Cycles In Biology Essay examples

Carbon Cycle
Carbon in air and in water is absorbed by plants and becomes carbon compounds in their tissues when they photosynthesise. The carbon, from these plant tissues, is passed on to primary consumers when they eat the plants, and then onto secondary, tertiary etc consumers when they eat the consumers lower down. When they die, as all living things do, saprobiontic nutrition is carried out by microorganisms as the carbon compounds are digested by decomposers which, as they respire, produce Carbon Dioxide which is released and returned to the air and water. If decomposers don't digest the dead organic matter due to it settling in areas where there aren't any bacteria or fungi, the carbon compounds will become fossil fuel over millions which are then burned, at which point Carbon Dioxide is release back into the air.
Nitrogen Cycle
During the Nitrogen Cycle there are four main stages; Nitrogen fixing, Ammonifiction, Nitrification and Denitrification. Rhizobium bacteria, found either in root nodules of leguminous plants or free in the soil, convert nitrogen gas from the atmosphere into ammonia which can then be used by plants. The plans then die and the nitrogen compounds are turned into ammonium compounds by decomposers before being changed into nitrates, by nitrifying bacteria, and then nitrates to be used by the plants again. Theses nitrates can also be converted into nitrogen gas by denitrifying bacteria via respiration under anaerobic conditions.

Synthesis of ATP
During aerobic respiration, 38 ATP molecules have the potential to be produced when Glycolysis, the Link Reaction, the Krebs cycle and the Electron Transport Chain occur. Glucose is phosphorylated as two ATP molecules donate their Pi to it. This phosphorylated glucose is then split into two Triose Phosphates which is then changed into 2 pyruvate molecules as two lots of NAD are reduced into NADH and four molecules of ATP are released. The pyruvates then go on to form AcetylcoenzymeA as CO2 is released, NAD is reduced into NADH and CoenzymeA binds to the pyruvates (this happens twice as two pyruvates are produced in the first step). This then leads onto the Krebs Cycle, which again happens twice for each glucose molecule used and so produces twice the amount described in the following. The acetylcoenzymeA binds with oxaloacetic acid which releases coenzymeA and forms citrate. This is then converted back into oxaloacetic acid as two CO2 molecules are released, three NAD's are reduced to three NADH's, an FAD is reduced into FADH and an ADP is converted into ATP as a Pi is added. Hydrogen is then oxidised into a H+ ion and an electron. The H+ ions remain in the matrix while the electrons pass down along carrier molecules, each at a lower energy level than the previous one meaning energy is released every time the electron is passed on. This energy is then used to transport the H+ ions from inside the matrix into the inter membrane space. They will then diffuse through a protein channel via facilitated diffusion and activate ATPsynthase causing an ATP molecule to be generated by the protein channel for each H+ ion that travels through.
Light-Independent Reaction
During the Light independent reaction, RuBP binds with CO2 (with Rubisco catalysing the reaction) to form a six carbon intermediate with is so unstable it immediately splits into two molecules of GP. These are the reduced into two molecules of GALP by NADPH with ATP providing the energy. The GALP is then used to regenerate the five carbon RuBP with ATP providing the energy and the Pi for this to happen. This also leaves one carbon (meaning the cycle must happen six times for one molecule of glucose) to go on to form the hexose sugar.
Cardiac Cycle Cell Cycle

Muscle Contraction
Myosin and Actin filaments slide over one another to make the sarcomeres contract. Simultaneous contractions of lots of sarcomeres means the myofibrils and muscle fibres contract. When an action potential from a motor

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