When a stimulus is applied to a neuron, the resting potential is (-map) is reversed – this is the action potential (deportations). The energy of the stimulus causes the intrinsic sodium voltage-gated channels to open, allowing sodium ions to diffuse into the axon along their electrochemical gradient. Entry of these An+ ions causes the inside of the axon to be less negative. As threshold is reached, there is a greater influx of sodium ions and the potential difference increases to +map, so the inside is positive, and the outside is negative.
This is when the sodium channels start o close and the voltage-gated potassium channels begin to open, so the K+ ions move out of the axon. Therefore, the potential difference begins to drop and the sodium ions are pumped out, and the potassium ions back in, and the membrane returns to its resting potential. This is a cycle because this process repeats every time a nerve impulse is passed down the axon, and is important as it allows the action potential to be passed along the axon. Examples of biological cycles at a cellular level include the cell cycle, mitosis and meiosis.
Most eukaryotic cells follow this process, which includes a growth stage, testis or nuclear division, and cytokines. Throughout enterprise, the cell undergoes growth and metabolic activities. Enterprise can be further broken down into GIG (where normal cell functions occur, as well as cell growth), S (where DNA replicates and produces 2 copies of each chromosome) and 62 (where the cell continues to prepare for mitosis and cell division). Next, mitosis has 4 stages – proposes, metastases, anapest and telephone. During proposes the chromosomes become visible and condense, becoming shorter and thicker.
The nuclear envelope breaks down and the controllers separate. During metastases, the chromosomes line up along the equator of the cell, and spindle fibers attach to the sister chromatics (from the controllers). During anapest the sister chromatics of each chromosome begin to separate, and move to opposite poles. In telephone, the chromosomes reach opposite ends of the cell and a nuclear envelope starts to form. The chromosomes also uncoil. Next is cytokines – the division of the cytoplasm. The result is two genetically identical cells. Mitosis and meiosis also.
The Krebs cycle is a part of cellular respiration – it’s a series of chemical reactions seed by all aerobic organisms to generate energy. This cycle involves a series of oxidation-reduction reactions that takes place in the matrix of mitochondria, and comes after the link reaction. The C acetylene’s A from the link reaction reacts Witt exaltation acid 4 to produce a C molecule (citric acid) This gets converted to accoutering acid, succinct acid and then mammal acid (so it loses hydrogen’s and carbon dioxide, and TAP is produced). The mammal acid is then converted back into exaltation acid, and this cycle repeats.
During this cycle, AND and FAD are reduced y the hydrogen’s, which get carried to the electron transport chain where they are oxidized and more TAP is formed. These electron carriers then return to the Krebs cycle, ready for the next acetylene’s A. This cycle is very important in respiration as 1 molecule of TAP is formed per acetylene’s A, and also, the reduced AND and FAD have the potential to produce more TAP molecules in the electron transport chain. Another example would be the cardiac cycle – the sequence of events that occur when the heart beats.
One cardiac cycle is completed when the heart fills with blood, ND the blood is pumped out of the heart. There are two phases – diastole (when the ventricles are relaxed and the heart fills with blood) and systole (when the ventricles contract and pump blood to the arteries). During the first diastole phase, degenerated blood from the body flows into the right atrium. The therapeutically valves mean the blood can pass into the ventricles. The tricuspids valve prevents blood flowing backwards. During the systole phase, the right ventricle gets impulses from the Pureeing fibers, and contracts.
The therapeutically valves close and the milliner valves open, and the blood enters the pulmonary artery (which takes the blood to the lungs and is oxygenated). The pulmonary valve prevents backfill. Then a second diastole and systole phase follows, but in the left atrium and ventricle, with oxygenated blood, which then goes to the rest of the body. We have this double circulatory system to ensure there is enough pressure for the blood to go to all of the cells. This is a cycle because the blood from the body enters the right atrium again via the even cave, and the whole process repeats.
Biological cycles can also be seen at a population level – predator prey cycles. All living things within an ecosystem are interdependent, and a change in one population often affects another. Predators need to be adapted to efficient hunting, and the prey species must be adapted for escaping them. If the prey population grows, predator numbers will also increase as there is an increased food supply. However, an increased predator population means the food is consumed at a higher rate and the food supply decreases. A decreased food supply cannot sustain the predator population, so this drops as well.
This means the prey population will increase once again, and so on, the cycle repeats. This pattern can be see with the predator prey cycle for the Canadian lynx and the snowshoe hare. Biological cycles can be seen at greater scales as well, for example, the Nitrogen cycle. Nitrogen is essential for the formation of amino acids in proteins, and there is a lot of nitrogen in the air, but as it is so enervative, it cannot be used by plants directly. The nitrogen gas is therefore converted to ammonium by notifying bacteria in the soil or root nodules (which requires a lot of energy from respiration).
Nitrite bacteria then convert this into nitrites (NON-) by an oxidation reaction, and nitrate bacteria convert these further into nitrates (NON-), which is also an oxidation reaction. Nitrate ions can be more readily absorbed by plants. The nitrate ions are washed into the water table, lakes, sea etc. Identifying bacteria use NON- as a final electron acceptor in the electron transport chain (as no 02 present in water logged soil), and break it down into NO gas, which is released back into the atmosphere. The cycle then repeats all over again.