Quiz 6: Ground Rules of Metabolism


First law of thermodynamics : The first law of thermodynamics deals with the quantity of energy. According to this law, energy of an isolated system is constant. Energy cannot be created or destroyed. The energy can be converting from one form to another form. Second law of thermodynamics : This law deals with the quality of energy. According to the second law of thermodynamics, energy tends to flow from high concentrated region to low concentrated region spontaneously. It also states that the entropy of an isolated system will not decrease. Entropy is nothing but the measure of how much and how far, energy from concentrated region has been distributed after an energy transformation.

The life's primary source of energy is sunlight. The light energy from sun is the base for the life on earth. By absorbing sunlight, plants and many microorganisms are preparing the food molecules through photosynthesis process. Upon these photosynthetic organisms all the remaining organisms (from single celled to multicellular organisms) are depending. So, the correct option is (c) sunlight. Food, water and adenosine triphosphate (ATP) are not the primary source of energy. So, the options (a), (b) and (d) are incorrect.

Electron transport chain (ETC) is very important because from this only adenosine triphosphate (ATP) is produced. ATP is the energy carrier in many metabolic pathways and is the cell's energy currency. The final step after the aerobic respiration and fermentation is the ETC. The cyanide is a very toxic compound it inhibits the enzyme cytochrome oxidase in mitochondria. It is the fourth complex of the electron transport chain (ETC). It attaches to the iron molecule. Cyanide will binds to this enzyme and stops the transport of electrons from cytochrome oxidase to oxygen molecule. As a result, the ETC is interrupted. This results the blocking of ATP formation. As the cytochrome oxidase is blocked by cyanide, cells cannot utilize the oxygen present in the blood. This condition leads to cytotoxic hypoxia or cellular asphyxiation. The oxygen deficiency leads to turning of aerobic condition to anaerobic in which lactate is produced. Due to hypoxia and lactate acidosis central nervous system will be affected that results in respiratory arrest and death. Due to cyanide toxicity, many vital organs of an effected person will be damaged, mainly heart and central nervous system.

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