
intercostal muscles must contract, and as muscles work in pairs, the internal intercostal muscles
relax. This causes the ribs to be pulled upwards and outwards, increasing the volume of the thorax.
The diaphragm muscles also contract, causing it to flatten, further increasing the thoracic volume.
This increased volume results in a reduction of pressure in the lungs. Atmospheric pressure is now
greater than pulmonary pressure, causing air to be forced into the lungs. Once air is forced into the
lungs, oxygen diffuses across the alveoli epithelium and into the red blood cells found surrounding
the alveoli. Carbon dioxide diffuses out of the red blood cells into the alveoli, down its concentration
gradient. This carbon dioxide then leaves to leave the lungs so the cycle can restart. The external
intercostal muscles relax and the internal intercostal muscles contract. This pulls the ribcage down
and in, increasing thoracic pressure. The diaphragm also relaxes, so is pushed up against the
contents of the abdomen, further increasing the thoracic pressure. Atmospheric pressure is then less
than pulmonary pressure, resulting in air being forced out of the lungs. The cycle then starts again,
meaning the lungs are ventilated to maintain a steep concentration gradient of oxygen into the red
blood cells and carbon dioxide out of them. During normal breathing, the recoil of elastic tissue in
the lungs is the main cause of air being forced out. This is known as passive breathing. When
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