cycles in biology
CYCLES IN BIOLOGY
This essay will give examples of cycles in biology from different scales of magnification, ranging from molecular level to populations and ecosystems. Cycles are sequences of events which repeat themselves in the same order, one event leading to the next. There are many examples of these in Biology. Cycles can be seen even at a molecular level in the body. An example of this would include the passage of action potentials down neurones in the nervous system. When the cell membrane is at its resting potential, the sodium potassium pump is turned off. When a stimulus is applied to a neurone, the resting potential is (-70mV) is reversed – this is the action potential (depolarisation). 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 Na+ 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 +40mV, so the inside is positive, and the outside is negative. This is when the sodium channels start to 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, mitosis or nuclear division, and cytokinesis. Throughout interphase, the cell undergoes growth and metabolic activities. Interphase can be further broken down into G1 (where normal cell functions occur, as
This essay will give examples of cycles in biology from different scales of magnification, ranging from molecular level to populations and ecosystems. Cycles are sequences of events which repeat themselves in the same order, one event leading to the next. There are many examples of these in Biology. Cycles can be seen even at a molecular level in the body. An example of this would include the passage of action potentials down neurones in the nervous system. When the cell membrane is at its resting potential, the sodium potassium pump is turned off. When a stimulus is applied to a neurone, the resting potential is (-70mV) is reversed – this is the action potential (depolarisation). 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 Na+ 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 +40mV, so the inside is positive, and the outside is negative. This is when the sodium channels start to 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, mitosis or nuclear division, and cytokinesis. Throughout interphase, the cell undergoes growth and metabolic activities. Interphase can be further broken down into G1 (where normal cell functions occur, as