This continuous cycle shows the interdependence of the two processes. During photosynthesis, plants through chlorophyll capture sunlight energy and convert inorganic molecules of water and carbon dioxide into energy organic molecules. This occurs in two steps, namely, light-dependent and light-independent reactions. The light-dependent reaction is a step where electrons found in the chlorophyll get invoked and the active electrons get transferred to electron transport systems. On the other hand, light-independent reactions occur as a cycle of chemical reactions referred to as Calvin cycle. Audesirk et al. (2008) categorize this cycle into three steps, namely; carbon fixation, glyceraldehydes-3 phosphate, G3P, synthesis and the ribulose biphosphate, RuBP generation. Carbon fixation entails carbon being assimilated from carbon dioxide into a larger molecule. A plant protein, referred to as Rubisco, would then fix carbon in photosynthetic organisms and accept oxygen instead of carbon dioxide, CO2. This forms a CO2 molecule which combines with the RuBP molecule producing an unstable molecule containing six carbon molecules. This immediately splits into two molecules of phosphoglyceric acid, PGA. In the G3P synthesis, various reactions cause the energy from adenosine triphosphate, ATP and NADPH to propagate the conversion of the six PGA molecules into six G3P molecules (Audesirk et al., 2008). G3P is a sugar with three carbon molecules. Finally, RuBP would be generated through reactions that
utilize ATP produced due to the light reactions of the six G3P molecules. The regenerated RuBP serves as an important ingredient for the repetition of the Calvin cycle, causing the release of the last G3P molecule. The energy from the sun captured by chloroplasts during photosynthesis enables glucose to be produced from CO2 and H2O, with oxygen being the by-product. Cells then break down this glucose, generating energy that gets captured and stored in ATP, an energy-carrying molecule (Hodson & Bryant, 2012). The ATP would then carry energy to cells where it breaks off releasing energy. The resultant molecule referred to as adenosine diphosphate, ADP could be converted further to adenosine monophosphate, AMP, releasing more energy. The released energy would be utilized for cellular functions. To fuel further activities, cells replenish the supply of ATP. 2. In the absence of oxygen, some cells and organisms can use glycolysis coupled to fermentation to produce energy from the sugar created by photosynthesis. Explain the role of fermentation in allowing an organism to generate energy for its cell(s) in the absence of oxygen. In the absence of oxygen, cells exclusively rely on glycolysis so as to produce ATP. Here, fermentation would cause hydrogen atoms resulting from glycolysis to be donated to organic molecules. According to Audesirk et al. (2008), it allows NADH, a product of glycolysis, to revert back to nicotinamide adenine dinucleotide, NAD. This process needs to be continuous for the sustainability of glycolysis. Through cellular respiration, organisms regenerate NAD, a process that encompasses energetic electrons in NAHD being given to the electron transport chain, ETC. +NADH +NAD+ Organic molecule Reduced organic molecule Nonetheless, oxygen would be required for this to occur.